Investigating Cochlear Responses Using a Physiologically Based Model

The mammalian cochlea bestows humans and other mammals with remarkable hearing ability over a wide range of frequencies and stimulus levels. This is achieved in part through an active feedback mechanism, termed the cochlear amplifier, which boosts the cochlear response to low-level stimuli. Cutting edge experiments over the last few decades have probed mechanical and electrical responses inside the cochlea with unprecedented detail. These studies have shown that the organ of Corti, which is a strip of cells in the cochlea that mediates sound transduction to nerve signals, exhibits complex relative motions rather than rigid body motion as previously thought. In turn, these new findings have challenged traditional theories about how the cochlear amplifier, which is facilitated by outer hair cells in the organ of Corti, functions. In this dissertation, a computational model of the mammalian cochlea is implemented with a reformulated structural model of the organ of Corti that improves the feasibility of changes to model assumptions. The model is used to show that some structures within the organ of Corti move more than others because they are more compliant. Furthermore, the Deiters' cells in the organ of Corti are made much more compliant than the basilar membrane, based on new evidence. The influence of this more realistic compliance on power transfer to cochlear traveling waves is evaluated. The results of this study challenge the traditional theory of how outer hair cells amplify cochlear responses, and a new theory of how they may do so is presented. By varying model parameters, expanding model assumptions based on experimental evidence, and characterizing power delivery of the cochlear amplifier, the research in this thesis expands understanding of cochlear mechanics.