PSY610 — Final Term Summary (Lectures 23–45)

📘 Lecture 23 — Development of the Nervous System

📖 Overview: This lecture examines the various influences that affect normal brain development, both prenatally and postnatally. It covers critical factors such as oxygen levels, drug exposure, prenatal motor activity, external stimulation, and the role of enriched environments in shaping neural growth and plasticity. Understanding these influences is crucial for comprehending how disruptions during sensitive periods can lead to irreversible brain damage or developmental deficits.

🗂️ Topics Covered

This lecture continues the discussion on influences affecting normal brain development, covering the critical role of oxygen levels for fetal brain growth and the consequences of hypoxia. It explores prenatal motor activity and its role in strengthening muscular connections and pathways. The teratogenic effects of drugs like thalidomide, morphine, heroin, alcohol, and nicotine are detailed. The importance of external stimulation for normal organ and muscle development is explained through classic experiments. Finally, the impact of a complex environment on brain weight, cortical thickness, neuron size, and dendritic growth is discussed.

📝 Lecture Summary

Influences on Brain Development (Continued)

Oxygen Level

Oxygen is essential for brain cells during growth and throughout life. The embryo depends entirely on the mother for its oxygen supply. Any reduction in the normal oxygen level will affect the growing brain. If the mother is not getting enough oxygen during the last trimester, this leads to hypoxia (low oxygen levels) of the fetus. Faulty blood circulation in the mother (e.g., due to anemia or heart disorders) can damage brain areas that may have developed normally. This damage is similar to that of mental retardation because neurons die off, and a lesser number of cells remain, leading to deficient functioning of these areas.

🔑 Definition — Hypoxia: A condition of low oxygen levels in the body, which during the last trimester of pregnancy can damage the fetal brain. 💡 Why this matters: Adequate maternal oxygen supply is critical during the final stages of pregnancy to prevent neuronal death and subsequent cognitive deficits.

Prenatal Motor Activity

Prenatal motor activity is important, as evidence shows that increased activity in the uterus leads to stronger muscles. This activity exercises muscular connections and their pathways, strengthening motor connections even within the womb. Sensory responses also occur; evidence has shown that the embryo/fetus responds to the mother's lullabies and voice. Fetuses stimulated during the prenatal period are more alert when they are born.

Drugs

Though the placental barrier protects the embryo, some substances manage to pass through the protective membranes. It was discovered in the 1960s that drugs affect the normal growth of the fetus, leading to serious deformities. Thalidomide was the first drug identified to have teratogenic effects. This sedative was given to expecting mothers in the first three months and caused major deformities in the growing embryo. Similarly, morphine, heroin, alcohol, nicotine, cocaine, and tobacco also affect the embryo. Mothers are warned against taking these or other pharmaceutical substances during pregnancy due to their teratogenic effects.

🔑 Definition — Teratogenic Effects: The ability of a substance (teratogen) to cause developmental malformations or defects in a growing embryo or fetus. 📌 Example: Thalidomide, a sedative given to pregnant women in the 1960s, caused major limb deformities in the growing embryo.

External Stimulation

External stimulation is very important for the growing embryo. Unless external stimulation is received, the organs and muscles do not develop normally. Therefore, sensory deprivation leads to irreversible defects in the normal growth of the brain. In the now-classic experiments, Hubel and Wiesel (1963) closed one eye in newborn kittens, creating monocular deprivation. They found a monocular response to visual stimuli (only one eye could respond, even though the visual system was not damaged). In another experiment, kittens kept in a dark room from birth showed that visual pathways atrophy and visual cortical brain areas also degenerate, causing irreversible damage and blindness. Thus, early sensorimotor stimulation is important for the brain to grow normally. To stimulate the brain, brightly colored toys and mobiles are placed in cots for newborns.

🔑 Definition — Monocular Deprivation: An experimental condition where visual input to one eye is blocked, leading to impaired development of the visual pathways for that eye, even if the eye itself is undamaged. 📌 Example: In Hubel and Wiesel's experiment, kittens with one eye closed showed only monocular visual responses, as the deprived eye's neural pathways failed to develop normally.

Complex Environment

Rosenzweig et al (1969, 1972) raised rats in an enriched environment (with more toys, swings, ladders, etc.). They removed the brains and measured various parts, reporting: a) increased brain weight (especially the cerebral cortex), b) increased thickness of cortical tissue, c) larger size of neurons, d) more glial cells, e) more dendritic spines, and f) different brain chemistry (enzyme activity). Greenough (1975) and colleagues reported that rats raised in a complex environment a) had increased dendritic sprouting and b) responded to a novel environment in the same way as mildly stimulated rats.

🔑 Definition — Dendritic Spines: Small protrusions on the surface of dendrites that receive input from other neurons; more spines indicate more synaptic connections. 🔑 Definition — Dendritic Sprouting: The growth of new dendrites from a neuron, which increases its capacity to receive signals from other neurons.

Critical Periods for Stimulation

External stimulation and a complex environment are extremely important, but only during the specific critical periods in which the system requires that input to develop. Beyond that, neither the normal effect nor repair is possible.

⭐ Key Takeaways

The developing nervous system is highly vulnerable to a range of environmental influences during critical periods, particularly the last trimester and early postnatal life. Adequate oxygen supply is essential to prevent hypoxia-induced neuronal death and cognitive deficits. Teratogenic substances like thalidomide, alcohol, and nicotine can cross the placental barrier and cause severe structural deformities. External sensory stimulation is not optional but necessary for normal organ and neural development, as demonstrated by Hubel and Wiesel's classic eye-deprivation experiments. Finally, an enriched environment during sensitive periods can measurably increase brain weight, cortical thickness, neuron size, and dendritic complexity, while a lack of such stimulation leads to irreversible deficits.

🧠 Quick Revision Questions

1. What is hypoxia, and during which trimester is the fetal brain most vulnerable to it?
2. What were the teratogenic effects of thalidomide on the developing embryo?
3. In Hubel and Wiesel's experiment, what was the outcome of closing one eye in newborn kittens?
4. List at least four structural changes observed in the brains of rats raised in an enriched environment by Rosenzweig et al.
5. What is a critical period in the context of nervous system development?

📘 Lecture 24 — BASIC NEUROANATOMY

📖 Overview: This lecture provides a foundational introduction to neuroanatomy, covering the cellular building blocks of the nervous system—neurons and glial cells—their structure, types, and functions. It explains the protective layers surrounding the brain, the cerebrospinal fluid system, the blood-brain barrier, and the fundamental codes (digital and analog) neurons use to communicate. Understanding these basics is critical for grasping how the brain processes and transmits information.

🗂️ Topics Covered

The lecture begins with an introduction to the brain and spinal cord, focusing on neurons and glial cells as the basic components. It then details the types and functions of glial cells (astrocytes, oligodendrocytes, microglia, phagocytes), followed by the protection of the brain (meninges and the three layers). The cerebrospinal fluid (CSF) and the ventricular system are explained, along with the blood-brain barrier. The structure and types of neurons (unipolar, bipolar, multipolar) and their special characteristics are covered. Finally, the lecture explains the two neuronal codes of communication—digital and axonal transmission—as well as junctional transmission, comparing their properties.

📝 Lecture Summary

Systems, structure, Cells of the NS Neurons, Types of neurons, axonic and dendritic communications

The nervous system is composed of neurons (specialized cells for reception, conduction, and transmission of information) and glial cells (supportive cells). The adult brain contains about 10-12 billion neurons, with 10-12 glial cells for each neuron. The lecture first discusses glial cells, followed by the cerebrospinal fluid, the blood-brain barrier, and finally the neuron.

Glial cells

These are supportive cells with three major functions: A) They hold neuronal systems together, supporting the synapse, neuron, and dendrites. B) They perform housekeeping chores, such as removing dead cells and cleaning debris. C) They provide nutrients to the cell and its processes. The three major types are astrocytes, oligodendrocytes, and microglia (along with phagocytes).

🔑 Definition — Astrocytes: Glial cells whose extensions cover blood vessels and capillaries, forming the blood-brain barrier. They cover neuronal cell bodies and branches, keep them in place, and provide nutrients and chemicals that pass through the blood into the cell.

🔑 Definition — Oligodendrocytes: Glial cells that send out layered extensions which wrap around axons. These extensions are rich in myelin, a fatty sheath that provides insulation and support to axons and dendrites, increasing transmission efficiency and speed. Gaps between folds are called Nodes of Ranvier, where messages renew and jump. One oligodendrocyte can send extensions to many axons simultaneously.

🔑 Definition — Microglia: Smaller glial cells that keep cells clean by moving debris out of the cell.

🔑 Definition — Phagocytes: Glial cells that act like “Pac-man,” eating away unattended debris and dead cells.

💡 Why this matters: Glial cells are not passive; they are actively involved in chemical transmission, controlling, establishing, and maintaining synapses.

Protection of the brain

The brain is highly protected. First, it is encased by a bony skull. Additionally, three coverings called the meninges (connective tissues) hold the brain in a protective net. The outermost meninx is the Dura mater (“tough mother,” white-colored). Inside this lies the arachnoid membrane (web-like, made of spongy filaments). Beneath this is the subarachnoid space, containing large blood vessels and the cerebrospinal fluid (CSF). The innermost, most delicate covering is the Pia mater (“soft or pious mother”), which sticks to every convolution and groove.

Cerebrospinal fluid: CSF

CSF fills the arachnoid space, the spinal cord’s central canal, and the brain’s ventricles. It supports the form and shape of the brain. CSF travels through the ventricular system, which includes four ventricles. The first two (lateral) are large cavities in both hemispheres. The third ventricle lies in the midbrain at the level of the diencephalon. The fourth ventricle is at the brain stem/cerebellar level and connects to the central canal of the spinal cord. The Choroid plexuses in the Pia mater produce CSF. CSF is constantly produced and circulated; about 125 millilitres is present, and half is replaced every 3 hours.

🔑 Definition — Cerebral aqueduct: The link between the 3rd and 4th ventricles.

Blood brain barrier

This is not a visible fence but consists of cerebral blood vessels and glial cells tightly and densely packed together. It provides protection by insulating glial cells, making it difficult for large molecules (like some proteins) to pass through, though large glucose molecules are actively transported through blood vessel walls. The barrier is selective depending on location.

Neurons: Structure and Types

Neurons have three distinct features: a) the cell soma (cell body), b) the axon (one output end carrying commands out of the cell), and c) the dendrites (input ends bringing information to the cell). Neurons are classified into three major categories:

• Unipolar: Has only one process emerging from the cell body, extending to both ends for quicker communication.
• Bipolar: Has two poles—one axon (output) and one dendrite (input)—mainly for horizontal communication as sensory neurons (found in the eye and ear).
• Multipolar: The most common type, with more than two processes (one axon and multiple dendritic connections). Includes interneurons (short branches, for quick integration) and Pyramidal cells (very long apical dendrites but short axons).

Neurons: Special Characteristics

Neurons differ from other body cells in two ways: a) They can conduct bioelectric signals over long distances without loss in signal strength. b) They form multiple intercellular connections with other cells and tissues. Groups of neurons are called nuclei, and fiber systems connecting them are called tracts.

Neuronal Codes of Communication

Information is coded in two codes: Digital code and Analog code.

🔑 Definition — Digital code: Used by a neuron to pass information from one end to the other. It is like Morse code, where the rate of change is constant. This is electrical in nature.

🔑 Definition — Analog code: Used when two neurons communicate with each other. This is a biochemical signal that varies with the intensity of the message (more intense message = more neurotransmitter released).

💡 Why this matters: The two codes are constantly linked and transformed into one another. The frequency (digital) determines the amount of neurotransmitter released (analog) at the synapse. When neurotransmitter crosses to another neuron, it transforms back into an electrical signal. This is a continuous electrical → chemical → electrical change.

Axonal transmission and Junctional transmission

Axonal transmission: The impulse travels from cell body to terminal (orthodromic/anterograde) or from terminal to cell body (antidromic/retrograde). It has no time delay, is not affected by drugs, and is an all-or-none firing with no after-discharge.

Junctional transmission: The impulse travels only one direction (presynapse to postsynapse). There is a time delay (0.1 to 0.2 milliseconds as neurotransmitter moves across the synapse). It allows spatial and temporal summation at the axonal hillock before a decision to fire is made (reaching threshold). It is affected by drugs and is a graded response, not all-or-none.

⭐ Key Takeaways

The nervous system is built from neurons (10-12 billion) and glial cells, with glia providing support, insulation (myelin from oligodendrocytes, with Nodes of Ranvier), cleaning (microglia, phagocytes), and forming the blood-brain barrier (astrocytes). The brain is protected by the skull, three meninges (Dura mater, arachnoid, Pia mater), and cerebrospinal fluid circulating through four ventricles. Neurons are classified as unipolar, bipolar, or multipolar, and they communicate using a digital code (electrical, within the neuron) and an analog code (chemical, between neurons). Axonal transmission is all-or-none, fast, and unaffected by drugs, while junctional transmission is graded, slower, affected by drugs, and allows summation at the axonal hillock. These fundamental concepts are essential for understanding all higher-level neural processing and behavior.

🧠 Quick Revision Questions

1. What are the three major types of glial cells, and what is the primary function of each?
2. Name the three layers of the meninges from outermost to innermost, and describe the subarachnoid space.
3. What are the two neuronal codes of communication, and how are they linked in the process of neural signaling?
4. Compare axonal transmission and junctional transmission in terms of direction, time delay, drug effects, and whether they are all-or-none or graded.
5. What is the function of the blood-brain barrier, and which type of glial cell is primarily responsible for forming it?

📘 Lecture 25 — BASIC NEUROANATOMY

📖 Overview: This lecture introduces the foundational building blocks of the nervous system, focusing on the structure and function of neurons and their components. It explains how neurons communicate through their specialized parts—cell body, axon, and dendrites—and why understanding these cellular elements is critical for linking brain anatomy to behavior.

🗂️ Topics Covered

The lecture covers the systems and structure of the nervous system, focusing on neurons and glial cells as basic components. It details the three distinct parts of a neuron: cell soma (including all organelles), axon (output end with myelin sheath and synapses), and dendrites (receiving ends). It also examines the cell membrane’s active role in signal transmission, reception, and molecular regulation.

📝 Lecture Summary

Objectives

The students will be familiarized with the functioning of the neurons and their components, including systems, structure, cells of the NS, neurons, types of neurons, axonic and dendritic communications. Neuronal conduction and functioning, ionic and electrophysiological properties are covered. Localizing brain areas using planes of reference (anterior-posterior etc.) is introduced. The Brain and the Peripheral systems: Brain: Forebrain, Mid brain, Hind Brain functioning of each anatomical location in the CNS, starting from the posterior located areas up to the anterior-most. Cerebral Cortex: its layers, Corpus Callosum and the two hemispheres are outlined.

Brain and spinal cord

When we study the brain and the spinal cord we will first study the basics of neuroanatomical structure and systems. The basic component, like all systems in the body, is the cells. The building blocks which the Nervous System is composed of are the neurons, the brains cells and the glial cells. There is also the cerebrospinal fluid (CSF) which cleans and insulates the brain.

💡 Why this matters: Understanding the cellular and fluid components of the nervous system provides the foundation for all later study of brain function and behavior.

Neuron Structure

The neuron is like the other cells of the body but is a specialized cell. It is similar in structure and composition of cell structures but then it differs in other characteristics. The neuron comprises of three distinct parts: the Cell body or cell soma, the axon (output end), and the dendrites.

Cell Soma

The Cell soma is made up of cytoplasm and contains the nucleus, the nucleolus, the free ribosomes which are sites for ribonucleic proteins, the Rough endoplasmic reticulum and smooth endoplasmic reticulum, Mitochondria and other bodies.

Cytoplasm: The jelly-like semi fluid in which all the components of the cell float around in. Nucleus: The center, the master mind of the cell which contains the genetic code, the DNA. It uses the DNA as a template to manufacture the mRNA (messenger Ribonucleic acid), which carries the required information to the Ribosome, where this is needed to manufacture structural proteins, and enzymes needed for catalytic action within the cell.

🔑 Definition — Nucleolus: the structure within the nucleus which manufactures the ribosomes to carry the genetic code outside the center.

Ribosomes: manufacture amino acids basics for proteins for use within the cell and for use outside where they are transported via the Endoplasmic reticulum.

Endoplasmic reticulum: There are two kinds found in the cell, the Smooth Endoplasmic Reticulum (SER) and the Rough Endoplasmic Reticulum (RER). These are folds of membranes (like folds of cloth). Both are for transporting material within and outside the cell. The RER’s look rough because of the beaded appearance, which is caused by the ribosomes being transported by RERs. The SER’s transport lipids.

Golgi Apparatus: named after the discoverer Camillo Golgi, are where the membranes for vesicles are prepared.

Mitochondria: The power house of the cell. It provides energy needed to run the cell. Interestingly they are the respiratory organs of the cell, and they are microorganisms which have survived within the cell because of the evolutionary advantage to both the cell and the mitochondria. All metabolism of the cell takes place in the Mitochondria.

Microfilaments and microtubules: supportive network of tubes and fine membrane filaments which are continuously being formed and broken down as the cell changes (learning requires cells shape and form to change).

The Axon

The Axon is the output end of the cell. It emerges from the cell at the axonal hillock where summation of messages takes place. It has neurotubules for supporting the shape and form from inside and also providing a transport system. There are vesicles for carrying neurotransmitters, since the axon is involved in using a large amount of energy for transmitting messages, there is mitochondria floating around in the axonal processes. Myelin Sheath covers the axon with gaps which are called Nodes of Ranvier across which message jumps across. At the pre-synaptic end the axon has synaptic boutons which have vesicles and process the transmission using neurotransmitters.

🔑 Definition — Axonal Hillock: the region where the axon emerges from the cell body and where summation of messages takes place.

🔑 Definition — Nodes of Ranvier: gaps in the myelin sheath covering the axon across which the message jumps.

Dendrites

Dendrites are the receiving ends of the neurons, they have multiple branches and there can be extensive branching and synapses depending on the sites.

Cell membrane

The cell membrane is highly active cytoplasm where constantly ionic and electrical changes are taking place. Further, complex biochemical processes are also taking place within the cell membrane. These processes are important as they play an active role in: a) Transmission of signals through the axon to other neurons, b) Biochemical processes of the soma and c) Receiving of the transmission by the dendrites, d) These processes also sustain and keep the cell alive and free of toxins, e) Controls the number and amount of molecules leaving or entering the cell body.

The cell membrane is important because of its main role in:

1. Conductance of signals along the axon,
2. Reception in the dendrite,
3. Control the molecules moving in and out of the cell.

The Intracellular membrane is composed of a double layer composed of fats and phosphates, known as the phospholipid. These molecules have 2 parts: hydrophobic (water repelling) tail, and hydrophilic (water seeking) head. Fatty acid tail inside and phosphate head outside. All the hydrophilic heads are on the outside facing the intracellular and the extracellular medium which is made up of mainly water and other chemicals. These look like little beads. The hydrophilic ends are towards the inside (like the bread in a three-layer sandwich), and they are retained where each layer's lipid tails face each other. There are also some proteins (glycoproteins), channel proteins, and cytoskeletal elements, which float around the layers, as these are needed for any living organism. Within this there is a system of regulation of the movement of molecules across the pores of the membrane.

⭐ Key Takeaways

The neuron is the fundamental specialized cell of the nervous system, composed of three distinct parts: the cell soma (containing the nucleus, mitochondria, endoplasmic reticulum, and other organelles), the axon (the output end with myelin sheath and Nodes of Ranvier), and dendrites (the receiving ends). The cell membrane plays a critical active role in signal transmission, reception, and regulating molecular movement, and is composed of a phospholipid bilayer with embedded proteins. Understanding these cellular structures is essential for comprehending how neural signals are generated, conducted, and communicated.

🧠 Quick Revision Questions

1. What are the three distinct parts of a neuron, and what is the primary function of each?
2. What is the function of the mitochondria within the neuron, and why are they described as the "power house of the cell"?
3. What is the purpose of the myelin sheath and the Nodes of Ranvier on the axon?
4. What are the two main types of endoplasmic reticulum, and what does each transport?
5. Describe the structure of the cell membrane, including the roles of the hydrophobic and hydrophilic parts of phospholipids.

📘 Lecture 26 — BASIC NEUROANATOMY

📖 Overview: This lecture explores the ionic and molecular movements that generate electrical signals in neurons, focusing on how membrane permeability and ion gradients produce resting and action potentials. It also introduces fundamental neuroanatomical terminology for describing brain structures, directions, and planes of reference, which is essential for understanding brain organization and function.

🗂️ Topics Covered

The lecture covers neuronal membrane control of molecules; ionic concentration gradients and the resting potential; osmotic and electrostatic gradients driving ion movement; the sodium-potassium pump; the transition from resting to action potential including hyperpolarization and depolarization; action potential propagation as an all-or-none phenomenon; excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs); spatial and temporal summation; and basic neuroanatomical axes, directions, and planes of reference including anterior-posterior, dorsal-ventral, medial-lateral, and related terms.

📝 Lecture Summary

Control of molecules

In the phospholipid layers, lipid molecules and smaller molecules move more easily through the membrane. The cell membrane allows materials to move in and out depending on changes in membrane permeability. Increased permeability means the membrane can allow materials to pass that previously could not, while decreased permeability means the gates are closed.

Membrane permeability is determined by ionic state of membrane

Neurons communicate through constant movement of ions (molecules that are negatively or positively charged depending on the number of electrons they carry) in the intracellular and extracellular spaces. This constant flux generates electrical charges that enable neurons to send out electrical signals. Electrical charges are measured in millivolts (mV), and the difference of electrical charge between the intracellular and extracellular membrane is known as the potential.

Using a voltmeter with one electrode inside the cell and one outside, we find the inside has a large concentration of negatively charged ions while the outside has more positively charged ions. Thus, the inside is negative relative to the outside, and the difference in potential is recorded at -70 mV (about 1/15th of the difference in a household battery). This is the Resting Potential of the neuron. When positively charged ions enter the cell, the inside becomes positively charged (recorded at +50 mV), and the cell will fire an action potential. The voltage difference to reach an action potential is about 120 mV.

🔑 Definition — Resting Potential: The electrical potential difference across the neuronal membrane when the neuron is not active, typically -70 mV, with the inside negative relative to the outside.

🔑 Definition — Action Potential: A brief electrical impulse that travels along the axon when the neuron's membrane potential reaches threshold, involving a rapid reversal of charge (depolarization) to about +50 mV.

📌 Example: The inside of a neuron at rest has a large concentration of negatively charged ions, while the outside has more positively charged ions. When positively charged sodium ions rush in, the inside becomes +50 mV, triggering an action potential.

Ion Concentration Table

The table shows concentrations (in arbitrary units) inside and outside the cell at rest:

There is a high concentration of negatively charged molecules inside the cell, and these ions are trying to equalize the two sides of the cellular membrane.

Ionic movement follows two processes

Ions move along their osmotic/concentration gradient and electrostatic gradient. When molecules move from areas of high concentration to areas of low concentration to create equilibrium across a permeable or semipermeable membrane, this process is known as osmosis (nature strives for equilibrium). If concentration of ions is low on one side, ions move to equalize the balance on both sides. This is the osmotic gradient.

Similarly, the law of electricity states that like charges repel and unlike charges attract, so molecules move toward balancing the electrostatic gradient. Both osmotic and electrostatic forces work together continuously to create a constant state of movement of ions.

🔑 Definition — Osmotic gradient: The difference in concentration of ions across a membrane that drives movement from high to low concentration to achieve equilibrium.

🔑 Definition — Electrostatic gradient: The difference in electrical charge across a membrane that drives movement of ions toward opposite charges.

📌 Example – Glass of water analogy: Take a glass of water divided by a muslin cloth (sieve). Drop salt (sodium chloride = NA⁺ CL⁻) on one side. Diffusion occurs as molecules move to equalize both sides (osmotic gradient). However, the sieve does not allow large ions to pass, leaving CL⁻ on one side and NA⁺ on the other. Then the electrostatic gradient comes into action – negatively charged molecules on one side attract positively charged ones, allowing only smaller positively charged molecules to cross. This creates continuous flux.

This same kind of action takes place in the neuronal/axonal membrane, leading to resting and action potentials.

In the resting state of the axon, the membrane is impermeable to both large ions: positively charged sodium ions (outside) and anions (inside). The smaller chloride (negative) and potassium (positive) are continuously moving back and forth according to osmotic and electrostatic gradients. This changes when the axon receives inputs from the cell soma to fire – the cell membrane becomes permeable and large sodium ions rush in, making the inside positively charged.

Sodium-potassium pump

When cell permeability changes, large NA⁺ ions rush in and the inside becomes positively charged. The cell becomes impermeable again but is stuck with large sodium ions inside. Then, the cell membrane uses a biological pump called the sodium-potassium pump to push out NA⁺ and carry potassium molecules back inside the cell. This uses up to 40% of the cell's energy as it pushes ions against their osmotic gradients.

🔑 Definition — Sodium-potassium pump: A mechanism that actively transports sodium ions out of the cell and potassium ions into the cell, using energy (ATP) to maintain the resting potential against concentration gradients.

How resting potential changes to action potential

The cell at resting state receives inputs from all over, summated at the axonal hillock. Changes in the cell's electrical threshold occur. The inside is -70 mV relative to the outside.

• Hyperpolarization: Increase in negativity from -70 mV to -80 mV
• Depolarization: Decreases in negativity from -70 mV to -65 mV or -60 mV (small depolarizations)
• A larger depolarization leads to crossing the threshold and going up to +50 mV – this is an action potential that causes the cell to fire

Once the peak action potential is reached, the inside electrical charge starts becoming negative, dropping below -70 mV. After an action potential, the cell enters a refractory state (hyperpolarized) to about -75 mV. It will not fire until it returns to the resting state. The action potential lasts about 1/1000th of a second, and the refractory period can continue for several milliseconds.

🔑 Definition — Hyperpolarization: An increase in the membrane potential's negativity, making the cell less likely to fire (e.g., from -70 mV to -80 mV).

🔑 Definition — Depolarization: A decrease in the membrane potential's negativity, making the cell more likely to fire (e.g., from -70 mV to -60 mV).

📐 Formula: Threshold to action potential: Resting potential (-70 mV) → Depolarization crosses threshold → Peak (+50 mV) → Repolarization → Hyperpolarization (-75 mV) → Return to rest.

Firing and conductance

Firing of the action potential leads to conductance of the signal. The rate and speed of conductance is equivalent to 224 miles/hour (100 meters per second in cat brain; in humans, about 60 meters per second). The axonal conduction is an all-or-none phenomenon – the cell fires an action potential once threshold is reached, and the action completes once it begins.

