Effects of individually calibrated white and pink noise vestibular stimulation on standing balance of young healthy adults

Imperceptible noisy galvanic vestibular stimulation (nGVS) improves standing balance due to the presence of stochastic resonance (SR). There is, however, a lack of consensus regarding the optimal levels and type of noise used to elicit SR like dynamics. We aimed to confirm the presence of SR behavior in the vestibular system of young healthy adults by examining postural responses to increasing amplitudes of white and pink noise stimulation scaled to individual cutaneous perceptual threshold. Forty (40) healthy young participants (19 males, 25.1 +/- 5.6 years) were randomly divided into a group that received nGVS with white (WHITE group) or pink noise (PINK group). Participants performed a cutaneous perceptual threshold detection task followed by 8 trials of quiet standing and eyes closure (60s) with nGVS applied during the last 30s. Balance stabilization was quantified in the ratio of the stimulus versus pre-stimulus Centre of Pressure (CoP) 90% ellipse area, Root Mean Square (RMS) and mean velocity. Cutaneous perceptual threshold was similar across groups. Group analysis confirmed that the mean CoP velocity increased across nGVS intensities, particularly for the PINK group while the other two variables remained unchanged. Single subject analysis indicated that 55% of WHITE and 30% of PINK group participants showed an SR-like response judged by three experts. Results are puzzling with respect to the presence of SR-like response dynamics in young healthy adults and highlight the need for further research using individual calibrated stimulus intensities. White noise seems more effective than pink noise in revealing an SR-like response to nGVS.