The University of Southampton
Engineering and the Environment

Research project: Modelling the voltage distribution due to a cochlear implant

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As presented at the Signal Processing and Control Group Away Day, June 2012.

Project Overview

A number of different models have been used to study the voltage distribution within the cochlea due to electrical stimulation from individual electrodes of a cochlear implant. A resistive cable model is first used to illustrate the fall-off of the voltage with distance along the cochlea. This can be used to predict the voltages at the other electrode positions, and thus build up an electrical impedance matrix that can be compared with that measured in cochlear implant patients. The purpose of such tests is to improve the power consumption and performance of during stimulation leading to improved perception and a more efficiently designed cochlear implant.

The cable model is, however, only a one-dimensional representation of a three dimensional voltage distribution. A three-dimensional geometric model of the cochlea was produced to obtain the voltage distribution at positions closer to the site of neural stimulation.

A finite element model of the voltage distribution was thus developed and this was used to demonstrate the way voltage spread varies with geometry of the cochlea and the electrode array. This can be used to investigate pathological and natural variation in the cochlea as well as to simulate varied electrode array configurations and positioning within the cochlear chambers. The model was used to confirm that placing the array closer to the modiolus resulted in higher impedances implying increased stimulation. It was discovered that stimulation focussing could be improved by using impedance information at the neural level along the spiral ganglion as opposed to along the electrode array. This leads to improved perception but required more power. It was also found that placing the return electrode of the implant within the modiolus as opposed to the outside of the cochlea resulted in higher stimulation for the same current input, which implies that power requirements could be reduced or the extra power could be used to implement stimulation focussing.

Related research groups

Signal Processing and Control Group

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