Postsynaptic potentials

Once axonal transmission crosses to the postsynaptic site, it can lead to two types of action:

• Excitatory Post Synaptic Potentials (EPSPs): Cause the postsynaptic site to fire an action potential; stimulates action in the postsynaptic site
• Inhibitory Post Synaptic Potential (IPSPs): Inhibits ongoing firing of the cell it synapses on; brings activity to a resting state

Since multiple synapses exist on each cell (at dendrites and cell soma), some may be IPSP and some EPSP. These stimulations are summated – if stimulation crosses the excitatory threshold, the cell fires; otherwise, it stays in the resting state.

🔑 Definition — EPSP (Excitatory Postsynaptic Potential): A depolarizing potential that increases the likelihood the postsynaptic neuron will fire an action potential.

🔑 Definition — IPSP (Inhibitory Postsynaptic Potential): A hyperpolarizing potential that decreases the likelihood the postsynaptic neuron will fire an action potential.

Spatial and temporal summation

Multiple synapses continuously add together EPSPs and IPSPs. Two kinds of summation occur at the cell soma and axonal hillock:

A) Spatial summation: When a neuron receives inputs from several locations (EPSPs causing depolarization and IPSPs causing hyperpolarization), these spread across the cell membrane and reach the axonal hillock at the same time. They are integrated and summated algebraically. If the sum is slightly negative, small hyperpolarization occurs (from -70 mV to -75 mV).

B) Temporal summation: When a neuron receives input from the same location repeatedly over time (could be EPSPs or IPSPs), these are summed together one after another. One stimulation is received and has not yet faded when the second arrives, adding up, and so on. After summation at the axonal hillock, the neuron may depolarize further or hyperpolarize.

🔑 Definition — Spatial summation: The integration of postsynaptic potentials from multiple different locations on the neuron at the same time.

🔑 Definition — Temporal summation: The integration of postsynaptic potentials from the same location arriving over a short period of time.

Basic Neuroanatomy: Anatomical Axis, Directions and Planes of Reference

Before studying the brain, we must understand basic concepts of locations, sites, and their relationships. Just as we use North-South and East-West in geography, specialized terms identify directions in the brain.

Basic neuroanatomical axis: Anterior-posterior, dorsal-ventral, lateral-medial:

Anterior-posterior: Anterior is towards the front (nose end); posterior is towards the back (tail end). Structures in the front are anteriorly located; structures in the back are posteriorly located. This is also known as the rostral-caudal axis (rostral: towards the face; caudal: towards the tail).

Dorsal-ventral: Dorsal means towards the back (e.g., the dorsal fin of a shark); ventral is towards the chest/stomach region or bottom of the head. In humans, the dorsal surface becomes the back side as we stand – the top of the head and back side facing the vertebral column are dorsal areas.

Medial-lateral: Medial refers to areas towards the center or midline (the nose is medially located relative to the face). Lateral refers to areas towards the sides (ears are laterally located). Brain areas towards the outside are laterally located.

Other important terms:

Planes of reference: When the brain is dissected for study, sections are cut and referred to in planes of reference:

• Horizontal sections: Cut slicing the brain through from dorsal to ventral areas (or vice versa)
• Sagittal cuts: Made when moving in the lateral to medial-lateral direction; the mid-sagittal section is made through the middle of the two hemispheres at the point of joining
• Frontal section: Cut from the front of the brain towards the back

⭐ Key Takeaways

The resting potential of a neuron (-70 mV) results from unequal distribution of ions across the membrane, maintained by the sodium-potassium pump which consumes up to 40% of the cell's energy. Action potentials occur when depolarization reaches threshold, causing sodium ions to rush in and reverse the charge to +50 mV in an all-or-none fashion, followed by a refractory period. Neurons integrate multiple signals through spatial and temporal summation of EPSPs and IPSPs at the axonal hillock, determining whether the cell fires. The speed of axonal conduction is about 60 meters per second in humans, and action potentials last only about 1/1000th of a second. Understanding neuroanatomical directions (anterior-posterior, dorsal-ventral, medial-lateral) and planes of reference (horizontal, sagittal, frontal) is essential for localizing brain structures and functions.

🧠 Quick Revision Questions

1. What is the resting potential of a neuron, and what causes the inside to be negative relative to the outside?
2. How does the sodium-potassium pump work, and why does it require so much energy (up to 40% of the cell's energy)?
3. What is the difference between hyperpolarization and depolarization, and how does each affect the likelihood of an action potential?
4. Explain the difference between spatial summation and temporal summation in neuronal integration.
5. Define the following neuroanatomical terms: rostral, caudal, dorsal, ventral, medial, lateral, ipsilateral, and contralateral.

📘 Lecture 27 — Basic Neuroanatomy

📖 Overview: This lecture provides a foundational overview of basic neuroanatomy, detailing the major divisions of the brain—forebrain, midbrain, and hindbrain—and their key structures and functions. It emphasizes the phylogenetic concept of encephalization, where higher brain areas control more complex behaviors, and explores the specific roles of the brainstem, cerebellum, and midbrain nuclei in survival, movement, and sensory processing. Understanding this structural and functional organization is crucial for linking specific brain areas to behavior and neurological deficits.

🗂️ Topics Covered

The lecture begins with the objectives and assumptions of basic neuroanatomy, including the concept of encephalization. It then systematically describes the three major brain divisions: the forebrain (telencephalon and diencephalon), midbrain (mesencephalon), and hindbrain (metencephalon and myelencephalon). The structure and functions of the myelencephalon (medulla oblongata, cranial nerves, reticular formation), metencephalon (cerebellum, pons), and mesencephalon (tectum with superior and inferior colliculi) are explained in detail, including the effects of damage to these areas.

📝 Lecture Summary

Objectives and Main Purpose

The lesson aims to study the brain and peripheral systems, focusing on the forebrain, midbrain, and hindbrain, and the functioning of each anatomical location in the CNS. The main purpose is for students to become familiar with various brain areas' locations, functions, and their relationship to other areas, understanding how control and modulation of behavior occur at each neuroanatomical site.

Basic Neuroanatomy: Assumptions

Basic neuroanatomy is based on four key assumptions:

• The cortex is newly evolved and controls all major functions, especially in higher animals.
• Higher brain areas cover and grow over lower areas, requiring lower areas to send information up and receive commands back (e.g., the thalamus sends messages to cortices and receives commands).
• Lower underlying areas are more primitive and involved in survival functions (e.g., brain stem areas).
• These lower areas are similar in location, site, and function across lower and higher-order animals (e.g., the hypothalamus, the thalamus).

💡 Why this matters: This hierarchical organization is central to understanding how brain damage at different levels can produce different deficits, from basic survival reflexes to complex cognitive functions.

Encephalization

Phylogenetically, encephalization—the increasing control of functions by higher brain areas—has occurred, leading to greater adaptability. The greater the encephalization, the more functions are controlled by higher brain areas. Therefore, damage to these areas results in significant functional impairment (Bridgeman, 1988; Thompson 1980).

Major Divisions of the Brain

There are three major divisions: the Forebrain, Midbrain, and Hindbrain.

• Forebrain: Comprises the Telencephalon (cortical and some subcortical structures) and Diencephalon (the thalamus and hypothalamus).
• Midbrain: Consists of the older Mesencephalon.
• Hindbrain: The posterior-most part, with two sections: the Metencephalon and Myelencephalon.

These areas move from the frontal and dorsal areas to more caudal and ventral areas, with the telencephalon being the most anterior and dorsal, and the myelencephalon at the caudal-most end.

Telencephalon

The Telencephalon comprises the Cerebral Cortex, Corpus Striatum, Cingulate Gyrus, Septum, Amygdala, and Hippocampus (the last three are also part of the limbic system). This includes the phylogenetically newer cerebral cortex and older primitive structures that underlie it.

Diencephalon

The Diencephalon comprises the Thalamus, the junction and gateway for all sensory-motor and association pathways, and the Hypothalamus, which is the primitive survival center.

Mesencephalon

The Mesencephalon has the Tectum (comprising the Inferior Colliculi for auditory systems and the Superior Colliculi for the visual system), the Tegmentum, and the Cerebral Peduncles.

Metencephalon

The Metencephalon comprises the Cerebellum (which lies dorsally over the Pons) and the Pons.

Myelencephalon

The Myelencephalon comprises the Medulla Oblongata.

Brain Stem

The Brain Stem includes the Mesencephalon, Metencephalon, and Myelencephalon—technically everything between the spinal cord and cerebral cortex.

Myelencephalon: Medulla Oblongata

The Medulla Oblongata is an oblong, narrow structure that is a continuation of the spinal cord and the caudal part of the brain stem. Another important structure located here is the reticular formation.

The medulla contains all ascending and descending fiber pathways connecting the brain and spinal cord. It also has nuclei for the cranial nerves, especially those controlling respiration, heart rate, and digestive activity, which enter the brain at this level. Functions controlled here include breathing during sleep (sleep apnea), sneezing, swallowing, and vomiting.

🔑 Definition — Cranial Nerves (in the Medulla): Nerves that enter the brain at the level of the medulla, including those for the tongue, larynx, pharynx, ear, and vestibular system.

📌 Example: The Hypoglossal Nerve (Cranial Nerve XII) controls tongue movements. The Vagus Nerve (Cranial Nerve X) is involved in taste, larynx, pharynx, and ear functions. The Glossopharyngeal Nerve (Cranial IX) is related to taste in the posterior part of the tongue.

Sneezing and Vomiting

Sneezing: Occurs when the nasal mucosa is irritated. The sneezing center is located in the medial part of the medulla (also involving the trigeminal nerve). Vomiting: Found in the Medullary Reticular Formation.

Reticular Formation

The Reticular Formation is a crisscross of nerve fibers, nuclei, and cell bodies (reticulum means "the net"). It extends from the spinal cord to the thalamus. It is a phylogenetically old, well-organized area with both efferent and afferent ascending and descending fibers.

Ascending fibers go to the thalamus and cortex and are involved in sleep and awakening. The Raphe Nuclei produce serotonin and extend from the lower pons and medulla. Analgesia produced by electrical stimulation of the Periaqueductal Gray (PAG) occurs through the Raphe nuclei. The "Reticular Activating System (RAS)," important in arousal, was identified by Moruzzi and Magoun (1949) in cats. Stimulation of the Raphe Nuclei in a sleeping cat led to an arousal EEG response (low voltage, high frequency theta response), while lesions in this area caused a comatose stuporous state. Destruction of the Raphe Nuclei in cats led to insomnia, establishing the RAS's role in sleep and attention.

Metencephalon: Cerebellum and Pons

The Metencephalon contains many ascending and descending tracts and two important areas: the Cerebellum and the Pons.

Cerebellum

The Cerebellum lies over the pons. It is a phylogenetically older structure responsible for sensory-motor coordination, movement, and balance. It has two lobes like the cerebral cortex, with a large number of lobules separated by fissures (vermis, smaller grooves). Its nerve cell layer is 2mm thick, below which lies the white matter, and under that, the cerebellar nuclei.

The cerebellum receives inputs from the vestibular system, auditory and visual systems, reticular formation, and various regions of the cerebral cortex. It sends fibers to the reticular formation, thalamus, and vestibular system.

Damage to the cerebellum leads to disturbances of gait. Damage to one lobe causes postural imbalance. Damage to both cerebellar poles causes a tendency to fall backwards. In humans, ataxia (unsteadiness of gait) is seen, with symptoms including:

• Abnormalities in force, rate, and direction of rapid movements (e.g., overshooting targets, jerky movements).
• Impaired standing, walking, and coordinated movements.

🔑 Definition — Nystagmus: Rhythmic and involuntary oscillatory movements of the eyes, an oculomotor sign of cerebellar damage.

📌 Example: Cerebellectomy (removal of the cerebellum) leads to inability to maintain gaze, defective smooth pursuit movements, and difficulty with fixation.

The cerebellum contains specific neurons: Purkinje cells (long dendritic trees), Basket cells (short axons, dendrites cover Purkinje cells), Stellate Cells (axons terminate on Purkinje cells), and Granule cells (smallest, go vertical for communication).

💡 Why this matters: The cerebellum's role in fine-tuning movement explains why damage results in uncoordinated, jerky movements and balance problems, affecting daily activities.

Pons

The Pons is a bridge between the medulla, midbrain, and cerebellum. The medulla is caudally located, and the midbrain is rostrally located. The dorsal surface of the pons is covered by the cerebellum. Large, rounded pontine nuclei contain ascending and descending fiber bundles. One such bundle connects the brain stem and cerebellum and contains the pyramidal fibers from the cerebral cortex to the spinal cord (part of the cortico-spinal tract). The Trigeminal Cranial Nerve enters and leaves the brain at the level of the pons. Cranial nerves for feeding, facial expression, respiratory nuclei, and relay nerves for the auditory system are also located here.

The cortico-ponto-cerebellar tract is the largest group of fibers, originating from a wide area of the cerebral cortex (over 19 million fibers on each side). These fibers from primary cortical areas are involved in rapid correction of movements.

The Pontine Nuclei, specifically the Giant Pontine Cells, play an important role during rapid eye movement (REM) sleep by inhibiting body muscles to prevent damage from brain activation.

Mesencephalon

The Mesencephalon is a small, tubular portion between the hindbrain and the diencephalon—the anterior section of the brain stem. It has three main areas: tectum, tegmentum, and basis pedunculi.

The Tectum comprises two pairs of relay nuclei that look like four little lumps on the brain stem's surface: the Superior Colliculi and the Inferior Colliculi.

Superior Colliculi

The Superior Colliculi are composed of laminated grey and white matter. They are important in visual reflexes and eye movement. They are well-organized in terms of receptive fields and maps of visual space. They are part of the pathway from the optic tract to the visual cortex for eye movement and gross spatial localization. They are important for vertical gaze and pupillary reflexes. They receive inputs from the retina of the eyes, thalamus, and inferior colliculus, and send outputs to the thalamus and frontal and visual cortices.

Inferior Colliculi

The Inferior Colliculi are oval masses of small and medium-sized neurons and are major relay nuclei for the auditory pathway. Fibers come from the thalamus (Medial Geniculate Nuclei), auditory cortex, and cerebellar cortex. Fibers from the inferior colliculi project to the Medial Geniculate Nucleus (MGN), superior colliculi, and the cerebellum. Their function is the "turn-to-look-at-sound reflex" and localizing the source of sound. Therefore, both the inferior and superior colliculi work together as part of the reflex system for attending and turning towards the direction of a sound.

⭐ Key Takeaways

The most critical point is the hierarchical organization of the brain, with the phylogenetically newer forebrain (especially the cerebral cortex) exerting control over older, more survival-oriented midbrain and hindbrain structures. The brain stem (medulla, pons, midbrain) houses critical nuclei for basic life functions (respiration, heart rate, sleep-wake cycles) and cranial nerve reflexes, while the cerebellum is essential for motor coordination and balance. The reticular formation, particularly the RAS, is central to arousal and attention. Finally, the superior and inferior colliculi of the midbrain are key relay stations for visual and auditory reflexes, respectively, integrating sensory information for orienting responses.

🧠 Quick Revision Questions

1. What are the three major divisions of the brain, and which major structures does each contain?
2. What are the functions of the medulla oblongata, and what is the role of the reticular activating system (RAS)?
3. Describe the primary function of the cerebellum and list at least three symptoms of cerebellar damage.
4. What is the function of the superior colliculi and the inferior colliculi in the midbrain?
5. Explain the concept of encephalization and how it relates to the hierarchy of brain function.

📘 Lecture 28 — BASIC NEUROANATOMY

📖 Overview: This lecture continues the study of the Mesencephalon, examining the Tegmentum, Substantia Nigra, and Red Nucleus. It then explores the Corpus Striatum (Basal Ganglia) and the Limbic System, explaining their roles in motor control, movement disorders like Parkinson’s and Huntington’s disease, and emotional and memory functions.

🗂️ Topics Covered

The lecture covers the remaining structures of the Mesencephalon (Tegmentum, Substantia Nigra, Red Nucleus) and their functions. It then details the Mid Brain areas including the Corpus Striatum (Basal Ganglia, Caudate Nucleus, Globus Pallidus, Putamen) and their role in motor modulation and disorders. Finally, it describes the Limbic System, including the Hippocampus, Amygdala, Septum, and Cingulate Gyrus, and their involvement in emotion, memory, and survival behaviors.

📝 Lecture Summary

Remaining Areas of the Mesencephalon

• Tegmentum: This area lies between the Tectum and Substantia Nigra. It contains nuclei and relay fibres of ascending and descending tracts, as well as the motor cranial nerves for eye movements (oculomotor and trochlear). The three major fibre bundles are the Medial Lemniscus (ML) , the Trigeminal Lemniscus (TL) , and the Spino-thalamic tract (STT).

• The ML lies above the Substantia Nigra (SN) and conveys kinesthetic and discriminative touch sensory information to the Thalamus.

• The TL are tracts which also travel up to the Thalamus.

• The STT conveys pain and temperature sensations from the contralateral hemisphere (e.g., from the left arm to the right side of the brain).

• PAG (Peri-Aquaductal Gray) : This is the grey matter surrounding the cerebral aqueduct. It contains neural circuitry for sequences of movements for species-specific behaviors (fight, flight, and mating). Research has shown this to be an important area for pain sensations; if opiates are injected here, they reduce sensitivity to pain (raise the tolerance threshold).

• Cerebral Peduncles: In the basal portion of the tegmentum, these are large fiber bundles placed in the ventral region of the mesencephalon. They carry fibers of the cortico-spinal tract and the cortico-pontine tract. There are also large projections such as the parieto-occipito-temporo-pontine projections, which carry projections from the cerebral cortex down through the pontine area into the spinal cord.

• Substantia Nigra: A dark pigmented mass of neurons located between the cerebral peduncles and tegmentum. The zona compacta is rich in Dopamine and brain opiate receptors. This is part of the brain's motor control and modulation system and is involved in movement and balance. A unilateral lesion creates an imbalance, resulting in asymmetric body posture (the body turns from the high to the low region). If the Dopaminergic neurons degenerate in this area, it leads to Parkinson’s disease, characterized by tremor, rigidity, slowness of motor activity, stiffness in muscles, pin rolling movement, and loss of adaptation (facial expression and gait). Inputs come from the Neostriatum, cerebral cortex, Globus Pallidus, and other parts of the Tegmentum.

• Red Nucleus: An important area in the Tegmentum with neurons that have a pinkish hue. Inputs come from deep cerebellar nuclei and the cerebral motor cortex. If the deep cerebellar input is damaged, tremor is manifested when the hand or foot is in motion (reaching out). It controls gross movements of the body; unilateral electrical stimulation leads to circulatory motion, and lesions result in disturbances of gait (walking).

💡 Why this matters: The brain stem areas (Medulla, Pons, Mesencephalon) connect the Telencephalon and Diencephalon to the Spinal Cord. They show evolutionary differences: fish have large colliculi for direction while swimming, while bats have larger inferior colliculi for audition.

Mid Brain Areas: Corpus Striatum

The Corpus Striatum (Striated bodies) includes the Basal Ganglia, the Caudate (tail-like) Nucleus, Globus Pallidus (Pale Globe), and Putamen. These areas lie underneath the cerebral cortex.

The Corpus Striatum receives input from and sends output to the cerebral cortices, especially the frontal areas (motor lobe). It also sends fibres to the Thalamus (output). These areas modulate motor movement, especially the contralateral aspect of the body. They control initiation of movement, contralateral head turning, circling, licking, chewing, and gnawing. This is an important part of the Dopaminergic pathway involved in Parkinson’s disease. Bilateral lesions of the pallidus lead to a hypoactive and sleepy animal, which is the basis of decreased movement and hypokinesia in Parkinson’s disease. The Caudate promotes arousal of the motor system, balancing the controls of motor movement.

🔑 Definition — Gating function: The Basal Ganglia's role in limiting the access of information to motor systems, essentially preparing and executing movement. As motor skills are learned, the basal ganglia take over, making movements more automated and programmed (e.g., a child learning to walk). When basal ganglia are damaged, the individual reverts to slower, less automatic cortical responses.

• Huntington’s chorea is due to degeneration of Basal Ganglia, which reduces the inhibitory output of BG. This leads to increased access of sensory information, causing hyperkinesis, sudden jerks, tics, jerky movements of head, trunk, and extremities, facial grimaces, and repetitive dancing movements.
• In Parkinson’s disease, decreased Dopaminergic input inhibits action in Basal Ganglia, allowing cortical areas to stimulate the motor system. There is increased inhibition of inhibitory BG output, leading to hypokinesia. Damage to Basal Ganglia also results in deficits in cognitive functions, such as spatial memory and inability to switch to appropriate behaviour.

Limbic System

• Limbic System: This borders the Telencephalon and Diencephalon, appearing like a ring around the Thalamus. First described by Broca in 1878, it is also known as the Circuit of Papez, identified by Papez (1937) as a reverberating circuitry important in emotions. Limbic areas are spread into parts of the Frontal, Parietal, and Temporal lobes, giving it diverse connections and functions. These are mainly emotions, but also memory, homeostatic, and survival functions (fight, flight, feed, and mating). The areas part of the limbic system are: Cingulate Gyrus, Septal Nuclei, Hippocampus, Amygdala, Hypothalamus, Anterior Thalamus, and Mammilliary Bodies.

• Hippocampus (shaped like a sea horse): Important in the formation of memories, especially long-term. Bilateral lesions damage learned emotional responses and severely affect memory (both recent and long term). The hippocampus is involved in emotions, memory, homeostatic responses (fight/flight), and motivational states.

• Fornix: A large fibre bundle shaped in the form of an arch that connects the hippocampal formation to subcortical areas such as the thalamus, hypothalamus, and septum. It runs directly under the corpus callosum.

• Amygdala (almonds): A major part of the limbic system, located at the tip of the temporal lobe beneath the cortex and rostrally to the hippocampus. It has connections with the hippocampus, septum, mediodorsal thalamus, and prefrontal areas. The amygdala is important in emotional responses like love, friendship, fear, and rage aggression. It is involved in the physiological response of emotions (heart rate, pulse), orienting to novel stimuli, and déjà vu. Stimulation can lead to olfactory and gustatory hallucinations (temporal lobe epilepsy). Bilateral lesions lead to Kluver-Bucy syndrome: hyperorality, hypersexuality (animate or inanimate objects), docility, loss of learned fears (e.g., snakes put in mouth), lack of affect, apathy, and blunted expression. This syndrome was first described by Kluver and Bucy in 1939 after bilateral lesions in monkeys.

• Electrical stimulation of the Amygdala leads to a rage reaction. The amygdala is involved in identification of danger, important for self-preservation. When triggered, it gives rise to fear and anxiety, leading to a stage of alertness, ready for flight or fight.

• Septum: Lesions in the septum lead to intense rage reaction (called the Septal Rage), similar to stimulation of the amygdala. Septum leads to increased activity in a novel situation and increased reward feeling with stimulation. It also plays an important role in motivational states such as feeding and drinking.

• Cingulate Gyrus (Cingulate: encircling): Located between the cingulate sulcus and the corpus callosum. The anterior area gives rise to déjà vu (smells and sights with pleasant memories of previous emotions). It also plays an important role in emotional reaction to pain and aggression. A cingulectomy tames unruly and wild animals. If a single bundle of this gyrus is cut (cingulotomy), it interrupts the limbic areas' communications with each other (reverberating circuitry affected), leading to reduced depression and anxiety levels.

⭐ Key Takeaways

The lecture details the critical roles of midbrain structures in motor control and modulation. The Substantia Nigra's dopaminergic neurons are essential for movement, and their degeneration causes Parkinson's disease. The Basal Ganglia (part of the Corpus Striatum) acts as a gate for motor commands, and its dysfunction leads to either hyperkinesia (Huntington's chorea) or hypokinesia (Parkinson's disease). The Limbic System, including the Amygdala, Hippocampus, and Septum, is the central circuit for emotions, memory, and survival behaviors, with specific syndromes like Kluver-Bucy (amygdala lesions) and Septal Rage (septal lesions) illustrating its functions.

🧠 Quick Revision Questions

1. What are the three major fibre bundles of the Tegmentum, and what sensory information does each convey?
2. What is the function of the Substantia Nigra, and what disease results from the degeneration of its dopaminergic neurons?
3. Explain the "gating function" of the Basal Ganglia, and how does its dysfunction lead to symptoms in Parkinson's and Huntington's disease?
4. Describe the location and primary functions of the Hippocampus and the Amygdala within the Limbic System.
5. What is Kluver-Bucy syndrome, and which brain structure's bilateral lesion causes it?

📘 Lecture 29 — BASIC NEUROANATOMY

📖 Overview: This lecture explores the fundamental anatomical structures of the brain, focusing on the diencephalon (hypothalamus and thalamus) and the telencephalon (cerebral cortex and corpus callosum). It explains how these regions control survival functions, sensory processing, movement, and higher cognitive behaviors, linking specific locations to their behavioral outcomes.

🗂️ Topics Covered

The lecture begins with the diencephalon, detailing the hypothalamus (survival functions, hormonal control, feeding/thirst) and the thalamus (sensory relay, multimodal integration, sleep/attention). It then moves to the telencephalon, covering the corpus callosum and the cerebral cortex—its layers (allocortex, mesocortex, neocortex), lobar organization (frontal, parietal, temporal, occipital), cytoarchitectonics (six layers), and hemispheric specialization (speech, spatial skills, aphasias, apraxias).

📝 Lecture Summary

Diencephalon

This comprises two major areas: the hypothalamus and the thalamus, both critical for a wide range of behaviors and connections.

Hypothalamus: It lies at the base of the brain, on both sides of the 3rd ventricle. It is very small but extremely important. Hypothalamus is located immediately beneath the thalamus and lies above the pituitary. It is part of the Limbic system and is involved in all survival responses (fight-flight). The Medial forebrain bundle (MFB) carries major neurotransmitters through it. The superchiasmatic nucleus (SCN) lies underneath and controls day-night (diurnal) cycles. The mammillary bodies are important for memory. The hypothalamus secretes its own hormones that act as releasing factors for the pituitary, establishing the crucial hypothalamic-pituitary connection for neural-endocrine communication. It regulates fear, aggression, temperature, food/water intake, and mating. The Anterior hypothalamus regulates thirst via sensors that monitor fluid balance. The Ventromedial hypothalamus (VMH) is the satiety center (stop-eating signal), while the Lateral hypothalamus (LH) is the center for initiation of feeding. 💡 Why this matters: The hypothalamus manages body survival functions rather than intellectual functions.

