Effects of noisy galvanic vestibular stimulation on reactive postural and neuromuscular responses to surface perturbations

Postural control requires continuous sensorimotor feedback to maintain balance and prevent falls. Noisy galvanic vestibular stimulation (nGVS), a weak stochastic electrical stimulus applied to the peripheral vestibular apparatus, can reduce postural sway during unperturbed steady standing. Although nGVS is proposed to modulate balance by enhancing vestibular-mediated feedback control, the specific underlying neural mechanisms are unknown. Whether nGVS modulates balance during destabilising perturbations has not been explored. We therefore interrogated the effect of nGVS on dynamic balance in response to a discrete perturbation to posture. We further assessed electromyographic (EMG) activity to provide insight into the neuromuscular mechanisms driving any observed behavioural effects. A randomised double-blinded, sham-controlled trial of 30 healthy young adults was conducted. Perturbations consisted of discrete forwards platform movement (peak acceleration = 0.1g, maximum forward displacement = 24.5cm). Random noise GVS or sham was delivered continuously during each experimental condition. Initial backward trunk angular velocity in response to the perturbation was used as the primary kinematic outcome. EMG activity of the tibialis anterior and medial gastrocnemius was assessed both pre and post perturbation. Reduced initial backward trunk angular velocity (p = 0.021 [Holm-Bonferroni corrected]) was observed during nGVS compared to sham. There were no significant between-condition differences in any assessed post-perturbation EMG outcomes; however, tonic pre-perturbation tibialis anterior and medial gastrocnemius activity was significantly increased during nGVS. Our findings provide evidence that nGVS can modulate responses to perturbations, consistent with a sustained elevation of pre-perturbation ankle EMG activity, indicating a shift in tonic vestibulospinal drive.