Effects of Low-Intensity Vestibular Noise Stimulation on Postural Instability in Patients with Parkinson's Disease

Background: Postural instability is a major disabling factor in patients with advanced Parkinson's disease (PD) and often resistant to treatment. Previous studies indicated that imbalance in PD may be reduced by low-intensity noisy galvanic vestibular stimulation (nGVS). Objective: To investigate the potential mode of action of this therapeutic effect. In particular, we examined whether nGVS-induced reductions of body sway in PD are compatible with stochastic resonance (SR), a mechanism by which weak sensory noise stimulation can paradoxically enhance sensory information transfer. Methods: Effects of nGVS of varying intensities (0-0.7 mA) on body sway were examined in 15 patients with PD standing with eye closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal reductions of sway at intermediate nGVS intensities to be indicative of SR. An established SR-curve model was fitted on individual patient outcomes and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR. Results: nGVS-induced reductions of body sway compatible with SR were found in 10 patients (67%) with optimal improvements of 23 +/- 13%. In 7 patients (47%), nGVS-induced sway reductions exceeded the minimally important clinical difference (optimal improvement: 30 +/- 10%), indicative of strong SR. This beneficial effect was more likely in patients with advanced PD (R = 0.45; p = 0.045). Conclusion: At least half of the assessed patients showed robust improvements in postural balance compatible with SR when treated with low-intensity nGVS. In particular, patients with more advanced disease stages and imbalance may benefit from the non-invasive and well-tolerated treatment with nGVS.

Automated summary

This study found that low-intensity noisy galvanic vestibular stimulation (nGVS) can improve postural instability in patients with advanced Parkinson's disease, and this therapeutic effect may involve stochastic resonance (SR). The beneficial effect was more pronounced in patients with more advanced disease stages and imbalance.