The effect of galvanic vestibular stimulation on postural balance in Parkinson's disease: A systematic review and meta-analysis

Individualising Galvanic Vestibular Stimulation Further Improves Visuomotor Performance in Parkinson's Disease

Impaired motor function is a defining characteristic of Parkinson's disease (PD). Galvanic vestibular stimulation (GVS) has been proposed as a potential non-invasive intervention to enhance motor performance; however, its efficacy depends on both stimulation parameters and electrode configuration. In this study, we examined the effects of two-pole and three-pole GVS configurations, utilising different stimulation parameters, on motor performance in individuals with PD. Twelve participants with PD were administered eight distinct subthreshold amplitude-modulated GVS stimuli, along with sham stimulation, while performing a visuomotor target tracking task. Analysis of tracking error demonstrated substantial inter-individual variability in response to different stimuli and electrode configurations. While the three-pole configuration yielded superior motor performance in some cases, the two-pole configuration was more effective in others. The most effective overall stimulus across all subjects, characterised by an envelope frequency of 30 Hz and a carrier frequency of 110 Hz, improved motor performance by 25% relative to the sham stimulus. Moreover, tailoring the stimulation parameters to the individual further enhanced performance by an additional 24%. These findings suggest that GVS can yield significant motor improvements in individuals with PD. Furthermore, individualised optimisation of stimulation parameters, including the selection of the appropriate electrode configuration, may further enhance therapeutic efficacy.

A wide-ranging review of galvanic vestibular stimulation: from its genesis to basic science and clinical applications

Galvanic vestibular stimulation (GVS) involves applying small electrical currents to the vestibular organs via electrodes placed on the mastoids, providing a powerful tool for investigating vestibular function. Despite its long history, GVS remains highly relevant for researchers due to its ability to probe the vestibular system's role in posture, gaze control, perception, and cortical processing. Recent technical advances have considerably expanded its application in both basic research and clinical practice. Despite the fact it is not realistic to cover all aspects of GVS within the constraints of a manuscript, this narrative review summarizes the history and neurophysiological mechanisms of GVS and provides new insights and perspectives for current and future studies, both in fundamental and clinical applications. We synthesize the main findings from neurophysiological, behavioral, and neuroimaging studies, focusing on the effects of GVS on postural control, ocular responses, cortical activity, and self-motion perception. Then diagnostic and therapeutic applications are explored in balance disorders, stroke rehabilitation, and neurodegenerative diseases. Clinical approaches could benefit from greater reliance on laboratory research to refine stimulation protocols, for maximum efficacy in its therapeutic use. A final discussion summarizes what is currently well-established with regard to GVS and opens up new and exciting perspectives in basic science and clinical applications.

Galvanic vestibular stimulation for postural rehabilitation in neurological disorders: a systematic review

Background

Galvanic vestibular stimulation (GVS) may potentially improve postural rehabilitation. However, the postural control role of GVS in the neurological disorders has not been systematically reviewed.

Methods

We conducted a systematic review on PubMed, EMBASE, and Web of Science to synthesize key findings of the effectiveness of single and multiple sessions of GVS alone and combined with other interventions on balance in adults with neurological disorders. Diagnosis of neurological disorders, sample size, age and gender of participants, GVS parameters, postural assessments, and study findings were extracted following the PRISMA guidelines. Newcastle-Ottawa scale was used to assess study quality.

Results

Twenty-five studies were included in the systematic review. Clinical application of GVS for postural control included Parkinson's disease, bilateral vestibulopathy, stroke-induced hemiplegia, multiple sclerosis, progressive supranuclear palsy, persistent postural-perceptual dizziness, and unilateral vestibulopathy. GVS effectively improves postural control in most neurological disorders. Risk of bias assessment showed that most studies had a low risk of bias.

Conclusion

GVS is a promising complementary therapy to improve postural control and balance in adults with neurological disorders. Future high quality studies should be performed to confirm these findings.

The vestibulo-ocular and vestibulospinal reflexes minimally impact the freezing of gait in patients with early-to-moderate Parkinson's disease

Introduction

Freezing of gait (FOG) is a disabling condition that often leads to falls and severe postural instability in patients with Parkinson's disease (PD). This study aimed to determine whether FOG is associated with the integrity of the vestibulo-ocular (VOR) and vestibulospinal reflexes (VSR).

