Cat auditory nerve fiber recovery functions

Abstract

The literature contains few examples of auditory nerve fiber response recovery functions. To provide more information, hazard functions were compiled from 10–120 s samples of spontaneous and driven activity. Responses formed two groups that differed only in the amount of activity at short (<1.5 ms) inter-spike intervals. The larger group possessed hazard functions described by an equation with one time constant, i.e., R(t)=3D 1-e(S-t)/t, where R(t) is the amount of response recovery at time t, S is the starting time of the recovery process (analogous to absolute refractoriness), and t is the time constant. The other, smaller group possessed hazard functions similar to that reported by Gaumond et al. [J. Neurophysiol. 48, 856–873 (1982)], in which a portion of the response recovers rapidly at the end of the absolute refractory period and the remainder recovers more slowly. This behavior was described well by a two-process equation, i.e., R(t)=3DM (1−e(Se−t)/t e)+(1−M)=(1−e(Sl−t)/tl) where Se and Sl are the starting times of the ‘‘early’’ and ‘‘late’’ recovery processes, t e and t l are their time constants, and M is the amount of recovery attributable to the early process. S, Se and Sl ranged from 0.7–1.3 ms, t e ranged from 1.2–1.5 ms, t and t l ranged from 3–6 ms and usually decreased somewhat with level, and M ranged from 0.2–0.4.