http://www.nytimes.com/2006/03/30/science/30brain.html
Scans Show Different Growth for Intelligent Brains
By NICHOLAS WADE
Published: March 30, 2006
The brains of highly intelligent children develop in a different
pattern from those with more average abilities, researchers have
found after analyzing a series of imaging scans collected over 17 years.
The discovery, some experts expect, will help scientists understand
intelligence in terms of the genes that foster it and the childhood
experiences that can promote it.
"This is the first time that anyone has shown that the brain grows
differently in extremely intelligent children," said Paul M.
Thompson, a brain-imaging expert at the University of California, Los Angeles.
The finding is based on 307 children in Bethesda, Md., an affluent
suburb of Washington. Starting in 1989, they were given regular brain
scans using magnetic resonance imaging, a project initiated by Dr.
Judith Rapoport of the National Institute of Mental Health.
This set of scans has been analyzed by Philip Shaw, Dr. Jay Giedd and
others at the institute and at McGill University in Montreal. They
looked at changes in the thickness of the cerebral cortex, the thin
sheet of neurons that clads the outer surface of the brain and is the
seat of many higher mental processes.
The general pattern of maturation, they report in Nature today, is
that the cortex grows thicker as the child ages and then thins out.
The cause of the changes is unknown, because the imaging process
cannot see down to the level of individual neurons.
But basically the brain seems to be rewiring itself as it matures,
with the thinning of the cortex reflecting a pruning of redundant connections.
The analysis was started to check out a finding by Dr. Thompson: that
parts of the frontal lobe of the cortex are larger in people with
high I.Q.'s. Looking at highly intelligent 7-year-olds, the
researchers said they were surprised to find that the cortex was
thinner than in a comparison group of children of average intelligence.
It was only in following the scans as the children grew older that
the dynamism of the developing brain became evident. The researchers
found that average children (I.Q. scores 83 to 108) reached a peak of
cortical thickness at age 7 or 8. Highly intelligent children (121 to
149 in I.Q.) reached a peak thickness much later, at 13, followed by
a more dynamic pruning process.
One interpretation, Dr. Rapoport said, is that the brains of highly
intelligent children are more plastic or changeable, swinging through
a higher trajectory of cortical thickening and thinning than occurs
in average children. The scans show the "sculpturing or fine tuning
of parts of the cortex which support higher level thought, and maybe
this is happening more efficiently in the most intelligent children,"
Dr. Shaw said.
The I.Q. was tested when the children entered the program. Further
tests were not needed because I.Q.'s are so stable, Dr. Rapoport said.
Dr. Thompson said the new study opened huge possibilities because
researchers should be able to identify the factors that influence the
brain by looking at the scan patterns identified by the researchers.
The Bethesda children have had genetic samples taken from their
cells, so genes that have even the mildest influence on the brain
should be detectable, Dr. Thompson said. The pattern of development
may also be affected by factors like diet, hours spent in school or
the number of siblings, and these may come to light by asking parents
how they raised their children.
"There are many enigmas of intelligence that they can now solve," he said.
I.Q. scores and measuring intelligence have long been controversial.
Brain-imaging studies by Dr. Thompson and the study group have
advanced the field by identifying physical features of the brain that
correlate with I.Q.
In 2001, Dr. Thompson reported that based on imaging twins' brains
the volume of gray matter in the frontal lobes and other areas
correlated with I.Q. and was heavily influenced by genetics. Despite
the great importance of genes in brain function, Dr. Thompson said
experience could also change the brain.
"Unless you have strong natural potential, you won't become a
world-class marathon runner," he said. "But that disillusionment is
rapidly replaced by the notion that you can improve your own performance."
The institute's team has many genetic studies in progress. The
analysis reported today was not intended to look at the relationship
between genes and intelligence.
"A lot of research in intelligence has not been that great," Dr. Shaw
said. "I would hope by this modest descriptive study to put things on
an empirical footing."
One goal of the study was to establish normal development patterns,
to diagnose what goes awry in children with schizophrenia or
attention deficits. Dr. Shaw said his team did not have the full
answers as to how the brain differed in those cases.
