Guinan John J
Eaton-Peabody Lab, Mass. Eye and Ear, 243 Charles St., Boston MA 02114, USA.
Harvard Medical School, Dept. of Otolaryngology Head and Neck Surgery, Boston MA, USA.
Hear Res. 2022 Dec;426. doi: 10.1016/j.heares.2022.108641. Epub 2022 Oct 21.
Many details of the operation of the mammalian cochlea are known, but how they all work together to produce cochlear amplification is not understood. Outer-hair-cell (OHC) motility produces two kinds of amplification: non-propagating amplification (NPA) that is from local OHCs, and traveling-wave amplification (TWA) that increases basilar-membrane (BM) motion. Proposed here are a series of hypotheses that provide a new explanation, the "OoC-area-pump", for TWA: (1) In the short-wave region OHC vibrations cause cyclic longitudinal motion of fluid in the organ of Corti (OoC) and peri-Deiters-cell tissue, (2) the longitudinal motion changes the local OoC area, which (3) by reticular-lamina (RL) movement drives the fluid in scala media in a way that amplifies the fluid-pressure traveling wave. (4) At the NPA-TWA changeover frequency, an abrupt change in the OoC frequency-wavenumber relationship is due to positive feedback between TWA and the mode of cochlear motion that is dominant, aided by focusing of the pressure traveling wave. It is hypothesized that OoC radial expansion and radial force from the Deiters-cell phalangeal process act to advance RL and/or lateral-compartment phase. Finally, it is hypothesized that human and lab-animal frequency tuning have similar bandwidths in distance along the cochlea because their traveling-wave wavelengths are similar in the corresponding short-wave regions. Experiments are needed to test these hypotheses and to determine for TWA whether the OoC-area-pump hypothesis replaces or supplements the "OHCs-act-on-BM" hypothesis. Several tests are outlined that can be done with current methodology. A key step in the evolution of mammalian hearing was the development of the complex OoC anatomy, including Deiters cells and OoC fluid spaces that allow local wide-band NPA to produce TWA that enables small local increments of gain to accumulate in the traveling wave and sharpen tuning.
哺乳动物耳蜗运作的许多细节已为人所知，但它们如何协同作用以产生耳蜗放大作用尚不清楚。外毛细胞（OHC）的能动性产生两种放大作用：来自局部外毛细胞的非传播性放大（NPA）和增加基底膜（BM）运动的行波放大（TWA）。本文提出了一系列假设，为行波放大提供了一种新的解释，即“耳蜗管区域泵”：（1）在短波区域，外毛细胞振动引起柯蒂氏器（OoC）和Deiters细胞周围组织中液体的周期性纵向运动，（2）纵向运动改变了局部耳蜗管区域，（3）通过网状层（RL）的运动，以放大液体压力行波的方式驱动中阶内的液体。（4）在行波放大-非传播性放大转换频率处，耳蜗管频率-波数关系的突然变化是由于行波放大与占主导地位的耳蜗运动模式之间的正反馈，压力行波的聚焦也起到了辅助作用。据推测，耳蜗管的径向扩张和来自Deiters细胞指状突的径向力有助于推进网状层和/或外侧隔室的相位。最后，据推测，人类和实验动物的频率调谐在沿耳蜗的距离上具有相似的带宽，因为它们在行波放大的相应短波区域中的行波波长相似。需要进行实验来检验这些假设，并确定对于行波放大来说，耳蜗管区域泵假说是取代还是补充了“外毛细胞作用于基底膜”假说。概述了一些可以用当前方法进行的测试。哺乳动物听觉进化的一个关键步骤是复杂的耳蜗管解剖结构的发展，包括Deiters细胞和耳蜗管液体空间，它们允许局部宽带非传播性放大产生行波放大，从而使行波中局部增益的小增量得以积累并锐化调谐。
