The influence of moderate-intensity noise on the click-evoked compound action potential of the guinea pig, Cavia porcellus.

Noise-induced alterations of the click-evoked compound potential (CAP) were studied by means of electrodes chronically implanted near the round window in 15 pigmented guinea pigs aged 3-6 months. The potentials were recorded before, during and after exposure to continuous pink noise maintained at an intensity of 80, 90 or 100 dB SPL for 120 h. During the exposure phase the CAP thresholds of all the animals tested increased exponentially, nearly leveling out by approximately 48 h to form an asymptotic threshold shift. Recovery after the end of exposure also occurred exponentially, with a return to the original threshold for neural excitation after at most 72 h. There was no detectable change in amplitude, latency or inter-peak interval of the CAP when correlated with the change in threshold.