CHICAGO -- Hyperactive children and teens have slightly smaller brains than those without the disorder, a study shows.
Exactly why this is so is not clear, but the researchers said the smaller brain volume does not appear to be related to the use of hyperactivity drugs such as Ritalin, as some parents had feared.
The finding could be reassuring to parents in another respect as well: It suggests that hyperactivity is biological in origin, not a product of bad parenting.
The researchers said it appears that that the brains of hyperactive children develop at a normal pace but never entirely catch up in size with the brains of other youngsters. However, they said that people with smaller brains are not necessarily less intelligent.
The findings were reported in Wednesday's Journal of the American Medical Association.
Other studies also have suggested biological differences in the brains of people with attention deficit hyperactivity disorder.
"It's strong support for a very strong biological contribution to what causes ADHD," said one of the researchers, Dr. Judith Rapoport, chief of child psychiatry at the National Institute of Mental Health in Bethesda, Md.
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