NEW YORK (AP) -- Very smart children,
despite their reputation for being ahead of their peers mentally,
actually lag behind other kids in development of the "thinking"
part of the brain, a new study says.
The brain's outer mantle, or cortex, gets
thicker and then thins during childhood and the teen years. The
study found that in kids with superior intelligence, the cortex
reaches its thickest stage a few years later than in other children.
Nobody knows what causes that or how it
relates to superior intelligence. But researchers said the finding
does not rule out a role for environment -- such as intellectual
stimulation -- in affecting a child's level of intelligence.
In fact, the brain's delay in thickening
may promote higher intelligence because it means a child is older
and processing more complex experiences while the cortex is building
up, said study co-author Dr. Judith Rapoport.
Rapoport, with researcher Dr. Philip Shaw
and others at the National Institute of Mental Health in Bethesda,
Maryland, followed development of the cortex in 307 children.
They used repeated magnetic resonance imaging (MRI) scans from
childhood to the latter teens.
Results appear in Thursday's issue of the
journal Nature. Researchers also found that despite the delayed
schedule, the cortex thickens and thins faster in brilliant kids
than in other children.
The overall findings are especially strong
for cortex development in the front part of the brain and in a
strip over the top of the head, areas where complex mental tasks
are done, Shaw said.
One analysis found the cortex in kids with
the highest IQs -- 121 to 149 -- didn't reach maximum thickness
until age 11. Children who were just slightly less bright reached
that point at age 9, and those with average intelligence at around
6. In all cases, the cortex later thinned as the children matured.
Nobody knows what's happening within the
cortex to make it get thicker or thinner, Shaw said, so it's impossible
to say why those changes would be related to intelligence. Brain
development is influenced by intellectual stimulation, so that
probably plays a role, he said.
The study findings are "certainly
not a recipe for how to change intelligence," he said. Nor
do they suggest that MRI scans can reveal how intelligent an individual
child is, he said.Elizabeth Sowell of the University of California,
Los Angeles, who has studied cortex thickness in children, said
she found the results convincing.
While the findings show that the pattern
of cortex development is related to high intelligence, they can't
show which is causing the other, she said.
She also said that by tracing out patterns
of normal development, such studies help scientists understand
what goes wrong in children with brain disorders.