Methods

We retrospectively collected 138 patients with de novo PD at a tertiary medical center between February 2022 and February 2025. Each patient was queried and assessed for FOG status during the initial assessment. All patients underwent video head-impulse tests (video-HIT), cervical vestibular-evoked myogenic potential (cVEMP), ocular vestibular-evoked myogenic potential (oVEMP), and motion analysis.

Results

FOG was observed in 23 patients (23/138, 17 %). The head impulse gain of the VOR did not differ between freezers and non-freezers in any semicircular canal. The new FOG questionnaire score showed no correlation with the VOR gain for any canal. The oVEMP and cVEMP parameters did not differ between freezers and non-freezers either. Multivariable logistic regression analysis revealed a positive association between FOG and MDS-UPDRS-III (p = 0.016). However, FOG was not associated with the VOR gain in any canal or abnormalities on oVEMP or cVEMP.

Conclusions

Our preliminary data suggest that FOG is associated with the severity of motor symptoms in patients with early-to-moderate PD. While the integrity of the VOR or VSR is not currently associated with FOG, a well-designed future study could provide more nuanced insights into the relationship with these factors.

Exploring Non-invasive Brain Stimulation Effects on Physical Outcomes in People With Parkinson's Disease: An Umbrella Evidence Mapping Review With Meta-analyses

Background. Non-invasive brain stimulation (NIBS) is sometimes used alongside medication to alleviate motor symptoms in people with Parkinson's disease (PD). However, the evidence supporting NIBS's effectiveness for improving motor function in PD patients is uncertain. Objective. This umbrella review aims to synthesize recent systematic reviews and meta-analyses that have evaluated the effectiveness of NIBS in improving motor function in people with PD, with a key focus being to examine the quality of the evidence presented. Methods. The review protocol was registered in PROSPERO (CRD42022380544) and conducted per Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The search strategy was guided by the Population, Intervention, Comparison, and Outcome framework, focusing on individuals with idiopathic PD (Hoehn and Yahr stages 1-4). The review included studies comparing various NIBS techniques (eg, repetitive transcranial magnetic stimulation and transcranial direct current stimulation) to sham or alternative treatments, targeting motor and cognitive regions. Six databases were searched up to June 2024. Methodological quality was assessed using Assessment of Multiple Systematic Reviews 2 (AMSTAR2), and random-effects meta-analyses were performed to pool standardized mean differences (SMDs). Results. The final analysis included 31 meta-analyses and 10 systematic reviews. Overall, the reviews were rated as moderate quality (54% average for AMSTAR2). NIBS showed a small-to-moderate effect on motor function (Unified Parkinson's Disease Rating Scale-Section III scores; SMD = -0.80), functional mobility (gait speed and timed-up-and-go; SMD = -0.39), and freezing of gait (SMD = -0.58), but no significant effect on balance. Conclusion. NIBS offers small-to-moderate benefits for motor symptoms and functional movement in PD, though it does not significantly impact balance. Practitioners should consider the variety of techniques and treatment parameters before application.

The Vestibulo-Ocular Reflex is Associated With Visuospatial Dysfunction in Patients With Parkinson's Disease

BACKGROUND

Visuospatial impairment is one of the most frequent cognitive deficits in patients with Parkinson's disease (PD). It remains unknown whether the vestibulo-ocular reflex (VOR) function affects visuospatial perception and memory in patients with PD.

OBJECTIVE

To delineate the relationship between VOR and visuospatial function in patients with PD.

METHODS

We prospectively evaluated video head-impulse tests in 151 patients with PD (mean age± $\; \pm \;$ standard deviation, 68± $\; \pm \;$ 9 years; 77 male). All patients conducted the Rey Complex Figure test (RCFT).

RESULTS

RCFT-copying and RCFT-delayed recall were impaired in 11 (11/151, 7%) and 15 (15/151, 10%) patients, respectively. The VOR gain was normal in 55 patients with PD (55/151, 36%). However, 69 patients overestimated VOR gain for at least one canal, and 34 patients showed a decreased gain for at least one canal (seven patients showed an overestimated gain for some canals and decreased gain for other canals). Multivariable logistic regression analysis showed that abnormal RCFT-copying was negatively associated with the VOR gain for the horizontal canal (odds ratio [OR]: 0.001, 95% confidence interval [CI]: 0.001-0.08, p = 0.007). In contrast, abnormal RCFT-delayed recall was negatively associated with Mini-Mental State Examination scores (0.70, 0.52-0.93, p = 0.013), positively with age (1.11, 1.00-1.22, p = 0.041), male sex (12.82, 1.17-142.86, p = 0.036), years of schooling (1.41, 1.09-1.82, p = 0.009), but not with the VOR gain for any canal.