🔑 Definition — Hypothalamus: A small brain region at the base of the diencephalon that regulates homeostasis, survival behaviors (feeding, thirst, temperature), and hormonal release via the pituitary.

Thalamus: This is the largest component of the diencephalon, with an oval shape and two lobes connected by the mass intermedia through the midline of the third ventricle. It comprises large clusters of nuclei and acts as a staging area—receiving sensory information and projecting it to relevant cortical areas. Sensory relay nuclei receive all afferent sensory input: visual and auditory input goes through the lateral geniculate nuclei and medial geniculate nuclei, while somatosensory fibers go to somatosensory cortices. There is a reciprocal one-to-one relationship—if a cortical fiber degenerates, the relevant thalamic area atrophies. The Dorsal group of fibers is multimodal, receiving input from within thalamic regions and projecting to association cortex. The Intrinsic (non-specific) group, when stimulated, causes widespread electrical discharge in the cortex, indicating its role in electrical activity, sleep-wake cycles, and attention. Lesions to the midline thalamic area cause severe amnesia. Thus, the thalamus is important in every aspect of behavior.

🔑 Definition — Thalamus: The largest structure of the diencephalon that relays sensory and motor signals to the cerebral cortex and regulates consciousness, sleep, and attention. 📐 Formula: Sensory input → Thalamus (relay/sort) → Relevant cortical areas

Telencephalon

The end brain comprises the cerebral cortex, parts of the Corpus striatum, and the limbic system. The two hemispheres are connected by commissures (bands of fibers).

Corpus Callosum: This is the major band of fibers joining the two hemispheres. It is wide, white, and visible to the naked eye. The commissures allow interaction and crossing over of information so the two hemispheres can coordinate decisions.

🔑 Definition — Corpus Callosum: The largest commissural fiber bundle connecting the left and right cerebral hemispheres, enabling interhemispheric communication.

Cerebral Cortex: (cortex means outer covering or "bark" of the brain). It is made of layers of grey matter covering white matter. Thickness varies from 1.5 to 4.5 mm (average ~2.00 mm), thickest in the primary motor cortex (4.5 mm) and thinnest in the primary visual cortex (1.5 mm). Total surface area is about 20 sq. feet, folded into irregular convulations and grooves called sulci (small) and fissures (large). The area between two fissures is called a gyrus; 2/3rds of the cerebral cortex is in these gyri. The two major fissures are the Central fissure (Fissure of Rolando) separating frontal from parietal lobe, and the Temporal fissure (Sylvian fissure) separating frontal from temporal lobe.

There are several types of cortices: Neocortex (newly evolved), Allocortex (older cortex divided into paleocortex and archicortex). The paleocortex includes the primary olfactory cortex; the archicortex includes the hippocampal formation (similar to human cerebral cortex in connections, characteristics, and neuron types). Mesocortex (middle cortex) is found in the cingulate gyrus and parahippocampal areas. The Neocortex (iso cortex) has 6 layers and is more recent evolutionarily. In humans, 90% of the cortex is neocortex, with rough, convulated surfaces (smooth in primitive animals). The cortex is organized in a one-to-one manner: incoming information to specific areas, outgoing from motor cortex, and association cortex for higher functions.

🔑 Definition — Gyrus: A ridge or fold between two sulci or fissures on the cerebral cortex. 🔑 Definition — Sulcus: A shallow groove on the surface of the cerebral cortex. 🔑 Definition — Fissure: A deep groove separating major brain regions (e.g., central fissure). 🔑 Definition — Neocortex: The six-layered, evolutionarily newest part of the cerebral cortex, responsible for higher-order functions (90% of human cortex).

Lobes of the Cerebral Cortex

Frontal Lobe: Lies rostrally to the Central fissure. Caudally to the precentral fissure is the primary motor area, most important for body movement. The motor homunculus maps motor movements and muscles in a disproportionate manner (e.g., tongue and thumb have greater representation than torso). Electrical stimulation leads to movement in the contralateral body; lesions cause contralateral paralysis (as in stroke). Rostral to the precentral sulcus is the premotor area, involved in initiating and changing movement. Rostral to that is Brodmann's area 8 (frontal eye fields) for conjugate eye movements. The Broca's area is important for speech articulation; lesions cause aphasia.

🔑 Definition — Motor Homunculus: A distorted topographic map of the body in the primary motor cortex where body parts are represented proportionally to their need for fine motor control.

Parietal Lobe: Lies caudally (behind) the central sulcus. The primary somatosensory cortex is here. The sensory homunculus maps body sensations (disproportionate to size, proportional to need). Stimulation causes tingling/numbness in the contralateral part. It is involved in behavioral interaction with personal space. Lesions cause sensory neglect of contralateral space (e.g., patient shaves only half the face, eats half the plate). The parietal lobe is also involved in object recognition and language comprehension.

Temporal Lobe: Lies caudal to the lateral gyrus. The superior area contains the primary auditory cortex and Wernicke's area (important for speech comprehension). The inferior temporal lobe processes perception of visual form and color (close to occipital and parietal lobes).

Occipital Lobe: Contains the primary and secondary visual cortex for visual processing, laid out in well-organized layers (Brodmann areas 17, 18, 19). This is the striated cortex where left and right eye images are represented. Hubel and Wiesel identified ocular dominance columns.

Cytoarchitectonics: Layers of Cerebral Cortex

The cellular architecture of the cerebral cortex has six layers, organized in terms of cell layers:

Key cells: Granule cells have short branching axons and dendritic branches. Pyramidal cells are pyramid-shaped, send axons to layers below, have long apical dendrites extending to other layers (even to spinal cord), requiring a bigger cell body for energy.

Cerebral Cortex: Two Hemispheres

The two independent lobes are connected by commissures. Research by Gazzaniga, Milner, Sperry showed that hemispheres are specialized: speech in the left hemisphere (Broca) and spatial functioning in the right hemisphere. Milner's WADA test (anesthetizing one hemisphere via sodium amytal through the carotid artery) showed that 92% of right-handed persons have left hemisphere speech dominance.

Aphasias are language/speech disorders with left hemisphere damage. Apraxias are movement disorders where the patient fails to perform on verbal command but can do so spontaneously.

Theories of cerebral asymmetry: Levy and Sperry state two basic modes—analytical (LH) and synthetic/gestalt (RH), with differently wired neural circuitry. Lenenberg states both hemispheres are equipotential up to two years. Kinsberg states specialization is present at birth (the planum temporale in the temporal lobe is larger on the left side in the fetus).

🔑 Definition — WADA Test: A procedure where one cerebral hemisphere is anesthetized to determine language dominance; left hemisphere dominance is found in most right-handed individuals.

⭐ Key Takeaways

The diencephalon (hypothalamus and thalamus) is critical for survival functions and sensory relay: the hypothalamus regulates homeostasis (thirst, feeding, temperature, hormonal release via the pituitary), while the thalamus relays all sensory information to the cortex and influences sleep, attention, and memory. The telencephalon includes the cerebral cortex (neocortex with six layers, each with specific cytoarchitectonic features) and the corpus callosum connecting hemispheres. Each lobe has distinct functions: frontal (motor, speech production via Broca's area), parietal (somatosensory, spatial awareness), temporal (auditory, speech comprehension via Wernicke's area), and occipital (vision). Hemispheric specialization shows left dominance for speech (verified by WADA test) and right for spatial skills; theories debate whether this is innate or develops later. The cortex's folded structure (gyri, sulci, fissures) maximizes surface area within the cranium.

🧠 Quick Revision Questions

1. What are the two major components of the diencephalon, and what are their primary functions?
2. How does the hypothalamus control feeding behavior, and which specific regions are involved?
3. Describe the six layers of the neocortex and the types of cells found in each layer.
4. What is the role of the corpus callosum, and what happens when it is damaged?
5. Explain the difference between aphasia and apraxia, and which brain regions are associated with each.

📘 Lecture 30 — Basic Neurochemistry

📖 Overview: This lecture introduces the fundamental concepts of neurochemistry, focusing on the classification and functions of neurochemicals found in the brain. It explains the critical role of neurotransmitters in neural communication, the structure and function of the synapse, and the strict scientific criteria that a chemical must meet to be classified as a neurotransmitter. Understanding these basics is essential for linking brain chemistry to behavior and the effects of psychoactive drugs.

🗂️ Topics Covered

This lecture covers the definition and classification of neurochemicals into neuromodulators, neuroregulators, neurohormones, and neurotransmitters. It details the historical breakthroughs in neurotransmitter research, the structure and function of the synapse (pre-synaptic, synaptic cleft, and post-synaptic membranes), and the process of neurotransmission. Finally, it provides a comprehensive, step-by-step breakdown of the twelve criteria required for a chemical to be classified as a full neurotransmitter.

📝 Lecture Summary

Definition and Classification of Neurochemicals

Neurochemicals are chemicals found within the brain, either manufactured there or transported via blood circulation. They are essential for cellular metabolism, ionic movements, enzymatic actions, and neural communication. All neurochemicals share three main characteristics: a) they have demonstrated electrophysiological activity (changing the electrical potential of neurons), b) they are found in high concentrations only in the Central Nervous System (CNS), and c) changes in their concentration lead to changes in brain and behavioral states. They are classified into four major categories based on their chemical composition, roles, and functions: neuromodulators (modulate ongoing action in neuronal systems), neuroregulators (act as second messengers to regulate ongoing transmission, e.g., calcium-gated channels), neurohormones (secreted by the pituitary and hypothalamus to regulate motivational states, circadian rhythms, and stress), and neurotransmitters (involved in the direct transmission of neural messages). The first neurotransmitter identified was Acetylcholine (Ach), which acts at neuromuscular joints.

💡 Why this matters: This classification helps us understand that brain chemicals have distinct, specialized functions—some directly pass messages (NTs), while others regulate or modulate broader brain states (hormones, modulators).

Historical Breakthroughs in Neurotransmitter Research

Three major breakthroughs in the 1950s and 1960s advanced the field. First, the discovery of monoamines (serotonin, dopamine, epinephrine) in the brain. Post-mortem studies of Parkinson's disease patients showed degeneration in dopaminergic brain areas, and treatment with L-Dopa (a dopamine stimulant) remarkably reduced symptoms, linking dopamine to Parkinson's disease. Second, the development of biochemical procedures like spectrophotoflourescence allowed for the detailed examination of putative neurotransmitters. Third, increased interest followed the manufacture of drugs like reserpine and chlorpromazine (for treatment) and recreational drugs like LSD, mescaline, and marijuana. These events opened the door for extensive neurotransmitter research. Putative neurotransmitters are those suspected to be neurotransmitters but have yet to fully complete the strict criterion for NT status, including many neuropeptides like endorphins.

🔑 Definition — Putative Neurotransmitters: Chemicals suspected of being neurotransmitters but have not yet satisfied all the established scientific criteria to confirm that status.

The Synapse: Structure and Function

The synapse is the junction between two neurons where communication occurs. It has three main components: the pre-synaptic ending, the synaptic cleft, and the post-synaptic ending. The pre-synaptic membrane contains synaptic vesicles (storage containers for NT), mitochondria (for energy), and releases NT through exocytosis (vesicle fuses with membrane, ruptures, and releases NT molecules). The synaptic cleft is the minute space between membranes, surrounded by extracellular fluid, and held together by a synaptic web of glial cells. It contains enzymes to inactivate stray NT molecules. The post-synaptic membrane can be on the cell soma (axo-somatic), dendrites (axo-dendritic), or axons (axo-axonic). Here, NT molecules bind to receptor sites, leading to either an Excitatory Post-Synaptic Potential (EPSP) or an Inhibitory Post-Synaptic Potential (IPSP). The effect depends on the type of NT, the neuroanatomical site, and the amount of NT released.

🔑 Definition — Exocytosis: The process by which a synaptic vesicle fuses with the pre-synaptic membrane and ruptures to release its neurotransmitter molecules into the synaptic cleft.

Criterion for a Neurotransmitter

A neurochemical must satisfy a strict, twelve-part criterion to be classified as a full neurotransmitter (NT). These criteria ensure the chemical is actively involved in synaptic transmission.

1. Localization: The NT molecules must be identified within the presynaptic ending of the neuron using methods like histoflourescence and autoradiography.
2. Storage: There must be clear evidence of synaptic vesicles containing the NT in the presynaptic terminal.
3. Precursor and Enzymes: The precursor chemical and appropriate synthesis enzymes must be found within the presynaptic neuron, as each neuron manufactures its own NT.
4. Release on Stimulation: With appropriate stimulation, the release of the NT from the presynaptic ending into the synaptic cleft must be demonstrated and measurable.
5. Synaptic Mimicry: Drugs with the same chemical composition as the NT, when injected into the synapse, should mimic the NT's effect.
6. Recognition and Binding: Released NT molecules must travel across the synapse and recognize specific sites to which they can bind.
7. Existence of Receptors: There must be a clear demonstration of receptor proteins on the post-synaptic site that match the chemical configuration of the NT.
8. Effect on Post-Synaptic Membrane: The binding must lead to an action, either an EPSP or an IPSP.
9. Inactivating/Deactivation Mechanism: There must be demonstrated mechanisms (enzymes or reuptake) to inactivate free NT molecules in the cleft and presynaptic membrane.
10. Predictable Pharmacological Effects: Endogenous substances and synthetic compounds with similar properties must have the same demonstrable effects.
11. Post-Synaptic Effects: The post-synaptic effect should be enhanced by similar chemicals (agonists) and blocked by antagonists (blocking agents).
12. Correlation with Stimulation: Selective electrical or chemical stimulation should lead to NT release, and the amount of NT released should be correlated with the amount of stimulation.

⭐ Key Takeaways

The most critical concepts from this lecture are that neurochemicals are classified based on function into neuromodulators, neuroregulators, neurohormones, and neurotransmitters. The synapse, composed of a pre-synaptic terminal, cleft, and post-synaptic membrane, is the primary site of neural communication where neurotransmitters are released via exocytosis and bind to receptors. For a chemical to be considered a true neurotransmitter, it must satisfy a rigorous set of 12 criteria covering its synthesis, storage, release, receptor binding, effect, and inactivation. Understanding these processes is the foundation for studying how drugs and psychoactive substances alter brain function and behavior. Finally, the historical breakthroughs in the mid-20th century, particularly linking dopamine to Parkinson's disease, were pivotal in establishing the field of psychopharmacology.

🧠 Quick Revision Questions

1. What are the four major categories of neurochemicals, and what is the primary function of each?
2. Describe the three main components of a chemical synapse and the specific event that occurs at each component during neurotransmission.
3. What is exocytosis, and what is its role in neurotransmitter release?
4. List at least four of the twelve criteria that a chemical must meet to be classified as a neurotransmitter.
5. What was the significance of the discovery of dopamine deficiency in patients with Parkinson's disease in the 1950s and 1960s?

📘 Lecture 31 — Basic Neurochemistry

📖 Overview: This lecture explores the foundational principles of neurochemistry, detailing the step-by-step process of synaptic transmission, from synthesis to recycling of neurotransmitters. It also classifies the major neurotransmitters and explains their roles in behavior modulation, along with methods used to locate and study these neurochemicals in the brain. This knowledge is crucial for understanding how drugs affect behavior and how neurological aberrations arise.

🗂️ Topics Covered

The lecture covers the six major steps of synaptic transmission: synthesis, release, generation of postsynaptic potential, action in the postsynaptic membrane, inactivation, and vesicular membrane recycling. It then details the methods for locating neurotransmitters, including histofluorescence, receptor binding autoradiography, monoclonal antibodies, and microiontophoresis. Finally, it classifies the six major groups of neurotransmitters: amino acids, monoamines (catecholamines and indoleamine), soluble gases, acetylcholine, and neuropeptides.

📝 Lecture Summary

Neurotransmitters: synaptic transmission

Synaptic transmission is divided into several clear-cut, sequential steps, each dependent on the previous one.

1. Synthesis of the NT and storage in the synaptic vesicles

Synaptic vesicles are storage containers that protect neurotransmitters from deactivating enzymes. They are manufactured from proteins by the Golgi apparatus in the cell body and travel down the axon to the synaptic buttons via the axonal transport system. For Neuropeptides (short chains of amino acids), packaging occurs in the cisternae within the synaptic buttons. For non-peptide neurotransmitters, packaging into vesicles occurs within the cytoplasm before transport. The axonal transport system has two directions:

• Anterograde (forward) axonal transport moves materials from the cell body to the synaptic ending through microtubules. The fast anterograde transport moves synaptic vesicles at a speed of 400 millimeters per day.
• Slow anterograde transport is used when materials and vesicles ooze along the axon at a speed of less than 10 millimeters per day.

2. Release of the Neurotransmitter

When an action potential reaches the presynaptic ending, it triggers the opening of calcium-gated channels. Calcium entering the terminal button triggers the release of the neurotransmitter through a process called exocytosis. This involves: a) Vesicles moving to the terminal membrane. b) Vesicles fusing with the presynaptic membrane to release neurotransmitter molecules into the synaptic cleft. c) The vesicle membrane merging with the presynaptic membrane, which then mends.

3. Generation of the post synaptic potential

This describes the action at the receiving end after the neurotransmitter molecule crosses the synaptic cleft and binds to the postsynaptic membrane.

a) Binding of NT molecules to post receptor site: Molecules must chemically "bind" to a specific receptor protein on the membrane. Only molecules with the correct shape and chemical composition can bind, opening gates for specific molecules.

b) Changes in ionic gates: The binding leads to changes in chemically-gated ion channels via two methods: i) Direct method: Binding directly opens or closes the channels. ii) Indirect method: A series of chemical changes occur through a 2nd messenger, specifically Cyclic Adenosine Monophosphate (CAMP). CAMP is involved in converting ATP (Adenosine triphosphate) to cAMP, which is needed for cellular energy.

4. Action in the Post Receptor membrane

Two kinds of actions can occur in the postsynaptic membrane:

• Excitatory Postsynaptic Potential (EPSP): Generates an action potential in the postsynaptic membrane.
• Inhibitory Postsynaptic Potential (IPSP): Inhibits ongoing activity in the cell membrane.

These actions depend on the type of neurotransmitter involved and the site of action. A neurotransmitter may be excitatory at one site and inhibitory at another.

5. Inactivation of the NT

Neurotransmitters must be removed from the cleft to maintain system efficiency. Two main processes deactivate them:

• Reuptake: The neurotransmitter returns to the presynaptic area to be reabsorbed, repackaged into vesicles, and reused.
• Deactivating: Specialized enzymes locate and degrade free-floating neurotransmitter molecules in the synaptic cleft.

💡 Why this matters: Without these deactivation processes, a single dose of a stimulant could have a lifelong effect, and the synaptic cleft would become cluttered with molecules.

6. Recycling of the vesicular membrane

Vesicles that ruptured during exocytosis are recycled. Excess membrane pieces are broken off and returned to the cytoplasm. They can then be: a) Filled with non-peptide NT by the cisternae. b) Sent back to the cell body by retrograde transport (traveling at 200 millimeters per day). c) Refilled with NT by the Golgi bodies in the cell soma. d) Broken down and their molecules recycled.

Methods of Locating NT

Several techniques are used for localizing neurotransmitters and their projections:

1. Histofluoresence Technique: Developed by Falck and Hillarp in the early 1960s. When monoamine neurotransmitters are exposed to formalin fixative, they glow under a fluorescent light. This technique is useful for locating monoamines but cannot differentiate between different types within the class.

2. Receptor Binding Autoradiography: Neurotransmitters are radiolabeled with a radioactive isotope (e.g., Hydrogen-3 or Carbon-3). The labeled ligand (molecule that binds to a target) is then exposed to neural tissue. The tissue is placed on a photographic plate, where high radioactivity areas show up.

3. Monoclonal Antibodies: This uses immunocytochemistry procedures. Specific monoclonal antibodies are developed to target particular proteins (all NTs are chains of amino acids) and are injected to identify specific regions and target proteins.

4. Microiontophoresis (push pull cannulae): This procedure analyzes chemicals released within the synapse. A double-barreled pipette monitors the response of postsynaptic sites. A weak current stimulates the neuronal ending, causing a discharge that is pulled out for analysis and checked for EPSPs or IPSPs on an oscilloscope.

Major Neurotransmitters

There are six major groups of neurochemicals classified as neurotransmitters:

1. Amino acids: Formed from chains of amino acids. This large group includes Glutamate (excitatory), GABA (Gamma-Aminobutyric Acid) (inhibitory), Glycine, and Aspartate. These have relatively quick-acting synaptic connections.

2. Monoamines I: Catecholamines: Synthesized from a single amino acid and have one catechol group. Neurons have bulbous, bead-like knobs. The major catecholamines are: Dopamine, Norepinephrine (also known as Noradrenaline), and Epinephrine (also known as Adrenaline).

3. Monoamines II: Indoleamine: Also a monoamine but with a different structure (indoleacetic acid). The major indoleamine is Serotonin.

4. Soluble gases: Small molecule neurotransmitters that are lipid-soluble and diffuse through cell membranes. They work through 2nd messengers and break down immediately. Nitric oxide and carbon monoxide are two examples.

5. Acetylcholine: A small molecule transmitter that is unique; there are no other NTs in this group. It is the only NT that works on neuromuscular joints.

6. Neuropeptides: A large number of peptides that are possible NT candidates. Well-known examples include the brain opioids, Endorphins (large molecules), Enkephalins (small molecules), pituitary peptides, and Substance P.

🔑 Definition — Exocytosis: The process by which a vesicle's contents are released into the synaptic cleft by the fusion of the vesicle membrane with the presynaptic membrane. 🔑 Definition — Second Messenger: A molecule (like CAMP) that intervenes in a signal from a neurotransmitter binding to a receptor, translating the message for further action inside the cell. 🔑 Definition — Reuptake: The process by which a neurotransmitter is taken back into the presynaptic neuron for recycling. 📐 Formula: Fast Anterograde Transport Speed = 400 mm/day → The very fast speed at which synaptic vesicles are transported from the cell body to the synaptic ending. 📌 Example: Receptor Binding Autoradiography: A neurotransmitter like dopamine is radiolabeled. This labeled molecule is injected into a brain area. The animal is then killed, and the brain is sliced and exposed to a photographic plate. Dark spots on the plate indicate where the radioactive dopamine bound to its receptors.

⭐ Key Takeaways

Students must remember the six sequential steps of synaptic transmission, as this process is fundamental to all neural communication. The critical role of calcium in triggering exocytosis, and the distinct functions of the direct and indirect methods of ion channel opening, are essential. The difference between EPSP and IPSP is a core concept for understanding neural excitation and inhibition. Finally, knowing the six major neurotransmitter groups (Amino acids, Catecholamines, Indoleamines, Soluble gases, Acetylcholine, and Neuropeptides) and the function of key examples like Glutamate, GABA, and Dopamine is crucial for understanding behavior and the action of drugs.

🧠 Quick Revision Questions

1. What are the two directions of axonal transport, and what are their respective speeds?
2. Name the ion whose influx triggers the release of neurotransmitters via exocytosis.
3. What are the two main processes by which a neurotransmitter is inactivated in the synaptic cleft?
4. What does EPSP stand for, and what effect does it have on the postsynaptic neuron?
5. List the six major groups of neurotransmitters mentioned in the lecture.

📘 Lecture 32 — Basic Neurochemistry

📖 Overview: This lecture covers the fundamental principles of neurochemistry with a primary focus on dopamine as a major catecholaminergic neurotransmitter. It explains the synthesis pathway of dopamine, its three major neural pathways in the brain, and how pharmacological agents can modify dopamine function at each step of synthesis and transmission. The lecture also explores dopamine's critical role in modulating key behaviors including motor activity, depression, hyperactivity, and schizophrenia.

🗂️ Topics Covered

The lecture begins with an introduction to major neurotransmitters and classification systems including monoamines (catecholamines and indoleamines), acetylcholine, amino acids, and peptides. It then provides an in-depth examination of dopamine, covering its discovery, synthesis pathway from tyrosine, the D1 and D2 receptor types, and the three major dopaminergic pathways (nigrostriatal, mesolimbic, and tuberoinfundibular). The mechanisms of synaptic transmission and drug action are detailed, including the specific steps where agonists and antagonists can interact. The lecture concludes with a comprehensive analysis of dopamine's behavioral correlates, examining its involvement in motor activities, Parkinson's disease, depression, hyperactivity, and schizophrenia.

📝 Lecture Summary

Objectives

The objectives of this lecture are to familiarize students with various neurotransmitters and their role in modulating behaviors, the classification of neurotransmitters including monoamines (catecholamines and indoleamines), acetylcholine, amino acids, and peptides, the role of neurotransmitters in behavioral modulation and aberrations, the classification of psychopharmacological substances, behavioral correlates and treatment, and the mechanisms of synaptic transmission.

Major Neurotransmitters: Dopamine

Dopamine (DA) is a major catecholaminergic neurotransmitter discovered by Udenfriend in 1964. It is the first step in the synthesis chain of the Adrenergic (also known as Epinephrine) and Noradrenergic (also known as Norepinephrine) neurotransmitter systems. Dopamine was the last to be given the status of a neurotransmitter because it was initially thought to be only an intermediary step in the synthesis of Norepinephrine. Dopamine has a major influence on behavior, especially motor behavior and schizophrenia. These chemicals are also found in the body in the adrenal glands and are used in sympathetic action during emotional states; however, whatever is produced in the body cannot cross the blood-brain barrier to enter the brain. The brain manufactures all the chemicals it needs from precursors (the first compound in the chain), which are taken from the blood circulation.

DA has two types of receptors in the brain: D1 and D2.

🔑 Definition — D1 receptors: These are linked to the stimulation of adenylate cyclase. They are present in the Corpus Striatum, and the Butrypheneones (a class of drugs known as neuroleptics or antipsychotics) are weak antagonists for these receptors.

🔑 Definition — D2 receptors: These are linked to the inhibition of adenylate cyclase. They are present in the pituitary and the Corpus striatum. The Butrypheneones are potent antagonists for these receptors.

DA Pathways

There are three major pathways of the dopamine system:

1. The Nigrostriatal DA system: This is the largest and longest bundle of fibers of neurons containing DA. This major tract has 80% of the brain's dopamine. It originates in the Zona Compacta of the Substantia Nigra and sends projections to the Corpus Striatum. The degeneration of this system leads to Parkinson's disease (a major motor disorder where voluntary movements become increasingly difficult and only stereotypic movements are seen). This system is also involved in schizophrenia. Reduced levels of DA in this system lead to Parkinson's disease, and increased levels lead to schizophrenic symptoms.

