Noisy galvanic vestibular stimulation (nGVS)

Timothy C. Hain, MD. • Page last modified: September 29, 2022

Introduction:

This page provides more detail about an emerging treatment of bilateral vestibular loss involving electrical devices to add noise to the system.

A recent review of galvanic stimulation stated "Currently, three approaches are being investigated: vestibular co-stimulation with a cochlear implant (CI), EVS with a vestibular implant (VI), and galvanic vestibular stimulation (GVS). " (Sluydts et al, 2020) Here we are only discussing GVS.

Noisy Galvanic Vestibular Stimulation

There is now a modest literature concerning noisy galvanic vestibular stimulation (nGVS) in the treatment of bilateral vestibular loss. Electrodes that pass electric current through the inner ear (and surrounding skull) are used. Roughly 1 ma of current is applied, which is not especially painful. 5 ma is painful.

The hypothesis is that "stochastic resonance" is used to increase the firing rate of a nonlinear system operating at subthreshold levels by adding noise, bringing the system up to threshold. (Wuehr et al, 2018) Hm. So this idea would logically depend on having some useful vestibular input, that is made to work more efficiently by one of these devices. Schniep et al (2018) reported data supporting this idea.

Other hypotheses would seem reasonable -- could the effect be a placebo ? Well, if it is, thats OK -- whatever works.

Could there be a change in balance strategy in response to noise coming in from the vestibular system ? Perhaps people upweight other senses when they decide their vestibular system is even worse than before. Helmchen et al (2020) documented some changes in brain processing, that might be relevant here.

Could noise be better than distorted information from a partially functioning vestibular system. We doubt it.

Literature review of nGVS:

Rashid et al (2022) reviewed the literature concerning this method. This paper did not include any original data, but rather it was a statistical analysis of other investigators. They located 5 eligible studies, and reported that "Meta-analysis revealed a moderate effect in favor of nGVS improving postural control during standing and walking [pooled SMD = 0.47 95% CI (0.25, 0.7)]. nGVS-mediated improvements in postural control were most evident in observations of reduced sway velocity when standing on a firm surface with eyes closed, and in the reduced variability of gait parameters, particularly those measuring lateral stability.Conclusions Coincident nGVS in people with BVP improves postural control during standing and walking. This improvement appears to be context specific, in that vestibular augmentation is most effective in situations where visual inputs are limited, and where reliable context specific proprioceptive cues are available. "
Eder et al (2022) concluded that "nGVS does not induce synergistic treatment effects in combination with VRT in patients with BVP when applied during treatment sessions. Hence, rather than being applied in parallel, nGVS and VRT might be complementary therapeutic options with nGVS being used during postural activities in daily life, e.g., walking. "
Nooristani, M., et al. (2021). These authors reported "Our results also suggest that nGVS is beneficial for all older adults, and even more for those with a vestibular impairment. Therefore, it could be an approach to reduce falls. " They think it is "beneficial" for all older adults.
Fujimoto, C., et al. (2021). They reported a'RESULTS: A total of 129 anchors were analyzed. Subjective evaluations numbered 83 (64%) for unchanged and 33 (26%) for slightly improved. Anchor-based methods yielded estimates for MIDs of -0.43 cm/s in velocity improvement (p < 0.01), -0.77 cm(2) for area improvement (p < 0.01) and -0.23 cm for RMS improvement (p < 0.001). "
Fujimoto, C., et al. (2018). Wrote "GVS leads to an improvement in body balance that lasts for several hours after the end of the stimulus in BV patients with a reduction in the high-frequency components of their postural movement. " We find this difficult to understand using the stochastic resonance explanation. Could this be placebo ? Could it be a change in sensorimotor strategy ?
Schniepp, R., et al. (2018). They reported "All patients with rBVP but none with cBVP exhibited stimulation-induced vestibulospinal reflex responses with a mean threshold level of 1.26 +/- 0.08 mA. Additional nGVS resulted in improved processing of weak subthreshold vestibular stimuli (p = 0.015) and thereby effectively decreased the vestibulospinal threshold in 90% of patients with rBVP (mean reduction 17.3 +/- 3.9%; p < 0.001). CONCLUSION: The present findings allow to identify the mechanism by which nGVS appears to stabilize stance and gait performance in patients with BVP. Accordingly, nGVS effectively lowers the vestibular threshold to elicit balance-related reflexes that are required to adequately regulate postural equilibrium. This intervention is only effective in the presence of a residual vestibular functionality, which, however, applies for the majority of patients with BVP. Low-intensity noise stimulation thereby provides a non-invasive treatment option to optimize residual vestibular resources in BVP"
Helmchen, C., et al. (2020). reported "GVS elicits an increase of the reduced rs-fMRI in the patients' right Rolandic operculum, which may be an important contribution to restore the disturbed visual-vestibular interaction. The GVS-induced changes in the cerebellum and the visual cortex were associated with lower dizziness-related handicaps in patients, possibly reflecting beneficial neural plasticity that might subserve visual-vestibular compensation of deficient self-motion perception. ". They appear to be supported a change in strategy theory rather than stochastic resonance.
Iwasaki, S., et al. (2018). reported "Noisy GVS is effective in improving gait performance in healthy subjects as well as in patients with bilateral vestibulopathy. " This again would be against the stochastic theory. It favors the placebo theory.
Iwasaki, S., et al. (2014). "Noisy vestibular stimulation improves body balance in bilateral vestibulopathy." Neurology 82(11): 969-975. They reported "The amplitude of the optimal stimulus was 456 +/- 82 muA, and it improved the velocity, area, and RMS by 29.4% +/- 4.9%, 45.6% +/- 4.7%, and 22% +/- 3.3%, respectively (p < 0.01). CONCLUSIONS: Noisy GVS is effective in improving postural stability in healthy subjects as well as in patients with bilateral vestibular dysfunction. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that in patients with bilateral vestibular dysfunction, an imperceptible level of noisy GVS may improve postural stability. " So 1/2 milliamp, and improvements of about 20%.

