The brain is an organ meant to help genes survive, and in this respect it is no different from the heart, liver, and reproductive organs. A thinking brain may not like this assessment, and it may prefer to view the body and its organs, as well as the genes, as existing to serve the brain. But modern science, spearheaded by sociobiological insights, is once again forcing Mankind to move further down from his pedestal by discrediting another cherished belief. This chapter will describe brain anatomy and function. The next chapter will address their evolution.Return to Table of Contents
Part of my intent for this chapter is to remove some of the "mystery" from how the brain works. I want to convey a sense that the brain functions like a "machine," and that living things are automatons, consistent with this book's reductionist approach.Brain Anatomy
The human brain consists of a primitive hindbrain, a small mid‑brain section, and a large and complicated forebrain.The hindbrain, which began its evolutionary existence ½ billion years ago, resembles the entirety of a reptile brain, and has been referred to as our "reptilian brain." The hindbrain's "stem" connects to the body; it receives information from sense receptors and issues commands to muscles and body glands via the spinal cord. The hindbrain's cerebellum stores motor commands and produces smooth movements.
The mid‑brain has a minuscule function, and won’t be described here.The forebrain, on the other hand, is where uniquely human attributes are generated. It includes a limbic system, thalamus, basal ganglia, and two large cerebral hemispheres. The limbic system has many components; it maintains homeostasis (body temperature, heart rate, blood sugar, etc), and controls emotional state (things like hunger, anger, fear and sexual arousal). The limbic system's pea‑sized hypothalamus performs many of these functions using electrical commands, some of which activate hormone producing glands in the brain. The thalamus and basal ganglia control conscious state and initiate movement, respectively.
The cerebral cortex, comprising 70% of human brain volume, consists of a left and right cerebral hemisphere, with an interconnecting corpus callosum. Although the cerebral cortex is only 1/8‑inch thick, its surface area is about 1 ½ square feet, and it has evolved a folded configuration to allow the surface to fit within the human skull. The inside surface of the cortex (gray matter) has an immense number of nerve fibers (white matter) providing connections to other parts of the cortex, the limbic system and other brain components.The cortex is the most recently evolved part of the brain, and fortunately it is also the most accessible to study. The left cortex and the right cortex each consist of 4 lobes: occipital, parietal, temporal and frontal. The occipital "sees," the parietal "feels," the temporal "hears," and the "frontal" thinks and commands! The "see/hear/feel" lobes are referred to as "posterior lobes" (since they comprise the rear half). They can be thought of as "receptive lobes" since they receive input from the body and environment. The "see/hear" lobes receive "remote sensing" information (visual and auditory input), while the "feel" lobe receives in situ information (touch, temperature, pain and body part position). The frontal lobes, the front half of the brain, receives input from the posterior lobes, and they “think” about the situation, formulate action plans and issue commands to muscles.
Figure 7.01. Brain lobes: Frontal, Parietal, Temporal, Occipital. View is of the left side, front is toward the left.
The corpus callosum (not shown) connects all four lobes of one side to the corresponding lobes on the other side. This nerve bundle is located underneath the frontal and parietal lobes, at about the same level as the temporal lobe.Each of the 4 lobes, the frontal, parietal, temporal and occipital, consists of 3 cortical areas: primary, secondary and tertiary. These are shown in Fig. 7.02 using the numbers 1, 2 and 3.
The part of the parietal lobe bordering the frontal lobe, area P1 in Fig. 7.02, is the "sensory cortex" (or "somatic cortex"). This strip of cortex is where in situ sensory signals from the body arrive. Next to the somatic cortex P1 is an area, F1, located in the frontal lobe and called the "motor cortex" or "motor strip." The motor cortex issues commands for movement (requests, actually, since sub‑cortical regions may "veto" the requests).
Figure 7.02. Approximate boundaries for cortical primary (1), secondary (2) and tertiary (3) areas in each lobe.
There's a one‑to‑one mapping of body location to position along the sensory cortex strip, P1, and motor cortex strip, F1. Starting from the part of the strips closest to the center‑line (top of brain) and going outward, body positions are allocated in the following sequence: leg, neck, head, arm, elbow, etc, to face, lips, teeth and tongue.For the posterior lobes raw sensory information arrives at the primary cortical areas, which deliver processed versions to the secondary areas, which in turn deliver even further processed versions to the tertiary areas. The 3 posterior lobe tertiary areas border each other, and this is where the most "conceptualized" versions of perceptions are inter-compared and elaborated.
