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A brain imaging study has pinpointed exactly where the brains of children with attention deficit hyperactivity disorder differ from those of other children. Researchers say the finding could one day lead to better drugs and behavioral interventions to treat kids with ADHD.

Earlier studies have shown that children with ADHD tend to have brains that are slightly smaller than normal, and researchers have long suspected that the disorder is caused by a dysfunction in the frontal lobes of the brain, which control emotions and impulses.

The new study, published in the Nov. 22 issue of the journal The Lancet, is the most detailed look at the brains of kids with attention deficit hyperactivity disorder ever undertaken.

Investigators at UCLA used magnetic resonance imaging (MRI) to compare the brains of 27 children with ADHD to those of 46 children without the disorder. They found that the region of the brain associated with attention and impulse control, located on the bottom of the frontal lobes of the brain, was smaller in the ADHD kids than in the other children.

"We would expect that the abnormalities would be in this region, and this is what we found," lead investigator Elizabeth Sowell, PhD, tells WebMD. The researchers also found that children with ADHD had larger areas of the outer layers of the brain.

Previous research has indicated that the differences were limited to the right side of the brain, but Sowell and colleagues found that they occurred on both sides.

Sowell says pinpointing the exact location associated with ADHD could help in the development of new drugs for the treatment of the disorder. Child psychiatrist and senior investigator Bradley S. Peterson, MD, says brain imaging may also allow clinicians to better utilize the therapies that are already in use.

"One of the next steps is to see if these brain differences are predictive of treatment responses," he tells WebMD. "I think it is reasonable to assume that this will be the case. Imaging may help us predict who is going to respond to certain kinds of treatment."

ADHD symptoms disappear with age in some children, but not others. Peterson says brain imaging may also prove useful for distinguishing between the two. He says studies to test all of these theories are planned.

Agence France Presse, 11/20/03

Attention deficit hyperactivity disorder (ADHD), a little-understood condition that affects children, has been pinned to abnormalities in key parts of the brain's prefrontal cortex.

In the first large study to map cerebral areas that have been linked to ADHD, US doctors found that in children with this problem two parts of the brain known as the dorsal prefrontal and anterior temporal regions of the cortex were smaller than they should normally be.

Two other zones, known as enlarged posterior temporal and inferior parietal cortices, were larger.

These are strongly interconnected parts of the brain that help to process working memory, figure out time and inhibit impulses.

The findings suggest "this action-attentional network is anatomically disrupted in children who have attention-deficit hyperactivity disorder," the researchers report in next Saturday's issue of the British medical weekly The Lancet.

Twenty-seven children and adolescents diagnosed with ADHD took part in the study, and their brains were compared with those of 46 healthy counterparts.

Previous studies have suggested that there is a small reduction in brain volume, of between three and five percent, among children with ADHD compared with their counterparts.

But this is the first large-scale research to use magnetic resonance imaging (MRI) scanners to get an idea as to where, more precisely, the problem may lie.

ADHD is a recently-defined neuropsychiatric disorder. Children with it have trouble concentrating, keeping still and observing discipline, and often as a result do very poorly at school.

Between three and six percent of American schoolchildren have this condition, according to the authors, led by Elizabeth Sowell, assistant professor of neurology at the University of California, Los Angeles.

The cause of ADHD is unclear, but the frequent method of treatment is psychostimulants, a class of powerful drugs that is a stimulant in adults but in children has a calming effect. These medications can also have big side effects.

One of the useful consequences of the latest research would be to fine-tune these drugs so that they can specifically target affected parts of the brain, said co-author Bradley Peterson, a professor of psychiatry at New York's Columbia University.