Short-time course of adaptation pattern after noise exposure: electrophysiological studies in man

Tone burst and click-evoked potentials were recorded in both humans and guinea pigs to determine whether responses associated with the cochlea and brainstem regions show a pattern of recovery from noise exposure similar to the polyphasic changes found for the pattern of early recovery from temporary threshold shift reported by Hirsh and Ward in 1952 [J. Acoust. Soc. Am. 24, p. 131]. During the 'post-stimulatory' phase following exposure for 5 min to broad-band noise at various intensity levels between 90 and 110 dB SPL, changes in amplitude and latency of the dominant complexes of the cortical and brainstem-evoked potentials were monitored for 5 min with 1.5- and 60-second time resolution. There was clear evidence of polyphasic processes at the cortical level, whereas in the brainstem region, large post-stimulatory amplitude shifts were generally accompanied by an asymptotic recovery. The relevance of the results to the different stations in the auditory pathway is evaluated by comparison with published electrophysiological data on activities at the different levels of the brainstem and the brain as reflected in evoked responses and single-unit recordings.