Bipolar kids harbor unique brain trait.

Unlike the brains of adults who suffer from the unrelenting mood swings of bipolar disorder, the brains of children and teenagers diagnosed with this severe mental condition have an unusually small version of the structure associated with learning, memory, and emotion regulation, according to a new brain-scan investigation.

In the largest study of its kind, a team led by psychiatrist Jean A. Frazier of the Cambridge (Mass.) Health Alliance studied 43 youngsters, ages 6 to 16, with bipolar disorder and 20 kids in the same age range who had no mental ailments. Magnetic resonance imaging scanners measured tissue volume throughout each volunteer's brain.

Youths with bipolar disorder displayed lower overall brain volume than their mentally healthy peers did, Frazier and her coworkers report in the July American Journal of Psychiatry. The bipolar group--and its 20 female members in particular--exhibited especially low tissue volume in the hippocampus, an inner-brain region involved in managing emotions. No reduction in hippocampus volume had appeared in prior brain-scan studies of people who first experienced bipolar disorder as adults.

Brain development may occur differently in children with bipolar disorder than it does in people who develop the disorder later in life or not at all, the scientists propose. Disturbed hippocampus growth may underlie some of the unique bipolar symptoms observed in children, suggests psychiatrist Robert M.A. Hirschfeld of the University of Texas Medical Branch in Galveston in an editorial published with the new study. For instance, instead of bouts of escalating euphoria typical of adults with this disorder, children often exhibit severe irritability punctuated by violent outbursts, during which they're nearly impossible to calm.--B.B.