A new study confirms earlier findings that children and adolescents with attention deficit hyperactivity disorder have smaller brains than those without the disorder.
The study, “Developmental Trajectories of Brain Volume Abnormalities in Children and Adolescents With Attention- Deficit/Hyperactivity Disorder,” is available to subscribers or for a fee from the Journal of the American Medical Association.
But medication, given the blame previously in some quarters for the brain-size difference, is not the culprit, the report published last week says.
When previous studies reported structural brain differences in children with ADHD, some contended that drugs such as Ritalin given to treat the disorder stunted brain growth. The new research is the first major study to exonerate the drugs.
Researchers from the National Institute of Mental Health found that children and adolescents with ADHD had brains that were 3 percent to 4 percent smaller than those of youths without the disorder. The size difference occurred in the brains of both children who were taking stimulant drugs and those who never received medication, according to the study, which appears in the Oct. 9 issue of TheJournal of the American Medical Association.
Dr. Judith L. Rapoport, the chief of the child-psychiatry branch of the NIMH and a researcher on the study, said the results should be good news for educators embroiled in controversies over ADHD and its treatment.
“The main message is that there is a strong biological part to what causes ADHD,” Dr. Rapoport said. “We have no reason to think that stimulant drugs are harmful. We went out of our way to get kids without medication so we could reassure people.”
About 2 million school-age youngsters have ADHD, according to the NIMH. The condition can interfere with a child’s education because it causes hyperactivity, short attention spans, and impulsive behavior.
Between 1991 and 2001, the team of NIMH scientists used magnetic resonance imaging to look at the brains of 152 boys and girls with ADHD who were between the ages of 5 and 18. They compared the results with those for 139 children in the same age group who did not have the disorder. Researchers scanned the brains of some participants up to four times over the course of the decade to chart their brain development.
The children with the most severe cases of ADHD also showed the biggest differences in the sizes of certain areas of their brains. The study found that children with ADHD had a smaller volume of white matter, or fibrous nervous-system tissue. But the white matter increased with the children’s age.
Researchers noted the largest size difference in the cerebellum, the part of the brain involved in muscle tone, balance, and muscle activity.