UCLA researchers have obtained the first direct evidence that successful behavioral therapy for a relatively common form of mental illness can produce the same type of changes in brain circuitry that are observed with successful drug therapy.

The discovery has two major implications for the future treatment of a variety of mental disorders, including depression, experts said. First, a growing number of studies are showing that each disorder may have a characteristic pattern of brain activity that could allow easier diagnosis of the problem. Perhaps more important, the new study shows that successful treatment causes specific changes in mental activity, providing the opportunity for objective assessment of treatment success.

In the new study, the changes were found in the brains of people with obsessive-compulsive disorder, an incapacitating illness that affects as many as 4 million Americans and is characterized by unwanted thoughts and uncontrollable obsessions, such as the repeated washing of hands. One-third of the sufferers are children and adolescents.

Researchers have previously shown by sophisticated imaging techniques that the disorder is linked to excess activity in the right caudate nucleus, which serves as a thought-regulating center in the brain. Recently, Dr. Lewis Baxter and his colleagues at UCLA have found that this over-activity disappears when the disorder is brought under control with drugs.

Baxter reports today in the Archives of General Psychiatry that identical reductions in excess caudate activity are observed when the patients undergo successful behavioral therapy. This study "is a startling confirmation of what 'ought to be,' " said Dr. Daniel X. Freeman, a UCLA psychiatrist who is editor of the journal.

"Disordered behavior and altered brain function should not be a surprise, nor should shifts with effective treatments be," Freeman said. "But they are actually visible here for the first time."

"This is really terrific," added Dr. Thomas R. Insel, a behavioral neuroscientist at the National Institute of Mental Health. Some researchers had argued that Baxter's earlier findings of decreased activity after pharmacotherapy were either a coincidence or an unanticipated byproduct of the drug's action. "This paper makes it quite clear that that . . . possibility can be ruled out" and that the change is indeed due to therapy itself."