In this thesis the active and nonlinear dynamics of the mammalian cochlea in response to acoustic stimulation are simulated using a computational model of the physics and physiology of the cochlea. The model is based on a three-dimensional representation of the cochlear partition and intracochlear fluid and includes the electrical domain and linear feedback from outer hair cell (OHC) somatic motility.

A linear version of the model of the cochlea is first used to assess the role of structural longitudinal coupling in cochlear mechanics. Longitudinal coupling in the TM and BM mechanics is found to improve the predictions compared to a locally reacting model as it broadens the frequency response of the BM to acoustic stimulation and reduces the duration of the impulse response.

The linear model of the cochlea is then used to investigate the identity of the cochlear amplifier—prestin-based somatic motility or hair bundle (HB) motility. A nonlinear six-state channel model of the active HB is linearized for small harmonic perturbation around the operating point and implemented in the macroscopic model of the cochlea. A calcium binding event models fast adaptation of the transduction current and active HB force generation. The macroscopic simulations show that somatic motility underlies cochlear amplification and that the active HB force is insufficient to modulate the response of the BM to low intensity acoustic stimulation. However, the reduction of the sensitivity of the transduction channel to HB deflection due to the fast adaptation mechanism controls the energy delivered by somatic motility and thereby the sensitivity of the BM to acoustic stimulation, stabilizing the cochlea.

The nonlinear dynamics of the cochlea are simulated by introducing a physiologically relevant nonlinearity in the mechanotransdnction channel. An efficient alternating frequency/time method is used to compute the stationary response of the cochlea. The model predicts a realistic compressive response and generation of harmonic distortion in response to a single tone. The simulations of two tone interaction on the BM—two tone suppression and distortion products—are also in good agreement with published experimental data.