Mechanical-Electrical-Acoustical Modeling of the Cochlea

Karl Grosh
University of Michigan

The coupling of the mechanical and the electrical response of the cochlea is well known. Acoustical stimulation gives rise to the cochlear microphonic and electrical stimulation of the cochlea elicits both basilar membrane motion and otoacoustic emissions. Disruption of the resting electrical environment, through efferent stimulation, artificial injection of current and a variety of other means is known to affect hearing sensitivity and the mechanical response of the cochlea to stimulus. The key missing element in most models is the explicit coupling of the electrical to the mechanical degrees of freedom. By modeling this coupling, predictions of both mechanical forces and transducer currents are be made enabling comparisons and analysis of electro-physiological experiments.

A mechanical-electrical-acoustic (MEA) model of the cochlea is presented whose key components are a micro-electro-mechanical model for the cochlear structures, a two-duct acoustic model with structural-acoustic coupling at the basilar membrane (BM) and a global electrical circuit to model conductances in the different scalae. Incorporation of the electrical domain in the model enables computation of the cochlear microphonic and other cochlear potentials. Comparisons of predicted and experimentally measured receptor and extracellular potentials will be presented. Model response to pure acoustic input, round window electrical stimulation, and bipolar electrical stimulation are presented and differences between electric and acoustic stimulation explained via the model. The introduction of random perturbations (roughness) of specific cochlear structures (e.g. BM stiffness) is shown to produce fine structure in emissions. Model simulations show that the RC cut off of the hair cells can, in part, be overcome by a tectorial membrane inertia. This project is funded by NIH NIDCD R01 - 04084.

Presentation (PowerPoint File)

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