Efficacy of Stochastic Vestibular Stimulation to Improve Locomotor Performance During Adaptation to Visuomotor and Somatosensory Distortion

Abstract

Astronauts exposed to microgravity face sensorimotor challenges affecting balance control when readapting to Earth's gravity upon return from spaceflight. Small amounts of electrical noise applied to the vestibular system have been shown to improve balance control during standing and walking under discordant sensory conditions in healthy subjects, likely by enhancing information transfer through the phenomenon of stochastic resonance. The purpose of this study was to test the hypothesis that imperceptible levels of stochastic vestibular stimulation (SVS) could improve short-term adaptation to a locomotor task in a novel sensory discordant environment. Healthy subjects (14 males, 10 females, age = 28.7 ± 5.3 years, height = 167.2 ± 9.6 cm, weight = 71.0 ± 12.8 kg) were tested for perceptual thresholds to sinusoidal currents applied across the mastoids. Subjects were then randomly and blindly assigned to an SVS group receiving a 0–30 Hz Gaussian white noise electrical stimulus at 50% of their perceptual threshold (stim) or a control group receiving zero stimulation during Functional Mobility Tests (FMTs), nine trials of which were done under conditions of visual discordance (wearing up/down vision reversing goggles). Time to complete the course (TCC) was used to test the effect of SVS between the two groups across the trials. Adaptation rates from the normalized TCCs were also compared utilizing exponent values of power fit trendline equations. A one-tailed independent-samples t-test indicated these adaptation rates were significantly faster in the stim group (n = 12) than the control (n = 12) group [t(16.18) = 2.00, p = 0.031]. When a secondary analysis was performed comparing “responders” (subjects who showed faster adaptation rates) of the stim (n = 7) group to the control group (n = 12), independent-samples t-tests revealed significantly faster trial times for the last five trials with goggles in the stim group “responders” than the controls. The data suggests that SVS may be capable of improving short-term adaptation to a locomotion task done under sensory discordance in a group of responsive subjects.

Subthreshold stochastic vestibular stimulation affects balance-challenged standing and walking

“…For the sinusoidal-based condition, we set the SVS intensity to 50% of the participant's sinusoidal threshold [21,28]. For the cutaneous-based condition, we set the SVS intensity to 80% of the participant's cutaneous threshold [17,19,20].…”

“…In addition, joint range of motion and variability, step width and step-width variability, and metrics of local dynamic stability (quantified by maximum finite-time Lyapunov exponents) differ between these walking conditions [25][26][27]. Although Temple et al [28] recently found that SVS resulted in faster completion time on a mobility course that required overground walking on foam while adapting to a visual perturbation, they did not report the effects of SVS on measures of balance or gait performance. As such, it is unclear whether the improvements in stability reported in Mulavara et al [24] translate to overground walking.…”

Stimulating balance: recent advances in vestibular stimulation for balance and gait

“…Two recent studies have analyzed the effects of nGVS on gait (Iwasaki et al 2018;Temple et al 2018). Iwasaki et al (2018) investigated the effects of nGVS on walking speed in healthy people and people with BVP.…”

“…In this Neuro Forum, we discuss six recent articles (Inukai et al 2018a(Inukai et al , 2018bIwasaki et al 2018;Keywan et al 2018;Temple et al 2018;Wuehr et al 2018) that have explored the effects of nGVS on balance and gait in humans. Second, we discuss the potential mechanisms of the observed effects and, based on the current state of the art, give recommendations and directions for future research on nGVS for the purpose of improving balance and gait.…”

Adaptation in Gait to Body-Weight Unloading

“…Several studies have investigated motor adaptation using a variety of experimental paradigms. One of the ways is by studying the changes in the movement characteristics produced by adding and subsequently removing sensory (visual, proprioceptive, acoustic, and vestibular) distortions or perturbations while performing motor tasks [2][3][4][5]. One of the common locomotor adaptation paradigms involves studying locomotor changes by altering the normal interlimb relationship during walking by changing the speeds of treadmill belts relative to each other (commonly called split-belt treadmill participants were screened using a modified physical activity readiness questionnaire (PAR-Q) [37].…”