Brain Mapping

If you spread out your brain’s cerebral cortex, it’d be the size of a large pizza. It fits in your skull because it’s crumpled up. And your brain’s pattern of folds is more individual than your fingerprints.

The main structure of your brain is called your cerebral cortex . . . And you use different areas of it for different mental jobs — from solving a geometry problem to watching a football game. In the past decade, MRIs and PET scans have been helping scientists identify the boundaries between these so-called “cortical areas.”

David Van Essen is a neurobiologist at Washington University School of Medicine. He’s working with a group of scientists around the world to make a map of the human brain. Neurologists had hoped to identify a unique area for each function — one for music, one for identifying faces, and so on.

But it turns out some areas of the cortex do several things, while some jobs — such as vision — are divided among many areas. Van Essen says it’s an exciting challenge to understand differences between individuals.

David Van Essen: Why is one person better at algebra, and another person better at geometry and another person both loves music and is really good at analyzing music … those must be related to the diversity in the size and functioning and the patterns of connections amongst these many different areas carrying out the diverse functions of the brain.

Walter Wilczynski — a psychologist at the University of Texas at Austin — writes, “Scientists have been trying to map the human brain (and the brains of non-human animals) in a serious, scientific way for over a hundred years. Many people mark the start of modern neuroscience with Paul Broca’s (a French physician and scientist) attempt to localize language function on the basis of a brain injured patient in the 1860’s. What modern imaging techniques have done is greatly accelerate that process, make it more accurate, and allow mapping in normal, undamaged humans while they are alert and performing tasks that can be rigorously controlled or combined in complex ways. It also allows real analysis of individual differences because of that. And, like your story says, doing all this has made neuroscientists and psychologists realize the brain’s ‘mapping’ is way more complicated than once assumed (in just the way you put it.)”

Excerpts from an Interview with Dr. Van Essen:

Over a time period of millennia, we’ve gone from the most rudimentary understanding of just a small fraction of our earth’s surface to exquisitely high resolution with staggering amounts of data from satellite imagery and many other sources and so we’re still relatively early in mapping the human brain and dealing with this tremendous constellation of challenges, including … the variability in both the structure and the function of several billion individuals and knowing that those change dramatically with time.

The dominant structure of the human brain is the cerebral cortex and the cerebral cortex is basically a thin sheet of tissue, a fraction of an inch thick, and it has a very large surface area, about the size of a seventeen inch pizza, is what fits into the average human skull. To fit that large surface area into the skull requires that the surface by highly folded or crumpled, in much the same way that one would crumple up a newspaper, rather less messy than a pizza to get it compactly configured.

This process of folding the cortex, the development of the convolutions, occurs early on before birth, and it occurs in a way that has some consistencies from one individual to the next, but many differences, both large and small. Again, to use the crumpling of a newspaper analogy, it’s as though one respected some of the major creases between pages, but many of the minor folds are unique to each individual. And so that variability in the folding pattern is a fundamental challenge in terms of the structure of the brain and the cortex that anatomists and anybody interested in higher brain function needs to wrestle with when dealing with the experimental data that we acquire in many different ways.

We can think of the brain and the cerebral cortex early in development as a very smooth sheet, akin to a beach ball in its inflated state, and then we can imagine on that beach ball a mosaic of many different little subdivisions — what we call cortical areas, and in the human, we still don’t know the total number of distinct cortical areas, there are almost certainly a hundred, and perhaps as many as two hundred separate areas forming the mosaic. Many of these areas are very well defined …. and when we can identify them, can see that they are, from one person to the next, they are all in approximately the same location and approximately the same size, and as far as we know, doing pretty much the same jobs… in the normal living brain

When we look in more detail, we see that some of these cortical areas, while they’re roughly the same from one person to the next, there actually is quite a bit of variability in their overall size

So you might have one particular area, one of the areas that’s associated with vision, that’s twice as large as mine, but in compensation, I might have some other area that’s larger than yours. …..each person has… this mosaic of areas in which the general layout on this patchwork is roughly similar in terms of the location … but there’s tremendous diversity in terms of the exact size of … each little area within the mosaic.

One of the exciting challenges that we face is to try to better understand this diversity, this individual variability and to try to relate it to differences in function and behavioral capacities. Why is one person better at algebra, and another person better at geometry and another person both loves music and is really good at analyzing music … those must, in some deep way, be related to the diversity in the size and functioning and the patterns of connections amongst these many different areas carrying out the diverse functions of the brain.

When we start looking closely …we see that that the nature of what we call functional specialization is far richer and more complex.

The second level is to think about this mosaic of little areas that we’ve been talking about. If I’m, for instance, a piano player and I’m hitting the keyboards from dawn till dusk for thirty years of training… are there changes — expansion for example — in the regions of cortex that are specifically involved in touch and control of hand movements? We don’t have a clear answer to that … there are some indications that the size of the somatosensory cortex — the “touch” cortex — is larger in piano players. But you can look at that in two ways, it could have been the experience that caused some enhanced growth, or it could be that they’re better piano players because they have more tissue, more cortical turf that they were endowed with that helped them to be specialized. So those kinds of distinctions are still under investigation.

So at the level of asking — does the basic arrangement of these many different areas in the cortex, does that change a lot or just a little? — I would say the jury is out. We don’t know.

When you learn to do a particular task … when you first learn it, there are some parts of the brain that are very active, heavily engaged in doing the task while you’re learning it. As you get better and better at it, then the job of carrying it out efficiently is handled by different parts of the brain. There’s actually a shift in the overall regions of the brain… that are visibly active

What you have in your mind?