Youths with superior IQ are distinguished by how fast the thinking part of their brains thickens and thins as they grow up, researchers at the NIH's National Institute of Mental Health (NIMH) have discovered. Magnetic resonance imaging (MRI) scans showed that their brains' outer mantle, or cortex, thickens more rapidly during childhood, reaching its peak later than in their peers—perhaps reflecting a longer developmental window for high-level thinking circuitry. It also thins faster during the late teens, likely due to the withering of unused neural connections as the brain streamlines its operations.
"Studies of brains have taught us that people with higher IQs do not have larger brains," says NIH Director Elias A. Zerhouni, M.D. "Thanks to brain imaging technology, we can now see that the difference may be in the way the brain develops."