A person receiving bimodal sensory stimulation for tinnitus. Note the earbuds for audio and electrodes on neck for pulses. (David Martel and Christopher Chang, Univ. of Michigan)
4 January 2018. A non-invasive system that combines coordinated electronic pulses and sounds is shown in tests with lab animals and humans to reduce tinnitus, phantom sounds often called ringing in the ears. Researchers from University of Michigan in Ann Arbor describe the device and their results in yesterday’s issue of the journal Science Translational Medicine.
The team led by Michigan’s Susan Shore, professor of otolaryngology — head and neck surgery — and biomedical engineering, is seeking to treat the root causes of tinnitus, a condition affecting some 15 percent of the U.S. population, according to data cited by the authors. Tinnitus is characterized by a constant sound pattern in the ears, like ringing, buzzing, or even roaring. The National Institute on Deafness and Other Communication Disorders (NIDCD) at NIH says tinnitus can be a symptom of a minor disorder, like an ear infection, or of more serious conditions, such as noise-induced hearing loss or a brain tumor.
The system developed by the researchers targets a part of the brainstem region of the brain called the dorsal cochlear nucleus, where tinnitus is believed to originate. “When the main neurons in this region, called fusiform cells, become hyperactive and synchronize with one another,” says Shore in a university statement, “the phantom signal is transmitted into other centers where perception occurs. If we can stop these signals, we can stop tinnitus.”
To stop the signals, Shore and colleagues use a process known as bimodal auditory-somatosensory stimulation that combines sounds played into the ears of the individual, alternating with mild electrical pulses into the cheek or neck. The alternating sounds and electrical pulses triggers two senses with the goal of resetting activity in fusiform cells. Earlier tests with animals show this combination of sensory stimulation can change the rate at which nerves fire, and thus disrupt the conditions that produce the phantom sounds.
The researchers first tested bimodal auditory-somatosensory stimulation in guinea pigs induced with tinnitus by extended noise exposure, where the animals displayed both physiological and behavioral signs of the condition. After treatments of 20 minutes per day for 25 days, the animals show fewer of these physiological and behavioral signs.
The team then recruited 20 individuals with tinnitus for a clinical trial of the system. Participants in the trial had a type of tinnitus that allows for altering the signals with their facial muscles, for example by clenching their jaws or flexing their neck muscles. The individuals were randomly assigned to receive the biomodal stimulation or a sham auditory-only procedure, after which participants switched to the other biomodal or sham procedures.
The results show after 28 days of treatments, participants receiving biomodal sensory stimulation report quieter and less intrusive sounds making them easier to ignore, compared to individuals receiving only the audio signals. The earlier tests with guinea pigs reported similar findings. While the results are promising, the study has a small sample of participants, with one type of tinnitus. The team says the system needs to be tested in larger and more diverse samples.
Shore’s lab is already at work on an extended project. In August 2017, Shore’s lab received a 4-year $2.4 million grant from NIH to further evaluate biomodal sensory stimulation, not only for treating tinnitus, but also other central motor disorders, such as Parkinson’s disease.
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