Abstract
Objective: This study aimed to investigate whether galvanic vestibular stimulation with stochastic noise (nGVS) modulates the body sway and muscle activity of the lower limbs, depending on visual and somatosensory information from the foot using rubber-foam.Methods: Seventeen healthy young adults participated in the study. Each subject maintained an upright standing position on a force plate with/without rubber-foam, with their eyes open/closed, to measure the position of their foot center of pressure. Thirty minutes after baseline measurements under four possible conditions (eyes open/closed with/without rubber-foam) performed without nGVS (intensity: 1 mA, duration: 40 s), the stimulation trials (sham-nGVS/real-nGVS) were conducted under the same conditions in random order, which were then repeated a week or more later. The total center of pressure (COP) path length movement (COP-TL) and COP movement velocity in the mediolateral (Vel-ML) and anteroposterior (Vel-AP) directions were recorded for 30 s during nGVS. Furthermore, electromyography activity of the right tibial anterior muscle and soleus muscle was recorded for the same time and analyzed.Results: Three-way analysis of variance and post-hoc multiple comparison revealed a significant increment in COP-related parameters by nGVS, and a significant increment in soleus muscle activity on rubber. There was no significant effect of eye condition on any parameter.Conclusions: During nGVS (1 mA), body sway and muscle activity in the lower limb may be increased depending not on the visual condition, but on the foot somatosensory condition.
Highlights
The vestibular complex system is important for postural control (Dunlap et al, 2019)
In EMG-SOL, there was a significant difference between rubber on and off, indicating an increment of EMG activity of SOL muscle by standing on rubber foam during nGVS
There was a significant difference between rubber on vs. off in the Real-nGVS condition in EMG-SOL, meaning a significant increment of EMG activity of SOL by standing on rubber foam in the real-nGVS condition
Summary
The vestibular complex system is important for postural control (Dunlap et al, 2019). Head movement accompanies body sway and activates the vestibular nerve and contraction of muscles for postural control, and disturbance of this vestibulospinal response is known to cause falls (Whitney et al, 2015). Noise GSV (nGVS) (Wuehr et al, 2017) can modulate the threshold of motor responses from vestibular inputs (Wuehr et al, 2017) in a posture-dependent manner (Matsugi et al, 2020), resulting in improvements in balance (Fujimoto et al, 2016, 2018; Inukai et al, 2018b). The threshold of the vestibulospinal response is decreased during nGVS based on the stochastic resonance mechanism, resulting in a large body sway that may be inhibited
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