The brains of children with attention deficit hyperactivity disorder develop more slowly than those of other children but eventually catch up, according to a government study published Monday that suggests ADHD might be a transient condition, at least for some people.
Using advanced imaging techniques, scientists found that the cortices of children with ADHD reach peak thickness an average of three years later than children without the disorder.
The cortex is involved in decision-making and supports the ability to focus attention, remember things moment to moment and suppress inappropriate actions – functions often deficient in children with ADHD.
Dr. Philip Shaw of the National Institute of Mental Health, lead author of the report published in Proceedings of the National Academy of Sciences, said the results could help explain why many children with ADHD appear to grow out of the disorder and become less impulsive and fidgety as they mature.
Shaw said that although brain development was slower in children with ADHD, it followed a normal pattern, which should reassure parents.
“There has been a debate about whether ADHD is a delay or deviance from normal brain development,” he said. “This study comes down strongly in favor of delay.”
Researchers used magnetic resonance imaging equipment to scan the brains of 223 children and adolescents with ADHD and 223 youngsters without the disorder. The scans were repeated two, three or four or more times at three-year intervals.
Dr. F. Xavier Castellanos of New York University said the research helps explain why children with ADHD often choose younger playmates and should reassure parents who are worried about their children fitting in.
“They may be 11 but their brain is 8. They can’t act their chronological age. This lets parents know that having younger playmates is OK and to be expected,” said Castellanos, a former National Institute of Mental Health researcher involved in the early stages of the study.
The study, which focused on one aspect of brain development, did not explain why some people continue to experience ADHD symptoms as adults.
Dr. Bradley S. Peterson of Columbia University, who was not connected to the study, said that although the brains of children with ADHD reached the appropriate thickness, there was no way of knowing from the study whether individual cells were normal.
In addition, he said, the study did not examine the process of cortical thinning that takes place in late adolescence – a second developmental milestone in which unneeded connections are pruned to shape the adult brain.
Government researchers plan to continue tracking some study participants through adulthood, Shaw said.