The First Word by Christine Kenneally

Author:Christine Kenneally
Language: eng
Format: epub
Publisher: Penguin Publishing Group
Published: 2010-03-01T05:00:00+00:00

Brad Schlaggar, a pediatric neurologist and a professor at Washington University in St. Louis, says that the best way to think of plasticity is as a support structure. When he gives a talk about plasticity, he always shows students slides of the St. Louis Arch. “As the structure goes up,” he explains, “the relationship between the scaffolding and the leading edge of the two sides of the arch changes as they rise up to meet in the middle. The relationship between the scaffold and the emerging mature structure is dynamic, as opposed to a scaffold that surrounds a building and then comes down again.” So if damage occurs to the brain of a seven-year-old child, it occurs in a completely different context than if the child were much older or younger. “The scaffolding idea means that even in adults, the organization of the brain for learning a novel task or a challenging task is different from the organization of implementing that task once you have acquired the skill.” The scaffolding for language seems to be particularly flexible. Fred Dick describes the development of language as a moving target. If damage is sustained in one area, language may move, morph, and settle into another.

In his doctoral work Schlaggar transplanted the visual cortex of one fetal rat brain into another, placing it in the spot where the somatosensory cortex, which normally controls the body as it moves through space, typically develops. Schlaggar found that the transplanted visual cortex grew into a fully functioning somatosensory cortex. The inputs into the new region came from the body as it moved in space, and as a result that neural tissue became wired to process that kind of information.

We tend to think of the brain as developing on a completely separate trajectory from that of the body. Traditionally researchers imagined that the brain had some kind of central developmental controller instructing different parts to assume responsibility for different abilities (the visual cortex develops particular types of neurons, while the auditory cortex develops differently specialized neurons, and so on). But recent research has cast grave doubts on the existence of any kind of central controller. It looks as if the brain tissue that ends up becoming part of different specialized regions is not necessarily fated to end up that way, and that input to the brain coming through the filter of the body contributes to its architecture.

Leah Krubitzer, a professor of psychology at the University of California, Davis, also demonstrated how the immature brain isn’t fated to be mapped into the specific regions that are typical of the adult brain. She removed a big chunk of the brain of newborn marsupials, and then let them grow up and develop normally. After they reached adulthood, she took another look at their brains. The cortices had organized themselves into exactly the same areas as a normal brain would, all in the same spots relative to each other, but they were all slightly smaller, so as to fit within the smaller brain.

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