Table 2.
A summary of the articles included in the parameter scoping review.
| Study ID | Study design | Population description | n | Aim of study | Summary of findings |
|---|---|---|---|---|---|
| Asslander et al. (2021) | Randomized crossover | Healthy young | 21 | To investigate whether nGVS induced effects on body sway consistently follow a SR like bell shaped performance curve. | nGVS resulted in reduced postural sway in standing in most trials. However, the majority of participants did not demonstrate an SR pseudo bell shaped curve. |
| Chen et al. (2021) | Crossover | Healthy, BVP | 16 healthy 10 BVP | To investigate the effects of nGVS in straight walking and 2 Hz head yaw walking in healthy and bilateral, vestibular hypofunction, in light and dark conditions. | nGVS reduced walking deviations in people with BVP. This was particularly evident in visually deprived conditions |
| Eder et al. (2022) | Double blind randomized controlled trial | BVP | 23 | To investigate potential synergistic effects of nGVS when combined with vestibular rehabilitation. | After 2 weeks vestibular rehabilitation training people with BVP demonstrated improved balance. There was no significant difference between those that received nGVS during the training and those that received sham treatment. |
| Fujimoto et al. (2016) | Block randomized pre/post experimental | Healthy older adults | 30 | To investigate the aftereffects of imperceptible nGVS on body balance in elderly adults. | During 3 h of nGVS there was reduced mean velocity at 1 h. Post nGVS there was a significant reduction in COP after 30 min that was maintained for 4 h. A further 30 min of nGVS added to the improvement and was maintained for a further 4 h. |
| Fujimoto et al. (2018) | Pre post experimental | BVP | 13 | To examine whether 30 min nGVS continues to improve balance after the cessation of stimulus in BVP patients | Reduced COP mean velocity was observed after 30 min nGVS. This effect was sustained for 3 h |
| Goel et al. (2015) | Randomized crossover | Healthy young adults | 45 | To investigate the effect of SVS on balance functions. | SVS at 46–53% of perceptual motion threshold of 1 Hz sinusoidal waveform, significantly improved balance in 70% of people (9/15, 13/15, 10/15). Responders demonstrated significantly improved balance in 4 different experimental studies. |
| Inukai et al. (2018a) | RCT | Healthy older adults | 32 | To assess the influence of nGVS on COP sway in community dwelling older adults during standing | Reduced sway path length, and mean sway velocity in nGVS group compared to control. Correlation between initial sway path length and balance measures during nGVS. |
| Inukai et al. (2018b) | Crossover | Healthy adults | 18, 24, 16 | To clarify the influence of nGVS on the center of pressure sway measurement in standing EO and identify the responders to nGVS | Subthreshold nGVS decreased sway path length during 30 s and 5 s stimulation in healthy young people. When divided into high and low initial sway path nGVS effect was only significant in those who had high initial sway path. |
| Inukai et al. (2020a) | RCT | Healthy adults | 36 | To elucidate the effects of nGVS on COP sway during one legged standing at different current amplitudes | 200 μA nGVS reduced sway velocity and sway path length in healthy young people standing on one leg with EO. There was no significant effect for the 0 and 400 μA groups. Baseline values correlated with the stimulation effect in the 200 μA group only. |
| Inukai et al. (2020b) | Experimental | Healthy adults | 24 | To determine the effects of different floor surface and visual conditions on the stimulus effects of the nGVS intervention. | nGVS reduced AP sway velocity and sway path length at 0 min and 10 min after 6 x 30s standing EO on a firm surface but not with EC on foam. |
| Inukai et al. (2020c) | RCT | Healthy adults | 26 | To elucidate the after effect of nGVS on COP sway. To identify subjects for whom nGVS is effective. | Significant decrease in AP and ML COP velocity and sway path length compared to baseline during nGVS and at 10 min post nGVS. Significant correlation between baseline sway velocity and stimulation effect. |
| Iwasaki et al. (2014) | Crossover | Healthy adults, BVP | healthy 21 BVP 11 | To examine the effect of imperceptible level of nGVS on postural performance in healthy subjects and patients with BVP | nGVS at an optimal amplitude reduced COP velocity, area, and RMS in healthy and BVP subjects. There was no significant difference in balance parameters at the non-optimal amplitude. 76% of healthy participants and 91% of BVP participants showed an optimal response to nGVS. |
| Iwasaki et al. (2018) | Experimental | Healthy, BVP | 19 Healthy 12 BVP | To examine the effect of an imperceptible level of nGVS on dynamic locomotion in normal subjects as well as patients with BVP | nGVS had a significant effect, improving gait velocity, stride length and stride time in healthy and BVP as measured by a trunk worn sensor. |
| Ko et al. (2020) | Experimental | Healthy, BVP | 10 Healthy 7 BVP | To investigate the effect of nGVS on posture and neural activity during standing and walking with 2 Hz head turning. | Healthy and BVP groups demonstrated a significant decrease in COP RMS with nGVS and head turning was significantly more coherent to 2 Hz with nGVS. |
| Lotfi et al. (2021) | Single blind RCT | Multiple Sclerosis | 24 | To compare the effectiveness of vestibular rehabilitation therapy or noisy galvanic stimulation for dizziness and balance responsiveness in MS. | The vestibular rehabilitation group demonstrated improved postural control. nGVS 30 min twice a week for 6 weeks did not improve balance. There was no significant difference between the nGVS group and the control group |
| Matsugi et al. (2020) | Sham controlled crossover | Healthy young adults | 17 | To investigate whether nGVS modulates body sway and muscle activity of the lower limbs depending on visual and somatosensory information from the foot using rubber-foam | 1,000 μA nGVS increased body sway on foam. There was no significant difference on a firm surface, there was no significant difference with eyes open or closed. |
