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

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 destabilizing 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 behavioral effects. A randomized double-blinded, sham-controlled trial of 30 healthy young adults was conducted. Perturbations consisted of discrete forward platform movement (peak acceleration = 0.1 g, maximum forward displacement = 24.5 cm). 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 postperturbation. Reduced initial backward trunk angular velocity [P = 0.021 (Holm-Bonferroni corrected)] was observed during nGVS compared with sham. nGVS did not significantly alter any assessed postperturbation EMG outcomes; however, tonic preperturbation tibialis anterior and medial gastrocnemius activity was significantly increased during nGVS. Our findings provide evidence that nGVS can modulate postural responses to perturbations, with the sustained elevation of preperturbation ankle EMG activity indicating a shift in tonic vestibulospinal drive.NEW & NOTEWORTHY Noisy galvanic vestibular stimulation (nGVS) has previously been shown to reduce postural sway during quiet standing. But whether nGVS can modify balance during destabilizing perturbations is unknown. We demonstrate that nGVS reduces the initial backward trunk angular velocity in response to discrete perturbations. These effects occurred without changes in perturbation-evoked muscle responses, but with increased preperturbation ankle muscle activity. These findings suggest that nGVS alters preperturbation tonic vestibulospinal output, as evidenced by elevated preperturbation ankle EMG, rather than reactive feedback gain.