In Brief

Do the brains of people with attention-deficit hyperactivity disorder (ADHD) develop in abnormal ways, or is their development just delayed? New results from brain-imaging studies published in the November online edition of the Proceedings of the National Academy of Sciences suggest the latter, and also point to developmental patterns that could explain the impulsive behavior characteristic of people with the disorder.

Philip Shaw, MD, a psychiatrist at the Child Psychiatry Branch of the National Institute of Mental Health, led the team, which studied 220 children diagnosed with ADHD over a 15-year period. Using magnetic resonance imaging (MRI), the researchers tracked changes in the cortical thickness of the participants' brains. Normally, cortices reach a peak thickness at around age 7 or 8, and then get thinner as the child matures. But in children with ADHD, the researchers found, this peak thickness doesn't occur until around age 10.

Importantly, though, the overall pattern of development was the same, pointing to developmental delay in ADHD, not abnormal development. However, Shaw and his team found that children with ADHD did hit one developmental milestone slightly earlier than normally developing children: maturation of the motor cortex, which regulates voluntary muscle movements. That, combined with the fact that development in the brain's frontal cortex-the center of self-control-is delayed in ADHD, may explain some of the fidgeting and restlessness common in children with the disorder, says Shaw.

Although these results are promising, Shaw says MRI won't be used as a diagnostic tool anytime soon. But in the future, this brain imaging may help bring ADHD into clearer focus.

"I think in the future, [brain] imaging will help with tailoring treatments for people with ADHD and for refining our knowledge about how it develops," Shaw says.

--M. Price