Specially timed signals ease tinnitus symptoms

Based on years of scientific research into the root causes of the condition, the device uses precisely timed sounds and weak electrical pulses that activate touch-sensitive nerves, both aimed at steering damaged nerve cells back to normal activity.

Human participants reported that after four weeks of daily use of the device, the loudness of phantom sounds decreased, and their tinnitus-related quality of life improved. A sham "treatment" using just sounds did not produce such effects.

Results from tests in guinea pigs and a double-blind human study funded by the Coulter Foundation validate years of preclinical research funded by the National Institutes of Health, including previous tests in guinea pigs.

The U-M team has new NIH funding for an additional clinical trial to further refine the approach. U-M holds a patent on the concept behind the device and is developing it for potential commercialisation.

"The brain, and specifically the region of the brainstem called the dorsal cochlear nucleus, is the root of tinnitus," said Susan Shore, the U-M Medical School professor who leads the research team.

"When the main neurons in this region, called fusiform cells, become hyperactive and synchronise with one another, the phantom signal is transmitted into other centers where perception occurs.

"If we can stop these signals, we can stop tinnitus. That is what our approach attempts to do, and we're encouraged by these initial parallel results in animals and humans."

The approach, called targeted bimodal auditory-somatosensory stimulation, involves two senses. The device plays a sound into the ears, alternating it with precisely timed, mild electrical pulses delivered to the cheek or neck.

This sets off a process called stimulus-timing dependent plasticity, or STDP, which was first explored in animals and led to long-term changes in the rate at which the nerves fire.

The approach aims to reset the activity of fusiform cells, which normally help our brains receive and process both sounds and sensations such as touch or vibration—what scientists call somatosensory inputs.

Under normal conditions, fusiform cells help our brains focus on where sounds are coming from, and help us tune out sensations that result from the movement of our own head and neck.

But the U-M team's previous work in animals showed that loud noise can trigger a change in the nerve cells' activity—altering its timing so that they fire off synchronised signals spontaneously instead of waiting for an actual sound in the environment.

These events in animals parallel what happens in humans. After exposure to such things as loud noises, head or neck trauma, or other triggering events, some people develop a persistent sensation that they're hearing sounds like ringing or a grinding noise.

Approximately 15% of Americans have some level of tinnitus, but the worst symptoms occur in about 10% of sufferers, according to estimates based on interviews with nationally representative samples of Americans. Many of those with more severe tinnitus also have hearing loss.

Some cases are severe. As many as 2 million people can't work or carry out other daily activities because of the tinnitus itself, or the psychological distress it causes them. Tinnitus is the most common cause of service-connected disability among veterans of the U.S. military.

Current approaches to tinnitus treatment focus include efforts to address the psychological distress it causes, for instance through cognitive behavioral therapy. Other approaches use sound to mask the phantom sounds or attempt to modulate the brain response.

For more severe cases, some patients turn to invasive, and therefore riskier, approaches such as deep brain stimulation and vagal nerve stimulation. The current approach provides a novel and unique, non-invasive strategy that aims to modulate and correct the aberrant neural pathways that cause tinnitus.

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Image credit: University of Michigan.