Compound action potential and single unit haversine responses

Abstract

The auditory nerve compound action potential (CAP) response to a low‐frequency 1‐kHz haversine differs dramatically from the more familiar rectangular‐pulse (“click”) CAP. The haversine CAP consists of several negative peaks separated by about 1 ms whose latencies shift by about 0.5 ms when the stimulus polarity is reversed. We collected, from cats, haversine‐evoked single‐unit post‐stimulus time histograms (PSTHs) in an attempt to define the pattern of unit activity underlying the haversine CAP. Low characteristic frequency (CF) units have haversine PSTHs similar to click‐evoked PSTHs, with interpeak intervals equal to 1/CF. Above a CF of about 1.5 kHz, the interpeak intervals become fixed at about 1 ms, and the responses progressively decrease, in keeping with the reduced spectral density of the stimulus at those frequencies. Units with CF above 5 kHz show little or no response. These observations suggest that the haversine CAP originates primarily from nerve fibers of CF from 1 to 3 kHz. [Supported by NIH and The Pauline Sterne Wolff Memorial Foundation Fund.]