The ancients called it the vagus ("wandering") nerve because it extended from the brain down through the body, but its name had another connotation: No one knew exactly what it did. While modern doctors know it mediates between various organs and the brain, they still aren't sure how many functions it's responsible for, and sometimes it surprises them. In 1997, vagus-nerve stimulation was granted FDA approval for epilepsy patients who failed to respond to drug treatments. The "pacemaker for the brain" is a stopwatch-size stimulator implanted under the clavicle, where it shoots an electrical charge through a wire and into the vagus nerve in the neck anywhere from every few seconds to once every ten minutes, preventing half the seizures in more than half the patients who use it for up to a year.

But Dr. Douglas Labar, director of Cornell's Comprehensive Epilepsy Center, and his partner, Dr. Cynthia Harden, an associate professor of neurology, noticed an interesting side effect: It had a mood-lifting impact. Last month, the results of a twelve-week pilot study of the VNS's effect on patients suffering from severe depression were announced: Fifteen of the 30 patients involved showed a 50 percent improvement. In recent animal tests, VNS treatment also led to weight loss. How much can one long nerve do? "In terms of the places it connects to," says Labar, "we have too many possibilities."

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• Articles by Boris Kachka
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