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Foundations of the Brain (Part I)

By Michael Feldhake

Introduction

This is Part I of a two part series of articles that attempts to elaborate on the essential Physiological & Psychological aspects of the animal mind. If one were attempting to duplicate functionality and purpose, as in the case to reverse engineer it, it would mandate that the mind be dissected and analyzed. But since the brain is overly complicated and mysterious and without adequate analysis tools, it is difficult to ascertain functionality solely based on available empirical evidence. Therefore, in an attempt to overcome this problem, an examination of evidence of important parts shall be used to provide some insight into the “big picture” and help us understand what is going on. While Part II deals with the Psychological aspects of the brain, this part deals with the Physiological evidence. After review of the essential components, layout and infrastructure of the brain, a summary and conclusion is provided.

Neurons

Our brain is part of the central nervous system and is comprised of nerve cells, called neurons. Each neuron, protected by other cells, has a cell body, one or more dendrites which are like branches on a tree, and an axon stretching out from the cell body. This axon, the largest of the branches, is like a tree trunk ending in terminal nodes and connecting to other cells. Both dendrites, that can number into the thousands, and axons can reach short distances to adjacent cells or long distances spanning the entire brain.

There are two general categories of neurons. First, the myelinated neuron (white matter), has Schwann cells wrapped around the axon at regular intervals. Spaces between the myelin or Schwann cells are called Nodes of Ranvier. The myelin insulates the axon and the nerve impulse jumps from node to node down the axon. This greatly increases the speed that these cells transmit information. The second type of neuron is unmyelinated (grey matter), these neurons transmit the nerve impulses more slowly, but are able to branch and form far more interconnections for highly specialized controls and higher order thought. Both of these neuron types are critical for complex and efficient thought to occur.

The Synapse is the junction between each connection point between nerve cells. These small junctions provide important functions of signal relaying and inversion. Nerve impulses are generated by the cell body and reach the synaptic connections through the axon. These impulses are generated from terminal knobs, located at the end of the axon releasing chemical neural transmitters that excite or inhibit the connecting cell based on its interaction. Once this connecting cell reaches a stimulus threshold, it fires its own axon. Synaptic connections can also include connections between cell bodies, muscles or glands.

Many different neural transmitters are present in the body adding to its complexity and scale. These include; Monoamines Serotonin, located in the pons, medulla and midbrain areas, that regulate mood and pain; Dopamine, located in the midbrain & ventral tegmantal areas help manage movement, attention, learning and reinforcement; Norepinephrine, located in the pons, medulla and thalamus connect to a large number of areas including the hypothalamus, hippocampus and basal ganglia and controls the increase in vigilance or arousal; Gamma-aminobutyric acid or GABA, the most important inhibitory transmitter in the brain; Glycine, located in the spinal cord and lower portions of the brain, is also an inhibitory neurotransmitter; Peptides provide many different signals, including pain reduction, inhibition of fleeing & hiding responses and stimulation of reinforcement neurons, when these opiate receptors are stimulated.

The 3 Brain System

Papez-Maclean theory of brain evolution is comprised of three major parts commonly referred to as the 3-brain system. The reptilian brain, located at the top of the brain stem, acts to coordinate basic functions of behavior. The reptilian brain, wrapped with a paleomammalian brain, includes the limbic system. The limbic system controls the emotional and species-specific behavior characteristics (or hereditary traits) of the brain. Wrapped around this paleomammalian brain is the neocortex, responsible for complex thought and has been referred to as the “thinking cap.” All animal species on this earth possess one or all of these pieces. Birds have both the reptilian brain and the paleomammalian brain sections where as mammals such as dogs and humans possess all three.