Figure 7.03. Flow of nerve activity when something is "felt."
For example, when something is "felt" the flow of nerve activity "flows" according to the depiction of the figure above. When something is "heard" the flow of nerve activity "flows" according to the depiction of the following figure.
Figure 7.04. Flow of nerve activity when something is "heard."When something is "seen" the flow of nerve activity "flows" according to the depiction of the following figure.
Figure 7.05. Flow of nerve activity when something is "seen."
For each posterior lobe the pattern of nerve activity is the same: primary activity leads to secondary activity, which then leads to tertiary activity. The next step is for tertiary activity in adjoining areas to “compare notes,” or interact with each other.
<>When a familiar object is recognized a small set of tiny nerve circuits are set into "resonance." For example, when a coffee cup is seen, there's a flow of activity in the occipital lobe from primary to secondary to tertiary. When it reaches secondary cortex, i.e., O2, there will be sub‑features such as handle, rim, steam, etc "active" at their respective locations in O2 (created from interaction with the environment in childhood). These interact in O3 (occipital tertiary), setting into resonance a tiny circuit corresponding to "coffee cup seen."
Figure 7.06. Nerve activity when a "coffee cup" is seen.The same coffee cup can be felt. In this case the nerve activity will be as shown in the next figure.
Figure 7.07. Nerve activity when a "coffee cup" is felt.
The coffee cup may be heard, as it is set down on a table. In this case activity will occur in the temporal lobe, such shown in the next figure.
Figure 7.08. Nerve activity when a "coffee cup" is heard, as for example being set down upon a table.The concept "coffee cup" consists of the simultaneous activation of any, or all, of the three tiny regions in the three tertiary cortices of the posterior lobes. This is shown in the next figure.
Figure 7.09. Nerve activity corresponding to "coffee cup."The activity pattern corresponding to "coffee cup" depicted in Fig. 7.09 is said to be "generalized." That is, there are many specific ways a coffee cup can be perceived, and indeed there are many variations of coffee cup shape, appearance and sound, yet they all end up creating the one, generalized pattern "coffee cup."
<>The brain not only perceives, it also generates movement. A movement that is thought about and later commanded is the result of nervous activity in the frontal lobes. There's a "reverse" pattern for this activity; the process starts in tertiary cortex, and proceeds in the direction of primary cortex. This is depicted in the next figure.
Figure 7.10. Flow of nerve activity when some activity is planned and performed. The flow in this case is from tertiary to primary.
The frontal lobe architecture is analogous to that of the posterior lobes, in that the most conceptualized of ideas and plans are created in the frontal tertiary cortex, which delivers vague "executive" directives to the frontal lobe's secondary cortex, which formulates more specific action commands and delivers them (as necessary) to the motor strip. The motor strip requests permission from the sub‑cortical "reticular activating system" (RAS), and if the RAS approves the request it is acted upon by sub‑cortical brain areas (Luria, 1973), which carry out specific actions (orchestrated in detail by the cerebellum).The frontal lobe's secondary and tertiary cortices are also referred to by the two terms "prefrontal" cortex and "pre‑motor" cortex. The prefrontal cortex has undergone the greatest amount of recent evolution, according to arguments based on the increase in frontal lobe size versus phylogenetic location (i.e., ratio of frontal lobe size to total cortex is greatest for humans, next greatest for chimpanzees, etc). Functions performed by the frontal lobes in humans are often unique, or most advanced, in humans, whereas most areas in the posterior lobes have pre‑human analogues. The prefrontal lobes also reveal their evolutionary recentness by continuing to undergo rewiring until the age of (Thatcher, 1997), and even the "late teens." Giedd and Thompson (2001) write "In late teens, the prefrontal cortex is the area that's changing the fastest..." (according to neuro-imaging studies). This is consistent with the general principal that "ontogeny recapitulates phylogeny."
LateralityThe right side of the body is commanded to move by the left cerebral hemisphere's (frontal lobe) motor strip. Likewise, the left side of the body is commanded to move by the right cerebral hemisphere. This left/right crossing‑over architecture is also adopted by sensory input; sensory information from the right side maps to the left brain, and visa versa. The reason for this is still a subject for speculation. The corpus callosum, which interconnects the left and right cerebral hemispheres, allows for the coordinated movement of both sides of the body, and also allows for some of the computational results of specialized areas on one side to be exchanged with related areas on the other side.
