How to Think About the Brain

The Dana Guide to Brain Health
by Floyd E. Bloom, M.D., M. Flint Beal, M.D., David J. Kupfer, M.D., The Dana Foundation

Today, we know beyond any doubt that the brain plays a crucial role in our everyday health, and, indeed, makes us who we are. But the Internet, television, and newspapers abound in contradictory information about it, and, as a result, the insights we wish for and the medical choices we need to make are rarely as clear as they need to be — especially when a family member's well-being is at stake. For decades The Dana Foundation, a philanthropic organization founded in 1950 dedicated to science, health, and education, has focused its medical initiatives on brain research. The culmination of that relentless commitment is now all here in this complete health guide to the brain. The editors — Floyd E. Bloom, M.D.; M. Flint Beal, M.D.; and David J. Kupfer, M.D. — are three of the world's leading medical experts in neuroscience, neurology, and psychiatry. Together with more than one hundred of America's most distinguished scientists and medical professionals, they have created an essential, easy-to-understand, and practical reference guide to the brain and how it works.

The Dana Guide to Brain Health is a resource that today's health consumer can trust, or what Foundation chairman William Safire calls "a kind of basic 'bible' of the brain."

The first truly accessible all-in-one source of its kind, this illustrated home reference features the latest facts and medical discoveries, combined with clear, up-to-date information on seventy-two psychiatric and neurological disorders, their diagnoses, and their treatments.

Filled with informative diagrams, tables, sidebars, graphs, charts, photographs, and drawings, along with a section listing every major consumer advocacy/information organization, related to brain disorders, The Dana Guide to Brain Health sets a new standard. In its pages readers will discover:

• The crucial steps for taking care of our brains

• The intimate connection between brain health and body health

• How the brain develops from the prenatal period and childhood through adolescence and adulthood

• How the brain regulates breathing and blood flow

• How we learn, remember, and imagine

The Dana Guide to Brain Health is simply the most authoritative, comprehensive, and clearly written guide to the bodily organ that is the key to our everyday health. No home should be without it.

Chapter 1

Since a human brain weighs on average some three pounds, it is easy to hold one in your hands. This simple fact somehow makes it even harder to imagine how such a small mass of tissue can be the source of all that we think of as human. Yet that is what the brain is, and how that can possibly be is one of the most fundamental questions in brain science. What is the link between the anatomy of a brain and the workings of a human mind? The big challenge is that there are no obvious moving parts within the brain — it does not operate mechanically as our hearts and lungs do. If we simply look at the brain, our only remote clue about how it works is that it seems to be made up of different parts, easily discernible to the naked eye (see illustrations on page 4). In addition to the cerebral hemispheres (resembling a pair of large walnuts pressed together), the smaller structure that sits behind them (the cerebellum) is visible, as is the stalk that connects to the spinal cord (the brain stem). But there are many more regions than these three.

One easy way to think about the brain would be to view each of these different regions as having a clear function. Every part would be a sort of independent minibrain, controlling one aspect of our mental and behavioral repertoire: movement, emotion, ethics, balance, mathematical thinking, and so on. Simple and attractive though this idea is, it quickly runs into problems. After all, such a scenario would merely be miniaturizing the problem, not solving it; we would still have to figure out how each of those minibrains operates. And, as neuroscientists have learned through extensive observations and experiments, the brain just doesn't work that neatly.

Let's start with a straightforward way of trying to match up the brain's physical structures with specific functions. We know that within the animal kingdom, each species has a very different range of abilities and behavior patterns. If the brains of different animals diverge in form, that would give us significant clues about what structures are important for what kinds of functions. For instance, no animal has a language function anywhere near as sophisticated as ours. If there is a particular structure for language, it should be especially well developed in human brains, and small or nonexistent in the brains of other species.

However, the brains of very different creatures, such as a reptile, a bird, and a mammal, differ mainly in size. In all cases we can make out the same big features: the hemispheres, the brain stem, and the cerebellum. So whatever makes one species so different from another — and above all makes the human species so different even from other primates — is not some new, clearly conspicuous structure in their brains that no other animal has.

