ADHD May Be Just a Developmental Delay for Most Kids

Researchers at the National Institute of Mental Health published research in November 2007 showing that the brains of children with ADHD mature more slowly than, but in the same manner, as the brains of kids, without ADHD.

In other words, an 11-year-old with ADHD has a brain that is more similar to a non-ADHD 8-year-old than with peers, which may explain why kids with ADHD often feel more comfortable around playmates who are younger than themselves.

In ADHD-affected brains, the parts of the cortex most strongly associated with decision-making, attentiveness, short-term memory, and impulsiveness took the longest to develop.

However, the parts of the cortex associated with motor skills actually matured faster in ADHD kids than the control group. This may be one reason that kids with ADHD have higher activity levels and are more fidgety than kids without ADHD. Their brains are more tuned for movement and action than others their age but they have less ability to control themselves.

"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," explained research leader Philip Shaw, M.D., of the NIMH Child Psychiatry Branch.

Over three years, Shaw's team used magnetic resonance imaging (MRI) to scan and track the changes in the brains of 223 youth with ADHD and 233 kids without the disorder. The researchers scanned most of the 446 participants - ranging from preschoolers to young adults with an average age of about 11 - at least twice and up to four or even more times during the research period.

The scientists used the scans to measure the thickness of the brain's cortex. As the brain builds the connections that allow children to process and store information, the cortex thickens and grows. The thicker the cortex, the more processing power.

"Brain imaging is still not ready for use as a diagnostic tool in ADHD," noted Shaw. "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. The diagnosis of ADHD remains clinical, based on taking a history from the child, the family and teachers."

In future studies, the researchers hope to find the genetic causes for the delay and find ways to help stimulate the process. They are also hoping to continue studying the brains of some of the participants as they move into adulthood.

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