Compound action potentials and single unit responses to a 1 kHz haversine in the cat

The single-cycle 1 kHz haversine (one cycle of a 1 kHz sine wave beginning at -90 degrees) is a low-frequency impulsive stimulus which has been little use, but which has significant potential applications both as a clinical and a research tool. The auditory nerve compound action potential (CAP) and single unit discharge patterns evoked by a single-cycle 1 kHz haversine stimulus were studied in anesthetized cats. The haversine CAP waveform consisted of two or three short latency peaks with peak to peak intervals of about 1.0 ms. Latencies of the CAP peaks decreased with increased stimulus intensity and were also strongly dependent on stimulus polarity. Typically, CAP peak latencies changed by about 0.5 ms with stimulus polarity reversal. Single unit responses were classified by the peak latency pattern of their haversine post-stimulus time histograms (PSTHs). Low CF units had low thresholds and PSTHs resembling their click responses. High CF units had high thresholds and PSTHs comprised of one or two short latency peaks whose latencies were polarity-sensitive. Some units in an intermediate CF range (approximately 1.5-3.0 kHz) had PSTHs which were a transitional form between the high and low CF types of response. The unit discharge patterns strongly suggested a low frequency origin for the haversine CAP at all intensities.