| Matsugi et al. (2022) | Single blind crossover | Healthy young adults | 30 | To investigate whether noisy galvanic vestibular stimulation (nGVS) modulates the vestibulo-ocular reflex (VOR) and whether this effect is correlated with the effect of nGVS on body sway. | VOR gain was significantly decreased at 200 μA, and sway path length significantly increased at 600 μA. No correlation observed between the effect of nGVS on COP and VOR related parameters. |
| Matsugi et al. (2022) | Double blind crossover | Healthy adults | 17 | To identify the changes in lower limb muscle activity and joint angular velocity during nGVS | nGVS altered the physical response in different standing postural conditions (exploratory study). During nGVS lower limb angular velocity was significantly decreased in the transverse direction when standing on a foam surface with EC |
| Mulavara et al. (2011) | Crossover | Healthy adults | 15 | To investigate the effect of two different frequencies of nGVS on postural sway | An optimal level of SVS was found in 8/15 people at 1-2 Hz and 10/15 at 0–30 Hz. There was no significant difference in balance performance between the two frequencies. |
| Mulavara et al. (2015) | Randomized crossover | Healthy adults | 13 | To investigate the effect of SVS on the postural response to perturbations during gait. | SVS at an optimal level reduced gait cycle time variability and increased trunk stability walking on an oscillating treadmill. Optimum peak current was at 35% of perceptual motion threshold |
| Nooristani et al. (2019a) | RCT | Healthy adults | 36 | To determine the effect of current density on postural control during nGVS. | nGVS significantly reduced sway path length and sway velocity immediately after stimulation with 3cm2 electrodes (high current density) but not with 35cm2 electrodes (low current density) or sham stimulation. |
| Nooristani et al. (2019b) | RCT | Healthy adults | 28 | To investigate the lasting effect of nGVS on postural stability. | Significantly reduced sway path and COM velocity in both nGVS and sham immediately after and 1 h after stimulation. No significant difference between groups. |
| Nooristani et al. (2021) | Randomized controlled trial | Older adults and older adults with vestibular impairment | 24 Healthy older adults 12 Older adults with vestibular impairment | To determine the effect of nGVS on postural control in older adults with and without vestibular impairment. To examine the sustained effect of nGVS compared to sham stimulation | nGVS significantly reduced sway velocity and sway path length during and after stimulation compared to sham. There was a significantly greater effect in older adults with vestibular impairment compared to those with normal function. |
| Piccolo et al. (2020) | Crossover | Healthy adults | 13 | To determine whether SVS affects postural stability when balance is challenged during standing and walking tasks (EO). To compare the effect of amplitude optimization derived from sinusoidal or cutaneous threshold techniques. | 10 s SVS demonstrated improved balance in balance challenged standing and reduced step width variability during gait. There was no significant effect between trials whether amplitude optimization was determined by motion perception (sinusoidal GVS) or cutaneous threshold. |
| Samoudi et al. (2015) | Double blind crossover | Parkinson’s disease | 10 | To investigate the safety and effects of SVS in patients with Parkinson’s disease. | Significantly reduced sway path standing with EC on foam and significantly reduced recovery time to perturbation with SVS compared to sham stimulation |
| Sprenger et al. (2020) | Crossover | BVP, healthy | 30 BVP 24 healthy | To determine whether nGVS improves postural control in comparison to sham stimulus in context dependent conditions. | nGVS applied at 80% motion perception threshold did not significantly change standing balance on a firm surface with EO or EC or during a dual task. Standing on foam with EC nGVS resulted in significant deterioration in standing balance |
| Temple et al. (2018) | RCT (single blind) | Healthy adults | 24 | To determine whether SVS could improve short term adaptation to a locomotor task in a novel sensory discordant environment | 7/12 participants responded to nGVS. nGVS resulted in faster times on a functional mobility test while wearing prism glasses and demonstrated faster adaption to a complex novel locomotion task with sensory discordance, compared to control group. |
| Woll et al. (2019) | Crossover | PPPV and Healthy | 24 PPPV 23 Healthy | To investigate the effect of nGVS on patients with PPPV compared to healthy controls | The perceptual threshold for GVS was significantly reduced in PPPV compared to healthy controls. There was no significant difference in postural postural sway speed between nGVS and no nGVS conditions. Romberg quotient was significantly reduced with nGVS compared to the no GVS condition on both firm and foam surface conditions. |
| Wuehr et al. (2016a) | Crossover | BVP | 13 | To examine the effects of nGVS on dynamic walking stability in people with BVP | nGVS resulted in reduced gait variance and increased bilateral coordination, particularly during gait at slow speeds. |
| Wuehr et al. (2016b) | Crossover | Healthy adults | 17 | To examine the effects of nGVS on the walking performance in healthy adults walking with EC. | nGVS reduced gait variance and improved bilateral phase co-ordination during walking with EC at slow walking speeds only. |
| Wuehr et al. (2022) | Single blind crossover | Parkinson’s disease | 15 | To investigate the potential mode of action of the therapeutic effect of nGVS | At least half PD patients demonstrated reduced body sway compatible with SR. |
AP, anterior–posterior; BVP, bilateral vestibulopathy; COM, center of mass; COP, center of pressure; EC, eyes closed; EO, eyes open; hrs, hours; nGVS, noisy galvanic vestibular stimulation; RMS, root mean squared; SR, stochastic resonance; SVS, stochastic vestibular stimulation; VOR, vestibulo-ocular reflex; PPPV, Persistent Perceptual Postural Vertigo.