Response to a Pure Tone in a Nonlinear Mechanical-Electrical-Acoustical Model of the Cochlea

Abstract

In this article, a nonlinear mathematical model is developed based on the physiology of the cochlea of the guinea pig. The three-dimensional intracochlear fluid dynamics are coupled to a micromechanical model of the organ of Corti and to electrical potentials in the cochlear ducts and outer hair cells (OHC). OHC somatic electromotility is modeled by linearized piezoelectric relations whereas the OHC hair-bundle mechanoelectrical transduction current is modeled as a nonlinear function of the hair-bundle deflection. The steady-state response of the cochlea to a single tone is simulated in the frequency domain using an alternating frequency time scheme. Compressive nonlinearity, harmonic distortion, and DC shift on the basilar membrane (BM), tectorial membrane (TM), and OHC potentials are predicted using a single set of parameters. The predictions of the model are verified by comparing simulations to available in vivo experimental data for basal cochlear mechanics. In particular, the model predicts more amplification on the reticular lamina (RL) side of the cochlear partition than on the BM, which replicates recent measurements. Moreover, small harmonic distortion and DC shifts are predicted on the BM, whereas more significant harmonic distortion and DC shifts are predicted in the RL and TM displacements and in the OHC potentials.

A physiologically-based time domain model of the mammalian ear

“…The proposed time-domain model of the cochlea is based on the frequency-domain cochlear models developed by Ramamoorthy et al [11] and Meaud and Grosh [8,9]. In contrast to the previous approach, a two-dimensional model is used for the intracochlear fluids; however, extension to a three-dimensional model is straightforward using the approach used in previous models.…”

“…The model includes electrical degrees of freedom that account for the electrical potentials in the cochlear ducts and in the outer hair cells (OHCs). As in [9], the model includes nonlinear mechano-electrical transduction (MET) channels (modeled by a Boltzmann function) and linearized somatic electromotility. Model parameters are based on [9].…”

“…Frequency-domain models of the cochlea can be used to investigate many aspects of nonlinear cochlear mechanics, such as the presence of a compressive nonlinearity and harmonic distortion on the basilar membrane (BM) [9,10] and the generation of distortion product otoacoustic emissions (OAEs) [5]. However, phenomena such as spontaneous OAEs and transient evoked OAEs can only be simulated using a time-domain model of the cochlea [1].…”

“…A state-space approach has been used in recent years to develop time-domain models of the cochlea [2,3,6,12]. In this paper, we use a state-space approach to implement in the time-domain a previously developed nonlinear frequency-domain of the cochlea based on the finite element method [9]. The cochlear model is coupled to a lumped-parameter model of the middle ear.…”

“…In this paper, we present a physiologically-based time-domain model of the mammalian ear that couples a nonlinear model of the cochlea with a lumped parameter model of the middle ear. The cochlear model is an extension of a previous nonlinear frequency-domain model [9]. This model is based on the finite element method and includes mechanical degrees of freedom for the organ of Corti micromechanics, acoustical degrees of freedom for the intracochlear fluid mechanics and electrical degrees of freedom that represent the intracellular outer hair cell (OHC) potential and the electrical potentials in the cochlear ducts.…”