2. Mesolimbic system: This is a medially located diffuse (widespread projections) system. It sends nerve fibers to forebrain areas such as the frontal cortical area, the cingulated cortex, the amygdala, and the septum. As the name implies, it is involved with the limbic system (emotional system). Antipsychotic drugs act here to reduce the apathy and lack of affect (emotional content) characteristic of schizophrenia.

3. Tuberoinfundibular system: This is also known as the hypothalamic-hypophyseal connection. It originates from arcuate and periventricular regions of the hypothalamus, with very short fibers ending in the intermediate lobe of the pituitary. This system appears to play a role in hormonal controls and modulations.

Synthesis Pathway

As a rule, the brain manufactures its own neurochemicals including dopamine from the precursor taken in from the blood supply.

Step 1: Phenylalanine is taken in from food and is immediately hydroxylated (adding a hydroxyl molecule) by the enzyme phenylalanine hydroxylase to convert to tyrosine.

Step 2: Tyrosine is then immediately hydroxylated by tyrosine hydroxylase. This is known as the rate limiting step and is sensitive to pharmacological manipulations. This hydroxylation leads to the formation of DOPA.

Step 3: DOPA is similar to the drug L-Dopa, which is effective in treating Parkinson's disease. DOPA is then decarboxylated (removal of the carboxyl molecule) by the enzyme dopa decarboxylase to form Dopamine.

Step 4: Metabolic degradation: a) Dopamine is metabolized by Monoamine Oxidase (MAO), which converts monoamines to aldehydes to make them inactive. MAO is not specific for dopamine but acts on all monoamines (NE, E, and serotonin). It is found in the presynaptic region. b) COMT (catechol O-methyl transferase) acts to transfer the methyl from the catechol molecule to deactivate it. It is found in the synaptic cleft as well as the presynaptic areas.

📐 Formula: Synthesis Pathway → Phenylalanine → (by phenylalanine hydroxylase) → Tyrosine → (by tyrosine hydroxylase, rate limiting step) → DOPA → (by dopa decarboxylase) → Dopamine

📌 Example: The drug L-Dopa is effective in treating Parkinson's disease because it provides DOPA, which can then be converted to dopamine in the brain, compensating for the reduced dopamine levels characteristic of the disorder.

Pharmacological Interventions: Steps Where DA Synthesis Pathway Can Be Blocked or Altered

Pharmaceutical substances or drugs act in the central nervous system through the neurochemical systems.

🔑 Definition — Agonists: Drugs that copy/mimic the action of the neurotransmitter or have a similar effect as the NT, or have an excitatory effect on the NT systems.

🔑 Definition — Antagonists: Drugs that block, inhibit, or in any way oppose the action of the NT.

Drugs or exogenously administered substances can affect the NT pathway at various levels: a) They can act directly on neurons containing the NT b) They can act on various points of the synthesis pathway at the pre- or post-receptor site c) They can act on the inactivating enzymes in the cleft or within the presynaptic area

Steps where drugs can interact in the synthesis pathway:

Step 1: The conversion of phenylalanine to tyrosine can be blocked, as in the genetic disorder PKU (phenylketonuria), where phenylalanine builds up and transforms into toxins that damage brain cells. PKU blocks the transport of both tyrosine and tryptophan into the brain.

Step 2: The hydroxylation of tyrosine can be blocked by A-Methyl Para Tyrosine (AMPT), which methylates the tyrosine instead of hydroxylating it. This reduces the level of tyrosine available, leading to reduced dopamine, norepinephrine, and epinephrine. AMPT is effective in reducing catecholamine levels in the brain.

Step 3: The conversion of DOPA into dopamine by dopa decarboxylase can be blocked by a false enzyme A-methyl dopa. This enzyme competes for DOPA and uses it so it cannot be converted into the correct form to become dopamine.

Step 4: Storage vesicles are packed with dopamine. Reserpine, a drug manufactured from Rauwolfia Alkaloids classified as a major and long-lasting tranquilizer, ruptures all vesicles irreversibly and spills the contents into the presynaptic area. These vesicles cannot be repaired until new vesicles are manufactured. Another drug, Tetrabenazine, also opens vesicles and blocks reuptake of DA into the vesicles, but this is not irreversible.

Step 5: The release of the NT from the presynaptic ending and the reuptake back from the synaptic cleft can be blocked. Amphetamine (a stimulant) releases and blocks the reuptake of DA for a prolonged agonistic action. Similarly, Cocaine (another stimulant and street drug) and the Tricyclic group of antidepressants also block reuptake of DA and NE.

Step 6: The deactivation process can be blocked by drugs that block the action of MAO. The drug Pargyline, an MAOI, can increase the amount of DA available by blocking the deaminating process.

Step 7: The post-receptor site can also be blocked or stimulated. Apomorphine is a DA receptor stimulant at pre- and post-receptor sites, increasing levels of DA available for action. Haloperidol, a potent antipsychotic drug, is a DA blocking agent.

💡 Why this matters: Understanding these specific intervention points explains how different classes of drugs (antipsychotics, stimulants, antidepressants) produce their therapeutic and side effects by targeting distinct steps in neurotransmitter synthesis and transmission.

DA and Behaviors

Dopamine and Motor Activities:

The SN (Substantia Nigra) and Corpus Striatum: The Dopaminergic Nigrostriatal system is atypical in that SN fibers do not cross over to the contralateral hemispheres—they remain on the same side of the brain. This system innervates the extrapyramidal structures (the basal ganglia), which control motor behavior at the subcortical level.

A) Damage to SN leads to Parkinson's disease. The dopaminergic neurons in the Substantia Nigra have dark pigmentation; a pale SN indicates damage to the DA neurons. Reduced levels of DA in SN lead to Parkinson's symptoms. If we increase levels of dopamine by injecting Dopa (or L-Dopa) into the SN, we see a reduction in Parkinson's symptoms.

B) Evidence shows that rats injected with 6-OHDA (a toxic agent that selectively damages only DA pathways and neurons by retrograde transmission) exhibit the same symptoms as in Parkinson's (rigidity, tremor, etc.). This indicates that DA is involved in Parkinson's as well as motor behavior.

C) If DA levels are increased in animals or humans by injections of L-Dopa, it leads to stereotypic (repetitive) motor behavior. Stereotypic behavior is a symptom of higher than normal levels of DA in the brain. Apomorphine and Amphetamine (both strong agonists of DA) at high enough doses lead to stereotypic behaviors.

D) Injections of Haloperidol and Chlorpromazine (antipsychotic drugs that block DA activity) block the stereotypy induced by amphetamine injections.

📌 Example: Increase DA by amphetamine → Stereotypy. Block DA by Haloperidol → Reduce amphetamine-induced stereotypy.

E) Unilateral lesions of 6-OHDA lead to asymmetry in body postures—the body becomes lopsided. The body turns from the side with high DA to the side with low DA. This lopsided body posture is exaggerated by amphetamine and apomorphine (Ungerstedt et al., Najam 1980). Body postural asymmetry is from the side with more DA to the side with lesser DA.

F) Bilateral lesions with 6-OHDA lead to complete reduction of DA in the brain. Animals with bilateral lesions do not eat (aphagia), drink (adipsia), and cannot survive. They recover feeding only if force-fed.

Dopamine and Depression:

• Antidepressants such as Monoamine oxidase inhibitors (MAOI) and the Tricyclics both increase levels of DA.
• Alpha methyl para tyrosine (AMPT) if injected reduces both NA and DA levels in the brain. If we then inject MAOI, there is reduced effectiveness of the antidepressant effect of MAOI. However, evidence indicates that these have greater interaction with NA than DA (e.g., Desipramine has no effect on DA neurons).

Dopamine and Hyperactivity: Hyperactivity is due to increased levels of dopamine in the brain. This is also seen with injections of Amphetamine and Apomorphine. The market drug "speed" is actually amphetamine, which users take to feel tireless with increased energy and euphoria.

Dopamine and Schizophrenia: There is strong evidence that DA is involved in schizophrenia:

1. Drugs effective in treating schizophrenic symptoms are strong DA blockers. The more effective the drug is as a DA blocker, the greater its antipsychotic potency/efficacy.
2. The greater the efficacy of treatment (reducing DA), the greater the side effect of extrapyramidal symptoms (Parkinson's-like tremor, rigidity). These appear because DA is decreased postsynaptically. The DA synapses are blocked by antipsychotic drugs such as Phenothiazines (largectil and haloperidol: haldol).
3. Patients with Parkinson's when treated with L-Dopa start exhibiting symptoms of schizophrenia as a side effect.
4. Chronic users of amphetamine end up with symptoms of paranoid schizophrenia.

💡 Why this matters: Dopamine's involvement in such diverse behaviors—from motor control to mood regulation to psychosis—explains why drugs targeting the dopamine system can have both therapeutic effects (reducing schizophrenic symptoms) and significant side effects (inducing Parkinson's-like symptoms).

⭐ Key Takeaways

Dopamine is synthesized from phenylalanine through a four-step pathway (phenylalanine → tyrosine → DOPA → dopamine), with the hydroxylation of tyrosine by tyrosine hydroxylase being the rate-limiting step. The three major dopaminergic pathways—nigrostriatal, mesolimbic, and tuberoinfundibular—are responsible for motor control, emotional processing, and hormonal regulation respectively. Pharmacological agents can interact at each step of dopamine synthesis and transmission, with agonists like amphetamine increasing dopamine activity and antagonists like haloperidol blocking it. Dopamine is critically involved in motor behavior (Parkinson's disease results from reduced DA, while stereotypic behavior results from increased DA), depression (antidepressants increase DA levels), hyperactivity, and schizophrenia (antipsychotics are DA blockers; the more potent the DA blockade, the greater the antipsychotic efficacy). Understanding the specific points of pharmacological intervention in the dopamine pathway is essential for comprehending both therapeutic drug actions and their side effects.

🧠 Quick Revision Questions

1. What are the four steps in the dopamine synthesis pathway, and which step is considered the rate-limiting step?
2. Name the three major dopaminergic pathways in the brain and describe the function or behavioral correlate of each.
3. At which step of the dopamine synthesis pathway does reserpine act, and what is the effect of this drug?
4. What is the relationship between dopamine levels and Parkinsons disease, and how does L-Dopa treatment relate to schizophrenic symptoms?
5. Explain how amphetamine acts on the dopamine system and what behavioral effects result from its agonistic action.

📘 Lecture 33 — Basic Neurochemistry

📖 Overview: This lecture examines norepinephrine/noradrenaline (NA), a major catecholamine neurotransmitter involved in mood, arousal, reward, and stress responses. It covers NA synthesis, pathways, receptors, and how various psychotropic drugs modulate NA function at each step of neurotransmission, linking NA to specific behaviors like arousal and conditioned avoidance.

🗂️ Topics Covered

The lecture begins by introducing norepinephrine/noradrenaline as a catecholamine neurotransmitter synthesized from dopamine, then details its synthesis via dopamine B-hydroxylase, deactivation pathways producing VMA and MHPG metabolites, and the two major noradrenergic pathways (dorsal and ventral bundles originating in the pons and medulla). It describes alpha and beta receptor subtypes with their locations and functions, then systematically explains seven steps where drugs can modify NA synthesis and action (from enzyme inhibition to reuptake blockade). Finally, it covers NA’s role in behavioral arousal and conditioned avoidance learning.

📝 Lecture Summary

Basic Neurochemistry – Lesson 33 Objectives

This lesson aims to familiarize students with various neurotransmitters (NTs) and their role in modulating behaviors, the classification of NTs (monoamines such as catecholamines and indoleamines, acetylcholine, amino acids, and peptides), the role of NTs in behavioral modulation and aberration, drugs and behavior, classification of psychopharmacological substances, behavioral correlates and treatment, and the mechanism of synaptic transmission.

Major Neurotransmitter: Catecholamines – Norepinephrine/Noradrenaline

Norepinephrine (NE), also known as Noradrenaline (NA), is one of the major NTs of the brain, falling under the general category of monoamines and further categorized as a catecholamine because of its chemical composition. Synapses using NA are known as noradrenergic synapses. NA is found in various parts of the brain (hypothalamus, midbrain), the autonomic nervous system (important role in sympathetic functions and hormonal release for fight or flight), and the adrenal glands. NA is involved in a large number of behaviors with wider influence than dopamine (DA), including mood, emotional states, motivation (hunger, thirst, fight/flight), dream, rewards (learning), sleep, alertness, and wakefulness.

NA originates from a small group of neurons in the back part of the brain and projects via fibers and axons to widespread brain regions, explaining its involvement in many behaviors.

• Noradrenergic synapses lead to Inhibitory Post Synaptic Potentials (IPSPs) in the CNS and Excitatory Post Synaptic Potentials (EPSPs) in the Autonomic Nervous System (including the sympathetic nervous system) and target organs such as the heart.
• Noradrenergic neurons release NA through axonal varicosities (beadlike swellings of axonal branches) rather than from terminal buttons. Varicosities give NA axonal branches the appearance of beaded chains.
• NA is synthesized in the adrenal medulla and the brain from DA. The brain manufactures all NTs independently, including NA. Large amounts of NA cannot cross the blood-brain barrier to enter the brain.

🔑 Definition — Axonal varicosities: Beadlike swellings of axonal branches from which NA is released (instead of terminal buttons).

🔑 Definition — Noradrenergic synapses: Synapses that use norepinephrine/noradrenaline as their neurotransmitter.

NA Synthesis

1. Synthesis: A simple one-step process transforms DA into NA. DA is hydroxylated by Dopamine B-hydroxylase (discovered in 1960 in the adrenal medulla). Synthesis from DA to NE takes place within the vesicles (unlike other NTs where synthesis occurs in the cell body).
2. The hydroxylation process can be blocked by Disulfiram, leading to a buildup of DA while reducing NE levels.
3. Deactivating Norepinephrine by MAO (monoamine oxidase) and COMT (catechol-O-methyltransferase) leads to: a) Vanylmandellic Acid (VMA) — a metabolite found mostly in the body (very little in the brain as it is excreted quickly). b) MHPG (3-methoxy-4 hydroxyphenylglycol) — a glycol derivative; under stress, MHPG amounts increase in the locus coeruleus.

🔑 Formula: DA + Dopamine B-hydroxylase → NA (hydroxylation within vesicles) 🔑 Formula: NA + MAO/COMT → VMA + MHPG (deactivation metabolites)

Noradrenergic Pathways

There are two major NA pathways — the Dorsal bundle and the Ventral bundle with several projecting pathways (A1, A2, A4, A5, A6, A7). All originate in lower brain areas (pons and medulla) and ascend to the cortex, limbic system, and hypothalamus.

• A6 (Dorsal bundle): Originates in the locus coeruleus (located on the ventral areas of the ventricles) and sends diffuse innervations to the cerebellum, cerebral cortex, and hippocampus through the Medial Forebrain Bundle (MFB). Involved in sleep, awakening, moods, neuro-endocrine functions, and temperature regulation.
• A1, A2, A4, A5, A7 (Ventral bundle): Originate in the pons and medulla, innervating the brainstem and hypothalamus. Ascending fibers of A5 and A7 project to the cortex, hypothalamus, and parts of the limbic system (hippocampus and septum), while descending fibers go down into the spinal cord.

🔑 Definition — Locus coeruleus: A nucleus in the pons where the dorsal NA bundle originates; involved in sleep, arousal, and stress responses.

Receptors

There are two types of NA receptors identified by their sensitivities to various drugs: Alpha receptors and Beta receptors.

• Alpha1 and Beta1: Found mainly in post-receptor membranes.
• Alpha2: Primarily presynaptic autoreceptors (emerge from the presynaptic membrane area to monitor and control NT levels by self-inhibiting action).
• Beta2 receptors: Found in the CNS, associated with glia cells, muscles, and blood vessel walls.

Receptor Details:

• A1: Located post-synaptically on blood vessels, spleen, and peripheral tissues. Prazosin and Indoramin are selective antagonists working near the heart. These receptors carry brain commands directly to organs.
• A2: Located on presynaptic nerve terminals in the periphery (not in the brain). Yohimbine is a selective antagonist; Clonidine is a selective agonist. Also located in the pancreas.
• B1: Linked to stimulation of adenylate cyclase. Found in greater numbers in the heart and cerebral cortex. Epinephrine and NE are potent agonists. Presence varies across brain regions.
• B2: Linked to stimulation of adenylate cyclase. Found in high concentration in the lungs and cerebellum. Epinephrine (E) is more potent than NE at these receptors. Salbutamol is a selective agonist.

🔑 Definition — Autoreceptor: A receptor located on the presynaptic neuron that monitors and controls NT levels through self-inhibiting action (e.g., Alpha2 receptors for NA).

Steps in NA Synthesis Where Drugs Can Modulate Action

Step 1: Enzyme Synthesis

• a) Alpha Methyl Para Tyrosine (AMPT) blocks the hydroxylation of tyrosine by tyrosine hydroxylase (the rate-limiting step for both DA and NA). Reducing available tyrosine reduces both DA and NA.
• b) Disulfiram and FLA-63 block Dopamine B-hydroxylase action on dopamine, allowing DA buildup but preventing conversion to NA.

Step 2: Storage Vesicles

• Reserpine: Long-lasting, irreversible damage to storage vesicles (effect on NA is long-lasting).
• Tetrabenazine: Interferes with storage vesicles but effect is neither long-lasting nor irreversible.

Step 3: Release

• Amphetamine: Increases the release of NA molecules from the presynaptic area and also blocks reuptake for enhanced and long-lasting effects.

Step 4: Post-receptor Site Interaction

• Clonidine: Very potent receptor stimulant (agonist).
• Phentolamine: An A-blocking agent (antagonist).
• Sotalol: A B-blocking agent (antagonist).

Step 5: Reuptake

• Desipramine (tricyclic antidepressant): Blocks reuptake of NA molecules, enhancing NA levels in the synaptic cleft.

Step 6: Degradation by MAO

• MAO inhibitors (e.g., Pargylin): Block MAO action, leading to increased NA levels.

Step 7: Degradation by COMT

• Tropolamine: Blocks COMT action in the synaptic cleft.

🔑 Definition — Psychotropic drugs: Drugs that act on psychological states, modifying neurotransmitter function at various steps of synthesis, storage, release, receptor interaction, reuptake, and degradation.

NA and Behaviors

Arousal: Behavioral arousal and electrical arousal in the brain are correlated with increases in NE via MAOI (monoamine oxidase inhibition). Increased available NA leads to increased arousal seen in behavioral excitation and EEG activity. In states of stress, NA levels increase; stressed individuals who cannot sleep show increased brain NA levels. This is clearly NA involvement (no DA involvement — complete depletion of striatal DA still leads to waking and sleeplessness). Injecting NA intraventrically (directly into the brain) also leads to behavioral excitation. Increases in NA produce arousal, excitation, and increased activity.

NA and Conditioned Avoidance: NA is involved in conditioned avoidance in learning and conditioning paradigms. Injecting Reserpine (ruptures vesicles to spill NA) and Alpha Methyl Paratyrosine (blocks further tyrosine/DA/NA synthesis) results in complete abolishment of a learned conditioned avoidance response to electric shock. This shows NA’s role in avoidance behavior, possibly through reward/punishment mechanisms or learning/memory centers.

To confirm only NA decreases lead to this response: giving Disulfiram or FLA-63 (which increase DA but decrease NE by blocking NE synthesis) also abolishes the learned avoidance response.

🔑 Definition — Conditioned avoidance: A learned response to avoid an aversive stimulus (e.g., electric shock) that depends on intact NA function.

⭐ Key Takeaways

Norepinephrine/noradrenaline is a catecholamine neurotransmitter synthesized from dopamine via dopamine B-hydroxylase within vesicles, with deactivation by MAO and COMT producing VMA and MHPG metabolites. NA originates from the locus coeruleus (dorsal bundle) and medulla/pons (ventral bundle), projecting to widespread brain regions via axonal varicosities. NA receptors include alpha (α1 post-synaptic, α2 presynaptic autoreceptors) and beta (β1 and β2, linked to adenylate cyclase) subtypes with distinct locations and drug sensitivities. Psychotropic drugs modulate NA function at seven steps—enzyme synthesis (AMPT, Disulfiram), storage vesicles (Reserpine), release (Amphetamine), receptor interaction (Clonidine, Phentolamine, Sotalol), reuptake (Desipramine), MAO degradation (Pargylin), and COMT degradation (Tropolamine). Behaviorally, NA is essential for arousal (increased NA causes excitation and wakefulness independent of DA) and conditioned avoidance learning (decreased NA abolishes learned avoidance responses).

🧠 Quick Revision Questions

1. What enzyme converts dopamine into norepinephrine, and where within the neuron does this conversion take place?
2. Name the two major noradrenergic pathways and the primary nucleus of origin for the dorsal bundle.
3. What are the two main categories of NA receptors, and which subtype functions as a presynaptic autoreceptor?
4. Which drug blocks NA reuptake and belongs to the tricyclic antidepressant group, and what effect does it have on synaptic NA levels?
5. How does decreasing NA (without decreasing DA) using Disulfiram or FLA-63 affect learned conditioned avoidance behavior?

📘 Lecture 34 — Basic Neurochemistry

📖 Overview: This lecture continues the exploration of norepinephrine (NE) and its role in stress, feeding, self-stimulation, and depression. It then introduces serotonin (5-HT) as a major indolamine neurotransmitter, covering its synthesis, anatomical pathways, and how drugs interact at each step of serotonin transmission to modulate behavior and treat psychopathology.

🗂️ Topics Covered

This lecture begins by examining NE’s involvement in stress responses, feeding behavior regulation via the lateral hypothalamus and ventromedial hypothalamus, intracranial self-stimulation (reward), and the catecholamine hypothesis of depression. It then introduces serotonin (5-hydroxytryptamine, 5-HT) as an indolamine neurotransmitter, detailing its historical discovery, synthesis from tryptophan, storage, deactivation, and the anatomical locations of serotonergic pathways (raphe nuclei). Finally, it explains how drugs (PCPA, Reserpine, LSD, Tricyclics, MAOIs) can modulate serotonin at each step of synthesis, storage, release, receptor interaction, reuptake, and degradation.

📝 Lecture Summary

NE and Behaviors (continued)

Stress: Stress can be induced in the laboratory by giving continuous, inescapable foot shocks to rats. Stress induced by foot shocks leads to increased NA (norepinephrine) levels and turnover in the hindbrain. Increased turnover rates mean more NA is being used and metabolized. Trauma of all kinds also increases NA activity in the brain. Similarly, Electroconvulsive therapy (ECT) leads to increased NA levels in the forebrain.

NA and Feeding: The NA system is involved in the control of feeding behaviors. If NA is administered directly into the Lateral Hypothalamus (LH), it leads to increased eating in animals that have already eaten to the point of satiation. This effect is specific to NA: injecting phentolamine (an α-adrenergic blocker) blocks NA-induced feeding. 💡 Why this matters: Liebowitz (1971) demonstrated that NA may act to reduce the inhibition of the LH feeding center by the Ventromedial Hypothalamus (VMH). The LH starts feeding, and the VMH stops it by telling the LH to stop sending signals. When NA is injected, it stops the inhibition from the VMH, allowing feeding messages to continue.

🔑 Definition — Phentolamine: An α-adrenergic blocker that blocks NA-induced feeding.

NA and Self-Stimulation (ICS): Positive reinforcement or “reward” is linked to NA. Intracranial Self-Stimulation (ICS) areas in the brain correspond closely to the distributions of NA and DA systems. If alpha-methyl-paratyrosine (AMPT) is injected, it reduces tyrosine, DA, and NA, and also blocks the self-stimulation response. To determine which neurotransmitter is involved, researchers used drugs that block only DA, only NA, or only 5-HT one by one after AMPT. The AMPT blockade is reversed by α-receptor agonists of NA, not by β-receptor agonists, DA agonists, or 5-HT agonists, showing that NA is involved. Using push-pull cannulae in the ventricle, researchers reported that self-stimulation leads to an increase in the release of NA. The NA Dorsal bundle is more involved than the ventral bundle.

NA and Depression: The effectiveness of Monoamine Oxidase Inhibitors (MAOIs) in treating depression supports the Catecholamine Hypothesis of Depression, particularly the involvement of NA. Long-term antidepressant treatment in animals leads to a reduction in NA-stimulated cyclic AMP (involving beta receptors). This indicates that more NE stays available, so less needs to be released. Antidepressants increase the synaptic availability of NE. Reserpine (which destroys storage vesicles and depletes NE, DA, and 5-HT from presynaptic membranes) leads to a depression-like syndrome. Iproniazid (an MAOI and effective antidepressant) increases brain concentrations of NE and 5-HT.

Major Neurotransmitters: Monoamines: Indolamines

Serotonin: Indolamine (5-Hydroxytryptamine or 5-HT) Serotonin is a major neurotransmitter with an important role in several behaviors, from sleep to depression. Scientists knew since the mid-19th century that a substance caused powerful contraction of smooth muscles. In American labs, it was called serotonin; Italian scientists called it enteramine. These substances were eventually found to be identical to 5-Hydroxytryptamine (5-HT). It has a strong resemblance to the LSD molecule.

The precursor for 5-HT is tryptophan, which varies with daily intake of tryptophan-rich foods (milk, red meat, bananas, pineapples). About 90% of 5-HT is found in the gastrointestinal area, and only about 1-2% in the brain. The highest concentration of 5-HT in the brain is found in the pineal gland (a small organ on the dorsal surface of the thalamus). The pineal contains about 50% more serotonin per gram of brain than other brain areas. The extension of pineal serotonin is melatonin, which is enhanced by light and suppressed by darkness, bringing daily and seasonal changes in 5-HT content.

Serotonin Synthesis:

1. Tryptophan: This is the first step. Tryptophan enters the cells in competition with phenylalanine.
2. Hydroxylation of Tryptophan: This is the rate-limiting step. The hydroxylation of tryptophan at the 5th position forms 5-Hydroxytryptophan (5-HTP). The enzyme involved is Tryptophan Hydroxylase. This step can be blocked by the drug Parachlorophenylalanine (PCPA). One injection of PCPA (200 mg/kg) in rats depletes brain 5-HT drastically (to about 20%), and recovery can take weeks.
3. Decarboxylation: 5-HTP is immediately decarboxylated to form 5-HT. The enzyme L-Amino Acid Decarboxylase is involved (the same enzyme used for catecholamines).
4. Deactivation: Serotonin is deaminated by Monoamine Oxidase (MAO). The metabolite formed is 5-Hydroxy Indole Acetic Acid (5-HIAA).

