Comprehensive analysis of auditory nerve fiber responses using fiber-specific modeling

One important aspect of improving cochlear implant performance is a good, quantitative understanding of electrically stimulated nerve fibers and the effects of deafness on their behavior. The main principles of a nerve fiber's responses are well understood. The measures describing the responses, such as the refractory period or facilitation, and the effects of deafness on them, have been investigated in different publications and nerve fiber populations. However, a comprehensive analysis of many measures based on a single dataset is still lacking. Using a fiber-specific model-based analysis, we show that it is possible to extract multiple measures from existing pulse train recordings of 118 guinea-pig nerve fibers. This not only included eight basic measures, such as refractory period and facilitation, but also four spike-train-derived measures (spike rate, dip duration, interspike interval, and vector strength). Using these, we started two lines of investigation. In the first one, we investigated the response differences between fibers from acutely and chronically deafened animals. The results showed that, on average, the chronically deaf groups had a shorter refractory period and a higher discharge rate. In the second line, we investigated the relationship between the basic measures and the spike-train measures using fiber-specific modeling. This showed, e.g., an inverse relationship between the spike rate and the refractory period, confirming our previous findings. Overall, this paper provides a detailed characterization of both acutely and chronically deafened nerve fibers, and an analysis of the interaction between basic measures and spike-train responses.NEW & NOTEWORTHY Quantitative descriptions of electrically evoked auditory nerve responses are essential for improving cochlear implants. Using fiber-specific modeling, this study extracts a comprehensive set of response measures from pulse-train recordings of 118 auditory nerve fibers. Comparing fibers from acutely and chronically deafened animals reveals differences, e.g., in refractory properties and response rate. An investigation into the relationship between the measures revealed a dependency of the rate on the refractory properties and additionally on the dynamic range.