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.

中文翻译：

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终生暴露于环境噪声后无突触病的中枢听觉处理的时间变化

人们越来越多地通过职业和娱乐活动的累积暴露于环境噪声中，如果声音强度保持在<80 dB，则认为这对听觉系统无害。然而，尽管听力测定结果正常，但最近有证据表明噪声引起的外周突触损伤和听觉皮层中枢重组，这使人们对终生暴露于环境噪声的无害性产生了怀疑。我们通过将成年大鼠暴露在现实和非创伤性环境噪声中来解决这个问题，在人类每日允许的噪声暴露限制范围内（80 dB 声压级，8 小时/天），持续 3 到 18 个月。我们发现每天接触 6 个月后可以检测到暂时性听力损失，不会导致永久性听力损失或耳蜗毛细胞中突触带缺失。暴露 18 个月后听觉皮层中声音的退化时间表示与仅暴露 3 个月后观察到的效果有很大不同，这表明在暴露于噪声的整个生命周期中，对神经代码的修改会持续存在。