Temporal Alterations to Central Auditory Processing without Synaptopathy after Lifetime Exposure to Environmental Noise

Abstract

People are increasingly exposed to environmental noise through the cumulation of occupational and recreational activities, which is considered harmless to the auditory system, if the sound intensity remains <80 dB. However, recent evidence of noise-induced peripheral synaptic damage and central reorganizations in the auditory cortex, despite normal audiometry results, has cast doubt on the innocuousness of lifetime exposure to environmental noise. We addressed this issue by exposing adult rats to realistic and nontraumatic environmental noise, within the daily permissible noise exposure limit for humans (80 dB sound pressure level, 8 h/day) for between 3 and 18 months. We found that temporary hearing loss could be detected after 6 months of daily exposure, without leading to permanent hearing loss or to missing synaptic ribbons in cochlear hair cells. The degraded temporal representation of sounds in the auditory cortex after 18 months of exposure was very different from the effects observed after only 3 months of exposure, suggesting that modifications to the neural code continue throughout a lifetime of exposure to noise.

Alpha9alpha10 knockout mice show altered physiological and behavioral responses to signals in masking noise

“…This also results in an increase in afferent activity. Enhanced auditory input is known to broadly and significantly impact physiology in the brainstem and auditory cortex ( Ngodup et al , 2015 ; Occelli et al , 2022 ; Oliver et al , 2011 ; Willott et al , 2005 ; Zhang et al , 2001 ). Specific contributions from peripheral and central compensatory mechanisms to hearing-in-noise phenotypes in MOC mutants are unknown and should be explored in future studies.…”

Unexpected Motherhood-Triggered Hearing Loss in the Two-Pore Channel (TPC) Mutant Mouse

“…In addition to motherhood, exposure to loud sounds (above or just below the authorized level of 80 dBA during 8 h of work, ISO 1996-1, 2003) can be a way to reveal changes between the WT and TPC KO mice. However, in the case of noise exposure at 80 dBA, it is only with very long lasting noise exposure that effects can be observed [ 51 ].…”