Investigating Disinhibitory Brain Mechanism in Tinnitus and Hearing Loss

Tinnitus, the perception of sound in the absence of an external acoustic stimulus. Tinnitus is often perceived inside the head rather than the ear and is a common condition with a prevalence estimated between 10 and 15% in adults. Between 1 and 3% of this population are having a significant impact on their quality of life. Despite its high prevalence, the underlying mechanisms of tinnitus still remain unclear. The majority of tinnitus cases associated with some degree of hearing loss, making hearing loss the biggest risk factor for tinnitus. Recently, it has been suggested that hearing deficits, such as speech-in-noise difficulty, can exist in the absence of any overt hearing loss within the audiometric range (0.125-8 kHz). This is referred to as "hidden hearing loss" and has been suggested to be associated with hearing loss at above-audiometric (\> 8 kHz) frequencies. This project is aimed at studying the underlying mechanisms of tinnitus and the possible relation with overt or hidden hearing loss. Specifically, the investigators want to test the hypothesis that tinnitus is caused by maladaptive plasticity arising as a result of auditory input deprivation. This idea is supported by the finding that tinnitus may disappear when the hearing, and thus auditory input, recover. Disruptions at lower levels of the auditory pathway could lead to alterations in synaptic transmission and neurotransmitter release in more central regions of the auditory system (e.g., in the auditory cortex). This may create an imbalance between neuronal excitation and inhibition, and re-routing of auditory pathways, leading to abnormal neural excitability and connectivity. In this study, the investigators question whether auditory cortex disinhibition is specifically related to tinnitus, or is a consequence of hearing loss. To answer this question, the investigators propose to conduct a study that aims to investigate the inhibition mechanism by quantifying GABA concentration level, neural ac