Impact of Hearing Impairment on the Source Generators of Auditory Evoked Potentials

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Auditory evoked potentials are gaining popularity in assessing supra-threshold coding ability in the auditory brainstem. Because these aggregate population responses contain synchronized information converging from a large number of auditory-nerve fibers, they are particularly promising in diagnostics of noise-induced cochlear neuropathy, a newly discovered hearing deficit that affects the number and types of auditory nerve fibers available for a robust signaling of sound to the auditory brainstem.Even though auditory evoked potentials are well described in the literature, not much is known about their source generators or their relationship to the electrophysiology of single neurons. Additionally, it is not known how cochlear neuropathy interacts with the well-studied outer hair cell loss in affecting auditory evoked potentials. However, with an aim to develop sensitive diagnostic tools it is important to study these relationships. In this proposal, we plan to bridge the gap between animal physiology and human applications via the development of a computational model of the auditory periphery that includes single-unit models of the auditory nerve, cochlear nucleus and inferior colliculus into a model for human auditory evoked potentials. After studying how different combinations of hearing deficits affect the source generators of auditory evoked potentials to sustained amplitude-modulated stimuli, we plan on developing signal-processing strategies that enhance temporal fine structure and envelope representation in the auditory system. Experimental validation of the model simulations and signal-processing strategies is based on recordings of subcortical-steady state responses in normal and hearing-impaired listeners.