Brain images delve into hyperactivity.

Two new brain-scan studies, both published in the May AMERICAN JOURNAL OF PSYCHIATRY, offer a mix of puzzling and intriguing evidence about the biology of hyperactivity.

Adults suffering from hyperactivity, dubbed attention-deficit hyperactivity disorder (ADHD) by psychiatrists, improve after treatment with stimulant medication but display no accompanying changes in brain activity, report John A. Matochik of the National Institute of Mental Health (NIMH) in Bethesda, Md., and his colleagues.

The ways in which these drugs affect the brains of people with ADHD remain elusive, the researchers add.

However, areas at the front of the brain implicated in the control of relatively automatic motor responses may malfunction in ADHD, NIMH psychiatrist Jay N. Giedd and his coworkers assert in the second study. An inability to rein in such behaviors at appropriate times, rather than inattention, may lie at the core of the disorder, they propose.

Matochik's group administered one of two stimulants to 21 men and 16 women, all diagnosed with ADHD. Each participant received two positron emission tomography (PET) scans, the first before drug treatment began and the second after 6 to 15 weeks of daily medication. PET scans measured glucose metabolism, which indicates how hard various parts of the brain are working.

At the end of the trial, two-thirds of the volunteers showed markedly less restlessness and much improved attention, the investigators say. Yet PET scans revealed no differences in glucose metabolism between those helped by medication and the remainder, whose condition stayed about the same.

"These findings may strengthen the voice of those who have taken the position that adult ADHD is an important cause of unrecognized and untreated distress," writes David Shaffer, a psychiatrist at the New York State Psychiatric Institute in New York City, in the same journal.

But Shaffer emphasizes caution in diagnosing and treating adult ADHD. Other studies suggest that symptoms of childhood ADHD often decrease sharply by adulthood (SN: 7/31/93, p.70). Hyperactive adults also tend to suffer from other mental disorders, such as substance abuse, that may wreak the greatest havoc on their lives, Shaffer maintains.

Most studies of stimulant treatment for adult ADHD -- including the new report -- fail to use placebo controls, involve small numbers of volunteers, and measure only concentration and physical activity rather than broader aspects of social functioning, he adds.

Giedd and his colleagues used magnetic resonance imaging (MRI) scans to examine the corpus callosum -- a bundle of nerve fibers that runs between the brain's two hemispheres -- in 18 boys with ADHD and 18 boys free of neurological and psychiatric problems.

Two regions at the front of the corpus callosum were markedly smaller in the ADHD group, the scientists report. Fibers in these areas connect to parts of the brain involved in suppressing automatic bodily responses that create problems in certain situations, they argue. For instance, these structures may mediate a young student's ability to quell the impulse to fidget during class so that he can play at recess.

A smaller corpus callosum may also reflect communication problems between brain hemispheres, Giedd's group adds.

Further imaging studies of people with ADHD should look throughout the brain, they say, with a focus on regions linked to the front of the corpus callosum.

"It is doubtful that a single 'lesion' will be found to account for all of the complicated and varied symptoms of ADHD," the researchers note.