Shokrian Mohammad, Lin Wei-Ching, Macić Anes, Nam Jong-Hoon
Departments of Mechanical Engineering, University of Rochester, Rochester, New York 14627.
Departments of Mechanical Engineering, University of Rochester, Rochester, New York 14627
J Neurosci. 2025 Jan 15;45(3):e1033242024. doi: 10.1523/JNEUROSCI.1033-24.2024.
The mammalian cochlea amplifies sounds selectively to improve frequency resolution. However, vibrations around the outer hair cells (OHCs) are amplified nonselectively. The mechanism of the selective or nonselective amplification is unknown. This study demonstrates that active force transmission through the extracellular fluid in the organ of Corti (Corti fluid) can explain how the cochlea achieves selective sound amplification despite the non-frequency-selective action of OHCs. Computational model simulations and experiments with excised cochleae from young gerbils of both sexes were exploited. OHC motility resulted in characteristic off-axis motion of the joint between the OHC and Deiters cell (ODJ). Incorporating the Corti fluid dynamics was critical to account for the ODJ motion due to OHC motility. The incorporation of pressure transmission through the Corti fluid resulted in three distinct frequency tuning patterns depending on sites in the organ of Corti. In the basilar membrane, the responses were amplified near the best-responding frequency (BF). In the ODJ region, the responses were amplified nonselectively. In the reticular lamina, the responses were amplified near the BF but suppressed in lower frequencies. The suppressive effect of OHCs was further examined by observing the changes in tuning curves due to local inhibition of OHC motility. The frequency response of the reticular lamina resembled neural tuning, such as the hypersensitivity of tuning-curve tails after hair cell damage. Our results demonstrate how active OHCs exploit the elastic frame and viscous fluid in the organ of Corti to amplify and suppress cochlear vibrations for better frequency selectivity.
哺乳动物的耳蜗会选择性地放大声音以提高频率分辨率。然而，外毛细胞（OHC）周围的振动是无选择性地放大。选择性或非选择性放大的机制尚不清楚。本研究表明，通过柯蒂氏器中的细胞外液（柯蒂氏液）进行的主动力传递可以解释耳蜗如何在OHC的非频率选择性作用下实现选择性声音放大。利用了计算模型模拟以及对来自不同性别的幼年沙鼠的离体耳蜗进行的实验。OHC的运动导致OHC与Dieters细胞之间的关节（ODJ）产生特征性的离轴运动。纳入柯蒂氏液动力学对于解释由于OHC运动引起的ODJ运动至关重要。通过柯蒂氏液的压力传递导致了三种不同的频率调谐模式，这取决于柯蒂氏器中的位置。在基底膜中，响应在最佳响应频率（BF）附近被放大。在ODJ区域，响应被无选择性地放大。在网状板中，响应在BF附近被放大，但在较低频率下被抑制。通过观察由于局部抑制OHC运动而导致的调谐曲线变化，进一步研究了OHC的抑制作用。网状板的频率响应类似于神经调谐，例如毛细胞损伤后调谐曲线尾部的超敏反应。我们的结果表明活跃的OHC如何利用柯蒂氏器中的弹性框架和粘性流体来放大和抑制耳蜗振动以实现更好的频率选择性。