Mammalian Brain & Cerebellum

A primitive form of the cerebellum is present in all reptilian brains. This area is responsible for the ability of an organism to make smooth, rapid and complex movements. For example, when we learn to walk, it takes constant concentration. Once we have practiced enough, the cerebellum takes over and walking becomes “automatic.” Also included is the brain stem consisting of the midbrain, pons and medulla and located deep in the posterior part of the brain. This section of the brain represents vital response systems tapping into the auditory & visual cortexes and controlling respiratory control & cardiac systems.

Limbic System (Medial Temporal Lobe)

Primate survival can be attributed to its Limbic regions. Many highly evolved brain regions make up this critical region. The limbic region is located between the cerebellum and the cerebrum. It includes many parts, among which are the amygdala, parahippocampal gyrus, basal ganglia, hippocampus, hypothalamus and more. The limbic system generally produces chemical reactions that act upon other biological systems, including cerebral development, emotional reactions and motivation issues of the organism. Hereditary behaviors, the natural or innate ability of any species, are centered in this system.

Adding to the pronounced complexity of the brain is the forebrain and all its parts. The basal forebrain in the limbic region contributes to emotions through its connections with other prefrontal cortex and limbic forebrain structures. The limbic forebrain itself is believed to be the “chief executive part” of the brain. It works to control behavior through activity planning and reaction selection. This limbic forebrain also includes the orbitofrontal cortex that specifically alters moods and mental states.

The basal forebrain comprises many groups of structures and is located near the bottom of the front of the brain. These structures are responsible for the production of acetylcholine. Acetylcholine, distributed throughout many parts of the brain, controls information access, information flow and learning.

Cerebral Cortex (a.k.a. neocortex)

The cerebrum makes up 85% of the brain’s mass. It is made up of both white matter and gray matter. The outer covering of the brain, the cerebral cortex, is made up entirely of gray matter, giving the brain it’s gray color. In humans, when this part is stretched out, the cerebral cortex covers one-quarter square meter and is 2-5 millimeters thick. At the top layer of cells, we see very structured pyramidal cells and are primarily the motor areas of the cerebral cortex. They have long axons to communicate with the basal ganglia, brain stem, cerebellum, and the spinal cord. The next layer has a mix of granular and pyramidal cells and this is an area of association between the motor area and the sensory area, the third layer. The third layer is comprised of granular cells and is the primary sensory area of the brain. These neurons have short axons and transmit multiple signals within the neural network of the cortex. There are also horizontal cells between the adjacent areas of the cerebral cortex that are used to communicate information between the different areas of the cortex. Communications between these different layers and regions of the cerebral cortex is critical for appropriate responses.

Prime Circuits

Primate & mammalian brains are comprised of even more specific components that help in the overall process; Hippocampus, our novelty and information center works to develop memories. It is part of the Limbic system and is connected to the temporal lobes and other limbic system components. This system is responsible for novelty detection, memory formation and storage based on the emotional context of the information; Hypothalamus, a complex system of many parts, is also part of the limbic family and regulates body functions. These innate functions include body pressure, temperature & weight, vomiting reflexes, heart rate and also help regulate eating and reproduction.

The Superior Colliculus, located in the thalamus, innately helps us coordinate the Multi-Sensory-Spatial map. This system is involved in spatial orientation of the host to sensory stimulus like auditory noise and visual objects. Evidence also suggests that this large region assists in visual stability by compensating for motion on the images of the retina. Also included in visual skills is the Occipital lobe. This lobe provides attention controls and recognition of information being sent by the over 1,000,000 retina nerves that make up the visual cortex of each eye. The Parietal lobe is responsible for somatosensation - the relaying of information about touch, temperature and limb position – and is also linguistically important.

A dual system of interconnection, extremely important to the survival of the species, exists in the brain. Joseph LeDoux, a Professor at the center of Neural Science at New York University, explained the “low road” and “high road” of neural pathways. The low road was the direct interconnection of raw stimulus that was required for emergency action from the brain’s response system. Whereas the high road was the interconnecting pathways where the cortex was involved in allowing more robust information to be obtained about the danger.