🔑 Definition — Parachlorophenylalanine (PCPA): A drug that competes with tryptophan for tryptophan hydroxylase and binds irreversibly, depleting brain 5-HT. 📐 Formula (Pathway): Tryptophan → [Tryptophan Hydroxylase] → 5-HTP → [L-Amino Acid Decarboxylase] → 5-HT → [MAO] → 5-HIAA

Serotonergic Anatomical Location and Pathways

Dahlstrom and Fuxe (1964) identified about nine clusters of 5-HT neurons in the nuclei of the raphe system, located in the midline of the pons and upper brain stem. Ascending 5-HT bundles travel through the Medial Forebrain Bundle (MFB) with terminals in the reticular formation, hypothalamus, lateral geniculate nuclei, preoptic area, hippocampus, and cortex (crucial for sleeping and awakening). These also project into the telencephalon, diencephalon, and descend into the spinal cord.

Pathways:

• Nuclei Raphe Dorsalis (B7 receptors): Projects to the neocortex, olfactory bulb, thalamus, amygdala, hippocampus, substantia nigra, and locus coeruleus.
• Nuclei Centralis Superior (B8 receptors): Projects to the cerebral cortex, hippocampus, superchiasmatic nuclei (SCN), anterior hypothalamus, medial preoptic area, and the raphe dorsalis.
• Nuclei Raphe Magnus (B3 receptors): Extends to the medulla and anterior hypothalamic area.
• Nuclei Raphe Obscurus (B2 receptors): The powerful hallucinogen LSD acts here.
• Raphe Pallidus (B1 receptors): Contains substance P (a peptide involved in pain) and goes down into the spinal cord.

Steps in 5HT Synthesis Where Drugs Can Modulate Action

Step 1: Synthesis: Tryptophan is converted to 5-HTP by tryptophan hydroxylase. This can be blocked by PCPA.

Step 2: Storage: Reserpine damages storage vesicles for DA, NE, and 5-HT. When reserpine is administered along with 5-HTP or DOPA, there is increased sedation. Injections of PCPA (removing 90% of brain serotonin) before reserpine prevented the behavioral effects of reserpine.

Step 3: Release: There are no specific serotonin blocking agents, but LSD potentiates serotonin effects in low doses. LSD inhibits the release of serotonin by blocking the firing of serotonergic neurons. In high doses, LSD increases 5-HT levels by reducing breakdown. LSD appears to decrease the release of 5-HT.

Step 4: Receptor Interaction: LSD acts as a partial agonist at the receptor sites of the post-synaptic membrane.

Step 5: Reuptake: Serotonin action can be terminated by reuptake. Tricyclics (like Imipramine) increase 5-HT levels by inhibiting reuptake. Selective Serotonin Reuptake Inhibitors (SSRIs) are effective for treating anxiety.

Step 6: Degradation: Degradation by MAO can be inhibited by MAOIs. Iproniazid blocks MAO action in the presynaptic area.

⭐ Key Takeaways

• Norepinephrine is critically involved in stress, feeding (via the LH/VMH circuit), reward (self-stimulation), and depression, as supported by the catecholamine hypothesis and drug effects (Reserpine, MAOIs).
• Serotonin (5-HT) is an indolamine synthesized from tryptophan via the rate-limiting enzyme tryptophan hydroxylase, which is blocked by PCPA, and is deactivated into 5-HIAA by MAO.
• The serotonergic system originates from the raphe nuclei and projects widely through the MFB to the forebrain, cortex, and spinal cord, modulating sleep, mood, and pain.
• Drugs modulate serotonin at every step: PCPA blocks synthesis, Reserpine blocks storage, LSD affects release and receptors, Tricyclics/SSRIs block reuptake, and MAOIs block degradation.
• Understanding these systems and drug interactions is fundamental to explaining the mechanisms of action for antidepressants, antipsychotics, and hallucinogens.

🧠 Quick Revision Questions

1. What is the specific role of the α-adrenergic blocker phentolamine in the experiment on NA-induced feeding?
2. What is the evidence from the self-stimulation paradigm that points to NA (and not DA) as the main neurotransmitter for reward?
3. What is the rate-limiting step in serotonin synthesis, and which drug irreversibly inhibits it?
4. Name the specific raphe nucleus (and its receptor type, B2) where the hallucinogen LSD acts.
5. How does Reserpine affect serotonin levels, and what experimental result showed that serotonin depletion accounts for Reserpine’s behavioral effects?

📘 Lecture 35 — BASIC NEUROCHEMISTRY

📖 Overview: This lecture continues the discussion on the involvement of serotonin (5HT) in the modulation of various behaviors, and then provides a comprehensive overview of Acetylcholine (ACh), its synthesis, receptors, and the drugs that affect cholinergic synapses. Understanding these neurotransmitter systems is critical for grasping the neurochemical basis of behavior, neurological disorders, and psychopharmacology.

🗂️ Topics Covered

The lecture covers the regulation of behaviors by serotonin, including temperature regulation, sensory perception, sleep, depression, and sexual behaviors. It then transitions to a detailed exploration of Acetylcholine, beginning with its discovery and classification. The synthesis and breakdown of ACh are explained, followed by its neuroanatomical sites of involvement. Finally, the lecture details the specific drugs and toxins that act as agonists and antagonists at cholinergic synapses, including their mechanisms and clinical applications.

📝 Lecture Summary

5HT and Behaviors

This section details the specific behaviors modulated by serotonin (5HT), building upon previous discussions of the serotonergic system. Each behavior is linked to experimental evidence showing how manipulating 5HT levels alters the outcome.

1. Temperature regulation: This is an important motivational behavior dependent on day and night cycles. If 5HT is injected intraventricularly, it leads to increased body temperature. When PCPA is injected to deplete brain serotonin, and then raphe nuclei are electrically stimulated, no rise in body temperature takes place. The body temperature would otherwise rise with the stimulation of raphe nuclei, as increased serotonin leads to increased body temperature.

2. Sensory perception: 5HT is involved in producing the heightened sensory and visuomotor hallucinogenic effect of LSD. Injections of PCPA (which depletes brain serotonin) reduced motor activity and emotional reactivity but increased sensitivity to pain. This means in rats, the electrical current given for a response is much lower; they respond at a lower current with avoidance and other behaviors. Further, when 5HT levels are decreased, this slows down the process of tolerance to morphine (tolerance means that the effectiveness of a drug dosage is lessened, so the dosage has to be increased to have the same effect or response).

3. Serotonin and sleep: Evidence for the involvement of 5HT in sleep is provided by experiments in which levels of 5HT are increased by administration of MAOI (reduced deactivation) or 5HTP (increased enzymes) or 5HT itself. This treatment leads to an increase in levels of 5HT and also increases time spent in Slow Wave Sleep (SWS) . If 5HT is decreased, then the time spent in SWS is also decreased. PCPA administration (which depletes/reduces 5HT drastically) also leads to reduced Rapid Eye Movement sleep (REM) .

Jouvet (1973) was the first to identify the relationship between 5HT and sleep. Jouvet carried out experiments manipulating raphe nuclei and seeing its effect in cats (cats are best for sleep research as they spend 2/3 of their life in sleep). The electrolytic lesion of the raphe nuclei led to decreased 5HT and decreased time spent in sleep. When 5HT was reduced by 85%, time in sleep was reduced to 20% (insomniac cats!). Further, when PCPA was injected, 1-2 days after injection (when complete depletion of brain 5HT has taken place), increased insomnia followed. This was confirmed because injections of 5HTP (which increases 5HT and reverses PCPA-induced lower levels of 5HT) reversed the insomnia induced by PCPA.

4. Other behaviours: 5HT appears to be involved in depression, as there is evidence of decreased 5HT and 5HIAA (the 5HT metabolite) in brains of suicide victims (Bourne et al., 1968). This indicates that in depression, 5HT is lower than normal levels (antidepressants such as tricyclics and MAOIs also act to increase levels of 5HT). Decreases in 5HT lead to a disinhibition of behaviors (reduced controls on behaviors), increased impulsivity, increased aggressiveness, and increased suicidal tendencies. Serotonin is also involved in the control of sexual and reproductive behaviors. PCPA, which depletes 5HT, increased sex drive in males. In females, the ovulation cycle is blocked by narcotics; this blockade is removed by administration of 5HT.

💡 Why this matters: This section demonstrates that 5HT is not a simple "happy" chemical but a major neurotransmitter influencing a wide range of motivational and other behaviors, from basic homeostasis (temperature) to complex states like depression and aggression.

Acetylcholine: ACh

This section introduces ACh as one of the major neurotransmitters, distinct as a class by itself. Its effects have been studied since the 1920s via bioassay and neuromuscular transmission, demonstrated by frog muscle contraction when ACh is applied. ACh is used by neurons which terminate on the neuromuscular junction.

This is classified as an excitatory NT, as Excitatory Post Synaptic Potentials are released in the muscle cell. However, ACh has an excitatory effect on skeletal muscles but is inhibitory at the heart. The location is as important as the classification of the NT for its actions as excitatory or inhibitory. ACh is also found to play an active role in brain areas such as the hypothalamus and cerebral cortex. It is involved in learning and memory (known as the memory molecule) and Rapid Eye Movement sleep.

The study of ACh is easier than other neurotransmitters as it is easy to remove and study outside the brain in a petri dish. The nicotinic receptor was the first receptor identified. Acetylcholine is found in ganglions of the autonomic nervous system and the target organs of the parasympathetic nervous system.

ACh has two distinctive types of receptors:

• Nicotinic: Connects the muscle fibers and works through sodium channels (these are ionotropic receptors). Curare, a poison, can block the transmission of ACh at neuromuscular joints. In neuromuscular joints, nicotine mimics the excitatory effects of ACh.
• Muscarinic: Found in the CNS and these use G proteins and cyclic AMPs as second messengers. These are classified as metabotropic receptors. Atropine blocks these receptors, leading to loss of memory.

🔑 Definition — Cholinergic receptors: The receptors for acetylcholine.

Synthesis

Acetylcholine is synthesized in a catalytic action of cholinesterase on Co-enzyme A + its acetate ion and Choline. It acts to detach the acetate ion from co-enzyme A and attach it with choline to form acetylcholine and separate the Co Enzyme A. The Co Enzyme A is found in Vitamin B, and choline is broken down from lipids. Choline is the rate-limiting factor of ACh (no choline, no ACh). The ACh is further broken down by the enzyme Choline acetyl transferase, whereby ACh is broken down into choline and acetyl via a process of hydrolysis. Half of the choline in this chemical action is retrieved and recycled.

Involvement and neuroanatomical sites of ACh

ACh is formed in the cell bodies of the neuron and transported to the neuromuscular junctions. It is released by action potential, crosses over, and activates the muscle fiber.

I. Locations of ACh:

• Found at all neuromuscular junctions, autonomic ganglion, and parasympathetic systems.
• Hippocampus receives ACh input from the medial septal nucleus.
• ACh projects into the ascending reticular arousal system.
• Involved in auditory and visual systems.
• Found in the caudate nucleus.
• Found in the ventral basal hypothalamus.
• In the supraoptic nucleus of the brain stem.
• ACh acts as a sensory transmitter in thermal receptors. Pain is produced by directly putting ACh onto a blister on the skin.

II. Functional Roles of ACh:

• Involved in the release of catecholamines (works to balance other NTs and has interaction with DA, NE, and 5HT in all functions).
• Conduction of signals: it acts in axonal conduction by depolarizing the axon.

Steps in ACh synthesis where drugs can modulate action

This section details the specific drugs affecting cholinergic synapses at each step of neurotransmission.

Step 1: Synthesis: ACh synthesis can be blocked by styryl pyridine, a derivative.

Step 2: Release of ACh from the presynaptic membrane is enhanced by β-bungarotoxin and black widow spider venom and blocked by botulinus toxin (a deadly food poison). The latter acts to block ACh transmission, leading to total paralysis.

Step 3: Post receptor sites can be activated or blocked in both types of receptors. These are activated by Ach agonists or cholinomimetic drugs and anticholinesterases (blocking the enzyme which breaks down ACh).

• Nicotinic receptors are blocked by α-Bungarotoxin and Curare (Tubocurarine). Local anesthetics and drugs such as phencyclidine bind to these receptors to modulate action. Curare, a poison used by South American Indians in arrows, prevents ACh from reaching the post-receptor area (occupies the sites). Since the muscles do not get activated, this leads to blockade of all muscular responses. Since there is no post-synaptic response, no nerve command is processed, leading to total paralysis of muscles. Poison from cobra, alpha bungarotoxin, acts through this mechanism.
• Muscarinic receptors are blocked by atropine (belladonna) and scopolamine.

Step 4: Presynaptic receptor blockade: Atropine and scopolamine block these.

Step 5: Inhibition of inactivation activity leads to an increase in ACh in the brain by physostigmine, which blocks acetylcholinesterase from breaking down ACh. This leads to increased levels of ACh in the system, resulting in repeated stimulation of muscles, meaning the muscles would be repeatedly stimulated, resulting in violent muscular contractions. It is reported that there is a West Indian tribal custom where Calabar bean extract is used to find if a person is guilty or innocent. If guilty, the person who had taken the bean extract as a test would die; if they were innocent, the person would swallow and vomit.

Physostigmine is used as a therapy for Myasthenia Gravis: a neurological disorder where the muscles are extremely weak and do not have normal levels of ACh for muscles to act. The drugs given increase ACh (cholinomimetics, or anticholinesterases). Increases in ACh using this therapy can lead to nightmares, confusion, and hallucination.

Receptor Agonists:

• Muscarinic receptors: Affected by muscarinic agonists, one of which is the muscarinic extract from poison mushrooms. If taken, it increases ACh activity, leading to increased sweating, increased salivation, constriction of pupils, and decreased heart rate. Also muscarine, which mimics the inhibitory effects of ACh.
• Nicotinic receptor agonists: In neuromuscular joints, nicotine mimics the excitatory effects of ACh. Nicotinic agonists could be useful in the treatment of a variety of neurological disorders including Alzheimer's disease, Parkinson's disease, and chronic pain.

Receptor Antagonists:

• Muscarinic receptors: Atropine is an antagonist. Atropine Belladonna (night shade poison) blocks muscarinic receptors, acting as a false transmitter. It occupies the post-receptor sites and does not transmit the message forward. Atropine belladonna liquid leads to dilation of pupils when applied directly onto the eyes (Belladonna means "beautiful woman" because women used to apply it to their eyelids for a wider eye look). From Grecian times, Hippocrates used it for stomach ailments and cosmetics. Atropine and scopolamine lead to decreased ACh in the brain, leading to amnesia (reduced ACh in the Alzheimer brain is related to their memory loss). This also indicates that ACh is involved in learning and memory.
• Muscarinic antagonists are used to control and prevent vomiting and are also useful for the treatment of Parkinson's disease. In large doses, however, the muscarinic antagonists cause severe side effects such as hallucinations and memory disturbances.

Step 6: Choline uptake: This step is affected by β-Bungarotoxin and black spider widow venom.

The lecture concludes with a reference to Table 1, which summarizes the natural cholinergic agonists and antagonists.

⭐ Key Takeaways

The most critical points from this lecture are the specific behavioral roles of serotonin (5HT), from temperature regulation and sleep to depression and aggression, and the detailed pharmacology of the cholinergic system. For 5HT, remember that depleting it with PCPA reduces sleep, increases pain sensitivity, and disinhibits behavior, while increasing it has the opposite effects. For ACh, understand that it is the key neurotransmitter at the neuromuscular junction and is known as the "memory molecule." You must know the difference between nicotinic (ionotropic, blocked by curare) and muscarinic (metabotropic, blocked by atropine) receptors. Finally, memorize the "trophy" examples of drugs and toxins that affect each step of cholinergic transmission: botulinus toxin blocks release, physostigmine blocks breakdown (used for Myasthenia Gravis), and atropine is an antagonist at muscarinic receptors.

🧠 Quick Revision Questions

1. What is the effect of injecting PCPA on body temperature when the raphe nuclei are electrically stimulated, and why?
2. How did Jouvet (1973) experimentally demonstrate the relationship between serotonin and sleep in cats?
3. Name the two main types of receptors for Acetylcholine, and give one key difference in their mechanism of action (ionotropic vs. metabotropic).
4. What is the therapeutic use of physostigmine, and what is its mechanism of action at the cholinergic synapse?
5. Which drug blocks muscarinic receptors, and what is the effect of this blockade on memory?

📘 Lecture 36 — Basic Neurochemistry

📖 Overview: This lecture continues the exploration of neurotransmitters by examining acetylcholine (ACh) in detail, including its role in arousal, drinking, aggression, punishment, and Alzheimer's disease. It then expands to cover other major neurotransmitters, including glutamic acid, GABA, glycine, peptides such as brain opioids, and psychotogenic compounds, concluding with an introduction to psychopharmacology.

🗂️ Topics Covered

The lecture covers major neurotransmitters and their behavioral modulation, beginning with ACh's roles in arousal, drinking behavior, sham rage, punishment systems, and Alzheimer's disease pathology and treatment. It then addresses other neurotransmitters including glutamic acid, GABA (with its synthesis, distribution, and pharmacological agents), glycine, and peptides such as brain opioids. The lecture concludes with discussion of psychotogenic compounds like LSD and mescaline, and an introduction to psychopharmacology as a field.

📝 Lecture Summary

Major Neurotransmitter: Acetylcholine (continued)

Acetylcholine (ACh) has a unique and important neurotransmitter role in the brain. Without normal levels of ACh and its receptors working effectively, the brain would not be able to command the muscles of the body.

🔑 Definition — ACh: A neurotransmitter critical for muscle control, arousal, and various behavioral functions throughout the brain.

1. Arousal: ACh has an important role as an excitant of neural activity. Brain electrical activity is aroused and can be monitored by Electroencephalographic (EEG) recordings. When ACh is injected intravenously or applied to the cortex, it leads to increased EEG activity. When anticholinergics are administered, they block and reduce ACh levels in the brain, and EEG arousal is also blocked. Interestingly, this does not affect behavioral arousal. ACh is involved in sleeping and awakening via the locus coeruleus, which may explain the involvement of ACh in brain electrical activity arousal.

2. Drinking: ACh is important in drinking and fluid regulation. The regulation of water intake takes place via the ACh mechanism. Cellular dehydration is mediated by the cholinoceptive system of neurons in the preoptic area of the hypothalamus. They monitor the extracellular space for volumetric changes (changes in the volume of fluid) produced after changes in isotonic body fluids. Whenever the intracellular membrane runs short of fluid, it takes in fluids from the extracellular membrane. This leads to the release of Renin from kidneys, which leads to increased formation of Angiotensin, which then stimulates the neurons in the preoptic area. This communication goes from the brain to the kidneys and back, leading to an increase in fluid and salt intake.

3. Sham rage and attack: Sham rage is the physical appearance of rage without an object of rage in front of the animal (cats and rats). In cats, rage appears as hissing, spitting, and raised hair on the dorsal surface of the body and the tail. Sham rage is induced in cats and rats by cholinergic stimulation of the amygdala and septum. Aggression is also produced by the midbrain ventral tegmental area. Further, the killing attack pathways in rats (of mice) and cats (of rats) are cholinergically organized. Cholinergic stimulation of the amygdala, lateral hypothalamus (LH), and midbrain tegmental regions leads to a quiet biting attack in rats and cats. This attack is blocked by atropine.

4. Punishment: Reinforcing stimuli increase the probability of a response, whereas punishing stimuli decrease the probability of a response. Intracranial self-stimulation is part of the reward systems and is reinforcing, so an animal would keep self-stimulating for its own reward. On the other hand, the periventricular area in the hypothalamus is part of punishment systems. The ventromedial hypothalamus (VMH) is part of this punishment system. Rats previously trained for Variable Interval Schedule (VIS) for food are run in an experiment where every response is followed by a shock. (VIS is when the time between reinforcement varies.) When every response is followed by a shock, a reduction in VIS response follows. If we lesion the Ventromedial nuclei (VMN), it leads to an increase in the response which had been depressed (leads to disinhibition). Anti-ACh does the same—they lead to an increase in disinhibition of the punished response. Inhibition of punished response means the animal would stop responding, but disinhibition means the response would return as the inhibitor has been blocked. Anti-ACh are involved in removing the inhibition.

5. Alzheimer's: Alzheimer's is a disease of old age where degeneration of the brain takes place to the point where the person cannot carry out any function. The important feature of this disease is loss of memory. Recently, muscarinic receptor agonists have been used in the treatment of Alzheimer's disease. This replaces depleted ACh in the basal forebrain as the neurons in this area degenerate. Another treatment is administration of acetylcholinesterase inhibitors, which increases levels of ACh in the synapse as the breakdown is blocked, thereby increasing cholinergic activity in damaged brain areas. Physostigmine was used earlier but results indicated strong side effects. Tetrahydroaminoacridine (THA, or tacrine) was the first cholinesterase inhibitor approved for Alzheimer's patients. Patients given THA showed some reduction of Alzheimer's symptoms and were able to resume normal activity. However, not all patients can use it as it has strong side effects on increasing liver enzymes.

💡 Why this matters: ACh is also involved in learning, memory, motor behaviors (working in balance with dopamine for Parkinson's and other motor disorders), pain, and coordination with brain opioids.

Other NT's

In addition to the neurotransmitters already discussed—the catecholamines, indolamine, and acetylcholine—there are other neurotransmitters active within the CNS.

1. Glutamic acid: Glutamate and GABA are found in simple organisms. The first neurotransmitter to evolve in the brain is Glutamate. Glutamate is an excitatory neurotransmitter, and its receptors are found all over the brain. Chinese food contains a large amount of Monosodium Glutamate. There are three types of receptors: NMDA, quisqualate, and kainate receptors. These receptors are all important in working with other NTs.

2. GABA (Gamma Aminobutyric acid): GABA was first synthesized in 1883 and known to be a metabolite of plant and microbial metabolism. It was discovered in the mammalian brain in the 1950's, found in very high concentrations in the brain and spinal cord. In the brain, GABA is found in amounts 10-15 times greater than dopamine (DA), norepinephrine (NE), or serotonin (5HT); a minuscule amount is also found in the retina. It is generally classified as an inhibitory NT and accounts, along with other amino acids, for a major part of neuronal transmission. GABA works to balance the monoamines DA, NA, and 5HT wherever they are involved. GABA is implicated directly in Huntington's chorea, which is due to degeneration of GABAminergic neurons. GABA is indirectly involved in Parkinson's, epilepsy (abnormality in the biochemistry of GABAminergic neurons), and schizophrenia.

GABA Synthesis: This involves only two steps: one to synthesize it and one to break it down:

1. Synthesis: One-step synthesis from its amino acid precursor Glutamic Acid, which is decarboxylated by the enzyme Glutamic acid decarboxylase (GAD).

📐 Formula: Glutamic acid → GABA (catalyzed by glutamic acid decarboxylase and coenzyme pyroxidal phosphate; this process can be blocked by ions such as chloride and zinc)

2. Catabolism: GABA is trans-aminated by GABA-A-oxoglutarate transaminase. GABA is transformed into Succinic Acid Semialdehyde to return back into the Krebs cycle. In the transaminase process, GABA conversion is reversed to glutamic acid through alpha-ketoglutarate, which acts as an amine acceptor.

Distribution and pharmacological agents: From monkey to human brain (1968-1971 studies), the highest GABAminergic concentrations were found in the Substantia Nigra (SN), Globus Pallidus (GP), and the Hypothalamus (hyp).

Agonists: The post-receptor GABA agonist is muscimol. This leads to increased arousal, self-mutilation, and increased feeding if placed in the hypothalamus (disinhibition of inhibition).

Antagonists: Post-receptor antagonists or receptor blockade by picrotoxin and bicuculine. Benzodiazepines (Valium and Librium) stimulate a particular site of GABAminergic neurons. This alleviates anxiety symptoms/response.

Glycine

Glycine is another inhibitory neurotransmitter like GABA; however, research is still ongoing to identify its role. It is found in the mammalian spinal cord and brain. It is found in greater amounts in the spinal grey matter than the brain, suggesting it may be working with interneurons. However, no distinct and clear glycine pathways exist in the brain.

🔑 Definition — Strychnine: A poison that blocks the action of glycine and also blocks postsynaptic inhibition.

PEPTIDES

Neuroactive peptides are candidates for neurotransmitters. Some of these are like orthodox NTs, some are performing modulatory or regulatory roles, and some also act as neurohormones.

Key peptides include: Brain opioids, Angiotensin II (thirst), Oxytocin and Vasopressin, Luteinizing Hormone Releasing Hormone (LH-RH), Substance P, and Adreno-Corticotropic Hormone (ACTH).

Brain Opioids

Endorphins (large molecules) and Enkephalins (smaller molecules).

Hughes and Kosterlitz (1975) in Aberdeen discovered the existence of brain opioids in the brain. This was a landmark finding because for the first time, it was found that this chemical compound was similar in composition to the opiates morphine, heroin, etc. In later research, Huda Akil and her research group reported the highest concentration in Substantia Nigra, lateral hypothalamus, cerebral cortex, and periaqueductal gray.

Extracts taken from the brain, when administered to laboratory animals, led to analgesia, wet dog shakes upon application (in a manner similar to administration of opiates). Similarly, akinesia, hypothermia, rigidity, and catalepsy were also seen.

🔑 Question: Are brain opioids natural neuroleptics (antipsychotic drugs)?

In some cases, psychotic patients who are not responding to other treatment drugs (neuroleptics) have responded to short-term endorphin treatment (McGreer and McGreer, 1980). Brain opioids are also involved in emotions, growth, pleasure (acting through the mesolimbic DA pathways), stress-induced analgesia (Akil et al., 1975), growth, and development (Najam and Panksepp, 1980).

Opioid antagonists have also been found effective in the treatment of autism and childhood disorders. Panksepp et al.'s theory of brain opioids and attachment states that brain opiates are natural comforters in the brain; it is when they are blocked that addicts turn to morphine/heroin, and autistic children have higher than normal brain opiate levels. The discovery that pain and acupuncture pathways are similar to brain opioid pathways in the body and spinal cord provides strong evidence for the involvement of brain opiates in pain and acupuncture.

Narcotic analgesics such as morphine and heroin are severely addictive, have high tolerance value, are potent analgesics, potent anticongestants, and are also used for stomach and digestive problems. The interesting aspect of opiates' effect on pain is that it is only the affective component which is reduced (one does not feel the pain); the physical component is still there. Pain is still there, but the patients do not care about it—the reaction to pain is diminished.

