Problems in Coclear Micromechanics

作为与NIDCD的Richard Chadwick博士及其团队长期合作的一部分，我们在过去一年中参与了许多项目。 主要使用原子力显微镜（AFM），我们完成了测量的弹性模量的覆膜（TM）的听力中的作用是至关重要的，但其确切的作用机制仍然存在争议。 结果发现，TM是径向不均匀的，并且这种性质有利于毛细胞的剪切效率（对感觉细胞的刺激作用）。 另一个问题是关于哺乳动物耳蜗的螺旋形特征，这一特征多年来一直困扰着听力研究人员。 各种研究都没有定论，有人认为形状的唯一目的是将长通道包装在小体积中。 然而，最近的一些研究表明，低频灵敏度和螺旋圈数之间有很强的相关性。 我们的NIDCD合作者有兴趣研究螺旋耳蜗的简化数学模型，以研究形状对沿着螺旋能量流的各种参数的影响。 在这种情况下，计算表明，虽然能量流沿着螺旋通道保持恒定，但连续变化的曲率将能量集中到外通道壁。 能量聚焦效应朝着螺旋顶点逐渐变强，在那里分析低频。 这种现象可能对低频阈值产生深远的影响，从而可能解释哺乳动物螺旋形状的进化效用。 我们与伍兹霍尔海洋研究所的海洋哺乳动物专家合作，分析了大量哺乳动物耳蜗的组织学切片、CT扫描和其他解剖图像，以建立低频极限与螺旋沿着总曲率变化之间的假设相关性。 结果发现，螺旋耳蜗几何形状的一个简单的措施相关的海洋和陆地哺乳动物的低频限制令人惊讶的好。 这种相关性对研究听力的演变有一定的意义，但它也可能有助于指导未来的人工耳蜗植入更有效地实施。

As part of a long-standing collaboration with NIDCD's Dr. Richard Chadwick and his group, we have been instrumental in a number of projects during the past year. Using primarily the atomic force microscope (AFM), we completed the measurements of the elastic modulus of the tectorial membrane (TM) whose role in hearing is critical, but whose exact mechanism of action remains controversial. It was found that the TM is radially inhomogeneous and that such a property is favorable to the shearing efficiency of the hair cells (the stimulatory action on the sensory cells). Another issue addressed had to do with the characteristic spiral shape of the mammalian cochlea that has mystified hearing researchers for many years. Various studies have been inconclusive and it has been argued that the only purpose of the shape is packaging of a long channel in a small volume. Some recent work, however, showed strong correlation between low frequency sensitivity and the number of turns in the spiral. Our NIDCD collaborators were interested in studying a simplified mathematical model of a spiral cochlea to investigate the effect of the shape on various parameters of energy flow along the spiral. In this instance, computations showed that although energy flow along the spiral channel remains constant, the continuously changing curvature concentrates energy toward the outer channel wall. The energy focusing effect becomes progressively stronger toward the spiral apex, where low frequencies are analyzed. Such a phenomenon could have profound effect on low frequency thresholds leading to a potential explanation of the evolutionary utility of the spiral shape in mammals. In collaboration with marine mammal experts at the Woods Hole Oceanographic Institute we have analyzed histological sections, CT-scans and other anatomical images of a large number of mammalian cochleae to establish the hypothesized correlations between low frequency limits and total curvature change along the spiral. It was found that a simple measure of the spiral cochlear geometry correlates surprisingly well with the low frequency limit of both marine and land mammals. Such a correlation has implications for the study of the evolution of hearing, but it may also help guide future cochlear implants toward more effective implementation.