Simulation of auditory nerve fiber excitation with prostheses implanted in the scala vestibuli

Abstract

Since the 1970s, the cochlear implant (CI) is a widespread device to restore bad or missing hearing function. For this, electrodes which stimulate the auditory nerve fiber (ANF) are usually inserted in the scala tympani (ST). However, in case of an obstructed or ossified ST, electrode insertion becomes impeded or even impossible. Therefore, alternative locations for insertions are needed. The aim of this thesis is to compare the ANF excitation behavior between electrodes that are inserted in the scala vestibuli (SV), the other large cochlear duct, and ST-positioned electrodes. Four nerve fibers were analyzed by defining a model of the Hodgkin-Huxley type and conducting a simulation in Matlab R2021b. Anodic and cathodic threshold values were computed for each fiber and the performance of ST- and SV-positioned electrodes was compared. Moreover, the fibers were also simulated as degenerated fibers by cutting-off the dendrite. The outcomes of this thesis show lower threshold values for SV-positioned electrodes in non-degenerated fibers. In degenerated fibers higher currents are needed for excitation, especially for electrodes in the SV. This thesis also suggests mid-dendritic electrode position as the best electrode location. Although further research is needed, it can be stated that the SV is an adequate alternative for electrode insertion.