A group of Stanford researchers headed by John Barry may have discovered a new treatment for depression, a pacemaker for the brain. Doctors now believe that a device known as the vagus nerve stimulator, previously used to fight epilepsy, could help an estimated one million Americans with depression that is unresponsive to drug therapy.

“The vagus nerve is sometimes described as a superhighway into the brain,’’ said group co-director Dr. Charles DeBattista.

DeBattista explained in a March 6 San Jose Mercury News article that the pulses created by the vagus nerve stimulator travel through the body to many areas of the brain, including the limbic system, a region thought to have an important role in regulating emotion.

Researchers uncovered the device’s additional benefits in 1998, when epilepsy patients in a study reported mood improvements. These reports triggered Cyberonics, the Houston company that manufactures the stimulator, to launch a program to test it on 30 patients with drug-resistant depression.

After three months, according to results published in last year’s Biological Psychiatry journal, about half the patients showed vast improvements on two common standardized tests used to evaluate depression.

Despite these test results, doctors still do not fully understand how the vagus nerve stimulator works, but the results will likely help researchers understand the nature of depression, said Dr. John Barry, one of the overseeing Stanford psychiatrists, in the San Jose Mercury News article.

“One of the exciting things about this is, once you get something new that works, you learn a little more about the disease you’re treating,’’ he said. “I hope it will allow us to understand more about depression, and maybe even other diseases as well.”

The stimulator consists of an Oreo cookie-sized battery pack and a thin wire. Patients have the device surgically implanted under the collarbone, with a wire threaded up into the neck and wrapped around the left vagus nerve. The device sends out a 30-second stream of impulses every five minutes.

Researchers at Stanford installed the first vagus nerve stimulator in October of last year. Eventually, 200 people at 20 centers across the country will participate in tests, which are funded by Cyberonics.

Lauri Sandoval of Santa Fe, N.M., was one of the first to receive the new treatment. Sandova, who is 42, was diagnosed with depression at age 20, after her first suicide attempt. She remained depressed despite 15 years of psychotherapy and at least two dozen medications, sometimes three or four at a time.

In the San Jose Mercury News,, Sandoval said depression destroyed her ability to focus, and that she withdrew from the world. She said that, eventually, she had to resign from her job.

“My depression was so bad I could barely function,’’ she said. That’s when she heard about the stimulator study. She said she enrolled and recognized improvements about three months after she had the device implanted.

“When I had enough energy to plant a garden or walk my dogs, that’s when I noticed,’’ Sandoval said. She began “being interested in things again.’’

Researchers said that the vagus nerve stimulator has few side effects.

“The most common side effect is hoarseness in the voice that’s there when the stimulator is on,” Barry said. “But some people don’t notice anything at all.’’

Researchers also believe that the treatment will become more effective with time. Barry explained that many patients have continued to improve since the study’s publication, and several others, who did not initially react, have started to show promising signs.

“With the stimulator, we’re hoping that people will continue to improve over the years and won’t relapse,’’ Barry said.