The Caruso Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles, California 90033, and.
Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843.
J Neurosci. 2019 Mar 6;39(10):1805-1816. doi: 10.1523/JNEUROSCI.2608-18.2019. Epub 2019 Jan 16.
Mammalian hearing sensitivity and frequency selectivity depend on a mechanical amplification process mediated by outer hair cells (OHCs). OHCs are situated within the organ of Corti atop the basilar membrane (BM), which supports sound-evoked traveling waves. It is well established that OHCs generate force to selectively amplify BM traveling waves where they peak, and that amplification accumulates from one location to the next over this narrow cochlear region. However, recent measurements demonstrate that traveling waves along the apical surface of the organ of Corti, the reticular lamina (RL), are amplified over a much broader region. Whether OHC forces accumulate along the length of the RL traveling wave to provide a form of "global" cochlear amplification is unclear. Here we examined the spatial accumulation of RL amplification. In mice of either sex, we used tones to suppress amplification from different cochlear regions and examined the effect on RL vibrations near and far from the traveling-wave peak. We found that although OHC forces amplify the entire RL traveling wave, amplification only accumulates near the peak, over the same region where BM motion is amplified. This contradicts the notion that RL motion is involved in a global amplification mechanism and reveals that the mechanical properties of the BM and organ of Corti tune how OHC forces accumulate spatially. Restricting the spatial buildup of amplification enhances frequency selectivity by sharpening the peaks of cochlear traveling waves and constrains the number of OHCs responsible for mechanical sensitivity at each location. Outer hair cells generate force to amplify traveling waves within the mammalian cochlea. This force generation is critical to the ability to detect and discriminate sounds. Nevertheless, how these forces couple to the motions of the surrounding structures and integrate along the cochlear length remains poorly understood. Here we demonstrate that outer hair cell-generated forces amplify traveling-wave motion on the organ of Corti throughout the wave's extent, but that these forces only accumulate longitudinally over a region near the wave's peak. The longitudinal coupling of outer hair cell-generated forces is therefore spatially tuned, likely by the mechanical properties of the basilar membrane and organ of Corti. Our findings provide new insight into the mechanical processes that underlie sensitive hearing.
哺乳动物的听力灵敏度和频率选择性取决于外毛细胞 (OHC) 介导的机械放大过程。OHC 位于基底膜 (BM) 上的柯蒂氏器内，支持声音诱发的行波。众所周知，OHC 产生力以选择性地放大 BM 行波，在行波峰值处放大，并且放大从一个位置累积到下一个位置，跨越这个狭窄的耳蜗区域。然而，最近的测量表明，在柯蒂氏器的顶端表面，即网状层 (RL)，行波被放大的区域要宽得多。OHC 力是否沿着 RL 行波的长度累积，以提供一种“全局”耳蜗放大形式尚不清楚。在这里，我们研究了 RL 放大的空间累积。在雄性和雌性小鼠中，我们使用音调抑制不同耳蜗区域的放大，并检查 RL 振动在远离和靠近行波峰值的地方的影响。我们发现，尽管 OHC 力放大了整个 RL 行波，但放大仅在靠近峰值的区域累积，与 BM 运动放大的区域相同。这与 RL 运动参与全局放大机制的概念相矛盾，揭示了 BM 和柯蒂氏器的机械特性调节 OHC 力如何在空间上累积。限制放大的空间累积通过锐化耳蜗行波的峰值来增强频率选择性，并限制每个位置负责机械灵敏度的 OHC 数量。外毛细胞产生力来放大哺乳动物耳蜗内的行波。这种力的产生对于检测和区分声音至关重要。然而，这些力如何与周围结构的运动耦合以及沿着耳蜗长度整合仍然知之甚少。在这里，我们证明外毛细胞产生的力在整个波的范围内放大 RL 行波的运动，但这些力仅在行波峰值附近的区域内纵向累积。因此，外毛细胞产生的力的纵向耦合是空间调谐的，可能由基底膜和柯蒂氏器的机械特性决定。我们的研究结果为敏感听力所依据的机械过程提供了新的见解。
