Caruso Department of Otolaryngology, University of Southern California, Los Angeles, CA 90033.
Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089.
Proc Natl Acad Sci U S A. 2023 Oct 10;120(41):e2305921120. doi: 10.1073/pnas.2305921120. Epub 2023 Oct 5.
The intricate, crystalline cytoarchitecture of the mammalian organ of Corti presumably plays an important role in cochlear amplification. As currently understood, the oblique, Y-shaped arrangement of the outer hair cells (OHCs) and phalangeal processes of the Deiters cells serves to create differential "push-pull" forces that drive the motion of the basilar membrane via the spatial feedforward and/or feedbackward of OHC forces. In concert with the cochlear traveling wave, the longitudinal separation between OHC sensing and forcing creates phase shifts that yield a form of negative damping, amplifying waves as they propagate. Unlike active forces that arise and act locally, push-pull forces are inherently directional-whereas forward-traveling waves are boosted, reverse-traveling waves are squelched. Despite their attractions, models based on push-pull amplification must contend with otoacoustic emissions (OAEs), whose existence implies that amplified energy escapes from the inner ear via mechanisms involving reverse traveling waves. We analyze hybrid local/push-pull models to determine the constraints that reflection-source OAEs place on the directionality of cochlear wave propagation. By implementing a special force-mixing control knob, we vary the mix of local and push-pull forces while leaving the forward-traveling wave unchanged. Consistency with stimulus-frequency OAEs requires that the active forces underlying cochlear wave amplification be primarily local in character, contradicting the prevailing view. By requiring that the oblique cytoarchitecture produce predominantly local forces, we reinterpret the functional role of the Y-shaped geometry, proposing that it serves not as a push-pull amplifier, but as a mechanical funnel that spatially integrates local OHC forces.
哺乳动物耳蜗的复杂晶体细胞结构可能在耳蜗放大中发挥重要作用。目前的理解是，外毛细胞（OHC）的斜 Y 形排列和 Deiters 细胞的指状突起形成了差分“推挽”力，通过 OHC 力的空间前馈和/或后馈驱动基底膜运动。与耳蜗行波一起，OHC 感应和施力的纵向分离产生相移，产生一种负阻尼形式，在波传播时放大波。与局部产生和作用的主动力不同，推挽力具有固有方向性——前向传播波被增强，反向传播波被抑制。尽管具有吸引力，但基于推挽放大的模型必须考虑到耳声发射（OAE），其存在意味着放大的能量通过涉及反向传播波的机制从内耳逸出。我们分析混合局部/推挽模型，以确定反射源 OAE 对耳蜗波传播方向的限制。通过实施特殊的力混合控制旋钮，我们在保持前向传播波不变的情况下改变局部和推挽力的混合。与刺激频率 OAE 的一致性要求耳蜗波放大的主动力主要具有局部特征，这与流行观点相矛盾。通过要求斜细胞结构产生主要的局部力，我们重新解释了 Y 形几何形状的功能作用，提出它不是推挽放大器，而是机械漏斗，可对局部 OHC 力进行空间整合。
