Noise-induced threshold shifts in the Mongolian gerbil

Abstract

Mongolian gerbils were trained in a shuttlebox avoidance task and their auditory thresholds determined. Groups of six subjects each were exposed to a two-octave (1414–5656 Hz) band of noise for one hour at intensities of 100, 110, and 120 dB SPL. Thresholds between 0.1 and 16.0 kHz were determined 0.5, 3.0, 6.0, and 12.0 hours after exposure, and daily for 27 days. Final threshold determinations were made at least two months postexposure. A temporary threshold shift (TTS) was observed in all groups, the extent of which increased with increasing intensity of exposure. Recovery of thresholds followed an exponential course, and for extensive TTS lasted throughout the 28-day observation period. In some cases additional recovery was noted upon final threshold determination. No significant permanent threshold shift (PTS) was seen in the 100-dB exposure group, but PTS did occur in the 110-and 120-dB groups. PTS was limited to a relatively narrow band of frequencies, and exhibited a half-octave shift toward higher frequencies. In terms of both TTS and PTS, the gerbil appears to be less sensitive to noise than chinchillas exposed to the same stimulus. [Work supported by NINCDS and the Medical Research Service of the Verterans Administration.]