If, however, we look at various animals' brains for a difference not in quality but in quantity, then one clue about the physical basis of mental differences becomes apparent. The biggest discrepancy appears in the surface of the outer layer of the hemispheres. This layer is called the cortex, after the Latin for "bark," because it wraps around the brain the way its namesake wraps around a tree. In a rat or rabbit, for example, the surface of the cortex is completely smooth. In a cat it has clear convolutions. By the time we look at monkeys and apes, and eventually humans, the cortex takes on an ever more wrinkled appearance. Why?

Imagine trying to hold a sheet of paper in one fist. The more you crumple the paper, the more the sheet will fit inside your fingers. In a way, this is what has happened to the cortex within the skull. As species have become more sophisticated, the surface of their cortices has increased faster than the limited confines of their heads. The only way to develop more "working surface" in the cortex was to fold and wrinkle it. We can see this same evolutionary trend in the development of an individual human. The brain of the six-month-old fetus has a completely smooth cortex. But in the final three months of pregnancy, the baby's neurons proliferate at an astonishing 250,000 a minute. The cortex expands enormously so that by birth it has become as walnutlike as we know it. (For more on the brain's prenatal development, see chapter 5.)

Mapping the Regions — The Top-Down Approach

We can call this method of thinking about the brain — looking at its physical regions and their traits — the top-down approach. The surface area of the cortex and the degree to which it is wrinkled seem to hold a clue about how a species' brain relates to its mental abilities. Small wonder, then, that the cortex has fascinated many brain researchers. But how might it accommodate the uniqueness of our human traits?

The top-down approach has given us some valuable insights into how the cortex is organized and how it plays a part in brain function. We know, for example, that despite the way its surface looks the same everywhere, different parts of the cortex participate in different processes. Certain areas, along with many deep brain structures below the cortex, seem to relate directly to the processing of each of the senses: vision, hearing, smell, and so on. As an example, let's take one thin strip of cortex that straddles the brain a little like a hair band. This region is called the somatosensory (that is, body-sensing) cortex. (See pp. 138-39 for more about it.) The cells in this strip collect signals from other brain structures, which in turn are activated by impulses buzzed up the spinal cord that report on touch, pain, or temperature felt in certain parts of the body. Clearly, this strip of cortex must contain some sort of representation of the body. How else would you know that a pain was in your toe as opposed to your hand?

So far, so good. The most logical way of thinking about your body being "mapped" in the brain would be in direct relation to size. A large part of the body like the back would have a large allocation of brain territory, and a small area like the fingertips or the tongue would be represented by a correspondingly meager area of cortex. But here is a simple experiment you can do at home to prove that this "obvious" scenario is wrong. All you need are a pair of sharp pencils, or unbent paper clips, and a willing friend.

Ask the friend to close his or her eyes and turn away. Hold the pencils so their points are close together — three-eighths inch or so. Gently touch both pencil points to your friend's skin in different parts of the body, and ask if you are applying one or both points. (You can also try touching just one point at a time to see if your friend feels a clear difference between one and two points.) When you touch both pencils to your friend's back, he or she will almost always report feeling a single point. Now position the points much closer, only one-sixteenth inch apart, and apply them to your friend's fingertip or (with permission) tongue. Surprisingly, this time your friend will be able to feel two distinct points. Even though the fingertips and tongue represent only small fractions of our bodies, they are extremely sensitive to physical detail. Despite their small size, the fingers and the tongue have the lion's share of territory in the relevant strip of brain. That's because our brains are organized according to the functional needs of our bodies rather than simple physical size. Our fingers and tongue have to be more sensitive to touch than our back — so they have more brain territory allocated to them.

Thus we can start to see that the structures of our brains are in tune with our daily lives. But testing such primitive processes as touch doesn't help with the question of how our cortex works differently from those of other species. So let's go back to what is arguably the monopoly of us humans, language. Surely if we understood how our brains process language, we would have a route into understanding the physical basis of what makes us so special.

Paul Broca was a physician working in Paris during the mid-nineteenth century. He has earned his place in neurological history thanks to one of his patients, a Monsieur Leborgne. Everyone knew this unfortunate man by his nickname, "Tan," because that was all he could say. Leborgne had a severe speech problem, an aphasia (C70), which meant he could not articulate words. When Tan died, Broca examined his brain and discovered a clear hole in the side of its left hemisphere. Tan's aphasia was obviously related to the damage in this region, henceforth known as Broca's area. But does this mean that Broca had discovered the mind's center for speech? Far from it.

