Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida Gainesville, FL, USA ; Center for Smell and Taste, University of Florida Gainesville, FL, USA.
Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida Gainesville, FL, USA ; Center for the Study of Emotion and Attention, University of Florida Gainesville, FL, USA.
Front Syst Neurosci. 2015 Feb 25;9:12. doi: 10.3389/fnsys.2015.00012. eCollection 2015.
Cochlear outer hair cells (OHCs) are remarkable, mechanically-active receptors that determine the exquisite sensitivity and frequency selectivity characteristic of the mammalian auditory system. While there are three to four times as many OHCs compared with inner hair cells, OHCs lack a significant afferent innervation and, instead, receive a rich efferent innervation from medial olivocochlear (MOC) efferent neurons. Activation of the MOC has been shown to exert a considerable suppressive effect over OHC activity. The precise function of these efferent tracts in auditory behavior, however, is the matter of considerable debate. The most frequent functions assigned to the MOC tracts are to protect the cochlea from traumatic damage associated with intense sound and to aid the detection of signals in noise. While considerable evidence shows that interruption of MOC activity exacerbates damage due to high-level sound exposure, the well characterized MOC physiology and evolutionary studies do not support such a role. Instead, a MOC protective effect is well explained as being a byproduct of the suppressive nature of MOC action on OHC mechanical behavior. A role in the enhancement of signals in noise backgrounds, on the other hand, is well supported by (1) an extensive physiological literature (2) examination of naturally occurring environmental acoustic conditions (3) recent data from multiple laboratories showing that the MOC plays a significant role in auditory selective attention by suppressing the response to unattended or ignored stimuli. This presentation will argue that, based on the extant literature combining the suppression of background noise through MOC-mediated rapid adaptation (RA) with the suppression of non-attended signals, in concert with the corticofugal pathways descending from the auditory cortex, the MOC system has one evolved function-to increase the signal-to-noise ratio, aiding in the detection of target signals. By contrast, the MOC system role in reducing noise damage and the effects of aging in the cochlea may well represent an exaptation, or evolutionary "spandrel".
耳蜗外毛细胞（OHC）是一种卓越的机械活性受体，决定了哺乳动物听觉系统的高灵敏度和频率选择性。尽管 OHC 的数量比内毛细胞多三到四倍，但 OHC 缺乏明显的传入神经支配，而是接受来自内侧橄榄耳蜗（MOC）传出神经元的丰富传出神经支配。已经证明，MOC 的激活对 OHC 活动产生了相当大的抑制作用。然而，这些传出束在听觉行为中的精确功能是一个相当有争议的问题。MOC 束最常被赋予的功能是保护耳蜗免受与高强度声音相关的创伤性损伤，并帮助检测噪声中的信号。尽管大量证据表明，中断 MOC 活动会加剧高强度声音暴露引起的损伤，但 MOC 的特征生理和进化研究并不支持这种作用。相反，MOC 对 OHC 机械行为的抑制作用的自然性质很好地解释了其保护作用是一种副产品。另一方面，MOC 在增强噪声背景中的信号方面的作用得到了以下几个方面的支持：（1）广泛的生理学文献；（2）对自然环境声条件的研究；（3）来自多个实验室的最新数据表明，MOC 通过抑制对未注意或忽略的刺激的反应，在听觉选择性注意中发挥重要作用。本演讲将认为，基于现有的文献，结合 MOC 介导的快速适应（RA）对背景噪声的抑制以及与来自听觉皮层的皮质传出通路一起对未注意信号的抑制，MOC 系统具有一个进化功能——提高信噪比，有助于检测目标信号。相比之下，MOC 系统在减少耳蜗噪声损伤和衰老影响方面的作用可能代表了一种适应，或者是进化的“副产物”。
