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

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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.