Within a decade, a German physician, Carl Wernicke, identified a second site, also on the left-hand side of the brain but clearly well behind Broca's area, where damage gave rise to a different type of speech problem. Wernicke's aphasia is also referred to as jargon aphasia because although a person with this problem can articulate words perfectly well, all that comes out of his or her mouth is a string of gibberish.

By the end of the twentieth century, scientists had come to realize that there are still more brain regions involved in speech. Imaging techniques have made it possible for us to see the brain at work in conscious humans without causing any pain or harm. Positron-emission tomography (PET) and functional magnetic resonance imaging (fMRI) exploit the facts that the brain is very greedy for oxygen or glucose and that the hardest-working brain regions are hungriest of all. (For more on these technologies, see chapter 2.) Studies have now revealed that, during such seemingly simple behaviors as using language, many brain regions are working together, rather like the instruments in an orchestra. Each region will be making a specialized contribution, but the whole is somehow more than the sum of its parts. What we don't know yet is how all the different brain regions involved in any one task, be it language or vision or memory, somehow come together.

But what might we learn about the particular contribution of one brain region? Let's look at an area toward the front of our brains, the prefrontal cortex. This area is twice the size it should be for a primate of our body weight. Could this contain the secret of our awesome mental abilities?

Again, as long ago as the mid-nineteenth century people realized that there was something special about the prefrontal cortex. This was demonstrated in 1848 in a most dramatic way by Phineas Gage, a railway worker in Vermont. One day, Gage was working to clear the path for a new railroad when the gunpowder he was using exploded prematurely. As a consequence, the bar with which he had been tamping down the explosive shot right through his prefrontal cortex. In effect, he had speared himself through the head. Surprisingly, Gage lost sight in one eye but otherwise appeared to be unaffected by this horrific accident. His movements and senses all were as before, and he actually went back to work. Only then did his workmates start to notice a difference. Gage was not badly affected in how he walked, pronounced words, ate, or did other normal human activities, but a far more subtle change had occurred. He had become very unpleasant and antisocial, cursing in inappropriate situations. So could the prefrontal cortex be the brain's center for character (or good character)?

In fact, in the decades since Phineas Gage had his accident, scientists have studied many other patients suffering damage to the prefrontal cortex. More recently, they have observed the region's activity in healthy people. The prefrontal cortex has now been implicated in a welter of seemingly disparate functions, ranging from "forward planning" to "working memory." In people suffering from clinical depression this area appears overactive, and in those with schizophrenia it can be underactive. There is clearly no single common, easily identifiable theme to these findings. So where does that leave us in our effort to localize functions within the brain, to match up different functions with different structures?

The emerging picture is certainly not a brain composed of autonomous minibrains. Rather, every function is divided among many brain regions, and every brain region participates in the many functions that make up the human behavioral repertoire. We can say that certain regions of the brain are more active than others when it comes to certain functions, but we can't say those functions are confined to particular areas. And we are still a long way from knowing how to assemble the different structures of the brain to make up a human mind.

Copyright © 2003 by The Charles A. Dana Foundation

About the Author

is Chairman of the Department of Neuropharmacology at The Scripps Research Institute in California, President of the American Association for the Advancement of Science (AAAS), and former editor in chief of the journal Science. He lives in San Diego.

M. Flint Beal, M.D., is Neurologist in Chief of the New York and Presbyterian hospital, and Anne Parrish Titzell Professor and Chairman of Neurology at the Weill Medical Collage of Cornell University. He lives in New York City.

David J. Kupfer, M.D., is Thomas Detre Professor and Chairman of the Department of Psychiatry at the University of Pittsburgh School of Medicine, and Director at the Western Psychiatric Institute and Clinic there. He lives in Pittsburgh.

The Dana Foundation is a private philanthropic organization dedicated to furthering advances in science, health, and education. The Dana Press, which directed the Dana Guide to Brain Health, is the Foundation's publishing division.