Sensory contributions to human movement and balance.

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The task of maintaining upright stance in the human involves a complex control system that has to use and integrate sensory information from primarily three sensory sources: the vestibular system, the somatosensory system, and the visual system. The LONG TERM GOAL of my basic research program is to better understand the fundamental role played by these sensory inputs in the control of standing balance, locomotion and movement in humans. To continue with this direction of work, two main concentration areas of research will be carried out. The SHORT TERM goal of the first main concentration area of research will focus on the influence of descending pathways on the regulation of single motorneurons in human subjects. Recent research in our laboratory using surface and wire electromyography has demonstrated significant coupling between descending vestibulospinal and reticulospinal pathways onto human motorneurons in the lower limb. The proposed experiments will further investigate the influence of these inputs on motorneurons during non standing tasks and during quiet stance. The SHORT TERM goal of the second main concentration area will be to investigate the regulation of the human muscle spindle, and uses a research technique termed microneurography. In the first set of experiments, we will look at the response profile of muscle spindles of the lower limb during realistic physiological muscle lengthening and shortening during different levels of muscle activation (passive and voluntary concentric/eccentric contractions). In the second set of experiments, different types of stimuli, known to activate the descending brainstem pathways, and associated with vestibular (stochastic Vestibular stimulation) and reticular systems (acoustic stimulation), will be used to precondition the muscle spindle. Evidence suggests that these descending pathways play a role in gamma motorneuron regulation of the muscle spindle. The experiments in this grant proposal will provide us with insight into how certain descending and peripheral inputs regulate muscle spindle and motor unit behaviour during normal stance.