CONCLUSIONS

The VOR function may be associated with deficits in visuospatial perception and learning in patients with PD. This implicates the development of more targeted therapeutic interventions and offers insights into the broader implications of PD on sensory-motor integration and cognitive function.

Galvanic vestibular stimulation to rehabilitate postural instability in Parkinson's disease

BACKGROUND

 Galvanic vestibular stimulation (GVS) is a non-invasive technique employed to rehabilitate balance by delivering low-intensity, short-duration electrical stimulation to the mastoid bones, effectively activating the vestibulospinal tract.

OBJECTIVE

 To evaluate the effects of GVS on balance in patients with Parkinson's disease (PD) and postural instability.

METHODS

 In this clinical study, 25 PD patients with postural instability in the ON phase (best effect of dopaminergic medication) underwent GVS. Balance was assessed using the Berg Balance Scale (BBS), the Timed Up and Go (TUG) test, and posturography on a force platform. Electrical current intensity was progressively increased between the mastoids, starting at 1.0 mA and reaching 3.5 mA by the 6th session, with this level maintained until the 8th session. Stimulation duration began at 9 minutes in the 1st session, increased to 30 minutes by the 3rd session, and was sustained through the 8th session.

RESULTS

 A blinded comparison of pre- and post-GVS evaluations demonstrated significant improvements in BBS (p = 0.00001) and TUG (p = 0.00003) scores. Posturography showed an increase in the stability limit area (p = 0.026) and the general balance index (p = 0.001).

CONCLUSION

 In the therapeutic management of postural instability in PD, GVS emerges as a promising complementary strategy for enhancing balance. Further research is needed to determine whether these improvements persist after GVS cessation.

REGISTRATION OF CLINICAL TRIAL

 https://ensaiosclinicos.gov.br/rg/RBR-22j8728.

A systematic review of vestibular stimulation in post-stroke visual neglect

Unilateral visual neglect is a condition that negatively impacts the lives of many stroke survivors. Studies have investigated different forms of vestibular stimulation as a potential therapy, but evidence is yet to be systematically reviewed. We therefore reviewed the effects of vestibular stimulation on outcomes of neglect and activities of daily living (ADL) for people with visual neglect. We searched relevant databases up until September 2022. Eligible articles included any form of vestibular stimulation, study design, or control condition. Included participants were 18 years or older, presenting with neglect following a haemorrhagic or ischaemic stroke. Relevant outcomes were clinically validated measures of neglect and ADL. Cochrane risk of bias tools were used to assess study quality. Meta-analyses and narrative methods were used to synthesize the data. Our search returned 17 relevant studies comprising 180 participants. Meta-analyses showed no difference between galvanic vestibular stimulation and sham conditions on outcomes, whereas caloric vestibular stimulation led to improvement compared to pre-stimulation scores. Narrative syntheses showed mixed results. Clinical and methodological heterogeneity was found both within and between studies. Overall, results were inconsistent regarding the effects of vestibular stimulation as a treatment for neglect. Further trials are warranted but require more careful methodological planning.

Multisensory mechanisms of gait and balance in Parkinson's disease: an integrative review

Understanding the neural underpinning of human gait and balance is one of the most pertinent challenges for 21st-century translational neuroscience due to the profound impact that falls and mobility disturbances have on our aging population. Posture and gait control does not happen automatically, as previously believed, but rather requires continuous involvement of central nervous mechanisms. To effectively exert control over the body, the brain must integrate multiple streams of sensory information, including visual, vestibular, and somatosensory signals. The mechanisms which underpin the integration of these multisensory signals are the principal topic of the present work. Existing multisensory integration theories focus on how failure of cognitive processes thought to be involved in multisensory integration leads to falls in older adults. Insufficient emphasis, however, has been placed on specific contributions of individual sensory modalities to multisensory integration processes and cross-modal interactions that occur between the sensory modalities in relation to gait and balance. In the present work, we review the contributions of somatosensory, visual, and vestibular modalities, along with their multisensory intersections to gait and balance in older adults and patients with Parkinson's disease. We also review evidence of vestibular contributions to multisensory temporal binding windows, previously shown to be highly pertinent to fall risk in older adults. Lastly, we relate multisensory vestibular mechanisms to potential neural substrates, both at the level of neurobiology (concerning positron emission tomography imaging) and at the level of electrophysiology (concerning electroencephalography). We hope that this integrative review, drawing influence across multiple subdisciplines of neuroscience, paves the way for novel research directions and therapeutic neuromodulatory approaches, to improve the lives of older adults and patients with neurodegenerative diseases.

