Fundamentals of human hearing: from basic cochlear processing to cortical representations

Hearing loss is a prevalent and growing health problem that can cause considerable life burden, inhibiting social and work activities and lowering mood, and has recently been identified as a major risk factor for developing degenerative brain diseases, such as Alzheimer's, in later life. Hearing loss is diagnosed by a reduction in the patient's ability to hear faint sounds. However, in everyday life, inability to hear faint sounds is not usually the patient's primary problem. Rather, patients usually complain about difficulties hearing in noisy environments (e.g., following a conversation in a noisy pub), and these difficulties persist even when wearing a hearing aid. In addition, some patients also complain about experiencing certain everyday sounds as excruciatingly loud, and many hearing-impaired patients experience a continuous, and often irritating, ringing or hissing sound in the ear or head, referred to as "tinnitus". These problems are currently untreatable and their causes remain largely unknown. In this research programme, we will investigate the idea that they arise as a result of changes in the way in which sounds are processed and represented within the brain. We will focus on the highest-level, most sophisticated part of the brain referred to as "cortex", which is particularly well-developed in humans. Using cutting-edge brain imaging technologies, we will develop methods for mapping cortical sound responses at a sub-millimetre spatial scale, and tracing their temporal dynamics with millisecond accuracy. Using these methods, we will then investigate the exact mechanisms by which cortical sound processing is altered as a result of hearing loss. Insights gained from this programme may lead to the development of better, more individualized treatment options for hearing impairment, and help to understand how hearing loss impacts brain health.