The Inside Story

Understanding the structure of the brain

One of the articles in The Way Of Learning (IC#6)
Originally published in Summer 1984 on page 4
Copyright (c)1984, 1997 by Context Institute

DURING THE PAST FEW YEARS momentum has been building around a major shift in our understanding of how the brain/mind system works. In the old view, the brain was a large, but basically simple-minded computer. Some areas of the brain were specifically connected to each sense or to particular muscle groups, but the rest of it came into the world as a "blank slate" waiting to make connections between some specific stimulus and its specific response. Some people seemed better at making these connections than others, and this difference in skill could be described by one number known as the intelligence quotient (IQ). These connections and associations were one form of memory, and it was assumed that most of the brain was devoted to the rote recording of experience.

The new view turns much of this upside down. Researchers have been finding that the brain comes into the world with much more structure, behavioral as well as anatomical, than had been thought. This structure is mostly concerned with how experience and information is processed, and indeed the brain is a very sophisticated analyzer of the information it receives. Different parts of our brain deal with different perceptions and behaviors and/or "think" in different ways. Because of this, there is no one number that can characterize the diverse range of mental talents each of us possesses. And then the seemingly simplest mental operation, "memory", turns out to be much more mysterious than anyone expected. Extensive studies of brain damaged patients who regain most of their memory have led most researchers to give up on the idea that specific memories have a specific "location" in the brain. There is even growing evidence that much of our memory is not stored in our brain at all, but I’m getting ahead of the story.

Let us begin by looking at some of the basic processes that are involved throughout the brain. We will then turn to the larger scale "structure" of the brain/mind system.

Basic Processes

The basic building block of our whole nervous system is the nerve cell, and its structure reveals a great deal about the way the brain works. A typical nerve cell looks like a spidery octopus with many branches on each of its arms. Some of these branches and arms receive input (dendrites) while the others send output (axons). The nerve cell integrates the input from its dendrites, and if these have the right pattern, it sends an impulse of output. I say "right pattern" because some of the input encourages response while other types actively inhibit it. So each nerve cell functions like a little logical decision maker: if A and B but not C, send an impulse; otherwise keep quiet.

These nerve cells connect up with each other in complex networks, with each cell often receiving input from many sources and then sending its impulse to many other cells. Consider, for example, vision. The nerve impulses from the eye go through many steps on their way to the higher levels of the brain. The first step connects many receptors (rods or cones) in a circular area of the eye to one integrative nerve cell. This cell may be activated by light at the center of that circle and inhibited by light in the outer parts, or vice versa. In any case, these cells use comparison to detect contrast. They then pass their information on to higher order cells that detect particular kinds of patterns, like lines. The process repeats, but at the next level the integrative cells can put together the information about lines, curves, etc. into the detection of specific kinds of shapes.

Our brains thus work on the basis of patterns (with each integrative nerve cell assessing if its special conditions are met) and programs (or chains of decisions and actions with results at one level moving on to the next). Computers also operate on the basis of programs, but there is at least one major difference between the brain and a conventional electronic computer. In a computer, all of the processing, all of the decisions, are handled in one place, while in the brain, millions of decisions are being made at the same time throughout the system. This is called parallel processing and it is what makes the brain so good at recognizing patterns.

Where do these patterns and programs come from? Some of them are built-in, like the lower integrative levels in the vision system, but many are also learned. At least part of learning seems to involve the alteration of existing patterns of connection between nerve cells and/or the building of new connections. Our brains start out with more neural connections than we eventually use, with the density of connections being about 50% greater between ages 1 to 2 than in the adult brain. As we grow, many of these connections atrophy, and it is believed that part of learning involves a selective atrophy which leaves behind the patterns we have learned. More subtle chemical changes at these connections also change their strength. In addition, brain cells can continue to extend their "arms" throughout life, making new connections. How these cells know where to extend to, however, remains a mystery.

The above description of learning applies to what might best be called training – the acquiring of essentially automatic responses, patterns, and programs. It usually takes time and repeated exposure for these new patterns to become "wired" into the nervous system. There is, however, another kind of "learning" that is illustrated by simple recall of some fact or experience. Especially for subjects we are interested in, this kind of learning often takes only one exposure, and it is this kind of memory that has been impossible to localize in the brain. We will explore this in greater detail in the article on memory.

