A new treatment that retrains part of the brain that processes sound may help silence tinnitus, say US researchers.
Tinnitus, a constant ringing in the ears, afflicts 10 per cent of senior citizens and more than 40 per cent of military veterans
The researchers from the University of Texas in Dallas say a device that stimulates the vagus nerve in the neck while simultaneously playing different sounds for several weeks helped eliminate the condition in a group of rats.
A trial of the treatment in humans is set to start in Europe this year, said Dr Navzer Engineer of MicroTransponder, a medical device company affiliated with the university, whose study appears in the journal Nature.
Tinnitus is sometimes brought on by hearing loss. It occurs as cells in the inner ear are damaged, often from a loud noise. Current drugs help mask tinnitus, but the condition is incurable.
Engineer's team thinks tinnitus may be caused when too many brain cells become tuned to a specific tone in the brain. So his team set out to train the brain to ignore the nerve signals that cause the ringing sound.
Triggering changes in the brain
To do this, they paired a device that sends electrical impulses to the vagus nerve in the neck with different sounds.
Stimulating this nerve releases chemicals such as acetylcholine and norepinephrine that trigger changes in the brain.
The team tested this approach in a series of experiments with rats, using an indirect but accepted method of testing hearing in animals.
In one, they stimulated the vagus nerve while playing different sounds 300 times a day for 20 days to a group of eight rats with a form of tinnitus. The tones were close to the frequency of the ringing sound, and the hope was to trick some of the nerve cells into listening to the new tones rather than the ringing tone.
When the team checked the nerve responses to different tones, the tinnitus had disappeared in rats exposed to the tones and nerve stimulation, but it persisted in a group of control animals.
"Unlike previous treatments, we're not masking the tinnitus. We are eliminating the source of the tinnitus," says Michael Kilgard, who worked on the study.
The researchers are developing a wireless medical device to stimulate the vagus nerve and hopes to test it in people later this year.
The National Institute on Deafness and Other Communication Disorders, part of the National Institutes of Health, funded a large part of the research.