Neuroimaging correlates of hearing loss, tinnitus, and hyperacusis

Worldwide, hearing loss is the most prevalent and debilitating acquired sensory impairment, affecting a large proportion of the elderly population. The presence of hearing loss increases the chances of developing other auditory domain symptoms such as tinnitus and hyperacusis. Both tinnitus and hyperacusis are debilitating symptoms, and even though several treatment options are available, there is currently no cure for either condition. Since these conditions often co-occur, there is considerable overlap in their reported impact on the brain, which may hinder the development of specific treatments. We used Magnetic Resonance Imaging to show that hearing loss relates to pronounced changes in the structure of the gray matter, both within and outside of the auditory areas, and changes in the activity of the auditory cortex. In those with additional tinnitus, we observed that these changes were more conservative. Tinnitus is also related to a reduction in the acoustic radiation near the thalamus, the auditory system's largest white matter fiber tract. In our work we linked hyperacusis to hyperactivity in response to sound, which provides a neural correlate of the perceived increase in loudness that is characteristic of hyperacusis. Our findings show that age has a pronounced impact on both the gray and white matter of the brain. This means that older individuals are disadvantaged by the impact of both age and hearing loss on the brain. As a consequence, rehabilitation methods may need to consider the importance of the brain in auditory processing in addition to the conventional hearing aids.