Node emerges on brain's emotional network.

Scientific teams armed with high-tech imaging devices are enmeshed in a search for interconnected brain structures that coordinate emotion and influence the emergence of mood disorders. One part of this network lies near the front of the brain, adjacent to the bundle of nerve fibers that connects the cerebral hemispheres, a new study finds.

This region, situated within a neural locale called the prefrontal cortex, exhibits signs of sluggish activity during bouts of major depression and evidence of heightened activity during periods of manic euphoria and restlessness, contend psychiatrist Wayne C. Drevets of the University of Pittsburgh Medical Center and his coworkers in the April 24 Nature.

Moreover, the left hemisphere volume of this prefrontal site drops sharply in people suffering from major depression or manic depression, compared to folks free of past and current mental disorders, the group reports.

Prefrontal tissue loss of this magnitude reflects either disturbances in brain development or the ravages of repeated, extreme mood shifts, the researchers theorize. In either case, the resulting communication breakdown between this prefrontal location and other brain structures involved in emotion-such as the amygdala-distorts emotional responses and social decisions, they argue.

For example, a cerebral scenario of this type may contribute to the intense guilt and anxiety over one's actions often seen in people with major depression.

"This new finding is consistent with an evolving body of data that is defining an elaborate brain network involved in mood regulation," remarks psychiatrist Helen S. Mayberg of the University of Texas Health Science Center at San Antonio.

Mayberg and her colleagues have found that neural activity in the same general prefrontal segment noted in Drevets' study varies according to whether or not depressed individuals benefit from antidepressant drugs (SN: 3/8/97, p. 141).

Drevets and his colleagues studied positron emission tomography (PET) images and found a prefrontal area with reduced blood flow in the brains of 11 people with manic depression, compared to 39 individuals who had no history of severe psychiatric disorders. A higher-resolution PET camera then enabled the scientists to locate the site of the most severe drops in prefrontal blood flow in 7 additional volunteers with manic depression, compared to 12 more controls.

High-resolution PET scans also enabled the team to identify comparable prefrontal blood flow drops in 10 people diagnosed with major depression, Drevets' team asserts. At the time of testing, all participants with a mood disorder cited moderate to high levels of depression; none had received any psychoactive drugs for at least 4 weeks.

Preliminary PET data from four people in the manic phase of manic depression indicate that neural activity in the critical prefrontal region exceeds that observed in controls.

Another brain-viewing technique, magnetic resonance imaging, revealed marked volume reductions in the prefrontal area's left side for all the depressed volunteers, whether diagnosed with major depression or manic depression.

These findings delineate with unprecedented precision one component of a brain system that organizes emotional responses to complex personal and social situations, writes neuroscientist Antonio R. Damasio of the University of Iowa College of Medicine in Iowa City in an accompanying comment.