Maintaining balance in an unstable environment: A central role for the vestibular system

每年冬天，加拿大人都必须尽最大努力控制平衡，因为人行道就像一个巨大的溜冰场，简单地走到街角就像是一种艺术滑冰动作。因此，平衡控制是我们日常生活中必不可少的一部分，但使这些行为得以实现的神经机制仍然知之甚少。我的研究计划的长期目标是确定神经元相互作用的性质，使人类能够进行平衡控制。在接下来的5年里，我将专门评估涉及前庭系统的神经元相互作用。事实上，前庭系统被证明是平衡控制系统的关键组成部分，但其作用的实际机制在很大程度上是未知的。我提出的研究计划旨在填补这一知识空白，并将研究使平衡控制成为可能的关键神经元相互作用。在第一个目标中，我们将评估在支撑底座意外向后倾斜时前庭系统对脊髓内神经元的影响。我们的假设是，前庭系统通过促进脊髓中特定的中间神经元，即Ia抑制中间神经元，参与扰动后姿势反应的产生，使一块肌肉收缩，而另一块肌肉放松。这使得能够流畅地移动和快速的姿势反应。在第二个目标中，我们将评估运动皮质在调节站立时前庭输出中的作用。我们的假设是，大脑皮层控制平衡和姿势反应的部分方式是通过调节前庭系统，形成一个控制平衡的分级神经网络。我们进一步假设，当个体站在不稳定的表面上时，运动皮质将更加活跃，以保持平衡并防止摔倒。这将增加其影响力。在第三个目标中，我们将确定在平衡技能获得过程中，来自我们身体的感觉信息(躯体感觉)和前庭系统对我们肌肉的自愿激活(运动输出)的影响。我们的假设是，前庭和体感系统都有助于在平衡训练中塑造运动输出，以获得新的平衡技能。总体而言，拟议的研究计划将进一步加深我们对关键神经元相互作用的了解，这些相互作用使我们能够实现平衡控制，并获得平衡技能。它将进一步告诉我们，来自我们身体和前庭系统的感觉信息是如何进入中枢神经系统以实现平衡控制的。这项工作可能在预防日益老龄化的人口中摔倒以及在需要特殊平衡控制的运动员(如体操运动员)中推广不同的训练模式方面具有潜在的重要应用。这项工作还可能导致技术发展，以支持例如宇航员在空间探索期间的适应。

Every winter, Canadians must employ their best balance control efforts, as the sidewalks resemble a giant ice rink, and simply walking to the corner of the street can resemble an artistic skating routine. Balance control is thus an essential part of our daily lives, but the neuronal mechanisms that enable those behaviours remain poorly understood. The long-term objective of my research program is to identify the nature of neuronal interactions that enable balance control in humans. In the next 5 years, I will specifically assess neuronal interactions involving the vestibular system. Indeed, the vestibular system was shown to be a key component of the balance control system, yet the actual mechanisms underlying its contribution are largely unknown. My proposed research program aims at filling this gap in knowledge and will investigate key neuronal interactions that enable balance control. In the first aim, we will assess the influence of the vestibular system on neurons located in the spinal cord during unexpected backward tilt of the base of support. Our HYPOTHESIS is that the vestibular system is involved in the generation of the postural reactions following perturbation by facilitating specific interneurons in the spinal cord, the Ia inhibitory interneurons, which enable contraction from one muscle while the opposing muscle is relaxed. This enables a fluid movement and rapid postural reactions. In the second aim, we will assess the role of motor cortex in modulating the vestibular output during standing. Our HYPOTHESIS is that the cortex controls balance and postural reactions in part by modulating the vestibular system, forming a hierarchical neuronal network to control balance. We further hypothesize that when individuals will be standing on an unstable surface, the motor cortex will be more active to maintain balance and prevent a fall. This will increase its influence. In the third aim, we will determine the influence of sensory information from our body (somatosensory) and of the vestibular system on the voluntary activation of our muscles (motor output) during balance skill acquisition. Our HYPOTHESIS is that both the vestibular and somatosensory systems help shape the motor output during balance training to acquire a new balance skill. Overall, the proposed research program will further our knowledge on key neuronal interactions that enable balance control, and acquisition of a balance skills. It will further inform us on how sensory information from our body and from our vestibular system are included into the central nervous system to enable balance control. This work could have potentially important applications in terms of preventing falls in an increasingly aging population and to promote different training paradigms in athletes who require exceptional balance control (such as gymnasts). This work may also lead to technological developments to support for example adaptation of astronauts during space exploration.