Modelling of the electrode-auditory nerve fibre interface in cochlear prostheses

Abstract

The objective of this thesis is to provide additional insight into the electrode array-nerve fibre interface that exists in the implanted cochlea and to facilitate investigation of new electrode arrays in interaction with the cochlea and auditory nerve fibres. The focus is on potential distributions and excitation profiles generated by different electrode array types and factors that could have an influence on these distributions and profiles. Research contributions made by the thesis are the creation of a detailed 3-D model of the implanted cochlea that accurately predicts measurable effects in cochlear implant wearers and facilitates effortless simulation of existing and new electrode array variations; the establishment of the important anatomical structures required in a 3-D representation of the implanted cochlea; establishment of evidence that array location is the primary parameter that controls spread of excitation; definition of the critical focussing intensity of intracochlear electrode pairs; confirmation thatmonopolar stimulation could deliver focussed stimulation to approximately the same degree than that delivered by widely spaced electrode configurations and that the use of monopolar configurations over bipolar configurations are therefore advantageous under certain conditions; explanation of the effect that encapsulation tissue around cochlear implant electrodes could have on neural excitation profiles; extension of the information available on the focussing ability of multipolar intracochlear electrode configurations; and establishment of evidence that a higher lateral electrode density could facilitate better focussing of excitation, continuous shaping of excitation profiles and postoperative customization of electrode arrays for individual implant wearers.