Response of cochlear nerve fibers to brief acoustic stimuli: role of discharge-history effects.

The probability that a cochlear nerve fiber spike discharge occurs during a time interval delta t depends on both the acoustic stimulus and on aftereffects from earlier spike discharges. We have examined the influence of discharge-history on post-stimulus time (PST) histogram responses to acoustic click and tone-burst stimuli. Discharge-history effects were found to include the modification of observed interpeak times of PST responses to clicks, a loss of distinct peaks in the click response of high characteristic frequency (CF greater than 5 kHz) fibers, and changes in the ratio of initial to steady-state response portions of tone-burst responses. The method used to separate discharge-history from stimulus-related factors is based on a model developed in Gaumond et al. [J. Neurophysiol. 48, 856-873 (1982)]. The results are in general agreement with those obtained by the method of Peter Gray [Biophys. J. 7, 759-777 (1967)], which discards from consideration those portions of the response record not preceded by a silent interval of 20 or 25 ms or more. Our method requires more assumptions about the spike train, but produces less variable results by utilizing more of the spike train data.