Researchers have for the first time identified a brain abnormality associated with hyperactivity, the disorder that causes up to 5 percent of children to be restless, inattentive and often disruptive in the classroom.
Using a highly sensitive imaging technique to observe the activity of brain cells, psychiatrists from the National Institute of Mental Health found decreased activity in the portions of the brain that are involved in control of attention and motor functions.
Their results, to be reported today in the New England Journal of Medicine, "represent a clear advance in our understanding" of hyperactivity, said psychiatrist Gabrielle Weiss of Montreal Children's Hospital in an editorial in the same journal.
"It's exciting because it gets us much closer to more effective treatment," said Frederick K. Goodwin, head of the federal Alcohol, Drug Abuse and Mental Health Administration.
The results will also help to explain why the stimulant Ritalin can, paradoxically, calm the children and improve their attention span. Eventually, the studies could also lead to development of better drugs for the disorder, as well as to new ways to diagnose it -- a task that is often very difficult.
Hyperactivity, which is now formally called attention deficit-hyperactivity disorder, is the most common psychiatric disorder of childhood, afflicting from 2 percent to 5 percent of all youngsters. It usually begins before the child reaches school age and affects boys about eight times as often as girls.
Some previous evidence suggests that it is at least partially genetic in origin. As many as 60 percent of hyperactive children continue to display the symptoms in adulthood.
About 25 percent of hyperactive children have specific learning disabilities, and an additional 40 percent exhibit a pattern of starting fights, stealing and lying, or of disobedience, defiance and rule-breaking.
Between 70 percent and 80 percent have their symptoms alleviated by taking the stimulant Ritalin, the most common form of therapy.
Psychiatrist Alan J. Zametkin and his colleagues at the National Institute of Mental Health studied 25 adults who were mildly hyperactive and 50 normal adults using a technique called positron emission tomography, or PET. The researchers injected sugar molecules labeled with a radioactive isotope into the subject's bloodstream and used the PET scan to monitor the way brain cells use the sugar.
Dr. Zametkin and his colleagues found that the brains of the hyperactive adults used, on average, 8.1 percent less sugar than those of the normal controls, indicating that the brain cells were 8.1 percent less active. The largest reductions in activity were found in regions called the pre-motor cortex and the superior pre-frontal cortex -- regions involved in the control of attention and motor activity.
Dr. Zametkin cautioned that his studies involved a very select group of patients: adults with mild hyperactivity who have never taken Ritalin and who have a hyperactive child themselves.
The researchers are now studying teen-agers with no family history of hyperactivity in order to determine whether the results can be extended to all types of patients.