Single-unit response at the round window of the guinea pig.

In guinea pigs the unit contribution (unit action potential, ap) to the response of the round window was computed following the method used by Kiang and co-workers (1976), i.e., fibre discharges registered by a microelectrode in the nerve were used as trigger pulses for the averaging process of the corresponding ap registered with a gross electrode at the round window. Normally the ap was independent of the fibre-CF, had a diphasic waveform, and its amplitude was about 0.1 microV. Small inter-animal differences were found in waveform and amplitude of the ap. In a pilot experiment exploring pathological influences on ap, the auditory nerve was stretched to mimic the effect of some acoustic nerve tumors. We found that the waveforms of both ap and compound action potential (CAP) changed. The results indicate that in normal guinea pig cochleas the existence of an elementary unit waveform can be used in the convolution of the CAP [Goldstein, M.H. Jr. and Kiang, N.Y.S. (1958) J. Acoust. Soc. Am. 30, 107-114]. In abnormal cochleas, however, deteriorated aps may disturb the simple convolution concept of the CAP.