Proto‑humans probably had left/right symmetry, in the sense that the right and left cerebral hemispheres had identical capabilities, being mirror images of each other in layout. This would have provided redundancy in case one side was injured (by a fall or blow to the head). Modern humans have asymmetric brains: the left and right cerebral hemispheres, LB and RB, are somewhat different, and are "specialized" for certain types of tasks. RB has more long‑distance inter‑connections than LB, whereas LB has many areas that are highly intra‑connected, which in turn are connected to other highly intra‑connected regions within LB.
The best known of LB's highly intra‑connected areas are Wernicke's Area (language comprehension) and Broca's Area (language production). Wernicke's Area is located near the interface of the three posterior lobes, in LB only (right-most pattern of dots in Fig. 7.11, upper). Broca's Area is located in the frontal lobe's secondary cortex, in LB only (left-most pattern of dots in Fig. 7.11, upper). There's a discernible pattern for the tasks performed in these specialized, highly intra‑connected LB areas: namely, these tasks are inherently sequential, which means that the temporal order of events is crucial! For example, both receptive and productive language involves the processing of sequential events (sound perception and production). Changing word order can profoundly change meaning ("Ed ate the bear" versus "The bear ate Ed."). In contrast, RB tasks are holistic; they resemble those that a parallel computer processor (neural network) performs, such as instantaneous image recognition.
Figure 7.11 Upper panel shows location of language comprehension area, Wernicke's Area (right-most pattern of dots), and speech production area, Broca's Area (left-most pattern of dots). The lower panel shows the location of the inferior parietal lobule, IPL, which monitors the spatial relationship of body parts in relation to the immediate environment.
It is interesting that RB's counterpart to Wernicke's Area, shown in Fig. 7.11 (lower panel) is devoted to the task of monitoring the location of body parts in relation to each other and the immediate physical environment. This area, called the "inferior parietal lobule," or IPL, plays a critical role during manual interactions with the environment, such as reaching out to pick fruit from a nearby branch.
It is tempting to conjecture that before humans were capable of speech the left hemisphere's IPL counterpart region also functioned like the present‑day IPL in RB. Because reaching out to pick fruit had sequential components, it would have been natural for mutations to modify what once was an LB IPL in a way that later presented an opportunity for further modification that led to a simple form of language capability. This region must have been built-upon to produce our present‑day Wernicke's Area, which plays a critical role in language comprehension. This task consists of monitoring the relationship of sound percepts to each other over time, somewhat similar to the way the RB's IPL monitors body part relationships over time. As Wernicke's Area evolved in LB, it must have gradually displaced the former IPL function.A great deal of public interest was generated during the 1970s and 1980s by reports of LB and RB differences, or lateralization. For example, RB is described as being intuitive, holistic, inductive, timeless, visuo‑spatial, non‑verbal and pessimistic, whereas LB is described as being verbal, analytic, logical, rational, time‑oriented, deductive and optimistic.
Traditional psychologists must have resented the newcomers to their field who used instruments to measure things, and who used rigorous techniques to study long-standing matters that had been the subject of arm chair speculation. The old-fashioned psychologists accused those who studied split brain patients, and found LB and RB differences, as suffering from “dichotomania” – as if the new investigators were over-interpreting their data due to an excess of enthusiasm. But the data is convincing, and often dramatic.When LB is damaged (or when it is temporarily disabled by sodium pentathol injected into the left carotid artery) the patient's speech capability is almost non‑existent. Curiously, though, the still‑functioning RB does what it's able to do speechwise: the patient can swear, utter emotion‑laden pat phrases, sing songs with the right words, and recite the alphabet. RB cannot (usually) put together a sentence, since grammar capability resides in LB.
Occasionally, a patient whose corpus callosum has been cut can still manage to communicate in a simple way using the rudiments of grammar. These cases offer very interesting insights into the differing "personalities" of LB and RB. One famous example was reported by Gazziniga (1978) which suggests that LB and RB can have different goals in life. Their oft‑used subject P.S. was questioned about his job choice in an experiment that allowed only RB to answer, and "automobile race" was spelled out. As Gazziniga writes "This is most interesting, because the left hemisphere frequently asserts that he wants to be a draftsman" (p. 143). How poignant!Chicken Claw Experiment
My favorite illustration of the independent operations of LB and RB has been referred to as “the chicken claw experiment.” This experiment was conducted by Michael S. Gazzaniga and Joseph E. LeDoux using patient P. S., who had undergone a full callosal surgery (cutting of the corpus callosum, interconnecting LB and RB) to control seizures. I shall quote from descriptions appearing in two books: Gazzaniga and LeDoux (1978) and Gazzaniga (1985).
