Monday, May. 05, 1997
ANATOMY OF MELANCHOLY
By Christine Gorman
The images were so striking that researchers repeated the experiment three times just to make sure they had done it right. But each new set of pictures only confirmed what the previous ones had shown: that one portion of the brain is significantly smaller and less active in people suffering from hereditary depression. "Most of the time the differences we find in the brain are very subtle," says Dr. Wayne Drevets, who led the team of scientists from Washington University in St. Louis, Missouri. "To see something stand out to this degree is remarkable."
It may turn out to be the most detailed snapshot ever taken of the depressed mind, showing where melancholy is mapped on the gray matter of the brain. Writing in last week's Nature, Drevets and his co-workers reported that they had zeroed in on a tiny, thimble-size nodule of the brain located about 2 1/2 inches behind the bridge of the nose. Other scientists had already shown that this section of the brain, called the subgenual prefrontal cortex, plays an important role in the control of emotions. But Drevets, who has since moved to the University of Pittsburgh, discovered that it could also be the trigger point for both bouts of paralyzing sadness and the wildly euphoric highs of manic depression. "This area of the brain may act as a set of brakes for emotional responses," he explains. "When it does not function properly, abnormal swings in mood may occur."
The image was produced in a two-step process. First the researchers used pet scans, which measure how well cells are functioning, to probe the brains of dozens of people in the active throes of depression. Then they merged the results and compared them with those from a comparable number of normal patients. The pet scans showed a subtle but distinct difference: the subgenual prefrontal cortex was almost 8% less active in depressed patients than in the controls.
This gave scientists a target on which to focus their research. They began scanning that part of the brain with MRI technology, which uses subtle magnetic changes to capture the internal structure of organs in exquisite detail. To their surprise, they discovered that there was on average 39% to 48% less brain tissue in the affected region of depressed patients. Drevets speculates that the deficit may result from the catastrophic loss of a particular subset of brain cells, which his co-workers are trying to identify.
At the moment there's no way doctors can use the new research to identify people at risk of mental illness. There is just too much normal variation in the sizes of the structures within the brain. But this latest finding should help researchers understand exactly what goes wrong when the brain is overwhelmed by hopelessness and, perhaps one day, help prevent the millions of Americans who may have inherited a propensity to depression from falling into the downward spiral of despair.
--By Christine Gorman