Mulders Wilhelmina H A M, Chin Ian L, Robertson Donald
The Auditory Laboratory, School of Human Sciences, The University of Western Australia, Nedlands, Western Australia, 6009 Australia; Ear Science Institute Australia, 1/1 Salvado Rd, Subiaco, Western Australia, 6008, Australia.
The Auditory Laboratory, School of Human Sciences, The University of Western Australia, Nedlands, Western Australia, 6009 Australia.
Hear Res. 2018 Apr;361:45-51. doi: 10.1016/j.heares.2018.02.001. Epub 2018 Feb 14.
Noise exposures that result in fully reversible changes in cochlear neural threshold can cause a reduced neural output at supra-threshold sound intensity. This so-called "hidden hearing loss" has been shown to be associated with selective degeneration of high threshold afferent nerve fiber-inner hair cell (IHC) synapses. However, the electrophysiological function of the IHCs themselves in hidden hearing loss has not been directly investigated. We have made round window (RW) measurements of cochlear action potentials (CAP) and summating potentials (SP) after two levels of a 10 kHz acoustic trauma. The more intense acoustic trauma lead to notch-like permanent threshold changes and both CAP and SP showed reductions in supra-threshold amplitudes at frequencies with altered thresholds as well as from fully recovered regions. However, the interpretation of the results in normal threshold regions was complicated by the likelihood of reduced contributions from adjacent regions with elevated thresholds. The milder trauma showed full recovery of all neural thresholds, but there was a persistent depression of the amplitudes of both CAP and SP in response to supra-threshold sounds. The effect on SP amplitude in particular shows that occult damage to hair cell transduction mechanisms can contribute to hidden hearing loss. Such damage could potentially affect the supra-threshold output properties of surviving primary afferent neurons.
导致耳蜗神经阈值完全可逆变化的噪声暴露会在阈上声强时引起神经输出减少。这种所谓的“隐性听力损失”已被证明与高阈值传入神经纤维-内毛细胞（IHC）突触的选择性退化有关。然而，IHC本身在隐性听力损失中的电生理功能尚未得到直接研究。我们在10kHz两种强度的声损伤后进行了圆窗（RW）耳蜗动作电位（CAP）和总和电位（SP）测量。更强的声损伤导致了类似缺口的永久性阈值变化，并且CAP和SP在阈值改变的频率以及完全恢复的区域的阈上幅度均降低。然而，由于阈值升高的相邻区域贡献减少的可能性，正常阈值区域结果的解释变得复杂。较轻的损伤显示所有神经阈值完全恢复，但对阈上声音的反应中，CAP和SP的幅度持续降低。特别是对SP幅度的影响表明，毛细胞转导机制的隐匿性损伤可能导致隐性听力损失。这种损伤可能会潜在地影响存活的初级传入神经元的阈上输出特性。