Psychotogenic Compounds

Hallucinogens:

1. LSD (Lysergic acid diethylamide): A potent drug—a small dose of 1/10,000 gram is effective. It has great tolerance to the point that the same dose is not effective if taken a second time, meaning an increased dosage is needed every time for an effect to take place. The LSD "trip" depends on the mood and personality of the user and can be controlled.

2. Mescaline: A hallucinogenic compound made from plant extracts in Mexico. It is used in religious ceremonies by tribes in Mexico.

Psychopharmacology

This area of specialization is the study of the effects of drugs on psychological processes. It is both a basic and an applied science. "A recognition of the interrelationships between pharmacological agents, neuroregulators, and behavior has become essential for those involved in helping individuals who have psychiatric disorders." Therefore, to develop drugs, research in the laboratory is needed before the drugs can be tested and used—especially on humans.

The evidence is provided when the symptoms of a psychiatric disorder are removed when linked to a neurotransmitter, and then the normalization of behavior should occur with normalization of levels of NT in the brain. Further, known effective exogenous substances should have similar chemical effects as the endogenous (brain) chemicals. Pharmacological substances should be able to interact with NTs at given sites if they have the same chemical composition.

⭐ Key Takeaways

Students must remember that ACh plays critical roles in arousal, drinking, aggression, punishment systems, and Alzheimer's disease, with treatments involving muscarinic agonists and acetylcholinesterase inhibitors like THA (tacrine). GABA is the primary inhibitory neurotransmitter synthesized from glutamic acid via GAD, is found in highest concentrations in the substantia nigra, globus pallidus, and hypothalamus, and is modulated by benzodiazepines. Brain opioids (endorphins and enkephalins) are natural compounds that reduce the affective component of pain and are involved in pleasure, stress-induced analgesia, and attachment behavior. Hallucinogens like LSD and mescaline produce altered states of consciousness with high tolerance development. Psychopharmacology studies drug effects on psychological processes and relies on the principle that effective drugs should interact with specific neurotransmitter systems to normalize behavior.

🧠 Quick Revision Questions

1. What is the role of ACh in drinking behavior, and what is the chain of events from cellular dehydration to increased fluid intake?
2. How does anti-ACh produce disinhibition of punished responses, and what brain structure is involved in the punishment system?
3. What are the two steps in GABA synthesis and breakdown, and what enzyme catalyzes the conversion of glutamic acid to GABA?
4. What is the difference between endorphins and enkephalins, and how do brain opioids affect the experience of pain?
5. What evidence supports the use of opioid antagonists in treating autism, and what is Panksepp's theory linking brain opioids to attachment?

📘 Lecture 37 — Brain and Motivational States

📖 Overview: This lecture explores the neurological foundations of motivational states, focusing on homeostasis as the underlying principle that drives behavior. It details how biological systems like temperature regulation are managed by the brain through feedback and feedforward mechanisms. Understanding these processes is crucial for grasping how organisms maintain internal stability for survival and how disruptions can lead to pathology.

🗂️ Topics Covered

The lecture introduces the concept of homeostasis as a fundamental biological system maintained by neurological feedback. It details the brain’s modulation of temperature regulation, distinguishing between ectotherms and endotherms. The role of the hypothalamus as a master control center is emphasized, including its set point mechanism and the biochemical influences of endorphins. The lecture concludes with an explanation of fever as a pathological alteration of this set point.

📝 Lecture Summary

Objectives

This lecture aims to familiarize students with the process of homeostasis and the biological systems involved, the brain modulation of these systems, and how the body’s systems compete for survival. It specifically covers brain and motivational states, homeostasis (including temperature regulation, hunger, thirst, bio-rhythms, sleep, and awakening), pathology related to sleep cycles, and sleep disorders and treatment.

Homeostasis:

Homeostasis is the balance and optimal functioning system of the body that must be maintained for the survival of the organism. Well-defined, autonomous neurological feedback systems work to maintain an internally stable environment. These include feedforward and feedback systems that constantly monitor and inform the brain and organs of each other’s status. For example, somatosensory systems (skin sensors) send temperature information to receptors in the brain, which send messages for adjustments. Receptors exist both outside and within the brain. “It is only against a homeostatic background that other more active systems can function, and many of an animal’s activities are motivated by the homeostatic needs,” (Bridgeman 1988, p 237). Homeostasis evolved to support survival, and if any problems arise, the whole system needs readjustments. Minor issues are sustained and corrected, but major, unmanaged changes can lead to death. Actions and behaviors are motivated by these homeostatic signals of the body’s needs. There are internal receptors, external stimuli, brain mechanisms, and neurochemical regulatory systems, all well-synchronized. Receptors evolved for specialized functions like temperature regulation, hunger, thirst, and sleep.

Temperature Regulation

Temperature regulation is a motivated behavior with all its key characteristics: it is purposive (goal to warm or cool), persistent (behavior continues until the goal is reached), has periodicity (e.g., winter nest building), and is prioritized. This is a well-defined system with a clear evolutionary path for maintaining optimum body functioning. The development of a strong and sensitive thermoregulatory system was necessary for survival as species evolved in diverse environments.

🔑 Definition — Ectotherms: Amphibians and reptiles that depend on their external environment for temperature regulation. They are “solar powered,” adjusting by relocating to warmer or cooler places. They have evolved vasoconstrictors and vasodilators on the skin. This response is directly controlled by thermoregulatory receptors in the hypothalamus and brain.

🔑 Definition — Endotherms: Mammals and birds that have evolved an effective internal temperature control system with a set point, functioning like a thermostat. This allows for sustained activity for longer periods compared to ectotherms. They can also make environmental adjustments (e.g., seeking shade, building shelters).

🔑 Definition — Set point: An internal standard (e.g., temperature) that the body functions to maintain by cooling or heating through homeostasis. There is a neutral zone range around the set point within which temperature can vary slightly. If temperature goes beyond this range, thermoregulatory mechanisms are activated. Endotherms also make environmental adjustments: (a) to cool the body (e.g., perspiration, seeking shade) and (b) to heat the body (e.g., shelter, fire, huddling). 📐 Formula/Mechanism: Heat production is achieved by increasing basal metabolism, muscular activity, shivering, and sympathetic system activity. Heat loss is achieved by evaporation (sweating) and conduction (e.g., bathing). Response to cold is vasoconstriction of peripheral blood vessels, and piloerection in fur-bearing animals.

🔑 Definition — Brain/neural substrates of thermoregulatory behavior: The preoptic area of the anterior hypothalamus is the master control for both heating and cooling. Heating this area leads to sweating; cooling it leads to shivering. Lower phylogenetic areas in the brain stem and spinal cord are under hypothalamic control but have a wider neutral zone, making them less refined and potentially dangerous. The biochemical control is with endorphins (brain opioids); injecting them into the hypothalamus lowers body temperature, an effect blocked by naloxone (an opiate antagonist) because pain and temperature sensory systems are related. 📌 Example: In a laboratory experiment, lizards (ectotherms) were anesthetized by being kept in ice for surgery; they would return to a normal state when warmed.

What happens in fever?

Fever occurs when bacteria or viruses produce pyrogens which affect the hypothalamic set point. The set point rises (e.g., from 98.4°F to 101°F), but the body is still at 98.4°F. Signals are sent to heat up the body: shivering, cold hands and feet, faster metabolism. When an antipyretic like aspirin is taken, the set point is reduced back to 98.4°F. Now the body, which has been at 101°F, needs cooling. This leads to sweating and taking off blankets—the fever “breaks.” In humans, clothes and houses act as thermoregulatory devices. 💡 Why this matters: This explains the physiological and behavioral experience of having a fever and the effect of medication.

⭐ Key Takeaways

Homeostasis is the foundational principle for all motivated behaviors, maintained by sophisticated neurological feedback systems. The hypothalamus, particularly the preoptic area, is the master regulator of temperature, setting a specific set point and managing heat production and loss. Ectotherms rely on external environments, while endotherms have internal controls that allow for sustained activity. Fever is a clear example of a pathological state where pyrogens alter the hypothalamic set point, and antipyretics work by resetting it, causing the sensation of fever “breaking.”

🧠 Quick Revision Questions

1. Define homeostasis and explain its role in motivating behavior.
2. Differentiate between ectotherms and endotherms in terms of temperature regulation.
3. What is the role of the preoptic area of the anterior hypothalamus in thermoregulation?
4. Describe the sequence of events in the body when the hypothalamic set point is raised by pyrogens (fever).
5. How does aspirin (an antipyretic) affect the body’s thermoregulatory response during a fever?

📘 Lecture 38 — Brain and Motivational States

📖 Overview: This lecture explores the biological foundations of motivation, focusing on how the brain regulates fundamental survival behaviors. It covers biological rhythms, circadian cycles, body temperature regulation, and the neural and physiological mechanisms controlling hunger and feeding behavior. Understanding these systems is crucial for comprehending how internal states drive behavior and how disruptions can lead to disorders like obesity, sleep disorders, and seasonal affective disorder.

🗂️ Topics Covered

This lecture covers biological rhythms and their characteristics (period, frequency, amplitude, phase), circadian rhythms controlled by the suprachiasmatic nucleus (SCN), body temperature cycles tied to activity patterns, and the detailed neurobiology of hunger and feeding as a motivated behavior. It examines the multifactorial control of food intake including oral/peripheral, gastric, and metabolic factors, body weight set points, and the influence of cognitive, cultural, and experiential factors on eating behavior.

📝 Lecture Summary

Objectives

This section outlines the lecture's goals: to familiarize students with brain and motivational states, homeostasis including temperature regulation, cellular and brain controls of thirst, reward systems and addictions, fear, aggression, attachment, hunger, body weight set point theories, obesity, anorexia nervosa, thirst, bio-rhythms, sleep and awakening, pathology related to sleep cycles, sleep disorders and treatment, neurophysiology and biorhythms, sleep and awakening cycles, dreams, and sleep disorders.

Biological Rhythms

All biological systems operate on some cycle at any given time. When changes occur in the body or behavioral functioning on a regular, rhythmic basis, these are called biological cycles that follow a particular rhythm. These cycles can be short within a day (hunger), diurnal (day/night), monthly (menstrual cycle), or yearly (reproductive cycle in animals). These biological rhythms/cycles have important influence on behaviors of animals.

The characteristics of biological rhythms:

1. Period: The time required for a rhythm to be complete — from the beginning to the end of one cycle.
2. Frequency: The reciprocal of a period. For example, body temperature reaches a peak once a day, so the period would be 24 hours and frequency would be once in 24 hours. Reproductive behaviors in animals may have a 12-month period with a frequency of one (once a year mating season) per reproductive cycle.
3. Amplitude: The amount of change from the original starting point (e.g., 98.4°F + 1°F or 98.4°F + 1.5°F). This measures how large the change is from the set point or original point in the cycle. There are individual differences in amplitude — one person may have a rise of 0.5°F, another a rise of 1°F.
4. Phase: The peak of the rise in temperature may differ between individuals — one person may peak at 2 p.m., another at 3 p.m., and another at 4 p.m. Similarly, the drop in temperature may also differ (based on gender and metabolism). The phase is complete with the peak (highest) and trough (lowest). The phase is always with reference to the time of day, time of month, time of year, or some other external marker. People with different peaks would be out of phase with each other. Similarly, those who stay up all night and sleep during the day are totally opposite and out of phase with those who sleep at 10 p.m. and wake at 5 a.m. every morning.

Biological Rhythms

The biological rhythms/clocks control the functioning of most behaviors that are biological, including the thermostat, female estrus cycles, hunger and thirst, and sleep cycles. These are entrained with the light/dark cycles.

Circadian rhythms are biological rhythm cycles that follow a day cycle: circa means circle, and dian from diem means "of a day." The daily cycles are many, such as temperature and the most important (and obvious) cycle of sleep/awakening and feeding. There are other rhythms and cycles, such as the estrous cycle (in some animals, it appears once a year or so).

Studies have shown that there are rhythms for every biological response in the body measured: the epidermal (skin temperature) response, urine, blood, whole body temperature, physical rigor (energy to do work), weight, heart rate, blood pressure, respiratory peak flow, growth hormone levels, and even plasma ACTH (stress hormone levels). Studies have also shown that the body's response to drugs (such as pain killers) differs with the time of day, implying that smaller or larger doses may be necessary for therapeutic effect.

The circadian rhythms are controlled through the Suprachiasmatic Nucleus (SCN) located in the medial hypothalamus. Lesions in the SCN break down the behavioral circadian rhythms in rats — drinking and adrenal cortisone responses were affected in SCN lesioned rats (Zucker, 1972). In hamsters, the estrus cycles (female's ovulatory cycles) are also disrupted.

🔑 Definition — Suprachiasmatic Nucleus (SCN): A nucleus located in the medial hypothalamus that controls circadian rhythms.

Our circadian rhythms can be changed or influenced by phase shifts. Day and night shift workers have not just sleep to take care of, but their bodies adjust by making changes in other cycles as well. Studies on changes in 12-hour shifts have shown that adaptation of shifts to heart rate, norepinephrine, epinephrine levels, body temperature, stomach enzyme production, and performance peaks were also affected (Higgins, 1975).

Menstrual cycles of women were also found to be disrupted if they were traveling across continents and their sleep/awake cycles were disrupted (jet lag). Day/night and dark/light cycles also affect mental health. In countries with long dark winters, there is a behavioral syndrome known as the winter blues.

Circadian and other biological rhythms are important modulators of behaviors in humans and animals.

Body Temperature and Biological Cycle: Circadian (of a day)

The body temperature is not constant throughout the day. Depending on the type of species — whether they are nocturnal (night foragers/night hunters) or day foragers — their body temperature rises and falls accordingly. The temperature peaks whenever the animal is most active; therefore, for humans, horses, and other day animals, it peaks during mid-afternoon. The rodent rat is nocturnal, so its temperature peaks at night. Similarly, the lowest temperature occurs at night for day foragers and during the day for nocturnal animals. The set point for body temperature is set by the light/dark cycles, which set the biological clock, which in turn sets the biological metabolism (faster during awake, slower during sleep to save energy). Temperature is lowest during sleep because metabolism is lowered — sleep reduces demand on metabolic heat production.

Therefore, the L/D cycles set the biological clock, which in turn sets the temperature set point. In some species, thermoregulatory behavior is modulated for longer cycles such as hibernation. Hibernation occurs when an animal moves into a state where body temperature is reduced and metabolism slowed to a particular level. There is limited requirement for fats, and the body can go a long way on stored fat. Bears and other animals hibernate in winter, while others such as birds migrate away for winters (Siberian birds migrate toward the Arabian Sea coastal areas for winters).

Among the other important biological systems with an autonomic modulating mechanism, one of the most important is hunger, through which energy and nutrition are provided to ensure the survival of the organism's systems.

💡 Why this matters: Understanding biological rhythms helps explain why shift work disrupts health, why jet lag occurs, and why seasonal affective disorder (winter blues) affects people in northern latitudes.

Hunger/Feeding

Feeding is an essential behavior because provision of nutrients and energy for survival, heat production, and metabolism all depend on what is eaten by the animal. Animals must eat enough to maintain their requirements and to maintain body weight. If they exceed input and do not use it, it leads to obesity; if they do not take what is required in sufficient amounts, it leads to starvation. The seeking of food is hunger — a very strong motivating behavior. Humans and animals spend most of their awake hours foraging for food. Food seeking is part of the homeostatic systems to regulate the organism's internal needs.

Hunger/Feeding as a Motivated Behavior

Food intake/feeding/hunger is motivated behavior because feeding behavior is:

a) Periodic: It is tied to the body's energy consumption, metabolism, needs, and the external environment (temperature, etc.). The signals for onset of feeding and for stopping eating increase and decrease with internal and external signals and clocks. b) Priority: Feeding has high survival value, so it takes priority over other behaviors such as mating. Animals seek food over seeking other things. A hungry person sees the moon as a bread (roti), while a person with a full stomach can think of a beloved's face like the moon. c) Purposive: Very much goal-directed when food is sought and the animal is hungry. The behavior continues until hunger is sated. d) Persistence: Food seeking is persistent. It continues until the goal has been achieved and enough food has been taken in.

Although there are many set points within the feeding cycle, there are two major set points that must be maintained by feeding behaviors:

a) Body weight set point: This set point ensures that body weight is maintained at a constant level — if you are 120 or 200 pounds, your body works to maintain that weight. b) Body energy and fat content: Within each organism there is a glucose set point and a lipid set point that the body works to maintain and monitor.

However, if energy intake equals energy expenditure (Intake = Output), there would be no weight gain. Body weight would be maintained at a constant level. Weight gain and weight loss occur if the equation is imbalanced for either input or output of food.

What Are the Factors Regulating Food Intake?

This is an interesting question as feeding may occur in the absence of hunger signals. For example, when we see cakes in a bakery window or smell samosas frying, there is an urge to eat — an immediate desire that overrides the full stomach signals. Or we may defer eating because there is a high priority for some other activity (running for life, or preparing for exams — food becomes a low priority).

"Feeding is under a multifactor control and the multiplicity of signals means that there are a number of feedback loops for the initiation and termination of food intake" (Mogensen and Carlson, 1977, p10, cf Mogensen 1980). This can be understood by looking at the body's requirements: even though glucose and fats are the main sources of energy and metabolism, there is also need for proteins for growth, maintenance (and for NT systems).

Analyzing intuitively, we can identify several possible reasons why we eat and what sets our hunger signals. We feel hungry because: a) We salivate (Pavlovian dogs!) or our stomach sends signals (rumbles), or we smell food, or because the body sends signals. These can be classified into the following categories.

Oral/Peripheral (also odor), Gastric, and Metabolic (neural) factors:

Oral/peripheral factors: The taste, odor, sight, and texture of food play a role (though small) in the control of food intake. Animals eat more if the food looks and tastes good, and less if the food tastes bad. Mouth palatability (how good it tastes and looks) and variety increase food intake in rats and humans alike. Palatability is a very important source of obesity — eating when not required by the body.

Rats like high-fat foods very much, which increases total feeding response, and they become obese — the same for mice. Rats would eat quinine-adulterated food only if they are starving.

Teitlebaum and Epstein (1962) inserted a nasopharyngeal gastric tube that bypassed the mouth region. Rats were trained to send food through the tube to the stomach — their intake was only how much was required to maintain body weight.

Therefore, more than the mouth and the stomach region are involved in feeding. Snowdon (1969) reported that rats maintain lower than normal weight levels if food is not routed through the mouth (oral). There are some signals from the mouth (odor and taste).

Another study eliminating oral factors on food intake involved administering nutrients through intravenous infusions. Experiments by Nickoliadis and Rowland (1976): "When infusion equaled or was greater than the normal daily intake, there was an increase of oral intake of the diet..." indicating that there were some oral factors involved in feeding.

Sight of food stimuli also leads to initiation of and increase in eating response even when sated or full.

🔑 Definition — Palatability: How good food tastes and looks; a factor that increases food intake and is a significant source of obesity.

In humans and higher mammals, experience and cognitive factors are important in feeding behaviors. Therefore, eating different foods (raw or cooked), liking Chinese, Japanese, Thai, Greek, or Ethiopian food is learned. Using different cooking spices is also learned. Taste aversions are also learned, including cultural, religious, and other constraints. Some animals such as snakes, frogs, and lizards are not thought edible in the majority of the developed world, but there are some cultures where these are relished. We may like the head of the goat and trotters (siri paiy), but they may not be the food of choice in most countries. What we eat, how we eat (chopsticks, knives/forks, or banana leaves and hands), cooked or uncooked, vegetarian or meat depends on our region. Therefore, human food and eating is determined by cultural, religious, and regional factors.

📌 Example: Teitlebaum and Epstein (1962) used a nasopharyngeal gastric tube to bypass the mouth in rats. Rats trained to send food directly to the stomach consumed only the amount required to maintain body weight, demonstrating that oral factors alone do not control feeding. 📌 Example: Nickoliadis and Rowland (1976) found that when intravenous infusion of nutrients equaled or exceeded normal daily intake, rats still increased their oral intake, indicating oral factors are involved in feeding even when nutritional needs are met.

💡 Why this matters: Understanding the multifactorial control of feeding helps explain obesity (driven by palatability and external cues despite satiety) and why weight management requires addressing not just physiological hunger but also cognitive, cultural, and sensory factors.

⭐ Key Takeaways

Biological rhythms, especially circadian rhythms controlled by the suprachiasmatic nucleus, govern fundamental behaviors including sleep, temperature regulation, and feeding. The four key characteristics of rhythms—period, frequency, amplitude, and phase—determine how cycles function and how they can become disrupted (e.g., shift work, jet lag). Hunger is a motivated behavior with periodic, priority, purposive, and persistent qualities, driven by the need to maintain body weight and energy set points. Feeding is under multifactorial control involving oral/peripheral factors (palatability, taste, sight), gastric factors, metabolic factors (glucose and lipid set points), and cognitive/experiential factors (cultural learning, taste aversions). Importantly, feeding can occur in the absence of hunger signals, and oral factors play a significant role in overeating and obesity.

🧠 Quick Revision Questions

1. What are the four characteristics of biological rhythms, and how would you define each one?
2. Which brain structure controls circadian rhythms, and what happens when it is lesioned?
3. How does body temperature vary across the day in diurnal versus nocturnal animals, and what determines the set point?
4. List and explain the four properties that make hunger/feeding a motivated behavior.
5. What are the two major set points maintained by feeding behaviors, and what happens if energy intake equals energy expenditure?

📘 Lecture 39 — Brain and Motivational States

📖 Overview: This lecture explores the biological bases of motivated behaviors, focusing on the neural, metabolic, and physiological controls of feeding and hunger. It examines why set-point theories alone are insufficient and how the brain integrates multiple signals to regulate food intake, making it essential for understanding eating disorders, obesity, and addiction.

🗂️ Topics Covered

The lecture covers gastric factors in feeding control (including CCK peptide signaling), metabolic factors (glucostatic and lipostatic set-point theories), neural controls of feeding via the ventromedial and lateral hypothalamus, neurotransmitter involvement (norepinephrine), and the role of gut peptides. It challenges traditional set-point theories with evolutionary and cultural evidence.

📝 Lecture Summary

BRAIN AND MOTIVATIONAL STATES

This section introduces the lecture's objectives: understanding brain mechanisms in motivational states including homeostasis, temperature regulation, thirst, reward systems and addiction, fear, aggression, attachment, hunger, body weight set point theories, obesity, anorexia nervosa, bio-rhythms, sleep and awakening, and sleep disorders.

Factors that Control Food Intake Behaviors (continued)

The lecture continues from previous discussions of oral factors (palatability, smell, sight) and cognitive/learning influences, now examining gastric factors in feeding behavior.

Gastric factors:

The gastrointestinal tract is crucial for digestion, but the stomach's role in hunger is more complex than simple emptiness. Early experiments by Cannon and Washburn (1912) used a balloon preloading technique where Washburn swallowed a balloon and reported hunger pangs while Cannon measured stomach contractions. Hunger pangs correlated with stomach contractions, suggesting stomach importance. However, this theory was challenged by three findings: the stomach is rarely empty except during starvation; people can eat even when full (cultural hospitality); and patients with stomach removal or denervation still report hunger and fullness, maintaining body weight with smaller meals.

Koopmans (1981) performed an experiment attaching an additional stomach to animals, with blood vessels passing through the new stomach. When food passed from the additional to the real stomach, animals stopped eating in response to blood-borne signals, suggesting chemicals (not in food) stimulated satiety signals.

Smith, Gibbs, and Young (1973-1976) proposed that peptides (short amino acid chains acting as hormones or neurotransmitters) signal satiety. Ingested food triggers hormone release into the bloodstream. The gut peptide cholecystokinin (CCK) when injected led rats to eat smaller meals without illness or pain. However, CCK injection directly into the brain was less effective than into the bloodstream. Mineka and Snowdon (1978) showed this effect is short-lived, indicating multiple controlling factors.

🔑 Definition — Gastric factors: Signals from the gastrointestinal tract, including stomach distension and gut peptides, that contribute to the initiation and termination of feeding.

📌 Example: Patients with stomach removal still report hunger and fullness, eating smaller meals but maintaining body weight, proving gastric factors are important but not essential for feeding control.

Metabolic Factors:

Decreased glucose levels initiate eating; increased glucose leads to cessation. Campfield and Smith (1990) monitored rats with free access to food via catheters. Baseline blood glucose was ~2%, but just before eating, levels dropped to ~8%, indicating blood glucose signals food intake. This supports the set point concept—an energy set point with three components: set point mechanism (neuronal receptors), detector mechanisms (detecting deviations), and effector mechanisms (restoring balance). Set points exist for glucose, fat levels, and weight.

🔑 Definition — Set point: A theoretical mechanism that maintains body variables (like glucose, fat, weight) at a constant level through detector and effector mechanisms.

Glucostatic Theory proposed by Mayer

This theory proposes the feeding regulatory system maintains a constant glucose set point in blood. Gluco-receptors in the hypothalamus gauge blood glucose levels continuously. This is a short-term mechanism for feeding initiation and cessation.

When blood glucose falls, glucose from the pancreas is released, increasing eating. Glucogen injection decreased eating and reduced stomach contractions. Insulin injections cause hypoglycemia (reduced blood glucose) increasing eating as insulin facilitates glucose entry into cells. In experiments, after insulin injection, animals received: a) glucose injection, b) fructose or mannose (fructose cannot cross blood-brain barrier but liver uses it; mannose both brain and liver use), or c) ketone bodies (brain fuel). All showed reduced feeding, indicating peripheral controls—not brain signals—monitor feeding.

📐 Formula: Insulin injection → hypoglycemia → increased eating; Glucose injection → reduced feeding

📌 Example: After insulin-induced hypoglycemia, injecting glucose, fructose, or ketone bodies all reduced feeding, suggesting peripheral organs (not just brain glucoreceptors) monitor nutrient levels.

Lipostatic theory:

The lipostatic theory states a body set point for lipids exists; any decrease in body fat stores initiates feeding. This is a long-term mechanism for body weight maintenance. During starvation, stored body fats break down to provide glucose.

Difficulties with set point theories:

1. Inconsistent with evolutionary perspective—when food availability was uncertain, a fixed set point would be maladaptive.
2. Hunger and feeding don't follow glucose patterns alone; cultural variations in food patterns cannot be explained by glucostatic or lipostatic theories.

💡 Why this matters: Set point theories oversimplify feeding control, ignoring evolutionary and cultural factors that shape human eating behavior.

Neural Control of feeding:

Research since the 1940s has focused on two hypothalamic areas: Ventromedial Hypothalamus (VMH) and Lateral Hypothalamus (LH) . The hypothalamus is essential for eating and drinking; without it, no feeding or drinking controls exist.

