Abstract
Noisy galvanic vestibular stimulation (nGVS) at imperceptible levels has been shown to reduce body sway. This reduction was commonly attributed to the mechanism of stochastic resonance (SR). However, it has never been explicitly tested whether nGVS-induced effects on body sway consistently follow a SR-like bell-shaped performance curve with maximal reductions in a particular range of noise intensities. To test this, body sway in 21 young healthy participants was measured during varying nGVS amplitudes while standing with eyes closed in 3 conditions (quiet stance, sway referencing, sinusoidal platform tilts). Presence of SR-like response dynamics in each trial was assessed (1) by a goodness-of-fit analysis using an established SR-curve model and (2) by ratings from 3 human experts. In accordance to theory, we found reductions of body sway at one nGVS amplitude in most trials (75–95%). However, only few trials exhibited SR-like bell-shaped performance curves with increasing noise amplitudes (10–33%). Instead, body sway measures rather fluctuated randomly across nGVS amplitudes. This implies that, at least in young healthy adults, nGVS effects on body sway are incompatible with SR. Thus, previously reported reductions of body sway at particular nGVS intensities more likely result from inherent variations of the performance metric or by other yet unknown mechanisms.
Highlights
Noisy galvanic vestibular stimulation at imperceptible levels has been shown to reduce body sway
In a second step of analysis, we examined whether response dynamics of body sway across the range of applied Noisy galvanic vestibular stimulation (nGVS) intensities might be compatible with the presence of vestibular-induced stochastic resonance (SR)
Several previous studies reported that human postural sway can be reduced by the application of a particular intensity of nGVS22–34—an effect that was concordantly attributed to the exhibition of SR within vestibular signal transfer
Summary
Noisy galvanic vestibular stimulation (nGVS) at imperceptible levels has been shown to reduce body sway. By applying a noisy form of GVS (nGVS) to healthy young individuals, Galvan-Garza and colleagues could demonstrate that vestibular motion perception thresholds can get effectively reduced in the presence of a low-intensity stochastic vestibular stimulation[18]. They observed that in about 75% of participants nGVS-induced modulations of thresholds (assessed during a direction recognition task) followed a bellshaped performance curve with increasing noise amplitude. In light of these studies, vestibular SR has been proposed to have immediate clinical implications in terms of a potential treatment option for postural imbalance in the context of a peripheral and/ or central vestibular dysfunction[15]
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