Effects of Noisy Galvanic Vestibular Stimulation on Standing Balance – No Evidence for Stochastic Resonance in Young Healthy Adults

Noisy galvanic vestibular stimulation (nGVS) at imperceptible levels has been shown to reduce body sway. This improvement 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 optimal improvements at intermediate 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-compatible 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-compatible 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.