The influence of the electrode size of cochlear implants on the spatial selectivity

Abstract

Introduction. The authors aimed to study the influence of the electrode size on the spatial selectivity with cochlear implants. Material and methods. The Leiden cochlear implant project studies the key factors that determine the clinical outcome with cochlear implants. For this purpose the electrical field in the cochlea is computed, and from this the neural response is predicted. The present cochlear model consists of a 30 turn tapered spiral (guinea-pig). In this study we present calculations for both point sources and electrodes with realistic dimensions, comparable with the often-used Nucleus electrode. The size of the electrode relative to the scala tympani is varied. Furthermore, the consequences of the application of three poles (positive, negative, positive) instead of two poles (positive, negative) were investigated. Results. A higher degree of scala tympani filling results in the reduction of current thresholds without much influence on the spatial selectivity. Only when thin electrodes are used does the application of three poles result in an improved spatial selectivity. Such tripoles, however, exhibit relatively high thresholds. Conclusion. Favourable use of tripole stimulation (thin electrodes) easily results in high current densities. Thick dipoles result in reduced thresholds and current densities with comparable spatial selectivity relative to thin dipoles.