Effect of site of spike generation on temporal coding in the electrically stimulated auditory nerve

At least two sites of spike generation are observed in the electrically stimulated auditory nerve, namely, the peripheral axon and the central axon. The peripheral axon responds to the cathodic charge and the central axon to the anodic charge with an approximate spike-latency difference of 200 μs. The peripheral axon also shows longer refractory periods than the central axon. In this study, a phenomenological model of the electrically stimulated auditory nerve described in Joshi et al. [JARO 18(2), pp. 323–342] was used to understand the effect of spike generation sites on the temporal coding. Modulation detection thresholds for different carrier pulse rates were predicted from simulated responses of the auditory nerve, and refractoriness of both the axons was varied to test its effect on temporal coding. The results show that an increase in pulse rate increased the number of spikes generated at the central axon, hence decreasing the modulation detection thresholds. Refractoriness also played a crucial role in encoding the stimulus envelope such that extended refractory periods resulted in enhanced envelope coding. Increase in refractoriness at the central axon improved the envelope encoding. Implications of these findings for developing new stimulation strategies will be discussed.