Center for Neuroscience, University of California, Davis, California.
Department of Neurobiology, Physiology, and Behavior, University of California, Davis, California.
J Neurophysiol. 2020 Mar 1;123(3):1015-1025. doi: 10.1152/jn.00373.2019. Epub 2020 Jan 29.
Inhibition plays a key role in shaping sensory processing in the central auditory system and has been implicated in sculpting receptive field properties such as sound intensity coding and also in shaping temporal patterns of neuronal firing such as onset- or offset-evoked responses. There is substantial evidence supporting a decrease in inhibition throughout the ascending auditory pathway in geriatric animals. We therefore examined intensity coding of onset (ON) and offset (OFF) responses in auditory cortex of aged and young monkeys. A large proportion of cells in the primary auditory cortex (A1) and the caudolateral field (CL) displayed nonmonotonic rate-level functions for OFF responses in addition to nonmonotonic coding of ON responses. Aging differentially affected ON and OFF responses; the magnitude of effects was generally greater for ON responses. In addition to higher firing rates, neurons in old monkeys exhibited a significant increase in the proportion of monotonic rate-level functions and had higher best intensities than those in young monkeys. OFF responses in young monkeys displayed a range of intensity coding relationships with ON responses of the same cells, ranging from highly similar to highly dissimilar. Dissimilarity in ON/OFF coding was greater in CL and was reduced with aging, which was largely explained by a preferential decrease in the percentage of cells with nonmonotonic coding of ON and OFF responses. The changes we observed are consistent with previously demonstrated alterations in inhibition in the ascending auditory pathway of primates and could be involved in age-related deficits in the temporal processing of sounds. Aging has a major impact on intensity coding of neurons in auditory cortex of rhesus macaques. Neural responses to sound onset and offset were affected to different extents, and their rate-level functions became more mutually similar, which could be accounted for by the loss of nonmonotonic intensity coding in geriatric monkeys. These findings were consistent with weakened inhibition in the central auditory system and could contribute to auditory processing deficits in elderly subjects.
抑制在中枢听觉系统的感觉处理中起着关键作用，并且已经涉及到塑造感受野特性，例如声音强度编码，以及塑造神经元放电的时间模式，例如起始或终止诱发反应。有大量证据支持老年动物在听觉通路上的抑制作用减弱。因此，我们检查了老年和年轻猴子听觉皮层中起始（ON）和终止（OFF）反应的强度编码。初级听觉皮层（A1）和外侧场（CL）中的很大一部分细胞除了对 ON 反应进行非单调编码外，还对 OFF 反应显示出非单调的率-水平函数。衰老对 ON 和 OFF 反应的影响不同；ON 反应的影响幅度通常大于 OFF 反应。除了更高的放电率外，老年猴子的神经元还表现出显著增加的单调率-水平函数比例，并且最佳强度高于年轻猴子。年轻猴子的 OFF 反应与同一细胞的 ON 反应显示出一系列强度编码关系，从高度相似到高度不同。CL 中的 ON/OFF 编码差异较大，随着年龄的增长而减小，这在很大程度上可以解释为对 ON 和 OFF 反应的非单调编码的细胞比例的优先降低。我们观察到的变化与先前在灵长类动物上行听觉通路上抑制作用的改变一致，并且可能与声音时间处理的年龄相关缺陷有关。衰老对恒河猴听觉皮层中神经元的强度编码有重大影响。对声音起始和终止的神经反应受到不同程度的影响，它们的率-水平函数变得更加相似，这可以用老年猴子非单调强度编码的丧失来解释。这些发现与中枢听觉系统中抑制作用的减弱一致，可能导致老年受试者的听觉处理缺陷。