Horizontal Structure

The larger scale structure in the brain can be thought of as having two "dimensions," a "vertical" dimension of evolutionary age and a "horizontal" dimension of parallel capacities. The best known horizontal distinction is between the left and right sides of the outer part of the brain (the neocortex). Physically, they are identical mirror images of each other, but functionally they have developed an important division of labor. The first clues to this came from the work of Roger Sperry and his students at CalTech during the 1950s. Their initial focus was to understand the function of the corpus callosum, the thick bundle of nerve fibers that connect the two halves of the brain. The corpus callosum was clearly a major and strategically located part of the brain, yet research up to that time had shown that it could be completely severed without any apparent effect on behavior. By a series of ingenious experiments with animals that taught one pattern of behavior to one side of the brain (via one eye with the other eye covered with a patch), and then the opposite pattern to the other side, they were able to show that this nerve bundle was essential for communication between the two halves. But in the process they also found that the two sides could function independently. Their interest then shifted to exploring the capabilities of each side of the brain. Starting in the 60s, they were able to study human patients who had had their corpus callosum surgically severed as a (successful) means of controlling otherwise severe epileptic seizures. What they found was yet another surprise. Not only could each side of the brain work independently, each side seemed to use a different mode of thinking.

Studies with these "split-brain" patients as well as studies of the electrical activity from each side of the brain in normal subjects indicate that the left side is dominantly involved in speech, the use of symbols, analysis and logic, and keeping track of time, while the right brain is dominantly involved in visual, spatial, and musical activities, and the insight and synthesis that go on through imagination and daydreaming. The right brain also seems to have an important role to play in the translation of ideas into physical action. These are the normal pattern, but it is important to note that they are not universal, and when brain damage disables one side, the other can (depending on age) take over many of the damaged side’s normal functions.

These differences were initially interpreted to mean that the left brain style was analytic and step-by-step linear while the right brain was wholistic. More recent research by Justine Sergent at McGill suggests, however, that the distinction is more one of speed and detail. Both sides analyze and both perceive wholes, but the left brain is better at detailed processing while the right is better at quick "broad brush stroke" pattern recognition. Working together, they can be a very powerful team.

One of the major effects of this research has been a new appreciation for the right brain mode of thinking and the realization that we do very little in our current educational systems to systematically develop the skills of the right brain or, even more so, to develop the coordinated functioning of both sides. Yet where attempts have been made to "educate the whole brain," the speed of learning and the level of achievement are often astounding.

The idea that we have more than one mode of thinking has been carried further by Howard Gardner of Harvard in his recent book, Frames of Mind: The Theory of Multiple Intelligences. His goal was to find those major patterns of intellectual capabilities that can stand on their own and so form an independent area of mental competence. He used clues from selective brain damage, the existence of idiot savants and prodigies, and psychological studies to come up with six types of intelligence: mathematical, linguistic, musical, visual-spatial, bodily-kinesthetic, and inter and intra-personal. He does not attempt to locate these in any particular part of the brain, but it would appear that the first two would be associated with the left brain, the next three with the right brain, while the last may be associated with the prefrontal cortex (see below).

Whether or not Gardner’s particular groupings are the best ones remains to be seen, but it does seem clear that our potentialities are too complex to be measured by a single number (IQ) or for education to think it is doing an adequate job by addressing only some of these capabilities. Indeed, given the fundamental role of parallel processing throughout the brain, the surprise is not this multiplicity, it is that we experience as much unity of personality as we do!

Vertical Structure

The multiple talents we have been discussing are mostly associated with the outer layers of the brain – the neocortex – but they all depend on activities that are handled by older, lower level structures. One of the main explorers of this vertical dimension of the brain is Dr. Paul D. MacLean, Chief of the Laboratory of Brain Evolution and Behavior at the National Institute of Mental Health. What he and others have found is that, in evolving from simple organisms to humans, the brain has not simply grown bigger – like an expanding balloon. Rather, each new evolutionary development has added on to – but not replaced – the previous step. The human brain has four major levels. The oldest level, at the core of the brain, is what MacLean describes as reptilian or the R-Complex. The neurological structure and functioning of this part of the brain is very similar to that found in the complete brains of reptiles and in the core part of other mammals. The next level is called the old mammalian or limbic system, and is characteristic of most mammals. The third level, the new mammalian or neocortex, is found in the higher mammals, especially the primates. Finally, the prefrontal cortex is uniquely human, coming in with the transition from Neanderthal to Cro-Magnon humans.

What difference does all this make? The important thing about our four level brain is that each level has special functions and seems to be associated with particular kinds of behavior. Each level is able to operate somewhat independently, even in opposition to the others, although effective functioning (and especially learning) requires good coordination among the various levels. Let’s look now more closely at each level:

The Reptilian Brain Reptiles are creatures of habit and instinct, but they are nevertheless fully functioning, complex organisms. The reptilian brain has a lot to take care of. First there are the basic functions such as regulating internal body processes, coordinating muscular activity, and sensing the external environment (although indications are that reptilian senses are fairly crude). But there are also more specific patterns of complex behavior. MacLean suggests the following list of primal behaviors that occur in a wide range of land animals and are probably associated with the reptilian part of the brain:

1) Territorial Behavior: Establishing, "marking", and patrolling of territory; selection and preparation of homesite; showing place-preferences; defense of territory with ritualistic display, formalized intraspecies fighting, triumphal display with success, and the assumption of distinctive postures and coloration in signaling surrender; hoarding; and use of defecation posts.

