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ADHD 'slows brain growth'

13/11/2007

The brains of young people with attention deficit hyperactivity disorder (ADHD) develop more slowly than those without the disorder, researchers claim.

US scientists found that although brains in people with ADHD develop in a normal pattern in some regions development is delayed by an average of three years.

This delay was most prominent in regions important for the ability to control thinking, attention and planning.

Hyperactivity is shown by over-activity, inattention and impulsiveness occurring at the same time, with ADHD being an extreme form at a level that impairs learning and function.

The researchers discovered that both people with ADHD and those without it had a similar back-to-front 'wave' of brain maturation with different areas peaking in thickness at different times.

They studied brain scans of 446 children taken at least twice at three-year intervals.

Writing in the Proceedings of the National Academy of Science (PNAS), the research team says that half of 40,000 cortex sites (at the brain's outer mantle) in the 223 children with ADHD attained peak thickness at an average age of 10.5 years.

This compares to 7.5 years in the group without ADHD.

Just one area matured faster in children with ADHD: the motor cortex. This contrasts to the late-maturing frontal cortex areas that direct it, suggesting that this mismatch might cause the restlessness common among those with ADHD.

The researchers say the findings should reassure families and explain why many children eventually appear to "grow out" of the disorder.

But they warn that brain scans are not yet capable of diagnosing ADHD.

"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," the researchers conclude.

"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."