• Ventromedial hypothalamic (VMH) damage causes obesity (hyperphagia—overeating). First demonstrated by Anand and Brobeck (1943) . VMH lesions produce hyperphagia; LH lesions produce aphagia (no eating). Same effects in rats, dogs, monkeys, and humans.

VMH similarities in rats and humans:

1. Food Nutritive Content Challenge: Normals increase intake when nutritive content decreases; VMH animals are finicky eaters and cannot compensate.
2. Palatability: Increased palatability causes increased eating in VMH animals and humans; normals stop based on body signals.
3. Work for food: VMH-damaged rats and obese humans minimize work. In experiments with peeled vs. unpeeled almonds, VMH rats and fat humans ate more unpeeled almonds; normals ate ~50% of each.

Hypothesis: VMH may be the satiety center—controlling signals for stopping feeding. Damage removes inhibition, causing continued eating.

• Lateral hypothalamic (LH) damage causes starving rats—aphagic (no eating) and adipsic (no drinking). Without tube feeding, they die. Recovery occurs in phases: they recover eating but not drinking; eventually drink condensed milk but not water. They cannot compensate for initial weight loss and never fully recover normal weight.

Hypothesis: LH is the initiation center for eating. However, multiple neurotransmitters (NTs) pass through LH (including norepinephrine (NE) and dopamine (DA) ), making interpretation difficult. The damage may cause motivational deficit/inertia—animals lack spontaneous activity and show sensory neglect (no response to visual, tactile, or other stimuli).

Other factors:

• Norepinephrine (NE) : Liebowitz and colleagues found NE-rich neuron stimulation in LH initiates eating.
• Gut peptides: Emerging role in initiation and control of feeding.
• Serotonin: Large amounts exist in the gut, playing a role in feeding signals.

🔑 Definition — Hyperphagia: Excessive eating behavior, caused by VMH lesions. 🔑 Definition — Aphagia: Complete absence of eating behavior, caused by LH lesions.

📌 Example: VMH-damaged rats are finicky eaters who cannot compensate for reduced nutrient content and work minimally for food, while LH-damaged rats show aphagia, adipsia, and sensory neglect, recovering only partially over time.

⭐ Key Takeaways

The stomach's role in hunger is not absolute—gastric cues exist but are insufficient alone, as patients without stomachs still feel hunger. Gut peptides like CCK signal satiety but are short-acting. Glucostatic and lipostatic set-point theories explain some feeding regulation but fail to account for evolutionary and cultural variability. The hypothalamus is central: VMH serves as a satiety center (damage causes obesity), while LH serves as an initiation center (damage causes starvation). Norepinephrine and gut peptides modulate feeding, and recovery from LH damage is partial and slow.

🧠 Quick Revision Questions

1. What three pieces of evidence challenged Cannon and Washburn's balloon experiment suggesting stomach contractions control hunger?
2. What is CCK, and why is its satiety effect considered short-lived according to Mineka and Snowdon?
3. According to the glucostatic theory, what happens to eating when insulin is injected, and what do fructose/mannose injection experiments reveal about peripheral vs. brain controls?
4. What three behavioral similarities exist between VMH-damaged rats and obese humans?
5. Why is it difficult to interpret LH lesion effects solely as a feeding center—what alternative explanation do researchers propose?

📘 Lecture 40 — Brain and Motivational States

📖 Overview: This lecture explores the neural and biological foundations of motivated behaviors, focusing on eating and drinking. It examines why feeding behaviors go wrong, leading to disorders like obesity and anorexia nervosa, and details the homeostatic mechanisms that regulate hunger, thirst, and fluid balance, emphasizing the critical role of the hypothalamus.

🗂️ Topics Covered

The lecture covers the brain mechanisms underlying motivational states, beginning with a detailed analysis of eating disorders including obesity and anorexia nervosa. It examines the biological, metabolic, and psychological factors contributing to overeating and under-eating, such as metabolism, brown adipose tissue, and diet-induced thermogenesis. The second half focuses on thirst as a motivated behavior, explaining the two distinct mechanisms of fluid regulation: intracellular (cellular dehydration) and extracellular (hypovolemia), along with the roles of the hypothalamus, osmoreceptors, and hormones like ADH and angiotensin II.

📝 Lecture Summary

Brain and Motivational States

This lecture introduces the concept that motivated behaviors like eating and drinking are essential for survival. It explains that understanding why these behaviors go wrong (e.g., in obesity or anorexia) requires examining the neural mechanisms designed to maintain stability, such as homeostasis. The idea of a weight set point is introduced, and it is noted that when this mechanism breaks down, eating disorders emerge.

Eating Disorders: Obesity

Obesity is described as a major problem in the modern world, affecting millions. While it has a genetic link, its epidemic nature is attributed to evolutionary and lifestyle changes. During human evolution, storing fat was necessary for survival as hunter-gatherers who walked many miles. Modern sedentary lifestyles, along with changes in cooking and food storage (e.g., frozen foods), have made this stored fat unhealthy. The lecture highlights that the younger generation prefers fried and fast food with very little exercise, a shift from the healthier habits of older generations.

🔑 Definition — Obesity: A metabolic disorder where energy input (food) exceeds energy expenditure over time.

Eating Disorders: Acquired and Innate Factors

Eating disorders can be acquired, learned, biological, or metabolic.

• Acquired/Learned Factors: Children are taught to finish their food and associate eating with reward (e.g., candy for good behavior). As adults, they continue eating the same amounts despite reduced nutritional needs. Humans override inhibitory signals and continue eating because food looks or tastes good. Psychological variables leading to overeating include field dependence, reduced impulse control, eating too fast, maladaptive controls, depression, and tension.
• Innate/Metabolic Factors: Obesity is linked to differences in basal metabolic rate (BMR) . Some people have a higher metabolism than others. Research (Rodin et al., 1989) suggests that food intake between normal and obese people is not significantly different, but energy expenditure and metabolic states may differ.

🔑 Definition — Resting metabolic state: A state where the body becomes diet-resistant, making it difficult to lose weight even after decreasing caloric intake because the metabolic rate slows down with each diet.

📐 Formula: Weight Maintenance → If food/fat input = energy expenditure output, weight is maintained at a constant.

📌 Example: A person who repeatedly diets and binges sends their body into a "starvation mode." This signals the body to save what it has, activating mechanisms to store fat. This alteration in metabolic efficiency makes it harder to lose weight with each subsequent diet, explaining why diet binges are ineffective.

💡 Why this matters: 70-80% of a person's energy expenditure comes from resting metabolism (thermogenesis, fidgeting, maintaining muscle tone), not from exercise.

Brown Adipose Tissue and Metabolism

Individual differences in weight gain may be explained by brown adipose tissue (BAT) . These special cells convert calories directly into heat, a process known as non-shivering thermogenesis. This is important for animals that hibernate. BAT cells are rich in mitochondria, giving them a brown color and high metabolic rates. Their metabolism is controlled by B-adrenergic receptors.

• Increased norepinephrine levels lead to increased non-shivering thermogenesis, producing heat.
• This mechanism is controlled by the medial hypothalamus.
• A defect in BAT metabolism leads to defects in fat breakdown.
• In normal rats, BAT metabolism rises by 200% after a meal, but this does not happen in obese rats, suggesting deficient meal-induced thermogenesis is involved in eating disorders.

💡 Why this matters: Since each meal increases metabolism, having more frequent, smaller meals could burn more calories through this process, a suggested mechanism for weight reduction.

Treatment of Obesity

In extreme cases, therapy for obesity includes:

• Jaw wiring: To stop patient from eating.
• Intestinal surgery: Reducing the length of the intestines, leading to reduced gastric activity but causing great discomfort.
• Gastroplasty (stomach stapling) : Reducing the stomach size.

Anorexia Nervosa and Bulimia

Anorexia nervosa is a disorder where people, especially young women, under-eat to the point of starvation. It is often linked to cultural norms of thinness (e.g., models, film artists). In a related form, Anorexia/Bulimia, individuals eat very little and then binge and forcibly throw up. Their focus is on food in a different way: they like to cook, feed others, talk about food, and collect recipes, but they do not eat.

• Potential causes include: hereditary factors, enlarged sulci in the brain (which return to normal after recovery), enlarged ventricles (causing permanent damage), and defects in dopaminergic, noradrenergic, and brain opioid levels.
• Psychotherapy is not effective, but the drug Fenfluramine has been successful in treating anorexics.

📌 Example: The famous American singer Karen Carpenter died of anorexia in the 1970s, a well-known case of self-starvation driven by a distorted body image.

Thirst: Fluid Intake

Thirst is a motivated behavior that is purposive and periodic. Animals seek water when thirsty and stop when they have drunk enough. While dryness in the mouth (from dry salivary glands due to lowered water levels in blood) is a sensation associated with thirst, it is not the primary control mechanism. For survival, every living organism needs water, as each cell requires fluid.

• Daily Water Balance: For an average human adult, daily water intake and output equals about 2500 milliliters.
• Water is lost through the lungs (vapor), skin (perspiration), and kidneys (urination).
• Water is gained through drinking and eating high-water-content foods (e.g., melons, meat is 70% water).
• The human body is 50-60% water.

Mechanisms of Fluid Regulation: Intracellular and Extracellular

There are two different mechanisms by which fluid is regulated:

1. Intracellular: Monitors fluid within the cells (vascular blood and non-vascular tissue fluid components). It also monitors the 9% saline level in blood and CSF.
2. Extracellular: Monitors fluid outside the cells.

🔑 Definition — Cellular Dehydration: Loss of fluid from the intracellular compartment. 🔑 Definition — Hypovolemia: Loss of fluid from the extracellular compartment. Both conditions lead to thirst and drinking.

The regulation is driven by osmotic balance. If sodium ions increase in one compartment, fluid moves across cell walls to equalize the concentration on both sides.

Hypothalamic Mechanism of Thirst

The hypothalamus is the key brain region for fluid regulation. Wayner and Carey (1973) showed that two separate regions of hypothalamic receptors are involved in monitoring fluid levels.

• Lateral Hypothalamus: Involved in detecting cellular dehydration (changes in intracellular fluid levels).
• Anterior Hypothalamus: More sensitive to changes in extracellular fluid levels.

🔑 Definition — Osmoreceptors: Receptors located around the Lateral Pre-Optic Area of the hypothalamus that detect changes in intracellular fluid levels and send signals through cellular and neural systems.

🔑 Definition — Mechanoreceptors: Receptors that monitor hypovolemia (extracellular dehydration) by monitoring the tonic rate of discharge in vascular walls, especially near the heart, detecting changes in blood pressure.

Hormonal Control of Thirst

When cellular dehydration occurs:

1. The pituitary releases Antidiuretic Hormone (ADH) .
2. The animal starts drinking.
3. ADH is released by the anterior hypothalamus via the posterior pituitary.
4. Increased ADH acts on the kidneys to retain fluid (decrease urine volume/output).
5. Decreased ADH signals the body to save water.
6. Water intake helps reduce osmotic pressure, and water is absorbed by the intracellular compartment.

A second hormonal system is activated by the kidneys:

1. The kidneys produce Renin.
2. Renin acts on Angiotensinogen to produce Angiotensin II.
3. Angiotensin II acts directly on thirst receptors in the hypothalamus.

Primary and Secondary Drinking

🔑 Definition — Primary Drinking: Drinking in response to a loss of fluid from either the intracellular or extracellular compartment, intended to restore fluid levels. 🔑 Definition — Secondary Drinking: Drinking in the absence of water loss. This is not in response to cellular dehydration but can be caused by dryness of the mouth, psychogenic factors, or other pathological reasons.

⭐ Key Takeaways

A student must understand that motivated behaviors like eating and thirst are driven by complex homeostatic and neurochemical systems, with the hypothalamus acting as a central regulator. For eating, the key is the balance between energy input and output, influenced by metabolic rate, brown adipose tissue, and set-point theories; disorders like obesity and anorexia arise from disruptions in this system and are influenced by both biological (e.g., genetics, metabolism) and psychological/cultural factors. For thirst, remember that there are two distinct control systems—one for cellular dehydration (osmoreceptors in the lateral hypothalamus/ADH) and one for hypovolemia (mechanoreceptors/renin-angiotensin system)—that activate primary drinking to maintain fluid balance, distinguishing it from secondary drinking.

🧠 Quick Revision Questions

1. Explain the difference between resting metabolic rate and diet-induced thermogenesis. How do these concepts relate to difficulty in losing weight?
2. What is the role of brown adipose tissue (BAT) and the medial hypothalamus in non-shivering thermogenesis? How might a defect in this system contribute to obesity?
3. Distinguish between cellular dehydration and hypovolemia. Which hypothalamic regions are primarily responsible for detecting each type of fluid loss?
4. Describe the two main hormonal pathways (ADH and the renin-angiotensin system) involved in the regulation of thirst and fluid intake.
5. What is the critical difference between primary and secondary drinking? Give an example of a cause for each.

📘 Lecture 41 — Brain and Motivational States

📖 Overview: This lecture explores the neurophysiological basis of sleep as a fundamental motivated behavior. It examines the nature, characteristics, electrophysiological stages, and disorders of sleep, alongside the brain mechanisms that regulate these states, addressing the enduring question of why we spend one-third of our lives sleeping.

🗂️ Topics Covered

The lecture covers sleep as a motivated, cyclic, and species-specific behavior governed by circadian rhythms. It details the electrophysiological stages of sleep (wakefulness through REM), including EEG patterns. It also discusses the functions of sleep (memory consolidation, repair), various sleep disorders (insomnia, sleep apnea, narcolepsy, sleep paralysis), and the brain correlates of sleep regulation (Raphe nuclei, Reticular Formation, Locus Coeruleus, Pontine nuclei).

📝 Lecture Summary

Objectives and Introduction

The lecture aims to familiarize students with the brain and motivational states, specifically regarding neurophysiology and biorhythms, sleep and awakening cycles, dreams, and sleep disorders. Sleep is defined as one of the most important motivated behaviors. Eminent researchers such as Moruzzi and Magoun, Jouvet, Asertinsky and Klietman, and Dement and Klietman have contributed to the study of this enigma.

What is Sleep? What is the Function of Sleep?

Sleep is an intriguing behavior with species-specific patterns (e.g., cats sleep for 2/3rds of their lives; horses are light sleepers; birds tuck their beaks; dogs and cats curl up). It is cyclic, following a circadian rhythm (a day/light cycle). Sleep is purposive, having survival value and fulfilling the system’s needs (as seen in the negative effects of sleep deprivation). It also has high priority for survival. Sleep is a Circadian-Zeitgeber, one of the biological rhythms that influence behavior.

Our sleep is governed by internal clocks, with each person having a unique rhythm (e.g., "day persons" vs. "evening persons"). An experiment placed students in soundproof rooms with no time cues. At the end, most maintained 24-hour cycles, but some had cycles >24 hours, and some entirely reversed their alertness patterns, indicating their natural cycles.

The question remains: why spend 25-30 years (1/3rd of life) asleep? Sleep appears non-adaptive by making one vulnerable to predators. However, sleep deprivation affects cognitive and emotional responses, reducing attention and affecting memory.

Characteristics of Sleep

• Species Specificity: All animals are similar in some aspects and different in others (e.g., birds, horses, lions).
• Home Territory: Crucial for all animals for survival value—safety and security.
• Periodicity: Sleep has a cyclic nature. Adults are generally monocyclic and monophasic (one sleep period per day), while infants are polycyclic and polyphasic (sleep and awake multiple times throughout the day and night).

Function of Sleep

The most obvious function is rest, though the brain never rests.

• Memory Consolidation Theory: We sleep so consolidation of memories can take place, especially during the REM period.
• Sensory-Motor Practice: Important for infants and growing children, occurring during REM sleep.
• Cell Repair: REM sleep is important for repairing damage to cells.

Electrophysiology of Sleep

Researchers (Asertinsky & Klietman, Dement & Klietman, Jouvet, Hess) showed sleep has formalized stages distinguishable by electrical activity of the brain. Recordings of EEG, EMG, and Oculomotor (EOG) movements reveal a consistent pattern across species.

Based on EEG patterns, the distinct stages are:

• Awake State: Brain has Beta-waves — very high frequency, low voltage, low amplitude (12-18 cps).
• Stage 1: As the person relaxes, Alpha-waves emerge — slower, lower frequency, higher voltage (8-12 cps).
• Stage II: Comprises Delta-waves — very slow (1-4 cps), high voltage waves, interspersed with sleep spindles (13-15 cps) and K complexes.
• Stage III: Known as deep sleep. Here we see Delta-waves — the largest and slowest of slow waves (1-2 cps). It is difficult to wake a person up in this stage.
• Stage IV: More and more Delta-waves, very slow and large in height, resembling a comatose state.
• REM Sleep (Rapid Eye Movement sleep): There is a sudden change to an awake-like EEG pattern (Stage I with theta waves), but with a loss of muscle tone in the neck and rapid eye movements. It is also called PS (Paradoxical Sleep) due to the disappearance of tonic activity in muscles, especially the neck. The body appears paralyzed because the pons inhibits movement to prevent injury from dreams.

This is a 90-minute cycle that repeats throughout the night. Towards morning, the duration of REM sleep increases. REM sleep is the sleep during which you dream. When people are woken up during this stage, 80% report dreaming.

🔑 Definition — REM Sleep (Paradoxical Sleep): A stage of sleep characterized by rapid eye movements, an awake-like EEG pattern, and loss of muscle tone, during which most dreaming occurs. 📐 Formula: Sleep Cycle: One cycle of non-REM and REM sleep lasting approximately 90 minutes. 📌 Example: A person falling asleep will proceed through Stages 1 to 4, then return through Stages 3 and 2 before entering their first REM period. This cycle repeats about 4-6 times per night, with REM periods getting longer towards morning.

Sleep Disorders

• Insomnia: The most common sleep disorder, characterized by difficulty falling or staying asleep.
• Hypersomnia: Excessive sleepiness, related to hormonal states and body energy levels.
• Sleep Apnea: The person repeatedly stops breathing during the night and wakes up. This is due to loss of contraction of the diaphragm during sleep.
• Nocturnal Myoclonus (Restless Legs): Twitching of the legs at night which wakes the person involuntarily.
• Narcolepsy: Also known as a REM attack. The person moves directly from the waking state into REM sleep. The body loses tone and becomes flaccid. This can be dangerous if driving or operating machinery.
• Sleep Paralysis: Waking up but feeling unable to move. The muscles are still under the inhibitory control of the pontine gigantocellular nuclei.

Brain Correlates

• Raphe Nuclei: Jouvet lesioned the Raphe nuclei of cats, destroying about 80% of serotonin, which led to insomnia in the cats.
• Reticular Formation (Reticular Activating System): Moruzzi and Magoun (1949) showed that electrical stimulation of this area leads to desynchronization of all electrical activity of the brain. Sleep animals wake up, and awake animals become more alert.
• Locus Coeruleus: Contains Norepinephrine and is important for sleep and awakening. Lesions in this area caused animals to spend more time in sleep.
• Pontine Nuclei: Involved in REM sleep. A specific group of cells, the Gigantocellular Tegmental Field (FTG), controls D-sleep. Without the FTG, animals experience only slow-wave sleep.

⭐ Key Takeaways

• Sleep is a cyclic, species-specific, motivated behavior essential for survival, governed by internal circadian rhythms and brain structures.
• The electrophysiology of sleep consists of distinct, repeating 90-minute cycles moving from wakefulness (Beta-waves) through Stages 1 (Alpha), 2 (Delta with spindles), 3, 4 (deep slow-wave sleep), and finally REM (Paradoxical) sleep, where most dreaming occurs.
• REM sleep is characterized by an active EEG, rapid eye movements, and muscle paralysis. It plays a critical role in memory consolidation and cell repair. Depriving someone of REM sleep can have severe psychological consequences.
• Major sleep disorders include insomnia, sleep apnea, narcolepsy (a direct transition to REM), and sleep paralysis, each linked to specific neurophysiological dysfunctions.
• Key brain areas controlling sleep and arousal include the Raphe nuclei (serotonin for sleep), the Reticular Activating System (for alertness), the Locus Coeruleus (norepinephrine for waking), and the Pontine FTG (for REM sleep).

🧠 Quick Revision Questions

1. What is the difference between beta, alpha, and delta waves in terms of their frequency and voltage, and to which sleep stages do they correspond?
2. What is "paradoxical sleep," and why is it called that?
3. Describe the neurobiological basis of narcolepsy and one reason why it can be dangerous.
4. According to the lecture, which brain structure, when lesioned, led to insomniac cats by destroying serotonin?
5. What is the function of the 90-minute sleep cycle, and how does the proportion of REM sleep change as the night progresses?

📘 Lecture 42 — Higher Order Brain Functions

📖 Overview: This lecture examines the neurological bases of higher-order brain functions, focusing on the cerebral cortex's role in complex behaviors. It explores language as a uniquely human capability, its evolution, production, comprehension, and the disorders that arise when specific brain regions are damaged. Understanding these functions is crucial for linking brain activity to observable behavior and psychopathology.

🗂️ Topics Covered

The lecture covers brain correlates of language, including speech production and comprehension and their associated aphasias (Broca's and Wernicke's). It also touches upon visuospatial skills, apraxias, and brain correlates of learning and memory. The discussion begins with the evolution of language in humans compared to non-human primates and ends with detailed descriptions of the neuropsychological deficits caused by lesions in specific cortical language areas.

📝 Lecture Summary

Brain correlates

The lecture introduces the focus on cortical control of major functions, stating that higher animals on the evolutionary scale have more cerebral cortical control over functions like language, emotions, learning, and memory. The goal of behavioral neuroscience is to understand these functions and develop models that explain how cortical areas relate to behavior.

🔑 Definition — Higher Order Brain Functions: These are the complex cognitive abilities controlled by the evolved areas of the cerebral cortex, including language, emotions, learning, memory, and psychopathology.

Language

Language is introduced as among the most important higher-order functions and is uniquely human in its complexity, although other animals have communication systems (e.g., bird songs, dog growling). In humans, vocalization is both limbic (non-verbal: cries, groans) and cortical (verbal, symbolic). The evolution of language required the development of cognitive and communication abilities, a formal system of signs and symbols, and the capability for language development in children.

🔑 Definition — Language: A specialized, uniquely human form of communication intertwined with the development of both healthy and pathological behaviors.

Language in Non Human Primates

Non-human primate communication is primitive, involving gestures, postures, and different types of calls (alarm, distress, threat), but it is not complex communication. Experiments by Gardiner and Gardiner with a chimpanzee named Washoe showed that chimpanzees can learn over a hundred signs in American Sign Language and exhibit communication equivalent to a two-year-old human, but cannot verbalize. Premack and Premack's experiments, and studies with a chimpanzee named Lana at the Yerkes Primate Institute, who developed grammatical relationships on her own, suggest that primates closest to humans have latent language capabilities. However, language development requires learning by interaction and socialization, a crucial point illustrated by the example of children reared by wolves who do not develop human language.

Speech Production and Comprehension

The lecture discusses disorders of speech, specifically Aphasia, which is a disorder of comprehension or production of speech. Speech production relies on sensation, perception, memories, vocal capabilities, and articulation musculature. Paul Broca, a French neurologist, described patients with great difficulty producing speech due to damage to the inferior prefrontal cortex, now known as Broca’s area.

🔑 Definition — Aphasia: From the Greek "a" (without) and "phasis" (speaking out), it is a disorder of the comprehension or production of speech.

📐 Location — Broca’s area: Located in the inferior left frontal lobe, it controls the musculature and mechanisms for speech. It contains motor memories for coordinated, sequenced movements of the tongue, lips, and jaw.

🔑 Definition — Broca's aphasia: A disorder of expressive speech, resulting in slow, laborious, non-fluent, telegraphic speech. Patients have difficulty with small grammatical words (function words like "a," "the," "in") but content words come more easily. Speech comprehension is not impaired. 📌 Example: A patient with Broca's aphasia might say, “Ah Monday, Ah DAD, Paul and Dad, hospital.... Wed.... 9p.m.” instead of a full, grammatically correct sentence. Their speech conveys meaning but lacks grammatical structure.

💡 Why this matters: Broca's area is adjacent to the motor cortex controlling the face and lips, highlighting the link between brain structure and specific motor functions required for speech.

Speech Comprehension

The speech comprehension area is located in the middle and posterior region of the Superior Temporal Gyrus, known as Wernicke’s area. This area collects information, matches and analyzes it, and sends it to the articulation areas via the arcuate fasciculus. Recognition of a word involves sensation, perception, and memories of sound sequencing. Damage to this region leads to receptive speech disorder.

🔑 Definition — Wernicke's aphasia: A receptive speech disorder characterized by fluent, rhythmically correct speech that is meaningless. Patients have poor speech comprehension and produce strings of meaningless words. They are not aware of their deficit. 📌 Example: When asked "What do you do?", a patient with Wernicke's aphasia might reply, “Mista oxycge, wann tell happened when happened, herent, kell, cam ho, renrapiers” and be satisfied that they answered the question. The speech sounds correct to a foreigner but is nonsensical to a native speaker. 🔑 Definition — Arcuate fasciculus: A bundle of nerve fibers that connects Wernicke's area (speech comprehension) to Broca's area (speech production), allowing information to be sent to the articulation areas.

💡 Why this matters: The deficit in Wernicke's aphasia is at the semantic level (meaning of words), demonstrating that different brain regions are specialized for different aspects of language, from the mechanics of production to the understanding of meaning.

⭐ Key Takeaways

The cerebral cortex, particularly in the frontal and temporal lobes, is the seat of higher-order functions like language. Language is a uniquely human complex system, distinct from primate communication systems which are more limited and under limbic control. Damage to specific brain areas causes distinct aphasias: Broca's aphasia (expressive, non-fluent speech with preserved comprehension) and Wernicke's aphasia (receptive, fluent but meaningless speech with impaired comprehension). The location of Broca's area (frontal lobe near motor cortex) and Wernicke's area (temporal lobe near auditory cortex) are crucial for understanding their respective functions. The arcuate fasciculus is the critical neural pathway connecting these two language centers.

🧠 Quick Revision Questions

1. What is the primary difference between the communication systems of non-human primates and human language?
2. What are the two main types of aphasia discussed, and which specific brain areas are associated with each?
3. Describe the key symptoms of Broca's aphasia. What aspects of speech are impaired, and what aspect is preserved?
4. Describe the key symptoms of Wernicke's aphasia. Why might a patient with this condition not be aware of their deficit?
5. What is the function of the arcuate fasciculus? Damage to this structure would lead to which specific language disorder?

