Rather than targeting the brain directly in humans, Kilgard turned to the vagus nerve, part of the nervous system that connects the stomach, liver, and other organs to the brain. Implanted devices that stimulate the vagus nerve are currently approved to treat depression and epilepsy and are being tested for other disorders.

Researchers plan to test the concept in people with tinnitus in upcoming clinical trials in Belgium. Kilgard says the researchers will use simple electrodes, which are implanted at the neck and stimulated with an external device. While the exact parameters are still to be determined, patients will undergo treatment for half an hour to an hour each day, for days or weeks. Unlike vagus nerve stimulation for epilepsy, which involves chronic stimulation, treatment for tinnitus will likely be for a limited period of time, researchers say.

In conjunction with these clinical tests, Microtransponder is modifying its existing technology for tinnitus. Unlike other stimulation devices, Microtransponder's system is wireless and has no batteries. The implanted portion consists of small electrodes and a small coil. An external battery-powered coil worn like a cuff on the arm or leg powers the device. "The idea would be to inject the wireless device and then put a coil around the neck to activate it [during a treatment session]," says Kilgard. "If the tinnitus comes back five years later, the device is still there and you can do the treatment again.

Harvard's Melcher says the approach is very interesting, though "whether it works is an open question." She points out that "we are still trying to sort out what aspects of brain plasticity are involved in tinnitus. There may be different kinds of tinnitus, with different types of brain activity giving rise to the perception of sounds that aren't there." All of these may require different treatments.