2) Travel Behavior: Trail making; foraging; hunting; homing; and migration.

3) Social Behavior: Formation of social groups; establishment of social hierarchy by ritualistic display and other means; greeting; "grooming"; courtship, with displays using coloration and adornments, mating, breeding and flocking.

The reptilian brain is a great lover of order, familiarity, and automatic responses. It is always on the look out for danger, is quick to react, but is slow to learn.

The Old Mammalian Brain From the point of view of brain evolution, probably the most important difference between mammals and reptiles is that young mammals have a childhood, a period of dependence during which they must rely on their parents for survival. This new phase of life is intimately associated with those forms of behavior that mammals do not share with reptiles – emotionally based bonding, a sense of responsibility on the part of the strong to care for the weak, play, and a more significant role for learned behavior. It is not surprising then that the old mammalian brain is centrally involved in the expression of emotion, the bonding aspects of sexuality, and the elaboration of sense perceptions, especially smell and taste. The old mammalian brain is focused both inwardly, sensing the body’s internal feelings and closely connected to the hormonal system, and outwardIy, gathering sense input. It is the place where feeling is associated with experience, with all the implications that has for learning.

Robin Beebe says of this part of our brain that "It wants to be assured of nurturing, of belonging to a group, of emotional security, of sexual desirability. It is aroused or enlivened by touch, by stroking, by smells, by food, by music, by social contact, and, most basically, by love."

The New Mammalian Brain The initial step that the early mammals took into the greater flexibility that learned behavior permits proved to be a great evolutionary success. So much so, that the opportunities soon outgrew the capacity of the two older brains. The third level in the brain, the neocortex, is nature’s answer, and it is devoted primarily to learning and learned behaviors. To enable this capacity for learning required further elaboration and refinement of the senses, especially sight, hearing and tactile. In humans, the neocortex is the site of most of what we call "mental capacity" – language, abstract thought, imagination, the ability to give meaning to new experiences, etc. It is occupied primarily with events in the outside world, and functions like a coldly reasoning computer.

In direct opposition to the reptilian brain’s love of order, this part of our brain is always curious, always in search of novelty, new experience, and new meanings. It tends to see itself as the ruler of the mind, but it can’t act without the cooperation of the older brains, and is in many ways more dispensable than they are. Experiments with rats and hamsters raised without their neocortex show them to be capable of mostly normal lives. The other possibility – neocortex left intact while the connections from the body to the older brains are cut – has been explored in experiments with monkeys. They are able to recover the ability to move around and eat, but most normal monkey behavior simply disappears.

The Newest Brain The fourth level of the brain – the prefrontal cortex – occurs only in humans and is sometimes considered a part of the neocortex. But its functions are different enough from most of the neocortex to consider it as a separate level. It is the place where we are able to combine imagination (especially the ability to plan) with feeling (for both empathy and motivation). It has strong connections with both the neocortex and the old mammalian brain (especially the areas associated with parental care). As such it is the part of the brain that is most strongly focused on the integration of rationality and emotionality in such things as altruism and cooperative activities. Through it, we are able to identify with a large whole.

As we go though our daily lives, we tend to move back and forth among these levels. For example, as I write this, I am focused mostly in the neocortex and prefrontal cortex, with the old mammal providing underlying supportive motivation and the reptile placidly helping to coordinate my fingers as I type. All goes smoothly until I hear my two-year old cry. Immediately, the reptile is alerted (simply by the loud noise) and sets off the alarm. Lagging by only a split second, the old mammal has identified the sound as one of its special cues, and all the parental protection programs are rushing into place. Somewhat more slowly, the neocortex begins to gather sense information and analyze the situation. It turns out to be a cry of frustration, not hurt, so the old mammal is able to relax a bit. The prefrontal cortex is finally able to come into play, empathizing with the child and also seeing the opportunity that this situation offers for growth toward future abilities. Together with the neocortex it then envisions a plan of response that will help the child to learn most effectively and comfortably through this situation. Had the cry been one of genuine hurt, the old mammal would have flown into action, likely running well ahead of the newer parts of the brain. Only gradually or later would I "stop to think" about what was going on. Leslie Hart refers to this process as "downshifting" – going from more sophisticated but slower modes to the faster behaviors of the older brains when we are under stress – and it helps to explain why we sometimes behave in such different ways according to the level of stress we feel.

The implications of all this for learning is something we will explore in a following article, but first we shall turn – experientially – to re-integrating our brains.

In addition to being the editor of IN CONTEXT, Robert Gilman is one of the co-authors of At The Crossroads. Ten years ago, before he decided that "the stars could wait, but the planet couldn’t," Dr. Gilman spent a number of years teaching and doing research as a theoretical astrophysicist. Since then he has been exploring the development of a humane sustainable culture at a personal and community level, including building a solar home and founding a local "living lightly" association.