The brains of very intelligent children appear to develop in a distinctive and surprising way that distinguishes them from less intelligent children, a federal study reported Wednesday.
The study is the first to try to measure whether differences in brain development are linked to intelligence, said researchers at the National Institute of Mental Health, who did repeated brain scans on 309 healthy children between ages 6 and 19.
The scans showed that children with the highest IQs began with a relatively thin cortex -- the folded outer layer of the brain that is involved in complex thinking -- that rapidly grew thicker before reaching a peak and then rapidly becoming thinner, said Philip Shaw, the lead investigator. Children of average intelligence had a thicker cortex around age 6, but by around 13 it was thinner than in children of superior intelligence.
The study is the most definitive finding to date of a relationship between the physical characteristics of the brain and intelligence.
"Studies of brains have taught us that people with higher IQs do not have larger brains," said Elias Zerhouni, director of the National Institutes of Health, in a statement, but "thanks to brain imaging technology, we can now see that the difference may be in the way the brain develops."
"I was surprised that the relationship between intelligence and brain structure changed so much as a child grows up," said Shaw. "In early childhood, the smartest children had a thinner cortex -- this is the opposite of what you'd expect. By late childhood, the pattern had changed completely."
The cortex has long been known to get thinner in late adolescence, presumably because the brain prunes cells, neurons and connections that are not being used. The new study found that the cortex continued to thicken in gifted children until around age 11 or 12, much later than in children of average intelligence, whose cortex thickening peaked by age 8.
"It's almost like the most agile minds have the most agile cortex," Shaw added.
The study, being published today in the journal Nature, does not suggest any particular interventions that might boost a child's intelligence, but Richard Davidson, a brain imaging expert at the University of Wisconsin at Madison, said the fact the region of the brain being studied is highly malleable suggests that experience and environmental cues may play a very important role in shaping intelligence.