Why Some Kids Are Smarter

A large-scale study of brain development pinpoints the anatomical changes that are linked to IQ.

The brains of more intelligent children appear to develop in a characteristic way, growing quickly over an extended period between the ages of 5 and 12. These findings -- some of the most detailed research on brain development and IQ -- resulted from a 15-year study done by the National Institutes of Mental Health (NIMH.)

The study, which used magnetic resonance imaging (MRI) to gain a detailed picture of how the brains of children change over time, found that in kids who did better on standard IQ tests, the cortex grew thicker and faster and its growth peaked later than among their average peers.

[To view images from the study, click here.] 

Researchers say the findings could help scientists pinpoint genes involved in brain development and IQ levels. It could also give scientists a better picture of normal brain development and shed light on childhood developmental and psychiatric diseases, such as Attention Deficit Hyperactivity Disorder (ADHD.)

"The study shows that there are clear features in brain images that are different for smart children versus average children," says Paul Thompson, a brain-imaging expert at the University of California, Los Angeles (who was not involved in the project). "Now it should become extremely fast to identify some of the main factors that make the brain develop in a healthy way...such as how kids are taught, their diet, their parental upbringing, or...genetics."

Most previous studies of brain development have compared children's brains at a single time in their lives. The new study, published today in the journal Nature, took a broader look, by studying children as they grew. The researchers followed more than 300 children, ages 5 to 19, for a total of 15 years, taking MRI images of their brains at several different times in their development.

The cortex, which is made up of nerve-cell bodies covering the outer layer of the brain, is largely responsible for higher-order brain functions, such as reasoning and perception. All children show the same basic pattern of cortical development: the cortex grows during childhood, and thins in adolescence, as unused neural connections are pruned away.

According to this new study, children with the highest IQs start out with a thinner cortex, which undergoes rapid growth, peaking at around age 12, instead of age 8 or 9 for children who got average scores on IQ tests. "Children with the most agile minds have the most rapidly changing cortex," says Philip Shaw, a child psychiatrist at NIMH who led the research.