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Intelligence Linked to Childhood Brain Growth Patterns

A specific thickening, then thinning of the brain's cortex reflected high IQ

WEDNESDAY, March 29, 2006 (HealthDay News) -- While the scientific debate over brain size and intelligence continues, new research suggests a slightly different mechanism might separate highly intelligent kids from those with average smarts.

A team of American and Canadian scientists say brilliance is not related to brain size, but rather to changes in the developing brain's shape over time.

"All children showed the same basic pattern of a childhood increase in the thickness of the cortex, which peaked and then decreased," noted lead researcher Dr. Philip Shaw, of the Child Psychiatry Branch at the National Institute of Mental Health.

"What differed with intelligence was the rate of these changes, and the age of peak cortical thickness," said Shaw. "The most intelligent children started with a relatively thin cortex, it got thicker rapidly, and after reaching peak thickness at a later age, it also got thinner quicker."

In the study, published in the March 30 issue of Nature, Shaw's team drew on 629 brain scans of more than 300 healthy children between the ages of nearly 4 and 29. They analyzed cerebral cortex thickness at various points throughout childhood and adolescence.

In addition, the researchers conducted IQ tests, dividing the children into three groups -- superior, high and average intelligence -- based on scores for verbal and nonverbal knowledge and reasoning skills.

The researchers report that although cortical thickness ultimately declined among all the children as they aged, the pattern of this decline differed across IQ groups.

Boys and girls with superior intelligence scores started with relatively thin cortexes that grew thicker at a rapid pace, peaking around age 11. The cortex subsequently thinned out quickly during early adolescence.

In contrast, individuals of average intelligence underwent one of two patterns: a steady, but slower cortical thickness decline throughout childhood, or a short increase that peaked by age seven or eight, followed by a steady decline in thickness.

Children in the mid-range -- the "high intelligence" group -- followed a pattern that fell roughly between the two other groups, although their experience more closely resembled that of the average-intelligence kids.

No gender differences were apparent.

The brain's frontal cortex is most directly related to the development of intellectual activity -- functions such as abstract reasoning, planning and other complex thought processes. According to the researchers, it was this frontal cortex area that displayed the most striking IQ-related differences in developmental shape trajectories.

Shaw's team conclude that intelligence is related to cortical growth patterns during childhood and adolescence, rather than to the quantity of gray matter a child has at any particular age.

"Children with the most agile minds have the most agile cortex," Shaw said. "Brainy children are not cleverer solely because they have more or less gray matter at any one age. Rather, intelligence is related to the way in which the cortex matures."

"We don't know what underlies the changes in the cortex we see," added Shaw. "We know from other researchers that there is use-it-or-lose-it pruning of brain cells, neurons, and their connections as the brain matures and becomes more efficient during the teen years. It is possible that this process accounts for the thinning of the cortex."

One expert found the findings fascinating.

"The results of this study are striking: they reveal that intelligence, an aspect of our personality that is remarkably stable throughout childhood, is maintained by a mechanism that involves major systematic changes in brain structure," said Guinevere Eden, director of the center for the Study of Learning at Georgetown University. "The findings of the study also demonstrate that brain changes are advantageous, and this knowledge has important implications for educational outcome. Understanding the dynamic brain mechanisms that drive academic potential will shed further light onto why certain skills are easier or harder for children at different developmental stages."

More information

For more on intelligence, visit the American Psychological Association.

SOURCES: Philip Shaw, M.D., Child Psychiatry Branch, National Institute of Mental Health, Bethesda, Md.; Guinevere Eden, Ph.D., director, Center for the Study of Learning, Georgetown University, Washington D.C; March 30, 2006, Nature
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