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Smart Kids May Get a Slow Start: New Study Shows Intelligence Has More to Do With How a Brain Develops in Children Than Its Overall Size

March 30, 2006

By Jamie Talan, Newsday, Melville, N.Y.

Mar. 30–Brain development in the smartest kids has a different, slower growth course than that in average children, federal researchers have found.

“This tells us that early growth isn’t necessarily better,” said Dr. Jay Giedd, a scientist at the National Institute of Mental Health and one of the lead investigators of the research. The brain regions used to think, plan and reason mature two years later in those kids with high IQ scores, the research found.

Since 1990, 307 kids between ages 4 to 19 have been scanned with MRIs, many every two years. The scientists also obtained detailed neuropsychological tests, including measurements of intelligence, on the volunteers.

“There is probably an optimal speed of brain development,” Giedd said. He likens it to height, which is also under genetic and environmental control. Some kids who grow faster and reach puberty early may not be as tall in adulthood as a child whose growth is slower.

Giedd says the findings are good news for late bloomers. “A child who is not reading or doing math like his peers may end up doing even better than them years down the road,” he said.

The scanning device measures the thickness of the outer layer of the brain. The latest finding, published in Nature, shows children with the highest IQs – those who were rated as “superior” on intelligence tests with scores from 121-143 – were still undergoing a brain growth spurt when those children of normal (scores of 83-109) or above average intelligence (scores of 110-120) had reached their peak of cortical thickness.

Neurons in the brain grow throughout the early years of life and then prune back. This remodeling is important in strengthening brain connections and making the brain system more efficient. This study has helped dispel myths about brain size, thought to be associated with intelligence.

While the brains of all teenagers eventually thinned out by age 19, the researchers came to understand “it’s the journey and not the final destination that matters.” Those with superior intelligence had a slower developmental curve, but then “showed the highest rates of change throughout the journey,” Giedd said.

The thickness of the cortex (the brain’s gray matter) varies with age, especially in the most advanced part of the brain that helps with cognitive processes like thinking and planning.

In those with average intelligence scores, the thickness of the cortex peaked at age 7, and then gradually thinned. By contrast, the smartest 7-year-olds had a thinner cortex that peaked in thickness by age 11 or 12 before pruning back.

Dr. Judith Rapoport, director of NIMH’s child psychiatry branch and a co-investigator in the study, said this extended time of development may be important in strengthening these high-level cognitive circuits. “If the brain matures later, it might be using more complex environmental stimuli,” she said.

The team has done more than 1,000 scans. They have also observed major developmental differences between boys and girls, with girls’ brains maturing between 8 and 18 months earlier than boys. What they have not done yet is link these neural images back to behavior or performance. The researchers were able to predict a child’s IQ by studying the developmental journey, not by measuring the cortical thickness of the adult brain.

Later but smarter

Growth in the cortex, the thinking part of the brain, is delayed in smarter children, according to a long-term study of 307 children.

7 Years Superior intelligence

9 Years High intelligence

13 Years Average intelligence

SOURCES: National Institute of Mental Health; Nature

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Copyright (c) 2006, Newsday, Melville, N.Y.

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