Follow-up of latency and threshold shifts of auditory brainstem responses after single and interrupted acoustic trauma in guinea pig.

Thresholds of auditory brainstem responses (ABRs) are widely used to estimate the level of noise-induced hearing loss or the level of acquired resistance to acoustic trauma after repeated exposures, i.e., the "toughening" effect. Less is known about ABR latencies and their relation to threshold changes. Guinea pigs were exposed to a traumatic pure tone at 5 kHz, 120 dB SPL, as either single (2 h, 4 h) or repeated (1 h every 48 h, four times) sessions. Thresholds and latencies of ABRs were monitored up to 45 days following the acoustic trauma. We show that latencies are prolonged in the case of large temporary threshold shifts observed in the days following trauma. The latency shift decreases after several repeated exposures, then stabilizes, similar to thresholds, suggesting that the "toughening" effect also applies to latencies. Permanent latency shift is usually very small compared to the permanent threshold shift. This effect could produce a recovery in the ability to process auditory information through the precise timing of neuronal events. Our study indicates that when estimated at suprathreshold stimulation level (70 dB SPL), latency provides complementary information to the sole threshold.