Neuroscientists have long suggested that intelligence is related to some aspects of brain anatomy, with the size of the cortex (the outer part of the brain) thought to be the most likely feature to correlate positively with intelligence. However, according to a recent study, the way the cortex develops over time is a much better predictor.
Smart People Have Agile Brains
In a longitudinal study published in the March 30 issue of Nature, Philip Shaw and colleagues at the U.S. National Institutes of Health and the Montreal Neurological Institute in Canada used magnetic resonance imaging (MRI) to measure changes in cortical thickness in the brains of more than 300 children and teenagers over a period of about 10 years. The scientists obtained brain scans several times during this period from the participants, whose intelligence also was measured using standardized intelligence quotient (IQ) tests.
Although IQ is but one of many measures used to quantify higher brain function, there is some evidence that it is a valuable index that can predict future academic performance and occupational success.
There were no significant differences in the size of the cortex among subjects with various IQ levels, and everyone showed the same basic pattern of cortical growth throughout most of the brain, Shaw says: “The cortex initially got thicker, peaked, and then got thinner.”
However, the researchers also found that the rate of these changes differed markedly in the children studied, depending on how intelligent they were.
“In the most intelligent kids, the cortex started out very thin; got thicker very quickly, reaching its peak thickness relatively late; and then also got thinner very quickly,” Shaw says. “Children of average intelligence had the same pattern, but all of the changes were slower,” he adds.
Shaw says these results indicate that intelligence is related not to the size of the cortex but to the dynamics of how the brain develops. “It’s [as though] those with the most agile minds have the most agile cortex,” he says.