Nonlinear Dynamics of Auditory Hair Cells and Efferent Neurons

内耳中听觉信息的第一级处理是由毛细胞执行的--毛细胞是一种专门的细胞，负责检测声音并将信息传输到大脑。这些细胞表现出极高的灵敏度，对小于一纳米的运动做出反应。此外，它们表现出广泛的动态范围，因为它们能够承受更大的挠度，而不会造成永久性损害。目前还不清楚听觉系统是如何实现这种敏感度的，以及当暴露在嘈杂的环境中时，它如何迅速降低这种敏感度。传出神经元将信息从大脑传递到毛细胞，已经被认为起到了保护作用，减少了大声音对毛细胞的损伤。然而，到目前为止，人们对这一机制背后的物理原理知之甚少。在这个项目中，研究人员将直接测量刺激传出神经元如何影响毛细胞的敏感度，包括检测微弱信号和抵御强刺激的能力。他们的目标是将实验结果与基于非线性动力学的模型进行比较，以解释传出如何提供控制听力灵敏度的动态反馈系统。内耳包含一个极其灵敏的机械探测器，它通常对纳米级的偏转做出反应。在最低可感知的水平上，声音在内部听觉器官中诱导运动，这些运动小到很少。与此同时，听觉系统可以承受的外加压力超过六个数量级。一种动态增益控制机制将调节毛细胞检测的灵敏度，这将有助于解释系统如何在保持必要的稳健性的同时实现如此显著的灵敏度。这个项目的目标是确定传出神经元是否构成调节毛细胞非线性特性的动态反馈机制。研究人员的目标是通过在不同水平的传出活动下对活的和活跃的毛细胞进行体外直接测量，来探索传出活动如何影响感觉系统的机械反应。研究人员将把这些发现与基于非线性动力学理论的理论预测进行比较，后者提出，内部控制参数将系统自我调整到Hopf分叉附近。因此，这项研究是对该领域先前工作的补充，并将为先前在体内和体外以及理论模型中研究的领域提供桥梁。该项目还将提供重要的指导机会，因为PI的目标是通过参与APS Bridge计划从代表性不足的群体中招收研究生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The first level of processing of auditory information in the inner ear is performed by hair cells – specialized cells that detect sound and transmit information to the brain. These cells show extremely high sensitivity, responding to movements smaller than a nanometer. Further, they show a broad dynamic range, for they are able to withstand much larger deflections without permanent damage. It is still not understood how the auditory system achieves this sensitivity and how it can rapidly reduce it when exposed to a loud environment. It has been proposed that efferent neurons, which transmit information from the brain to the hair cells, serve a protective role that reduces hair cell damage induced by loud sound. However, thus far there is very little understanding of the physics behind this mechanism. The investigators in this project will measure directly how stimulation of efferent neurons affects the sensitivity of the hair cell, both in terms of its ability to detect weak signals and to withstand strong stimuli. Their goal is to compare the experimental findings to models based on nonlinear dynamics to explain how efference may provide a dynamic feedback system that controls the sensitivity of hearing.The inner ear contains an extremely sensitive mechanical detector, which routinely responds to nanoscale deflections. At the lowest perceptible levels, sound induces movements in the internal auditory organs that are as small as few Å. Meanwhile, the applied pressures that the auditory systems can withstand range over six orders of magnitude. A dynamic gain control mechanism which would modulate the sensitivity of detection by a hair cell would serve to explain how a system could simultaneously achieve such remarkable sensitivity while maintaining the requisite robustness. The goal of this project is to determine whether efferent neurons constitute the dynamic feedback mechanism which tunes the nonlinear properties of the hair cell. The investigators aim to explore how efferent activity affects the mechanical responsiveness of the sensory system by direct measurements performed in vitro on live and active hair cells under different levels of efferent activity. The investigators will compare the findings to theoretical predictions based on nonlinear dynamics theory, which has proposed that an internal control parameter self-tunes the system to the vicinity of a Hopf bifurcation. This study is therefore complementary to prior work in the field, and will serve to bridge areas previously studied in vivo and in vitro, as well as in theoretical models. The project will also provide important mentoring opportunities, as the PI aims to recruit graduate students from underrepresented groups through participation in the APS Bridge program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.