Written by Joyce Smith, BS. This study demonstrates that bimodal stimulation could reduce tinnitus by reducing the phantom sounds that occur due to unruly nerve activity in the brain.
Approximately 15 percent of the U.S. population has tinnitus, of which 20 million experience troubling tinnitus, and approximately 2 million are debilitated by it. Many of those with more severe tinnitus also have hearing loss. As many as 2 million people can’t work or carry out other daily activities because of the tinnitus and the psychological distress it causes 1. Tinnitus is the most common cause of service-connected disability among veterans of the U.S. military 2. Researchers believe the root of tinnitus lies within an area of the brainstem called the dorsal cochlear nucleus (DCN) and when fusiform cells (the main neurons in this region) become hyperactive due to noise exposure, they synchronize with one another and transmit phantom signals to the brain centers where perception occurs. The hope is that if these signals can be stopped, tinnitus will stop 3,4. Previous research has shown that only animals with tinnitus exhibit neurological changes in the DCN 5. When researchers subjected guinea pigs to bimodal stimulation involving concurrent auditory (sound) and electrical stimulation, they found that bimodal stimulation either strengthened or weakened the synchrony of the fusiform cells, depending on the stimulus order and timing 6.
Cognitive behavioral therapy is one of the current treatments designed to address the psychological distress caused by tinnitus 7. Other approaches use sound to mask the phantom sounds or attempt to modulate the brain response. In severe cases of tinnitus, invasive and riskier approaches such as deep brain stimulation and vagal nerve stimulation have been considered. The current approach 8 provides a novel, unique and non-invasive strategy that aims to modulate and correct the aberrant neural pathways that cause tinnitus.
Previously research has shown that animals exhibiting tinnitus behaviors had neurological changes in the fusiform cells of their DCN compared to animals that had no evidence of tinnitus. Additional research subjecting guinea pigs to bimodal stimulation involving concurrent auditory (sound) and electrical stimulation found that bimodal stimulation either strengthened or weakened the synchrony of the fusiform cells, depending on the stimulus order and timing. When guinea pigs were stimulated for 20 minutes per day over 25 days, researchers observed a reduction in behavioral evidence of tinnitus in these animals. Neither auditory stimulation nor somatosensory stimulation, when given alone, achieved the same results. Since aspects of the cochlear nucleus are similar in both humans and rodents, the researchers theorized that this protocol could translate to human studies to achieve similar results. Thus, they conducted a similar double-blinded, sham-controlled, crossover study in 20 human participants with somatic tinnitus. Using earphones and electrodes for 30 minute sessions each day, ten participants received the bimodal sound and electrical stimulation for the first four weeks, while the other 10 received just sounds. Following a 4-week break, the process was reversed. The loudness of phantom sounds relative to baseline decreased significantly only with the bimodal treatment (P=0.0035) and remained through the washout period. Eleven participants found that their tinnitus had become less “harsh” or “piercing” and more “mellow,” while others found that their tinnitus was noticeably less obtrusive and easier to ignore.
This study only tested one subgroup of tinnitus patients (those with somatic tinnitus); thus, it is unknown whether these results would translate to other subgroups. Hopefully the neural de-synchronization strategy presented in this study will offer a new treatment possibility for those with tinnitus.
Source: Marks, Kendra L., David T. Martel, Calvin Wu, Gregory J. Basura, Larry E. Roberts, Kara C. Schvartz-Leyzac, and Susan E. Shore. “Auditory-somatosensory bimodal stimulation desynchronizes brain circuitry to reduce tinnitus in guinea pigs and humans.” Science translational medicine 10, no. 422 (2018).
Posted November 17, 2020.
Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.
References:
- Axelsson A, Ringdahl A. Tinnitus–a study of its prevalence and characteristics. British journal of audiology. 1989;23(1):53-62.
- Folmer RL, McMillan GP, Austin DF, Henry JA. Audiometric thresholds and prevalence of tinnitus among male veterans in the United States: data from the National Health and Nutrition Examination Survey, 1999-2006. Journal of rehabilitation research and development. 2011;48(5):503-516.
- Weisz N, Müller S, Schlee W, Dohrmann K, Hartmann T, Elbert T. The neural code of auditory phantom perception. The Journal of neuroscience : the official journal of the Society for Neuroscience. 2007;27(6):1479-1484.
- Shore SE, Roberts LE, Langguth B. Maladaptive plasticity in tinnitus–triggers, mechanisms and treatment. Nature reviews Neurology. 2016;12(3):150-160.
- Berger JI, Coomber B, Shackleton TM, Palmer AR, Wallace MN. A novel behavioural approach to detecting tinnitus in the guinea pig. Journal of neuroscience methods. 2013;213(2):188-195.
- Stefanescu RA, Koehler SD, Shore SE. Stimulus-timing-dependent modifications of rate-level functions in animals with and without tinnitus. Journal of neurophysiology. 2015;113(3):956-970.
- Martinez-Devesa P, Perera R, Theodoulou M, Waddell A. Cognitive behavioural therapy for tinnitus. Cochrane Database Syst Rev. 2010(9):Cd005233.
- Marks KL, Martel DT, Wu C, et al. Auditory-somatosensory bimodal stimulation desynchronizes brain circuitry to reduce tinnitus in guinea pigs and humans. Sci Transl Med. 2018;10(422).