Thalamacortical System

Interconnected to every part of the brain’s neurology is the Reticular Activation Systems or RAS. The RAS, radiating from the thalamocortical system, is suspected of channeling attention, memory access and alertness. The brush like connections of the RAS provide a conduit for spatially & temporally oriented signals to digress into the cerebral cortex to control the body’s alertness level to stimulus and accessibility of memories. This network has been attributed to neurosis and social disorders because of its ability to control the information flow into the other regions of the brain. As in the case of psychopaths, they have a higher level of activation generating more information into the conscious parts of the brain making them overly extravert in nature.

Howard Hughes Medical Institute investigator Randy L. Buckner, Mark E. Wheeler and Steven E. Petersen at Washington University in St. Louis found that the upper regions of cerebral cortex were stimulated when people attempted to access memories. This confirms years of debate and propositions that the brain has the ability to direct attention towards specific memories. Because of the ability of the thalamacortical system to activate small portions of the cortex, as well as the hypothalamus, using chemo electric signals, the brain can reactivate neuron cells for memory recall.

Summary & Conclusions

Neurons, the infrastructure of the brain, operate more like logical components than analog ones and operate much differently than the computational version of the Neural Network. Since the synaptic configurations determine how the signals are interpreted, they provide logical functionality by stimulating or inhibiting the connected cell, muscle or gland. Also, once the neuron reaches a particular threshold, the cell fires pulses down its axon to connecting cells. Furthermore, the neural infrastructure is inherently asynchronous and temporal. Asynchronous neural networks provide a system where temporal signals can coincide adding to the complexity of the signal processing the brain can and must support.

Brain study and its impact to the understanding of its workings it is hampered by the physical nature of its existence. Since the brain must communicate over its vastness, the study & understanding of it is mired by the plethora of connections and cells that handle its management. Also, these structures provide more functionality due to their dual connection systems. These connections systems provide signal transmission as well as memory access operability that increase its purpose and effect.

Intelligence is not attributed to just one part of the brain. Whereas humans, monkeys and other primates have all components of the 3-brain system, birds and mice only have mammalian and paleomammalian brains. Further down in the animal kingdom, reptiles including lizards and fish have only the reptilian brain. Each part of the 3-brain system has adaptive qualities based on observable traits of each species, but it is clear that complex brain function is tied to the upper two parts of the brain. As brain size increases, there is an exponential rise in functionality due to signal processing capacity and heredity.

Heredity, the innate aspect of the brain, is mostly misunderstood and under-appreciated but turns out to be quite important. This quintessential part provides primates with survival skills, social skills, attention skills and learning skills. Learning, through emotional stimulus, becomes the basis of all learning developed and provides the supervisory response mechanism that is relied upon during life. All learning has a foundation upon our hereditary innate responses causing us to change the nature vs. nurture debate over behavior to a nature AND nurture derivation of behavior.

Similar to a distributive control system, the brain is designed with many specialized parts that are involved in the control and behavior of the host. These distributive circuits combine to provide the system with important & relative information pertaining to the circumstance at hand so a clear decision can be decided upon or the proper item learned. With one “executive level” component that is most likely fed with information that has already been preprocessed, tagged and weighted for an efficient but effective analysis.

Resources & Links

1up Info™ Online Encyclopedia

Guyton, Arthur. (1986). Textbook of Medical Physiology. W.B. Saunders Co., Philadelphia.

Hampden-Turner, Charles. (1981). Maps of the Mind. Mitchell Beazley Publishers, Ltd., London; Macmillan Publishing Co., New York.

HHMI News “Researchers Trace Roots of Vivid Memories”, September 26, 2000

James Madison University, Department of Integrated Science and Technology, Brain Knowledge Base

LeDoux, Joseph. (1996). The Emotional Brain: the Mysterious Underpinnings of Emotional Life. Simon & Schuster, New York.

PsychEducation.org Online Mental Health Information

Submitted: 02/11/2003

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