The brains of children with attention deficit hyperactivity disorder (ADHD) develop comparatively slower than other youngsters' brains, a new study says. The study found that there are developmental delays of up to three years in regions of the brain that suppress inappropriate actions and thoughts, attention focus, immediate memory, work for reward and control movement.

The findings, which were reported in Monday's edition of Proceedings of the National Academy of Sciences, were based on brain scans of children aged 6 to 16 who had the common psychiatric disorder.

Lead author Dr. Philip Shaw of the National Institute of Mental Health said, "Finding a normal pattern of cortex maturation, albeit delayed, in children with ADHD should be reassuring to families and could help to explain why many youth eventually seem to grow out of the disorder."

The researchers are now working to determine if all children outgrow the disorder or not, and what are the longterm effects.

Apart from the timing of maturation, the brains of children with ADHD appear to develop the same way typical brains do, from back to front. Between 3 percent and 5 percent of school-age children are thought to have the disorder.

"Although the delay in cortex development was marked, it could only be detected when a very large number of children with the disorder were included. It is not yet possible to detect such delay from the brain scans of just one individual," Shaw said. "The diagnosis of ADHD remains clinical, based on taking a history from the child, the family and teachers."