Modeling cochlear micromechanics and noninvasive measures of cochlear function

Georgia Institute Of Technology, Atlanta GA

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Abstract

PROJECT SUMMARY Normal hearing requires amplification of the cochlear response to low-level sounds through a mechanism known as the cochlear amplifier, which is closely tied to the electromechanical feedback from outer hair cells; however, our understanding of the mechanisms underlying cochlear amplification is still incomplete. Recent in vivo experiments have revealed that the micromechanical vibrations of the organ of Corti are influenced by outer hair cells in intricate and unexpected ways. Hydrodynamic coupling between the organ of Corti vibrations and the intracochlear fluid, which plays a role in cochlear amplification, is not well understood. In addition to facilitating the detection of low-level sound, the feedback from outer hair cells gives rise to measurable sounds in the ear canal called otoacoustic emissions. While otoacoustic emissions are not known to play any functional role, they provide highly valuable noninvasive information about cochlear amplification and health, including for clinical hearing screening. However, the precise connection between the micromechanical vibrations of the organ of Corti and otoacoustic emissions remains unclear, which hampers the ability of otoacoustic emissions to accurately locate cochlear damage for noninvasive diagnosis. Measurements of the cochlear microphonics (an electrical potential generated by outer hair cells) at the round window can also provide information about cochlear function but are limited in part by the lack of understanding of electrical coupling within the cochlear ducts. The overall objectives of this project are to advance knowledge regarding the key mechanisms of active cochlear mechanics and to clarify the potential of noninvasive measurements (specifically, otoacoustic emissions and round window cochlear microphonics) in offering valuable insights into cochlear function. This research is based on the development of novel, physiologically motivated computational models of the inner ear. These models are specifically designed to address crucial questions in cochlear mechanics highlighted by recent experimental findings. Throughout the project, models will be calibrated, validated, and tested using data from relevant literature and new experiments. Aim 1 will assess the impact of hydrodynamic fluid coupling to the upper surface of the organ of Corti on cochlear amplification. Aim 2 will determine the roles of two distinct mechanisms in giving rise to longitudinal motion of the organ or Corti. Aim 3 will evaluate the link between micromechanics of the organ of Corti and non-invasive measures based on round window cochlear microphonics and otoacoustic emissions using a high-fidelity model of cochlear electro- and hydro-mechanics.