Predicting objective measures of the electrode-neuron interface with an auditory model

Measurement of electrically evoked compound action potentials (eCAPs) provides means to assess the functionality of the electrode-neuron interface of a cochlear implant (CI) user. Interestingly, animal studies have provided encouraging evidence that eCAP metrics could also be used to assess the cochlear health of the CI user. Such findings have been somewhat questioned upon encountering difficulties in translating findings from animal studies into benefits for CI users. Here, we approach this dilemma from a computational modeling point of view, using a simplified 2-D model that emulates how the electrical signal from the stimulating electrode reaches the auditory nerve fibers distributed along the cochlea, evoking the neurons to create action potentials that can be recorded as a compound response at one of the recording electrodes. We applied the model in simulated eCAP amplitude growth function (AGF) measurements and obtained predictions that are in line with the data from literature: Steeper eCAP AGF slopes resulted from increased neural survival and from prolonging of the inter-phase gap (IPG) of the biphasic pulse, the magnitude of the IPG effect on the slope increasing with increased neural survival. In summary, our study shows how auditory models can be used to test theories of effects on objective measures of CI user's electrode-neuron interface