In the United States alone, tinnitus is estimated to affect the lives of 50 million people. People suffering from subjective tinnitus hear sounds (typically ringing or hissing) that no one else hears. In severe cases, the sounds are so loud that they produce great personal distress, disturbing, for instance, sleep and concentration.
Tinnitus is caused by a multitude of reasons. One common reason is exposure to a loud sound, for example, from listening to music on headphones with excessive volume or from attending a very loud concert without hearing protection. Exposure to loud sounds can damage the cells of the inner ear that respond to different sound frequencies. The syndrome itself, is however, suspected to originate from the brain processes that follow the exposure, from how the brain adapts to cell damage in the inner ear and to hearing loss.
A recently published review in the journal Nature Reviews Neurology comprehensively summarizes research on the mechanisms that give rise to tinnitus. To understand these mechanisms, we must understand how the different parts of the auditory pathway work. Hearing starts with activity in the inner ear where different parts of the hearing organ inside the cochlea react to different frequencies conveyed by the movement of the membrane of the eardrum. Information from the cells of the hearing organ travels through nuclei in the brain stem to the auditory cortex where different frequencies are processed in separate areas, resulting in what is called a tonotopic map. When exposure to a loud sound produces damage in the inner ear, this usually affects cells designated to the processing of a certain frequency. As a result, the neurons in the cortex responsible for the processing of that frequency no longer receive normal input.
What happens next is interesting: the brain starts reacting to this change in input. The auditory cortex starts reorganizing as the area deprived of input from the ear forms connections with neighboring areas that are responsible for the processing of other frequencies. This is called fusing of the cortical areas, which leads to changes in normal neural processes. It is believed that these changes - caused by the ways by which the brain reorganizes to adapt to hearing loss, ultimately cause the sensation of the tinnitus sound.
There is no cure for tinnitus, but luckily a lot can be done to manage the symptoms. One enjoyable way to treat the symptoms of tinnitus is, perhaps ironically, music listening. In a paper published in 2010, a group of researchers investigated use of music for the treatment of tinnitus. The scientists created a way to utilize the brain’s capacity for reorganization, the very same mechanism that causes the sensation of the tinnitus sound in the first place, to decrease the loudness of the tinnitus sound.
In order to harness the power of the brain’s reorganizing ability, the researchers first measured the pitch of the tinnitus sounds that the subjects in the their experiment experienced. Then, the researchers took a selection of the subjects’ favorite music pieces and altered (“notched”) them so that they contained no energy in and around the frequency corresponding to the pitch of the subjective tinnitus sound. Half of the subjects in the study then listened to these altered versions of their favorite music and half did not. After one year, the subjects who had regularly listened to the altered music reported experiencing a significant decrease in the volume of their tinnitus. Furthermore, MEG measurement showed that the neural areas responsible for processing the tinnitus frequency had decreased activity in the subjects who had listened to the altered music. This result means that most probably listening had resulted in reorganization of the auditory cortex, and had rewired the brain in a way that counteracted to mechanism that caused tinnitus.
Many people enjoy loud music. We “turn it up” to get the most out of the best part of music listening – immersion into the world conveyed by this fantastic art form. Unfortunately, this also makes hearing loss and resulting tinnitus a common ailment among music fans. The first step to ensuring long-lasting ability for musical enjoyment is to make sure that hearing is protected. Current neuroscientific research is deepening our understanding of the brain mechanisms that underlie tinnitus as well as producing insightful discoveries into possibilities for managing symptoms. For the music lover, music therapy that makes use of one’s favorite music and the brain’s capacity for reorganization is a fantastic innovation.
written by ketki karanam
Okamoto, H., Stracke, H., Stoll, W., & Pantev, C. (2009). Listening to tailor-made notched music reduces tinnitus loudness and tinnitus-related auditory cortex activity. Proceedings of the National Academy of Sciences, 107(3), 1207–1210. doi:10.1073/pnas.0911268107
Shore, S. E., Roberts, L. E., & Langguth, B. (2016). Maladaptive plasticity in tinnitus — triggers, mechanisms and treatment. Nat Rev Neurol, 12(3), 150–160. doi:10.1038/nrneurol.2016.12