Two problems are presented simultaneously, one to the talking left brain and one to the non-talking right brain. The answers for each problem are available in full view in front of the patient. Gazzaniga and LeDoux (1978).
Figure 7.12. “Chicken claw experiment.” The “task” (top) has two parts, presented to a brain half. The answer choices, below, are in full view to both brain halves.
...the experiment requires each hemisphere to solve a simple conceptual problem. A distinct picture is lateralized to one hemisphere: in this case, the left sees a picture of a claw. At the same time the right hemisphere sees a picture of a snow scene. Placed in front of the patient are a series of cards that serve as possible answers to the implicit questions of what goes with what. The correct answer for the left hemisphere is a chicken. The answer for the right hemisphere is a shovel.
After the two pictures are flashed to each half-brain, the subjects are required to point to the answers. A typical response is that of P.S., who pointed to the chicken with his right hand [controlled by the left brain] and the shovel with the left [controlled by the right brain]. After his response we asked him, "Paul, why did you do that?" Paul looked up, and without a moment's hesitation said from his left hemisphere, "Oh, that's easy. The chicken claw goes with the chicken and you need a shovel to clean out the chicken coop."
It is hard to describe the spell-binding power of seeing such things.
My interpretation is that the normal brain is organized into modular-processing systems, hundreds of them or maybe thousands, and that these modules can usually express themselves only through real action, not through verbal communication. Gazzaniga (1985).... a basic mental mechanism common to us all. We feel that the conscious verbal self is not always privy to the origin of our actions, and when it observes the person behaving for unknown reasons, it attributes causes to the action as if it knows, but in fact it does not. It is as if the verbal self looks out and sees what the person is doing, and from that knowledge it interprets a reality. Gazzaniga and LeDoux (1978).
Frontal LobesThe frontal lobes play a key role in orchestrating behaviors associated with LB/RB specializations. For example, RB prefrontal (RBF) originates emotional outbursts, whereas LB prefrontal (LBF) works to produce socially responsible behavior. The limbic system appears to be more strongly connected to RBF, and uses it to elaborate emotionally driven behaviors. LBF, on the other hand, appears to be the seat of the "conscience" and inhibits any RBF desires for socially inappropriate behaviors.
This was dramatically illustrated by the famous case of Phineas Gage, who suffered a railway construction accident in 1848 that caused a metal tamping rod to explosively penetrate and destroy his LBF (and a small part of RBF). Without the inhibiting effect of LBF upon RBF, his behavior was "fitful, irreverent, indulging at times in the grossest profanity... at times pertinaciously obstinate... he has the animal passions of a strong man." (If RBF and LBF could take positions concerning the idea that "the genes enslave us for their sometimes pernicious activities, and that individuals should rise up and become liberated from this genetic enslavement," it is obvious which side LBF and RBF would be on, and they wouldn't be on the same side! More on this in a later chapter.
Harlow, 1868). This old example illustrates the well known finding that RB's language ability is usually limited to profanity, songs and other memorized verbal material, such as the alphabet. A wealth of studies show that LBF is the site of the most advanced and human traits, such as conscientiousness, positive social behavior, rationality, strategic planning, and positive affect (mood). LBF is often referred to as the site of "executive function." RBF, by contrast, is associated with lack of inhibition, anti‑social behavior, emotionality, and negative affect. RBF is more closely connected to the sub‑cortical limbic system, the source of emotions.
This chapter's brief description of cerebral architecture, and the functional relationships of components, is part of the accepted neuropsychology literature. Every normal person's brain functions this way. If the brain was a "blank slate," as Francis Bacon initially suggested, and philosopher John Locke systematically expounded, then how amazing it would be for the blank slate to form itself into the same well‑defined areas, with corresponding functions, in all people ‑ regardless of their individual upbringing and environmental experiences! This old idea is best forgotten. Even Bacon and Locke would probably disown the outdated notion if they were alive today and could know about recent neuropsychology findings.The genes assemble brains with the same architecture, modules and functional relationships, and this process occurs automatically ‑ shall I say "mechanistically." This view of the brain is consistent with the reductionist theme found throughout this book. The next chapter is more speculative as it treats the brain’s role in evolution.