The brains of children with attention deficit hyperactivity disorder (ADHD) mature in a normal pattern, finds a new study. But that maturity is delayed three years in some brain regions, compared to kids without the disorder.
Dr. Philip Shaw, with the Child Psychiatry Branch at the National Institute of Mental Health in the U.S., used new MRI image analysis techniques to allow his team to pinpoint the thickening and thinning of thousands of sites along the brain's cortex, the outermost layers of the brain.
They looked at 223 kids diagnosed with ADHD, and 223 without the disorder. They found that among the children without ADHD, half of 40,000 cortex sites attained peak thickness at an average age of seven-and-a-half. But in the kids with the condition, the cortex sites didn't reach peak thickness until-10-and-a-half.
The delay in brain development in kids with ADHD was most prominent in regions at the front of the brain. Those areas support the ability to focus attention, remember things from moment to moment, suppress inappropriate actions and thoughts, work for reward, and control movement -- functions that are often disturbed in people with ADHD.
One of the last areas to mature, the middle of the prefrontal cortex, lagged five years in those with ADHD.
The only area that matured faster than normal in kids with ADHD was the motor cortex, the area of the brain that controls motor function. This mismatch might account for the restlessness and fidgety symptoms common among those with the disorder, the researchers suggested.
The researchers say the delayed pattern of brain maturation they observed in kids with ADHD is the opposite of that seen in those with other developmental brain disorders such as autism. In that disorder, it appears that the volume of brain structures peak at a much earlier-than-normal age.
The authors say the fact that the cortexes of the brains of kids with ADHD do eventually mature in a normal pattern -- even if it is delayed -- is reassuring. It could also help to explain why many kids with ADHD eventually seem to grow out of the disorder.
Dr. Alan Evans, a lab director of clinical trials and imaging at the Montreal Neurological Institute and Hospital, said the study offers good news, but parents of ADHD kids should still be cautious.
The institute had a key role in the study, using a recently activated brain imaging database to help collect the study data.
"I don't want to give the impression that everything will catch up in all children. Some ADHD kids improve and their symptoms ameliorate as they grow to adulthood and some don't," Evans told CTV's Canada AM.
He said there is a critical point when different parts of the brain begin to communicate with each other. If the brain is not mature at the point when that communication is beginning to happen, the child may not catch up, Evans said.
"About 50 per cent or so of ADHD kids do improve and get over the symptoms and some don't so I don't want to overstate the case."
The researchers hope next to find the genetic underpinnings of the brain maturation delay, as well as ways of boosting processes of recovery from the disorder.
The study appears in the latest issue of the Proceedings of the National Academy of Science.
