Department of Bioengineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
Department of Clinical and Experimental Medicine, Linköping University, SE-581 85 Linköping, Sweden.
PLoS Comput Biol. 2018 Jan 19;14(1):e1005936. doi: 10.1371/journal.pcbi.1005936. eCollection 2018 Jan.
The cochlea not only transduces sound-induced vibration into neural spikes, it also amplifies weak sound to boost its detection. Actuators of this active process are sensory outer hair cells in the organ of Corti, whereas the inner hair cells transduce the resulting motion into electric signals that propagate via the auditory nerve to the brain. However, how the outer hair cells modulate the stimulus to the inner hair cells remains unclear. Here, we combine theoretical modeling and experimental measurements near the cochlear apex to study the way in which length changes of the outer hair cells deform the organ of Corti. We develop a geometry-based kinematic model of the apical organ of Corti that reproduces salient, yet counter-intuitive features of the organ's motion. Our analysis further uncovers a mechanism by which a static length change of the outer hair cells can sensitively tune the signal transmitted to the sensory inner hair cells. When the outer hair cells are in an elongated state, stimulation of inner hair cells is largely inhibited, whereas outer hair cell contraction leads to a substantial enhancement of sound-evoked motion near the hair bundles. This novel mechanism for regulating the sensitivity of the hearing organ applies to the low frequencies that are most important for the perception of speech and music. We suggest that the proposed mechanism might underlie frequency discrimination at low auditory frequencies, as well as our ability to selectively attend auditory signals in noisy surroundings.
耳蜗不仅将声音引起的振动转换为神经冲动，还增强了微弱的声音以提高其检测能力。这个主动过程的驱动器是耳蜗中的感觉外毛细胞，而内毛细胞将产生的运动转换为电信号，通过听觉神经传播到大脑。然而，外毛细胞如何调节对内毛细胞的刺激仍然不清楚。在这里，我们结合理论建模和在耳蜗顶点附近的实验测量来研究外毛细胞长度变化如何使耳蜗的科蒂器变形。我们开发了一种基于科蒂器顶端几何结构的运动学模型，该模型再现了该器官运动的显著但违反直觉的特征。我们的分析进一步揭示了一种机制，通过该机制，外毛细胞的静态长度变化可以敏感地调节传递给感觉内毛细胞的信号。当外毛细胞处于伸长状态时，内毛细胞的刺激受到很大抑制，而外毛细胞的收缩导致毛束附近的声音诱发运动显著增强。这种调节听力器官敏感性的新机制适用于对语音和音乐感知最重要的低频。我们认为，所提出的机制可能是低频听觉频率下的频率辨别以及我们在嘈杂环境中选择性注意听觉信号的基础。
