Investigating the Role of the Dorsal Foot Skin During a Standing Vestibular Perturbation

Abstract

The aim of this thesis was to examine the role of the dorsal foot skin during standing control. Our experiment addressed two specific objectives: i) to determine if cutaneous input from the dorsal feet alters the reflexive muscle responses elicited by a standing vestibular perturbation (short-latency and medium-latency responses) and ii) to determine if cutaneous input from the foot dorsum affects the postural response to a vestibular perturbation (centre of pressure and centre of mass). Cutaneous input from the dorsal feet was reduced using a topical anesthetic (two skin conditions: control and reduced). Galvanic vestibular stimulation (GVS) was used to deliver a vestibular perturbation while subjects stood with the head turned over the left shoulder for both skin conditions. The reflexive muscle responses to GVS were measured using surface electromyography. The anterior posterior movement elicited by GVS was captured using an AMTI force plate and Optotrak motion capture. Contrary to our hypotheses, sensory reweighting of the vestibular input expressed as an increased reflexive muscle response was not necessary to maintain standing equilibrium during the initial response to GVS. We found that subjects took longer to recover from the vestibular perturbation and re-establish equilibrium (centre of mass) when cutaneous input from the dorsal feet was reduced. Our results suggest that subjects compensated for the reduction in dorsal foot skin input by employing a cautious postural strategy. Cutaneous input from the dorsal feet is used to control body movement during the recovery from a standing vestibular perturbation.