Institut de NeuroScience Paris-Saclay (NeuroPSI), University Paris-Sud, 91405 Orsay cedex, France; UMR CNRS 9197, University Paris-Sud, 91405 Orsay cedex, France.
Institute for Neurosciences of Montpellier, University of Montpellier, 34091 Montpellier cedex, France; INSERM - UMR 1051, University of Montpellier, 34091 Montpellier cedex, France.
Neuroscience. 2019 Apr 15;404:184-204. doi: 10.1016/j.neuroscience.2019.02.002. Epub 2019 Feb 12.
Aging is often considered to affect both the peripheral (i.e. the cochlea) and central (brainstem and thalamus-cortex) auditory systems. We investigated the effects of aging on the cochlea, brainstem and cortex of female Sprague-Dawley rats. The auditory nerve threshold remained stable between the ages of nine and 21 months, as did distortion product otoacoustic emissions and the number of ribbon synapses between inner hair cells and nerve fibers. The first clear signs of aging appeared in the brainstem, in which response amplitude decreased, with thresholds remaining stable until the age of 15 months, and increasing slightly thereafter. The responses of primary auditory cortex neurons revealed specific effects of aging: at 21 months, receptive fields were spectrally narrower and the temporal reliability of responses to communication sounds was lower. However, aging had a null or even positive effect on neuronal responses in the presence of background noise, responses to amplitude-modulated sounds, and responses in gap-detection protocols. Overall, inter-animal variability remained high relative to the variability across groups of different ages, for all parameters tested. Behavioral performance for the modulation depth of amplitude modulation noise was worse in 21-month old animals than in other animals. Age-related alterations of cortical and behavioral responses were thus observed in animals displaying no signs of aging at the peripheral level. These results suggest that intrinsic, central aging effects can affect the perception of acoustic stimuli independently of the effects of aging on peripheral receptors.
衰老是一个普遍的现象，它不仅会影响外周听觉系统（例如耳蜗），也会影响中枢听觉系统（脑桥和丘脑-皮层）。我们研究了衰老对雌性 Sprague-Dawley 大鼠耳蜗、脑桥和皮层的影响。在 9 至 21 个月龄之间，听神经阈值保持稳定，畸变产物耳声发射和内毛细胞与神经纤维之间的 ribbon 突触数量也保持稳定。衰老的第一个明显迹象出现在脑桥中，其表现为反应幅度减小，而阈值则保持稳定，直到 15 个月龄，此后略有增加。初级听觉皮层神经元的反应揭示了特定的衰老效应：在 21 个月龄时，感受野的频谱变窄，对通讯声音的反应时间可靠性降低。然而，在存在背景噪声、对幅度调制声音的反应以及在缺口探测协议中的反应时，衰老对神经元反应具有零效应甚至正效应。总体而言，与不同年龄组之间的变异性相比，所有测试参数的动物间变异性仍然很高。在调制深度为幅度调制噪声的行为表现中，21 个月龄的动物比其他动物差。因此，在没有外周感受器衰老迹象的动物中观察到了皮层和行为反应的与年龄相关的改变。这些结果表明，内在的中枢衰老效应可以独立于外周感受器衰老对听觉刺激的感知产生影响。
