Time lapse effects of impulse noise on cochlear microphonics in rabbits observed in chronic experiments.

Cochlear microphonics (CM) were recorded from awake rabbits with chronically implanted electrodes. Test frequencies used were 1,250, 2,500, 5,000 and 10,000 Hz, with intensities increased from 40 to 100 dB SPL. The rabbits were exposed to ten noise impulses of 144 dB SPL, which were then followed by impulse intensities of 153 and 164 dB SPL for the same animal. Input-output functions before and after each noise exposure were recorded, and recovery processes of the CM were tracked. After 144 dB SPL impulses, complete recovery of CM occurred; the effects of 153 dB SPL impulses varied from restitution up to complete CM loss. Impulses of 164 dB SPL caused an irreversible CM loss in all cases. Despite inter-individual differences, the threshold for irreversible CM loss in rabbits may occur between impulse noise intensities of 153 and 164 dB SPL.