Vestibular neurology for the generalist

This review of vestibular neurology for the general neurologist delves into the multifaceted realm of vestibular neurology where we address the diagnostic and therapeutic challenges associated with dizziness, vertigo and balance disorders. We outline the standard vestibular assessments that can be understood and incorporated by the generalist, discussing their use in common vestibular disorders. Key disorders covered include acute and chronic syndromes, benign paroxysmal positional vertigo, Meniere disease, vestibular migraine and persistent postural-perceptual dizziness. We also touch on emerging advances in vestibular genotyping and novel treatment approaches for balance problems.

Vestibular prepulse inhibition of the human blink reflex

OBJECTIVE

Auditory and somatosensory prepulses are commonly used to assess prepulse inhibition (PPI). The effect of a vestibular prepulse upon blink reflex excitability has not been hitherto assessed.

METHODS

Twenty-two healthy subjects and two patients with bilateral peripheral vestibular failure took part in the study. Whole body yaw rotation in the dark provided a vestibular inertial prepulse. Blink reflex was electrically evoked after the end of the rotation. The amplitude of R1 and the area-under-the-curve (area) of the blink reflex R2 and R2c responses were recorded and analysed.

RESULTS

A vestibular prepulse inhibited the R2 (p < 0.001) and R2c area (p < 0.05). Increasing the angular acceleration did not increase the R2 and R2c inhibition (p > 0.05). Voluntary suppression of the vestibulo-ocular reflex did not affect the magnitude of inhibition (p > 0.05). Patients with peripheral vestibular failure did not show any inhibition.

CONCLUSIONS

Our data support a vestibular gating mechanism in humans.

SIGNIFICANCE

The main brainstem nucleus mediating PPI - the pedunculopontine nucleus (PPN) - is heavily vestibular responsive, which is consistent with our findings of a vestibular-mediated PPI. Our technique may be used to interrogate the fidelity of brain circuits mediating vestibular-related PPN functions. Given the PPN's importance in human postural control, our technique may also provide a neurophysiological biomarker of balance.

Effect of Vestibular Stimulation on Balance and Gait in Parkinson's Disease: A Systematic Review

Background/Objectives: Parkinson's Disease (PD) can be associated with balance and gait impairments leading to increased risk of falls. Several studies have reported positive effects of various forms of vestibular stimulation (VS) for improving balance and stability in people with PD (PwP). The purpose of present study was to synthesise the current evidence on the effectiveness of VS, highlighting its potential benefits in improving postural stability and reducing gait impairments in people with Parkinson's Disease. Method: A systematic search was conducted across databases Cochrane, Medline, PEDro, PubMed, Web of Science, and Google Scholar. Studies were included if they involved PwP at stages 3 or 4 of the Hoehn and Yahr scale, aged 60 years or older. The Risk of Bias (RoB) was assessed using the ROBINS-I tool. The review followed the PRISMA guidelines and the protocol was registered with PROSPERO (CRD42022283898). Results: demonstrated that various forms of VS have shown promise in mitigating symptoms of vestibular dysfunction and improving gait and balance in PwP. However, the overall RoB ranged from moderate to critical, with variations across different domains. Conclusions: While VS appears to offer potential benefits in improving balance and gait in PwP, the presence of biases in the reviewed studies necessitate caution in interpreting the results. Further research should focus on addressing these biases to confirm the therapeutic potential of VS in PD.

No evidence for effects of low-intensity vestibular noise stimulation on mild-to-moderate gait impairments in patients with Parkinson's disease

BACKGROUND

Gait impairment is a key feature in later stages of Parkinson's disease (PD), which often responds poorly to pharmacological therapies. Neuromodulatory treatment by low-intensity noisy galvanic vestibular stimulation (nGVS) has indicated positive effects on postural instability in PD, which may possibly be conveyed to improvement of dynamic gait dysfunction.

OBJECTIVE

To investigate the effects of individually tuned nGVS on normal and cognitively challenged walking in PD patients with mild-to-moderate gait dysfunction.