Discussion:

The general idea that a tiny amount of noise added to the inner ear is slightly helpful is not very plausible.

One would think that other interventions that raise vestibular neuron firing, such as a strong cup of coffee, a stimulant, etc, might have a similar effect. Or just being a little anxious. Hm. Maybe no money is available to investigate the effect of a strong cup of coffee on vestibular function of bilateral patients.

Nevertheless, the literature is growing, and perhaps nGVS it is worth a try.

Conclusion:

There is now evidence for a modest effect of noisy galvanic stimulation in persons with bilateral vestibular loss, in the direction of improving balance.

References

Eder, J., et al. (2022). "Combining vestibular rehabilitation with noisy galvanic vestibular stimulation for treatment of bilateral vestibulopathy." J Neurol.
Fujimoto, C., et al. (2018). "Noisy Galvanic Vestibular Stimulation Sustainably Improves Posture in Bilateral Vestibulopathy." Front Neurol 9: 900.
Fujimoto, C., et al. (2021). "Minimally important differences for subjective improvement in postural stability in patients with bilateral vestibulopathy." Neurosci Lett 747: 135706.
Hain TC, Cherchi M, Perez-Fernandez N. The Gain-Time Constant product quantifies total vestibular output in bilateral vestibular loss, Frontiers, (2018)
Hain TC, Cherchi M, and Yacovino DA “Bilateral vestibular weakness. “Frontiers in Neurology-Neuro-Otology in Press (2018)
Helmchen, C., et al. (2020). "Effects of galvanic vestibular stimulation on resting state brain activity in patients with bilateral vestibulopathy." Hum Brain Mapp 41(9): 2527-2547.
Iwasaki, S., et al. (2018). "Noisy vestibular stimulation increases gait speed in normals and in bilateral vestibulopathy." Brain Stimul 11(4): 709-715.
Nooristani, M., et al. (2021). "Vestibular function modulates the impact of nGVS on postural control in older adults." J Neurophysiol 125(2): 489-495.
Rashid, U. (2022). "Efficacy of nGVS to improve postural stability in people with bilateral vestibulopathy: A systematic review and meta-analysis." Frontiers in Neuroscience.
Schniepp, R., et al. (2018). "Noisy vestibular stimulation improves vestibulospinal function in patients with bilateral vestibulopathy." J Neurol 265(Suppl 1): 57-62.
Sluydts, M., et al. (2020). "Electrical Vestibular Stimulation in Humans: A Narrative Review." Audiol Neurootol 25(1-2): 6-24.
Wuehr, M., et al. (2018). "Stochastic resonance in the human vestibular system - Noise-induced facilitation of vestibulospinal reflexes." Brain Stimul 11(2): 261-263.