The effects of primed and interrupted noise exposure paradigms on hearing loss

Exposure to low-level noise (priming) produces a protective effect on the auditory system evidenced by a reduced permanent threshold shift (PTS) from a subsequent high-level exposure. Similarly, regularly interrupting a high-level noise exposure causes the threshold shift following daily repeated exposures to the noise to be reduced with a concomitant lowering of PTS. These effects, collectively referred to as ‘‘toughening,’’ can exceed 35 dB. If the toughening mechanism elicited during both types of exposure paradigms has a common origin, then combining the paradigms should yield predictable results. Results from nine exposure paradigms with five to six chinchillas in each paradigm are reported. Impacts of 113 or 119 dB peak SPL and pink noise of 72 or 78 dB SPL presented over five or 20 days in an interrupted or noninterrupted paradigm were used. Results suggest that priming can affect the PTS but has little or no effect on the toughening produced during interrupted exposures or the asymptotic threshold shift (ATS) produced by an uninterrupted exposure. Similarly, the toughening produced during an interrupted exposure affects PTS but not ATS from an uninterrupted exposure. These results suggest independent mechanisms for the two toughening phenomena. [Research sponsored by NIOSH.]