METHODS

Effects of nGVS of varying intensities (0-0.7 mA) on body sway were examined in 32 patients with PD (ON medication state, Hoehn and Yahr: 2.3 ± 0.5), who were standing with eyes closed on a posturographic force plate. Treatment response and optimal nGVS stimulation intensity were determined on an individual patient level. In a second step, the effects of optimal nGVS vs. sham treatment on walking with preferred speed and with a cognitive dual task were investigated by assessment of spatiotemporal gait parameters on a pressure-sensitive gait carpet.

RESULTS

Evaluation of individual balance responses yielded that 59% of patients displayed a beneficial balance response to nGVS treatment with an average optimal improvement of 23%. However, optimal nGVS had no effects on gait parameters neither for the normal nor the cognitively challenged walking condition compared to sham stimulation irrespective of the nGVS responder status.

CONCLUSIONS

Low-intensity nGVS seems to have differential treatment effects on static postural imbalance and continuous gait dysfunction in PD, which could be explained by a selective modulation of midbrain-thalamic circuits of balance control.

Unraveling the threads of stability: A review of the neurophysiology of postural control in Parkinson's disease

Postural instability is a detrimental and often treatment-refractory symptom of Parkinson's disease. While many existing studies quantify the biomechanical deficits among various postural domains (static, anticipatory, and reactive) in this population, less is known regarding the neural network dysfunctions underlying these phenomena. This review will summarize current studies on the cortical and subcortical neural activities during postural responses in healthy subjects and those with Parkinson's disease. We will also review the effects of current therapies, including neuromodulation and feedback-based wearable devices, on postural instability symptoms. With recent advances in implantable devices that allow chronic, ambulatory neural data collection from patients with Parkinson's disease, combined with sensors that can quantify biomechanical measurements of postural responses, future work using these devices will enable better understanding of the neural mechanisms of postural control. Bridging this knowledge gap will be the critical first step towards developing novel neuromodulatory interventions to enhance the treatment of postural instability in Parkinson's disease.

Impact of galvanic vestibular stimulation electrode current density on brain current flow patterns: Does electrode size matter?

BACKGROUND

Galvanic vestibular stimulation (GVS) uses at least one electrode placed on the mastoid process with one or multiple placed over other head areas to stimulate the vestibular system. The exact electrode size used is not given much importance in the literature and has not been reported in several studies. In a previous study, we compared the clinical effects of using different electrode sizes (3 cm2 and 35 cm2) with placebo but with the same injected current, on postural control. We observed significant improvement using the smaller size electrode but not with the bigger size electrode. The goal of this study was to simulate the current flow patterns with the intent to shed light and potentially explain the experimental outcome.

METHODS

We used an ultra-high-resolution structural dataset and developed a model to simulate the application of different electrode sizes. We considered current flow in the brain and in the vestibular labyrinth.

RESULTS

Our simulation results verified the focality increase using smaller electrodes that we postulated as the main reason for our clinical effect. The use of smaller size electrodes in combination with the montage employed also result in higher induced electric field (E-field) in the brain.

CONCLUSIONS

Electrode size and related current density is a critical parameter to characterize any GVS administration as the choice impacts the induced E-field. It is evident that the higher induced E-field likely contributed to the clinical outcome reported in our prior study.

Scoping out noisy galvanic vestibular stimulation: a review of the parameters used to improve postural control

Objective

Noisy galvanic vestibular stimulation (nGVS) has been used to facilitate vestibular function and improve gait and balance in people with poor postural control. The aim of this scoping review is to collate, summarize and report on the nGVS parameters that have been used to augment postural control.

Method

A systematic scoping review was conducted up to December 2022. Data were extracted and synthesized from 31 eligible studies. Key nGVS parameters were identified, and the importance of these parameters and their influence on postural control evaluated.

Results

A range of nGVS parameters have been used to augment postural control, including; noise waveform, amplitude, frequency band, duration of stimulation, method of amplitude optimization, size and composition of electrodes and the electrode skin interface.

Conclusion

Systematic evaluation of the individual parameters that can be manipulated in the nGVS waveform identified that a broad array of settings have been utilized in each parameter across the studies. Choices made around the electrode and electrode-skin interface, as well as the amplitude, frequency band, duration and timing of the waveform are likely to influence the efficacy of nGVS. The ability to draw robust conclusions about the selection of optimal nGVS parameters to improve postural control, is hindered by a lack of studies that directly compare parameter settings or consider the variability in individuals' response to nGVS. We propose a guideline for the accurate reporting of nGVS parameters, as a first step toward establishing standardized stimulation protocols.