The influence of cochlear anatomy on the outcome of cochlear implants

Abstract

Introduction. The objective was to identify the influence of the cochlear anatomy on the electrode-to-neural interface in cochlear implants. Methods. A three-dimensional spiralling computer model of the implanted inner ear of man and guinea pig,1 including a new clinical perimodular electrode array (Clarion Hi-Focus with Positioner) was used to study the spatial selectivity and dynamic range of the device. At higher stimulus levels it was expected that excitation of nerve fibres from more apical turns would interfere with the concept of making use of the tonotopic organization of the cochlea. Results. In humans (in contrast with the guinea pig), a well-designed perimodular electrode yields lower current thresholds and a higher spatial selectivity than conventional electrodes, while preserving a good dynamic range. The apical turn of the human cochlea, however, is largely similar in this respect to the guinea pig cochlea, in which cross-turn stimulation reduces the dynamic range substantially. Conclusion. The clinical success of cochlear implantation in man and the favourable results with perimodular devices depend upon the anatomy of the human cochlea.