Peter Heil: Mechanisms of the phase–locking of auditory-nerve fibers: a modeling approach

Phase locking of spikes of auditory-nerve fibers, the primary auditory afferents, to the fine-structure of acoustic stimuli is a hallmark of the temporal precision of the auditory system and its processing speed. It manifests itself as a non-uniform distribution of spikes over a stimulus cycle, even if only a couple hundred microseconds long.

Phase-locked spikes constitute the inputs to neurons in the brainstem which extract interaural time differences in the microsecond range for sound localization. Phase locking may also be relevant for the perception of pitch, a salient feature of many sounds including speech and music.

In this project, we attempt to develop a parsimonious model that accounts for the detailed features of the phase-locked responses of primary auditory afferents and their changes with sound frequency and sound level, and to relate them to other response characteristics of these afferents. To this end, we developed a model that accurately accounts for the instantaneous spike probability of mammalian primary auditory afferents in the course of a stimulus cycle, as functions of sound frequency and level. We also developed a model of synaptic vesicle-pool depletion and replenishment that accurately accounts for spiking statistics (interspike interval distributions, serial interval correlations, and spike-count distributions) of these afferents during spontaneous activity. We now plan to combine the two models to also account for the spiking statistics of sound-driven phase-locked responses, as well as test the more general validity of our models by applying them to data from birds.