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Probing vestibular contributions during dynamic locomotor tasks using the techniqe of galvanic vestibular stimulation Bent, Leah Rachel

Abstract

Assessment of the vestibular system, its function and contribution to movement control during locomotor tasks in humans, has been examined in the past using various techniques, and only very recently using Galvanic Vestibular Stimulation (GVS). Studies utilizing GVS have indicated that vestibular information may have a larger role during dynamic tasks, such as locomotion, than during quiet standing. However, the nature of vestibular contributions and their timing during dynamic tasks have not been addressed. The current thesis examines vestibular contributions during specific dynamic tasks. The purpose was to determine if vestibular information was more heavily weighted at specific times during these dynamic tasks, and based on those findings address the possible roles that vestibular information has in successful task completion. Four studies were conducted that examined vestibular contributions in forward walking, step initiation, gait initiation and steady-state locomotion. Binaural bipolar GVS was delivered at specific times to probe the presence of vestibular contributions. The results of the four studies collectively contributed to four main conclusions. First, vestibular information has greater sensory weighting during the more dynamic phases of a task, even in the presence of vision. Second, the magnitude of the response is dependent on both the magnitude of the vestibular perturbation and the phase in the gait cycle at which the stimulation is delivered during the task. Third, the vestibular contribution during locomotor tasks has different roles, and is therefore differentially modulated, in the control of upper body versus lower limb movement. Finally, the up-regulation of vestibular information for the control of lower limb movement demonstrates gait phase dependency, which is greatest during double support in the gait cycle. To date, such a conclusion of phase related vestibular modulation has not been reached in any locomotor task examining vestibular contributions in humans. The observation of greatest vestibular up-regulation during double support leads to the postulation that vestibular information is important for the purpose of assessing the success of postural strategies during locomotion, as well as providing information on body position to facilitate programming of limb trajectory during locomotor tasks.

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