MONDAY, Nov. 12 (HealthDay News) -- While some regions of the brain mature a few years late in youngsters with attention deficit hyperactivity disorder (ADHD), their brains do develop in a normal pattern, concludes a study by researchers at the U.S. National Institute of Mental Health (NIMH).

They found that the delay in brain maturation in children with ADHD was most prominent in regions at the front of the brain's outer mantle (cortex), which is involved in thinking, planning and attention.

Magnetic resonance imaging (MRI) scans of the brains of 223 children with ADHD revealed that half of 40,000 cortex sites attained peak thickness at an average age of 10.5, compared to age 7.5 in a group of children without ADHD.

However, both youngsters with ADHD and those without the disorder showed a similar back-to-front progression of brain maturation with different regions peaking in thickness at different times.

"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," research team leader Dr. Philip Shaw, of the NIHM Child Psychiatry Branch, said in a prepared statement.

The study was published this week in the online edition of the journal Proceedings of the National Academy of Sciences.

These findings support the theory that ADHD is caused by a delay in cortex maturation, the researchers said. They plan to investigate the genetic roots of this delay and methods of promoting recovery from ADHD.

More information

The Nemours Foundation has more about ADHD.