Targeted sounds for the diagnosis and treatment of tinnitus in humans

Abstract

Due to the heterogeneity of potential tinnitus causes, a biomarker is needed that would relate to a ‘final common pathway’ for tinnitus, irrespective of specific contributory mechanisms. This biomarker should differentiate between tinnitus and other comorbid conditions. Previous research suggested that Intensity Mismatch Asymmetry may be such a biomarker. The hypothesis was that downward deviant stimuli sounded more similar in intensity to the default prediction of tinnitus intensity, so people with tinnitus would show a reduced response to this change, while the upward deviant was further from the default prediction, thus making the MMN response larger. The present project aimed to systematically explore design features that may affect responses to intensity deviants in people with tinnitus, hyperacusis, and healthy controls. The main factors explored included: having only one or a combination of the aforementioned conditions, attentional direction, and presence of close or widely spread frequencies. Several conclusions were reached. Hyperacusis, tinnitus with hyperacusis, and tinnitus without hyperacusis, potentially all have different underlying mechanisms. Generally, presence of hyperacusis enhances MMN responses to upward intensity deviants and disrupts adaptation mechanisms. Tinnitus without hyperacusis showed stronger MMN amplitude in response to downward deviants at tinnitus-like frequency. Tinnitus generally has normal adaptation processes, however, interference between close frequencies limits this adaptation/habituation. A similar pattern was elicited in controls when two nearby frequencies were involved in a roving paradigm experiment, pointing towards a specific interference effect, and possibly reflecting contrast gain theory mechanisms. The effectiveness of a novel covariance-cancelling sound therapy was tested as a potential treatment for participants with tinnitus. The aim of these sounds was to reduce synchronous activity between neurons that are responsible for frequencies around the tinnitus frequency of an individual. These sounds were successful in significantly reducing the perceived loudness of tinnitus after 6 weeks of daily listening