How the brain divides its labors


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Martha Farah with a phrenology head, mapping the areas of the brain once thought to be responsible for different emotions and personality characteristics.

Photo by Addison Geary

 

Using variously postal workers, computer simulations and photos of Baywatch babes, psychology Professor Martha Farah has studied why the brain is organized the way it is.

Farah, who is also director of the Center for Cognitive Neuroscience, and postdoctoral fellow Thad Polk (now at the University of Michigan) started with the knowledge, based on current research in cognitive neuroscience, that the brain has a collection of modules, or specialized areas, that serve specific functions and operate relatively independently. In other words, the area of the brain that allows you to recognize your mother may be different from, say, the area that stores the information that oatmeal is a breakfast cereal.

Then they posed some questions: How do those modules come about? What determines the division of labor? What determines which tasks will have their own separate modules? And what determines where these modules become localized?

The two basic alternatives are nature or nurture, Farah said. Originally, Farah thought she would find it was some combination of the two. She believed that perhaps genes predisposed people to form a certain general type of module but that the environment put the finishing touches on its exact function and locality.

Instead, she found some modules where there is a surprising degree of genetic preprogramming or, alternately, a surprisingly complete absence of genetic preprogramming.

One example Farah looked at was the module for reading. I got interested in reading because it seemed like a really clear case of a localized ability that couldnt possibly have a genomic basis, Farah said. Reading is a fairly recent innovation in the history of the human race so is unlikely to be a genetic characteristic.

Using functional magnetic resonance imaging (fMRI) scans and computer simulations of neural networks, she found that there are highly segregated parts of the brain for recognizing letters and for recognizing digits and that these formed as a result of learning.

The clincher was to test her results on real people. She chose people who often see the occurrence of numbers and letters together: postal workers who sort letters with Canadian postal codes. Using a behavioral test, she discovered that these workers did not have as highly segregated brain functions as those who usually see numbers and letters in separate contexts. Their environment their job affected the way their brains functioned.

The module for face recognition, she found, however, was largely genetically predetermined. Her research in this area was based on a boy who had a normal birth but when he was one day old suffered strokes that damaged the part of the brain used to recognize faces.

Farah wondered, Will it be possible for his brain to reorganize based on experience in the visual world so that other parts of the brain could partially take over the task of recognizing faces?

The answer seems to be no. Now in his midteens, the boy doesnt recognize his friends nor does he recognize photos of characters from his favorite TV show, Baywatch.

He couldnt recognize a single one of the characters despite spending literally hundreds of hours watching them, Farah said.

Fascinating as her research is, the practical application of it, Farah believes, may be far in the future. The issue of the brains ability to relearn functions obviously [has] implications for the rehabilitation of adults with brain damage or children who have congenital impairments, she said, but thats definitely a way down the line.

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Originally published on April 20, 2000