Biophysical and neural coding mechanisms of the ear

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Hearing is one of our most basic senses and plays a critical role in the daily lives of most animals. For example, consider the ubiquity of vocal communication and listening to music. Hearing impairment (e.g., difficulty detecting sounds and/or following conversations in noisy environments) is a major factor affecting the quality of life for a significant fraction of people in Canada and all around the world. The situation has been further exacerbated by the COVID-19 pandemic, where mask coverings make communication more difficult for those with hearing loss. Healthy ears exhibit remarkable functionality, being both highly sensitive (i.e., detect) and selective to (i.e., decompose) sounds. To achieve this, the ear is an active detector: Metabolic energy is used to selectively amplify sound-induced motions. As a consequence, healthy ears generate sounds that are measurable in the ear canal with a sensitive microphone. These signals are known as otoacoustic emissions (OAEs) and provide valuable clinical diagnostics (e.g., newborn hearing screening) and scientific insight into the active ear. However, much remains unknown about OAE generation mechanisms due to the morphological complexity and fragility of the mammalian cochlea. As such, our knowledge about the human cochlea is primarily inferred from invasive work done with animals. My research program studies auditory biophysics and neuroscience by taking a comparative approach, using the morphological diversity of the ear across the animal kingdom to our advantage. In particular, we focus on the Anolis lizard. Despite the absence of structures and features commonly thought essential for mammalian hearing, lizards demonstrate comparable sensitivity and selectivity. Thereby, their relatively simpler ears can provide an essential path forward for shedding light upon the active mammalian ear and how the breakdown of key processes lead to hearing impairment. This proposal combines mathematical modeling and several non-invasive state-of-the-art measurement methods: otoacoustics, auditory evoked potentials, and laser Doppler vibrometry. By testing several hypotheses relating these measures to their ability to determine sensitivity and selectivity, we will gain much deeper insight into the biomechanics and neural coding of our active ears. Together, the proposed objectives form a tapestry that will allow us to better understand the auditory periphery through the lens of cellular cooperativity, where the many parts of the ear work together to form something wholly different from the sum. Such synergies will allow us to expand our knowledge about principles underlying this remarkable sensory system and set a solid foundation for future translational research. Further, my training program will promote diversity and foster inclusion, thereby establishing confidence in the voices of tomorrow's scientists and helping Canada become an international leader in auditory science.