Frequency-dependent simulation of volume conduction in a linear model of the implanted cochlea

Volume conduction models of the implanted cochlea are useful tools for investigating cochlear implant function. To date, however, all existing models have assumed that the tissues of the cochlea are purely resistive, despite evidence to the contrary. In this paper, a preliminary attempt to incorporate frequency-dependent effects is made using a simple, extruded finite element model of the cochlea. It was found that resistive and dispersive formulations exhibited marked differences in the pattern of current flow, especially later in the phase. The scala tympani response remained largely resistive as per published experimental evidence. However, injected current was also diverted away from higher impedance bone and neural tissue towards lower impedance pathways, particularly the cerebrospinal fluid in the modiolus. Further investigation of these effects is warranted to better understand these differences and how they might affect existing models of neural excitation.