Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.
Hear Res. 2010 Mar;261(1-2):30-5. doi: 10.1016/j.heares.2009.12.025. Epub 2009 Dec 29.
Long-term, passive, continuous exposure of mature animals to moderate-level, band-limited sounds can profoundly decrease neural activity in primary auditory cortex (AI) to sounds in the exposure frequency range, and increase activity to sounds outside the exposure range. The resulting reorganization of the AI tonotopic map resembles that following a restricted lesion of the cochlear epithelium. Here we show qualitatively similar effects of passive exposure when it is limited to 12 h/day, simulating a noisy-work/quiet-living environment, albeit at substantially lower intensity levels (68 dB SPL) than are considered harmful to hearing. Compared to continuous exposure at the same SPL and over a similar duration (6-12 weeks), this intermittent exposure produced a smaller decrease in AI spike and LFP (local field potential) activity in response to sound frequencies in the exposure range, and an increase in activity only for frequencies above the exposure range. As expected at these exposure levels, cortical changes occurred in the absence of concomitant hearing loss (i.e., absolute threshold shifts). Our results have implications for occupational noise exposure standards, which presently may not prevent changes in central auditory function that cannot be detected on the standard behavioral audiogram.
长期、被动、持续地让成熟动物暴露于中强度、频带受限的声音中，会显著降低初级听觉皮层（AI）对暴露频率范围内声音的神经活动，并增加对暴露范围外声音的活动。由此导致的 AI 音调图的重组类似于耳蜗上皮受限损伤后的重组。在这里，当暴露时间限制在每天 12 小时，模拟嘈杂的工作/安静的生活环境时，我们观察到类似的被动暴露的效果，尽管暴露强度水平（68 dB SPL）比被认为对听力有害的水平低得多。与相同 SPL 下持续暴露且暴露时间相似（6-12 周）相比，这种间歇性暴露对暴露范围内声音的 AI 尖峰和 LFP（局部场电位）活动的反应降低幅度较小，而对暴露范围以上的频率的活动增加幅度较大。正如在这些暴露水平下预期的那样，皮质变化发生在没有伴随听力损失的情况下（即绝对阈值变化）。我们的结果对职业噪声暴露标准具有影响，目前这些标准可能无法防止在标准行为听力图上无法检测到的中枢听觉功能变化。
