Retraining the brain
In effect, Kilgard says, the rats' brains were retuned, unlearning the tendency to overfocus on one tone by increasing the number of brain cells dedicated to other sound frequencies.
Kilgard's study, published earlier this year in Nature, set the stage for a human trial by Dirk De Ridder, M.D., a neurosurgeon who heads a tinnitus clinic in Antwerp, Belgium.
De Ridder is implanting electrodes in 10 middle-aged tinnitus patients, each of whom has already tried various experimental techniques, including medication. He says he works with one patient at a time, as each undergoes vagus nerve stimulation coupled with sound therapy for 2 1/2 hours a day for four weeks. This is very much a pilot study, where the researchers hope to figure out some basic parameters (how long to continue treatment, among other things) that will guide a larger study.
"From the first preliminary results that we have, it still seems promising, but it will not be a hundred percent success rate," De Ridder says. Humans who have had tinnitus for a longer time than the rats, and who are more genetically diverse, are unlikely to respond in the same way, he says.
De Ridder's patients have a long, thin electrode threaded under the skin connecting the vagus nerve to a computer that synchronizes bursts of micro-current and tones. If this brain-training technique is eventually approved for human use, a more elegant option might be available from a Dallas company called MicroTransponder Inc., which is sponsoring De Ridder's trial.
Jordan Curnes, president of the company, says the firm has developed a tiny stimulator the size of three grains of rice that can be implanted in the neck next to the vagus nerve and be controlled by wireless signals.
MicroTransponder is exploring nerve stimulation to treat chronic pain and recover motor function in stroke victims, but the tinnitus technology holds the most promise, he says. "Nothing else has seen this much pre-clinical success," Curnes says.