Biophysical Mechanisms Underlying Auditory Transduction

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The ear is a remarkable detector: It is both highly sensitive and selective, and operates over a large dynamic range spanning more than 12 orders of magnitude. Direct physiological study of the ear however has been difficult, and thus there is much we do not know about the [complex array of cellular-based] amplification mechanisms at work in the ear. Hearing impairment commonly arises due to problems with these processes and affects the quality of life for a significant fraction of Canadians. Fortunately, we can make use of another extraordinary property of the ear: Not only does it respond to sound but emits it as well. These sounds, known as otoacoustic emissions (OAEs), can arise either spontaneously or be evoked by an external stimulus and are measurable non-invasively in the ear canal using a sensitive microphone. OAEs have been employed with great success in both scientific and clinical contexts (e.g., screening for hearing impairment) and further study will help crystallize our understanding of the fundamental biophysics underlying amplification in the ear. The aims of the study are targeted towards characterizing OAE generation mechanisms and their relationship to how the sensory cells of the ear encode sound information to the brain. Focusing primarily on lizards and combining experiment with mathematical modeling, the project's objectives will address several fundamental questions currently at the heart of basic auditory science. Despite the relative simplicity of their morphology and physiology when compared to mammals, lizard ears share many of the functional features common to more complex animals (e.g., low thresholds, sharp tuning, robust OAEs). Thereby, the simplicity of the lizard ear can be used to our advantage when trying to clarify many of the underlying biophysical processes believed crucial in vertebrate auditory function. Thus, the work proposed here will ultimately build on our knowledge of auditory function in humans and contribute towards Canada being an international leader in the study of hearing.