Scientists have found/ that brain growth/ in very intelligent children/ is different/ from that in other children. They say/ their study/ is the first/ to show a link/ between intelligence and brain development.

Researchers/ from the National Institute of Mental Health/ and Canada's University of McGill/ did the study. The findings/ appeared/ in the magazine Nature.

The researchers say/ they found developmental differences/ in the cerebral cortex. This is the outer part/ of the brain, often called/ the gray matter. The cerebral cortex/ plays some part/ in almost all brain activity. The researchers call it/ the “thinking” part of the brain.

The cortex/ goes through a process of development/ in which it thickens and thins/ as children grow up. But the researchers say/ the cortex/ reaches its thickest/ at a later age/ in highly intelligent children.

The study/ followed just over three hundred young people, ages five to nineteen years old. They were divided/ into three levels/ of intelligence: average, high and superior. They took traditional intelligence tests/ to measure their I.Q., their intelligence quotient.

Many experts say/ I.Q. levels/ change little/ over time. The value of I.Q. testing itself, however, is widely debated.

The children in the study/ were tested only once/ as they grew up. The scientists/ also took pictures/ of the children’s brains/ as they got older. They used magnetic resonance imaging. Most of the children/ got at least two M.R.I.’s, two years apart, during the study.

Study researcher Judith Rapoport/ says/ I.Q./ is related to cortex development, not to the amount of gray matter/ at any one age.

The researchers say/ the smartest children/ generally started with a thinner cortex. But it grew faster/ than the cortex of the average children. It also thickened/ over a longer period of time.

The researchers say/ the children/ in the average group/ completed the process/ by eight years of age. But thickening of the cortex/ continued in the most intelligent children/ until they were eleven or twelve. One possible explanation/ is that their brain had more time/ to develop high-level thinking abilities.

The children/ in all three groups/ did have something/ in common. Their cortex/ began to thin/ by their teen years. But during the late teen years, the smartest children/ had the fastest rate of thinning.

Thinning of the cortex/ is believed to represent the loss/ of unused brain cells, neurons and connections/ as young people become adults.

Philip Shaw/ led the study team. He says/ people with a more active mind/ generally have a more active cerebral cortex. But he also says/ intelligence/ is probably a complex mix/ of the brain/ a person is born with, and what it experiences/ in life.