Development of a Parametric Model of the Electrically Stimulated Auditory Nerve

Abstract

Cochlear implants (CIs) are used to restore the sense of hearing in people with profound hearing loss. Some CI users can communicate over the phone and even understand speech with some background noise, whereas some other CI users do not obtain the same benefit from the device. Due to differences in the interface between the electrodes and the auditory nerves, the best settings of the CI may be different for each user. In order to improve the fitting of CIs and to understand the electrode-nerve interface, a user-specific model of the auditory nerve activity has been developed. The model is based on a combination of existing models found in the literature. This chapter presents the basic components of the model: A three-dimensional finite element method to estimate the voltage distribution in the cochlea; and an auditory nerve model based on multi-compartment Hodgkin-Huxley-type equations fitted to known electrophysiological measurements. Using the above described model, intracochlear voltage distributions are reproduced. Additionally, amplitude growth functions of the evoked compound action potential (ECAP) were simulated using an artifact rejection forward masking paradigm. The model has been parameterized such that it can be personalized to each CI user by fitting its parameters to predict the individual voltage distributions and amplitude growth functions. The modeling results show that different amounts of nerve density and nerve degeneration lead to different shapes in the amplitude growth function. The future goal of the model is to create a tool to predict the most comfortable level of each CI user and to fit CI parameters in a personalized clinical situation.