The pattern of brain growth during development
may figure more importantly than overall brain size when it comes to
intelligence, according to a new study.

Scientists have found that the
smartest kids start off with a relatively thin cerebral cortex–the
outer layer of the brain associated with thought and other higher order
functions–that thickens rapidly by age 12 before undergoing the same
general diminishment as that of their peers of average intelligence.

"Brainy children are not cleverer solely by virtue of having more
or less gray matter at any one age," says Judith Rapoport of the
National Institute of Mental Health (NIMH) in Bethesda. "Rather, IQ is
related to the dynamics of cortex maturation."

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Rapoport
and her colleagues at NIMH and McGill University followed 307 children
of varying ages as they grew up, scanning them with an MRI machine
periodically. They then compared such measures as brain volume with the
results of a standard IQ test. Contrary to popular perception, the
brightest kids did not necessarily have the largest brains.

They did, however, exhibit a distinctive pattern of brain
development. Whereas an average child’s cortex thickness peaked around
age eight, the smartest children experienced thickening of the cortex
until early adolescence. In all of the subjects, the cortex waned
during adolescence, perhaps due to a pruning of neurons as the brain
becomes more efficient, the researchers speculate.

Complicating the picture, however, relatively
intelligent children–smarter than average but not the
smartest–followed roughly the same development pattern as their more
typical peers. And in the smartest kids the cortex shrank more than
most during adolescence, in some cases dropping them below their
relatively intelligent peers.

By David Biello
Scientificamerican.com