Experimental and analytic studies of synchronized responses in the chinchilla auditory nerve

Abstract

The current interest in the coding of sounds by the temporal aspects of spike trains in the auditory nerve suggested a parametric study of synchrony of firing to low frequency sounds and the various indices used to quantify synchronization. Index of synchrony and preferred phase were measured as a function of sound pressure and frequency for single units in the auditory nerve of the chinchilla. Results from several previous studies in other laboratories agree well with the current data which are, however, more complete. It was found that synchrony is a function of frequency and level relative to threshold but otherwise independent of fiber characteristic frequency (CF). Preferred phase, however, depended on the relation between frequency and CF as well as level. The maximum value of synchrony obtained for all fibers formed a low‐pass function of frequency with a high frequency rolloff of approximately 6 dB/octave. A simple model consisting of a half‐wave rectifier followed by a low‐pass filter could predict the period histograms remarkably well. Analysis of the indices of synchrony has shown them to be relatively insensitive to the scatter of firing over one half‐cycle, explaining, in part, the steepness of synchrony‐versus‐level functions. [Supported by NINCDS.]