📘 Lecture 43 — Higher Order Brain Functions

📖 Overview: This lecture examines the neurological bases of higher-order cognitive functions, focusing on disorders of language, movement, perception, and memory. It explains how damage to specific brain areas produces distinct clinical syndromes such as aphasias, apraxias, agnosias, and amnesias, and highlights the importance of neuropsychological assessment in diagnosis and rehabilitation.

🗂️ Topics Covered

The lecture covers brain correlates of language and speech disorders (aphasias, dyslexia), visuospatial deficits (including visual agnosia and prosopagnosia), apraxias (including construction apraxia), and brain correlates of learning and memory (including amnesia, verbal and nonverbal memory). It also discusses cross-cultural differences in aphasia presentation and the use of neuropsychological tools for assessment.

📝 Lecture Summary

Higher Order Brain Functions: Objectives

The objective of this lecture is to familiarize students with the role of higher order brain function in disorders of speech, motor and sensory apraxias, memory, and amnesias.

Brain Correlates

The lecture covers the following brain correlates:

• Language: Speech production, comprehension, and aphasias
• Visuospatial: Illustrated by the case of "The man who mistook his wife for a hat"
• Apraxias: Assessed using neuropsychological tools
• Brain correlates of Learning and Memory: Amnesia, verbal and non-verbal memory, also assessed with neuropsychological tools

Aphasia and Dyslexia

Aphasias and Dyslexia are related because spoken words are transferred to written language; reading and writing are closely tied to listening and speaking (auditory modality). Wernicke’s aphasia is often accompanied by dyslexia.

🔑 Definition — Aphasia: A language disorder resulting from damage to brain areas involved in language production or comprehension.

Cross-cultural differences in aphasia are notable. There are more dyslexics with Wernicke’s aphasia in English and other Western languages, but not so in Chinese, where each word is represented individually (pictographically) or when sign language (spatial, not auditory modality) is used. Chinese aphasics retain the ability to write accurately.

The Japanese language has two forms: Kanji and Kana. Kanji symbols are pictographs (visual representation of concepts). Kana symbols are acoustic or phonetic representations. Sasanuma (1975) reported that left temporal lobe lesions affected the writing of Kana symbols but not Kanji (where the visual cortex is involved).

📐 Mode Representation:

Generally, most languages use sound and acoustic signals to write. Interestingly, the deaf are not dyslexics with receptive aphasia because they read without phonetics (Braille, the language script of the blind, is a touch language).

Aphasias Related to Speech

A wide range of disorders exist within the major aphasias. Two examples are:

a) Conduction Aphasia: Produced when damage to the inferior parietal zone disconnects the axonal fibres connecting Broca’s and Wernicke’s areas. Conduction aphasics have meaningful, paraphrasic speech, fair comprehension, but poor repetition. They can repeat single and meaningful words, but not non-meaningful words.

b) Anomic Aphasia: An aphasia specific to names. Patients have difficulty finding the right word, so they use circumlocution (going the roundabout way). A patient with anomia, when asked to identify a stapler, could describe its use and demonstrate how it works, but could not produce its name. This illustrates that the patient knew what the object was and what it was used for, but could not name it. 💡 Why this matters: Anomic aphasia demonstrates that different aspects of semantic knowledge (use, function) can be preserved while specific lexical retrieval (the word itself) is impaired.

Other types include cortical aphasias, transcortical aphasia, and subcortical aphasias.

Dyslexia (Reading, Writing, Mathematics)

Reading and writing disorders are related to the kind of aphasia a patient has. A patient with Wernicke’s aphasia would have difficulty reading and writing, just as they do comprehending speech. Broca’s aphasics have difficulty reading out aloud; their writing and speech are both agrammatical.

1. Alexia with Agraphia: A difficulty in which the person has trouble reading and writing. This is caused by damage to the left angular gyrus in the parietal lobe. The angular gyrus is at the borderline of visual, auditory, and somatosensory cortices, so it may affect skills involving all three modalities.

2. Pure Alexia: Also known as word blindness, where alexia occurs without agraphia. The patient can write but cannot read what they have written. They can recognize words if spelled out to them. Pure alexia is a perceptual disorder, similar to pure word deafness, but is visual, not auditory.

3. Agnosias: Disorders related to sensory modalities, either auditory or visual.

Disorders of Auditory Perception: Agnosias

An auditory agnosia is the impaired capacity to recognize auditory stimuli, due to a disturbance of perceptual processes more than sensation. There is no problem with the input of information, but with giving it meaning and recognizing it.

a) Amusia: Subdivisions include: * Tone Deafness: Inability to discriminate various tones of musical scales. * Music Deafness: Impaired recall or recognition of a melody, tune, rhythm, measure, or tempo (beat). * Receptive Amusia: Difficulty in discriminating basic notes of music or series of notes of pitch, rhythm, etc.

b) Agnosia for Sounds: The inability to identify what different nonverbal sounds mean (a classification difficulty). For example, different kinds of bells (church, school, telephone) may all sound alike, or the patient may confuse them. This is a discrimination and categorization deficit.

🔑 Definition — Agnosia: A failure of recognition that is not due to sensory or intellectual problems; the sensory input is intact, but the brain cannot give it meaning.

Visual Deficits

These are deficits related to the integration or processing of visual information. Agnosia is a failure of recognition, not due to sensory or intellectual problems.

Visual Agnosia: An agnosia for visual stimuli. The patient can see but cannot put the pieces of visual input together in a coherent form.

Prosopagnosia: A very interesting visual agnosia for faces. Faces are the primary key to other people, and there is a "dictionary of features" where every face is immediately matched. Prosopagnosics have difficulty recognizing a face; they know it's a face, but not who it is. Patients report seeing parts such as eyes, nose, and lips but cannot integrate them. To recognize a face, one must match and put together the entire feature in a coherent face. In extreme forms, patients cannot recognize themselves in the mirror.

🔑 Definition — Prosopagnosia: A visual agnosia specifically for recognizing faces, caused by damage to the inferotemporal region.

Some patients have difficulty recognizing only familiar faces, while others struggle with unfamiliar faces. They can sometimes use a cue such as a mole or a scar to recognize a face. It is a visual-limbic disconnection (especially for familiar faces) of the right hemisphere.

Apraxia

Apraxia is a movement or motor difficulty when required to perform an action on verbal command, even though the task can be performed spontaneously (or copied) without problems. Apraxias are bilateral but are usually produced by a left hemisphere lesion. This deficit was first described by Hughlings-Jackson.

🔑 Definition — Apraxia: (Greek: praxis = action) The missing or inappropriate action is not due to paralysis, motor difficulty, misunderstanding of instructions, or lack of motivation, but a difficulty in carrying out the required action.

Construction Apraxia: Tested by asking the patient to copy, draw, or build blocks in a given design. This involves both left and right hemisphere damage. Left hemisphere damage leads to oversimplification with very few details, whereas right hemisphere damage leads to a loss of the overall gestalt (the big picture).

Conclusion

The deficits discussed are caused by damage to cortical areas and require complex neuropsychological examination. Rehabilitation strategies can be developed keeping each patient's individual deficits in mind.

⭐ Key Takeaways

The lecture demonstrates that higher-order cognitive functions like language, perception, and motor planning are localized to specific brain regions. Damage to these areas produces distinct clinical syndromes, such as aphasias, alexias, agnosias, and apraxias. Notably, a patient can understand an object's function without being able to name it (anomia), or can write without being able to read what they wrote (pure alexia). These dissociations prove that different cognitive processes are supported by separate neural systems. Understanding these syndromes is critical for neuropsychological assessment, allowing for the accurate diagnosis of brain damage and the creation of targeted rehabilitation strategies.

🧠 Quick Revision Questions

1. What is the difference between alexia with agraphia and pure alexia?
2. A patient can describe how to use a stapler but cannot say the word "stapler." Which type of aphasia is this, and what does it reveal about the organization of semantic knowledge?
3. Explain why Chinese aphasics may retain writing abilities, while English-speaking aphasics do not.
4. What is the key distinction between an apraxia and a motor paralysis?
5. What is prosopagnosia, and what brain area is typically damaged in this condition?

📘 Lecture 44 — Higher Order Brain Functions

📖 Overview: This lecture examines the neurological bases of learning and memory, exploring how the brain stores and retrieves information. It covers classic theories from Lashley's principles of equipotentiality and mass action, to Hebb's consolidation theory, and examines the biochemical and structural changes underlying memory formation, including the role of RNA and protein synthesis. The lecture also introduces amnesia types and the famous case of H.M., which provided critical insights into the role of the hippocampus and temporal lobes in memory.

🗂️ Topics Covered

This lecture covers Lashley's principles of equipotentiality and mass action, the distinction between short-term and long-term memory, Hebb's two-stage memory theory and consolidation, cross-modal transfer, problems in testing memory, biological systems including RNA and protein synthesis, plasticity and experience-dependent changes in the nervous system, and brain correlates of amnesia including the famous case of H.M., anterograde and retrograde amnesia, and Alzheimer's disease.

📝 Lecture Summary

Brain Correlates of Learning and Memory, Amnesia, Verbal, Nonverbal Memory

Memory is defined as information stored in the brain because of sensory and other experience (Bridgeman 1992, p324), and learning is the acquisition of new memories. Lashley was a pioneer in locating engrams — the physical trace of a memory. He formulated two principles:

🔑 Definition — Principle of Equipotentiality: Various parts of the cortex contribute to memory for complex behaviors; no one part is more or less specialized than another. Neurons within a given sensory area are all capable of participating in memory formation.

🔑 Definition — Principle of Mass Action: The greater the extent of a cortical lesion, the greater the deficit in memory. Retention is related to the size of the cortical area removed rather than which specific region is damaged. The cortex works as a whole, and the amount of remaining cortex is more important than the region.

📌 Example: Soldiers with head bullet wounds exhibited lower IQ test performance, and the lowering of IQ depended upon the overall amount of brain damage.

💡 Why this matters: These principles shifted thinking from memory being localized in one spot to being distributed across the cortex, laying the foundation for modern network theories of memory.

Short-term and Long-term Memory

In the 1950s, two different memory storage systems were hypothesized: Short Term Memory (STM), where memories are stored temporarily, and Long Term Memory (LTM), where memories are consolidated. Memories in STM are transferred to LTM through repeated thinking and reviewing.

Hebb's Two-Stage Memory Theory

Hebb proposed that memories remain in STM temporarily via reverberating neural activity (neural activity that goes round and produces structural changes in synapses), which leads to LTM storage. Changes in neuronal biochemical structure are the basis of LTM storage.

📌 Example: Unless you keep repeating a telephone number, it becomes difficult to recall it, supporting the two-stage theory.

Cross Modal Transfer

Cross modal transfer is the ability to learn with one sensory mode and use what is learned and retained in another mode. Humans and higher primates can easily perform cross-modal transfer, but lower animals cannot transfer information from one modality to another.

📌 Example: Visual scanning of mazes allows one to then go through it using the kinesthetic (touch/movement) mode.

Problems and Issues in Testing Memory

Four key problems are identified:

1. There is no adequate method to identify where memories are stored
2. Performance, not memory, may be affected
3. Lesions in one area may alter connections in other areas
4. It is difficult to assess whether the loss is of memory itself or of retrieval of memory

📌 Example: The joke about cutting frog legs causing frogs to forget to hop across lines illustrates that performance, not memory, was affected.

Biological Systems and Memory

Single cell recordings show that learning changes single cells, including increases in calcium in neurons, decreases in potassium flow, increases in number of certain synaptic receptors, and changes in RNA and proteins.

RNA

RNA molecules are considered the memory code molecules. Qualitative and quantitative changes in RNA and protein synthesis occur in animals that have learned a task. DNA is the template for RNA, which determines the structure of proteins.

📌 Example: Hyden and Colleagues (1962) trained rats to walk on a tight rope and found increases in RNA in brain cell nuclei compared to normal rats.

📌 Example: Glassman and colleagues (1974) trained rats on a shock avoidance task (jumping onto a platform at the sound of a buzzer). Rats injected with labeled Uridine (precursor for RNA) showed decreased RNA synthesis after training, while those injected with labeled Lysine (precursor for protein) showed increased incorporation into the cortex and hippocampus after training.

📌 Example: In some experiments, trained animals were decapitated, their brains homogenized, and injected into normal rats. The injected animals learned faster than untrained or uninjected rats.

Protein Synthesis

Protein synthesis is a necessary step in long-term memory, modifying the characteristics and properties of neurons. Drugs that inhibit protein synthesis impair LTM storage but not STM. The increased inhibition leads to increased deficits in learning (Bennet et al, 1977).

📌 Example: Anisomycin (a protein synthesis inhibitor) blocked rats' memory of the location of shock but not the memory of the location of food.

🔑 Other important biochemicals include Cyclic AMP, ACTH, Vasopressin, Acetylcholine, and NE (Norepinephrine).

Other Influences on Learning and Memory

Stress interferes with learning and retrieval of information. Electroconvulsive therapy (ECT) blocks protein synthesis. Hebb's consolidation theory states that time is required for STM to LTM transfer; any interference with consolidation results in disruption of long-term recall.

📌 Example: After head injury, memory of events prior to injury is lost (retrograde amnesia), but a small reminder can bring back memories. In head trauma, memory returns after delay or under tranquilizers.

📌 Example: Kalat (1980) stated that "ECT interferes with memories that are active at the time of ECS regardless of whether formed recently or long ago."

Plasticity and the Nervous System

Experiments by Hubel and Wiesel showed that anatomical changes take place in the visual cortex with experience.

📌 Example: Kittens wearing horizontal goggles during early development lead to neurons firing when horizontal stripes are seen as adults.

📌 Example: If one eye receives more stimulation, the brain area for that eye is enlarged (more neurons respond).

📌 Example: Shock to the foreleg of young kittens led to a greatly enlarged somatosensory cortical area.

📌 Example: Merzenich sewed the third and index fingers of monkeys together, and the cortical area for this "one" finger became larger. If the thumb was removed, the cortical areas for the thumb became smaller.

📌 Example: MRI studies of violinists' brains showed that their cortical auditory areas were enlarged compared to normals.

Super Plasticity in Growing Brain

Early start is important for learning — in language learning, the left hemisphere growth spurt is recorded on EEG between 2-4 years of age, and another at 12-15 years, only in the left hemisphere.

The Famous Case of H.M.

H.M. was a pure amnesic who had severe epileptic seizures and underwent surgery at age 27 to treat epilepsy. After surgery, he has been in a "time freeze," stuck at age 27 even 40 years later. H.M. has amnesia for events prior to surgery and has no LTM. He lives in the present, in STM, with no IQ loss.

🔑 Tests used with H.M.: mirror drawing task, digit span test, block tapping memory span test, incomplete pictures test, and eye blink Pavlovian conditioning response.

H.M. has damage in the temporal region, providing evidence of the importance of the temporal lobe and hippocampus in memory.

Amnesia

• Anterograde Amnesia: Loss of ability to learn new information. The amnesic can remember events before surgery or injury. Complex perceptual-motor learning abilities remain intact.

  • Korsakoff's syndrome is the severest form of Anterograde Amnesia, with damage to the mammillary bodies and temporal lobe.

• Retrograde Amnesia: Inability to remember events that occurred before brain damage. Confabulation is the creation of pseudo-memories to fill gaps.

• Alzheimer's disease: A major disease leading to severe memory loss and the most common cause of dementia (memory and intellectual impairment). Pathology includes neurofibrils, amyloid plaques, neural degeneration, and reduction in ACH (Acetylcholine).

🔑 Studies on amnesiacs have shown three key findings about the hippocampus:

1. It is not the location of LTM nor important for retrieval of LTM
2. It is not the location for immediate memories
3. It is involved in transforming STM to LTM

Studies also show the importance of mammillary bodies and the dorsomedial thalamus in memory.

⭐ Key Takeaways

Memory is not localized in a single brain region but involves distributed networks across the cortex, as shown by Lashley's principles of equipotentiality and mass action. The hippocampus plays a critical role in converting short-term memories into long-term memories, but is not the storage site itself. Biochemical changes, including RNA and protein synthesis, are essential for long-term memory formation, and drugs blocking protein synthesis impair LTM. The case of H.M. provided landmark evidence that the temporal lobes and hippocampus are crucial for new memory formation, while IQ and perceptual-motor skills can remain intact. Experience-dependent plasticity means the brain physically changes with learning, and early stimulation can enlarge corresponding cortical areas.

🧠 Quick Revision Questions

1. What are Lashley's two principles of memory localization, and what did his rat maze experiments demonstrate?
2. How does Hebb's two-stage memory theory explain the transition from short-term to long-term memory?
3. What biochemical changes occur in neurons during learning, and what role does protein synthesis play in LTM?
4. What type of amnesia did H.M. suffer from, and what specific brain structures were damaged?
5. What are the differences between anterograde and retrograde amnesia, and how does Korsakoff's syndrome relate to them?

📘 Lecture 45 — Higher Order Brain Functions

📖 Overview: This lecture explores brain hemispheric differences, laterality, and specialized roles in higher-order brain functioning. It examines how brain damage affects behavior, the fascinating findings from split-brain studies, and the tools used for neuropsychological assessment. Understanding these concepts reveals how our two cerebral hemispheres collaborate and compete to create unified conscious experience.

🗂️ Topics Covered

The lecture covers brain correlates of learning and memory including amnesia, split-brain studies revealing hemispheric specialization, the question of whether we have one brain or two, brain damage and plasticity, neuropsychological tests including the Luria-Nebraska and Halstead-Reitan batteries, and cerebral hemispheric specialization with its implications for language, handedness, and emotional expression.

📝 Lecture Summary

Brain correlates:

The lecture examines brain correlates of learning and memory, amnesia, verbal and non-verbal memory as assessed by neuropsychological tools. Split brain studies investigate brain hemispheric differences and laterality, asking whether we have one brain or two brains. The discussion includes brain damage and plasticity, along with neuropsychological tests and cerebral hemispheric specialization.

Two fundamental facts are established: the two lobes are connected by commissures, and there are specializations of functions with cooperation as well as competition between the two hemispheres.

The earliest study on specialization was reported by French neurologist Marc Dax in 1836, who found that stroke patients with speech problems all had damage to the left hemisphere. In the mid-1800s, Paul Broca reported cases of aphasia where left hemisphere damage affected speech production (now known as Broca's area). Shortly after, Carl Wernicke identified a left hemisphere area concerned with language comprehension (Wernicke's area).

🔑 Definition — Commissures: Fiber bundles that connect the two cerebral hemispheres. 🔑 Definition — Aphasia: Language disorder caused by damage to brain areas involved in language production or comprehension.

Two key studies in 1959 and 1961 by Roger Penfield and Ebert (1959) and Russel and Sapir (1961) produced evidence that unilateral lesions produced deficits demonstrating brain hemispheric specialization. Their results indicated language was dominant in the left hemisphere for both left and right hemispheric dominant persons.

💡 Why this matters: If you are right hemisphere dominant, you are left handed; if you are left hemisphere dominant, you are right handed. This relationship between handedness and language dominance was a critical discovery.

Brain Hemispheres: Two Brains or One?

Research was stimulated by commissurotomy or the split brain procedure, which uses a knife cut to sever the commissures (including the corpus callosum) so the two hemispheres cannot communicate. Outwardly, these individuals seem normal, but sensitive neuropsychological tests revealed deficits.

🔑 Definition — Split Brain Procedure (Commissurotomy): Surgical severing of the corpus callosum to separate the two hemispheres, used to study hemispheric specialization.

Special tests were devised so information could go to only one hemisphere. When words were presented to the right visual field (reaching the left hemisphere), the person could read aloud and write. But when shown to the right hemisphere, the person reported seeing nothing. However, when methodology changed and the person was asked to pick out words or objects from a group, he picked the right ones!

When the word HEART was flashed so "HE" went to the right visual field (left hemisphere) and "ART" to the right hemisphere, the person said "HE" but picked "ART" from a word block.

Thus, brain lateralization exists - the two halves are not exactly alike, and each hemisphere has functional specializations: some functions whose neural mechanisms are localized primarily in one half of the brain.

Handedness:

🔑 Definition — Handedness: Either (a) the hand that performs faster or more precisely on manual tests, or (b) the hand one prefers to use, regardless of performance.

Most people are right handers (left hemisphere dominant), with a reasonable number of left handers and a small number of ambidextrous individuals. There are also dominance patterns for foot, eye, and ear, which can be assessed by tests such as the Harris Tests of Lateral Dominance.

Asymmetry in faces was reported by Sackheim, Gur and Saucy (1978). They took photographs of expressed emotions, created left-left and right-right composites, and found subjects reported left-left faces more intense. This is because the right hemisphere cannot speak, so images must be more intense for visual input, while the left hemisphere expresses itself through words.

How do we explain asymmetry?

Two schools of thought exist:

1. The brain is equipotential for specialization, and around 2 years of age the division of labor is completed. The two hemispheres compete for control - when both try to speak at once, stuttering occurs (Orton, 1939).
2. Specialization is inborn and innate, present even before cultural or learning influences. For example, the planum temporale in the left hemisphere is larger in the fetus, so language is programmed for the left hemisphere.

Tests for Language and Other Functions:

1. The WADA test: Sodium Amytal (a barbiturate) is injected unilaterally through the carotid arteries. When the language hemisphere is anesthetized, speech becomes slurred until blocked completely. Milner, Branch and Rasmussen (1966) studied 212 patients to identify hemispheric dominance for speech.
2. Zeidel lens (specialized tachistoscope): Projects images to only one hemisphere to test verbal, visual, language and other asymmetries.
3. Dichotic listening tests: Sends two different auditory signals to left and right ears simultaneously (e.g., alphabets to left ear, numbers to right ear). The subject repeats what the dominant ear heard.

Unilateral neglect, unilateral sensory neglect

🔑 Definition — Unilateral Sensory Neglect: A disorder affecting response to one side of the body, somato-sensory, or visual field, characterized by the patient not attending to one side only. Occurs from damage to either hemisphere in the parieto-occipital area (spatial recognition).

This is a lateralized deficit - patients don't respond to the side opposite the damaged hemisphere. Assessment: ask patient to draw a clock face showing a specific time (e.g., 10 to 11 o'clock). Patients may draw only one half. In extreme cases, patients eat from one side of plate, shave one side of face, or put lipstick on only half the face. Interestingly, moving them around enables describing the whole.

💡 Why this matters: The frontal cortex may control the rest of the body and brain as the Chief executive.

Frontal lobe

Orbitofrontal area: The paper "No Longer Gage" describes Phineas Gage, a railway laborer whose personality changed completely after a rod went through his head. Injury to orbitofrontal areas changed him. Research indicates judgment, personality, foresight, "conscience," reduced impulsivity are located here. As a child grows, inhibitions from society and culture are programmed here, along with control of all emotions.

Neuropsychological tests:

a) Luria (father of Neuropsychology) developed tests assessing all abilities holistically by varying tasks. For handedness, he gave the same task using different modalities (visual, somato-sensory, language command). These are incorporated in the Luria Nebraska Neuropsychological Test Battery. b) Halstead Reitan Battery: Tests such as the grooved pegboard and tapping tests. c) Harris tests of laterality: Assesses dominance for hand, foot, eye, and ear.

Both hemispheres work and compete, sharing information through the corpus callosum, giving behavior a holistic, gestalt quality. Each hemisphere needs the other for backup.

If only one hemisphere remains through surgery, injury, or developmental trauma, the remaining hemisphere can take over functions without visible deficits. The earlier the trauma, the more easily functioning can take place.

Neuropsychological Tests

Neuropsychological assessment is carried out by trained neuropsychologists (brain-behavior relationship specialists). A formal interview is followed by review of medical records, school records, interviews with relatives, and formal neuropsychological testing.

🔑 Definition — Neuropsychological Testing: Formal assessment of higher-order functioning including attention, memory, speed of information processing, language, visual-spatial ability, sensory processing, motor ability, executive and intellectual functioning.

Referrals for neuropsychological assessments include: a) Stroke patients b) Head injury patients c) Children with slow development or difficulties in speech, attention or learning d) Chronic alcohol or substance abusers

Some neuropsychological tests

Two well-known batteries:

1. Halstead Reitan Neuropsychological Battery: Older, takes about 8 hours to complete.
2. Luria-Nebraska Neuropsychological Test Battery: Based on Luria's techniques, with subtests assessing motor, sensory, visual, language, kinesthetic, attention, memory, receptive and expressive speech (speech sounds, rhythm). Takes less time with more flexibility (qualitative information).

Trails Making A and B: Part of Halstead Reitan Battery. Part A requires joining lines of numbers - assessing visual motor coordination, visual scanning, short term memory. Part B requires alternating between numbers and letters - measuring higher order functioning, ability to learn and apply an organizing principle, verbal problem solving, and planning action beforehand.

Neuropsychological tests are effective tools for diagnosis, identifying deficits due to illness or injury, assessing learning problems, reasoning and problem-solving, language abilities, memory and attention post-trauma, visual-spatial memory, visual-motor coordination, and higher-order planning.

Course Recap

The course covered: development of behavioral neurosciences as a discipline with major contributors; evolutionary development stages and brain development from single cell layer to complex form; neuroanatomical sites and their contribution to behavior; neurochemicals and their effects (including psychopathologies); motivational states (hunger, thirst, sleep); higher order functioning, language deficits, learning and memory (amnesias), disorders such as apraxias, agnosias, aphasias.

⭐ Key Takeaways

The two cerebral hemispheres are connected by commissures and demonstrate functional specialization - the left hemisphere is dominant for language (Broca's and Wernicke's areas) while the right hemisphere is specialized for spatial and emotional processing. Split-brain studies reveal that each hemisphere can function independently, yet they normally cooperate through the corpus callosum to produce unified behavior. Lateralization appears to have both innate components (planum temporale is larger in the left hemisphere in fetuses) and developmental components (equipotential theory). Unilateral neglect demonstrates how damage to one hemisphere can cause profound unawareness of the contralateral side. Neuropsychological test batteries like the Halstead-Reitan and Luria-Nebraska provide systematic assessment of higher-order cognitive functions essential for diagnosis and rehabilitation planning.

🧠 Quick Revision Questions

1. What were the key findings from split-brain studies regarding hemispheric specialization for language?
2. How does the WADA test determine hemispheric dominance for speech?
3. What is unilateral neglect and which brain areas are typically damaged to produce this condition?
4. What does the Phineas Gage case reveal about the orbitofrontal cortex?
5. What is the difference between the Halstead Reitan and Luria-Nebraska neuropsychological test batteries?