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Galvanic vestibular stimulation : the effects on postural instability in Parkinson's Disease Tran, Stephanie


Postural instability and gait disorders (PIGD) are cardinal symptoms of Parkinson’s disease (PD) and a major source or morbidity; however, current treatments are largely ineffective. Galvanic vestibular stimulation (GVS) is a non-invasive stimulation technique previously reported to improve motor responsiveness in neurodegenerative disorders when applied at subthreshold levels. The response to GVS depends on the type of electrical signal and plane of stimulation (i.e. mediolateral (ML) or anterior/posterior (AP)). As such, the effect of subthreshold GVS in PD is not fully understood. This study is the first to investigate the comparative effects of GVS configurations by manipulating the type of electrical signal (stochastic vestibular stimulation (SVS) or multisine vestibular stimulation (MVS)) and plane of stimulation (ML or AP). Three types of stimuli are used: SVS-ML, SVS-AP and MVS-AP. Subthreshold GVS was first examined during standing, using a stable force platform, then during gait, using an electronic walkway and a dual task paradigm (serial-3 subtraction). Without stimulation, standing and gait patterns in PD were distinguishable from healthy age-matched controls (HC). Compared to HC, PD participants showed increased amplitude of postural sway, increased gait variability and decreased bilateral coordination. These baseline differences indicate that PIGD symptoms in PD are pathological, and not age-related, changes, that exist even with anti-Parkinsonian medication. Subthreshold GVS resulted in an effect at the level of the force plate, observed through significant coherences between ground reaction forces. SVS-AP reduced frequency of sway during standing and stride time variability during a dual task walk in PD participants to levels similar to those in HC. Multisine stimulation did not show superiority over stochastic stimulation. This study demonstrates the feasibility of subthreshold GVS as a potential method for improving PIGD symptoms and concludes that stochastic GVS, delivered in the AP configuration, is the most promising of the three tested methods for reducing sway frequency and improving stride time variability in people with PD.

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