Noisy vestibular stimulation improves vestibulospinal function in patients with bilateral vestibulopathy

Galvanic vestibular stimulation for Mal de Debarquement syndrome: a pilot study on therapeutic potential

Mal de Debarquement Syndrome (MdDS) is a debilitating neuro-otological disorder causing a persistent sensation of self-motion, often triggered by passive motion like being on a boat (MT-MdDS) or non-motion triggered (non-MT MdDS). Due to the unknown pathophysiological mechanism, available treatment options for managing symptoms are limited. Within the framework of a pilot study, our objective was to investigate the effect, safety, and feasibility of galvanic vestibular stimulation (GVS) as a potential alternative treatment option for MdDS. The trial included 12 MdDS patients and 12 controls. In Part 1, the perceptual threshold for movement perception was determined using both sine and noisy (white noise) GVS for both patients and controls. In Part 2, patients received up to eight four-minute GVS at varying intensities, determined by their individual threshold, during both sine and noisy GVS (i.e., at their threshold, 120%, 70%, and 20%). The effectiveness was evaluated using visual analogue scale (VAS) scores and static posturography. Five patients reported improvement with noisy GVS at 70%, two at noisy threshold, one at noise 20%, one at 120%, one at sine 20%, and one at sine 120%. Our findings show statistically significant positive trends in both subjective and objective outcome measures following specific GVS sessions. Particularly, notable improvements were observed with noisy GVS at intensities 70% and 20% below perceptual threshold levels. All patients found GVS to be safe and manageable, with no worsening of their symptoms. GVS demonstrated positive trends in posturographic stability, particularly with 70% currents and noisy GVS. While further research is necessary, the potential benefits, safety, and feasibility of GVS for MdDS patients have been demonstrated as promising.

The impact of bilateral vestibulopathy on quality of life: data from the Antwerp University Hospital registry

OBJECTIVE

Bilateral vestibulopathy (BVP) is a rare condition which causes significant impairments in balance, spatial orientation, and gaze stability. The goal of this study was to assess the impact of BVP on several outcome domains related to daily life.

STUDY DESIGN

Cross-sectional survey.

SETTING

Tertiary referral center for otology and neurotology.

PATIENTS

Sixty-one patients treated for BVP at the Antwerp University Hospital.

INTERVENTION

Questionnaire with items covering several outcome domains.

MAIN OUTCOME MEASURES

Impact of BVP on employment, mobility, activities of daily living, health outcomes, and finances.

RESULTS

A total of 61 patients with BVP completed the questionnaire. Of these, 47.5% were retired, 26.2% were actively employed and 23% were unable to work due to their symptoms. 4.9% had to change work in the past, and 6.6% had to adjust their work situation. 8.1% had been absent from work for more than 4 weeks in the last year. Of those who had driven in the last year, 42.6% reported that their balance problems had affected their driving ability. 54.1% reported having fallen as a result of their BVP symptoms and 39.4% of these required a visit to their general practitioner or a hospital due to a fall. 14.8% reported that they had visited the emergency room and 21.3% reported that they had been admitted to the hospital in the last year. 13.1% reported that they had borne extra financial costs in the last year due to their condition, with a median burden of €1,000.

CONCLUSIONS

BVP has a significant impact on daily life as measured across several domains. These findings indicate that there is a significant disease burden associated with BVP. New treatment or management modalities are needed to reduce this burden.

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.

Sensory feedback curbs the impact of nGVS on postural control in older adults

Noisy galvanic vestibular stimulation (nGVS) has been shown to improve postural control. However, the focus has been on the vestibular system, failing to account for other sensory inputs. The aim of the present study was thus to examine the relative impact of the various sensory feedback sources on the improvement of postural control following nGVS in older adults. Fourty-seven participants (20 controls; 27 older adults) were recruited for this study. Participants performed the modified clinical test of sensory integration as part of the postural control assessment. Older adults received an nGVS or sham stimulation which was compared to their baseline measurements and to an optimal performance (control group comprised of young adults). Results suggest that the nGVS-induced improvement of postural control in older individuals is significant only in conditions where visual and somatosensory feedback were hindered.The data also suggest that improvements in these conditions is more significant in individuals with reduced vestibular feedback. The study confirms the potential impact of nGVS for the rehabilitation of balance difficulties in the elderly population, most particularly in conditions with less reliable somatosensory and visual inputs. nGVS effects are thus modulated by sensory feedback with a dominant effect of somatosensory and visual sensory cues.

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.

Stochastic galvanic vestibular stimulation improves kinetic performance in adolescent idiopathic scoliosis during obstacle negotiation

Vestibular dysfunction has been reported as a potential cause in adolescent idiopathic scoliosis (AIS). However, it remained unclear how stochastic galvanic vestibular stimulation (GVS) affected kinetic performance of patients with AIS. This study aimed to investigate the effect of stochastic GVS on ground reaction forces (GRF) measures during obstacle negotiation among patients with AIS. Fifteen patients with AIS and 15 age/sex-matched healthy controls (HC) participated in this study. Stochastic GVS was applied via electrodes placed over bilateral mastoid process with the intensity of 80% of individual sensory thresholds. Six walking trials including 2 types of GVS (stochastic GVS/sham stimulation) and 3 obstacle conditions (Level/Low/High) were randomly allocated to each participant, and each trial was repeated 3 times. Four AMTI force plates were used to measure GRF peaks and impulses in anterior-posterior (AP1/AP2), medial-lateral (ML1/ML2), and vertical (V1/V2) directions. Significant interactions were observed in AP1 (F2,56=3.537, p = 0.036), V1 (F2,56=4.118, p = 0.021), ML1 (F2,56=3.313, p = 0.044) and medial-lateral impulses (F2,56=4.386, p = 0.017) for the step negotiating obstacles. Post-hoc comparisons showed that in comparison to sham stimulation, the application of stochastic GVS significantly (1) increased AP1 (Low: p = 0.038) and V1 (Low: p < 0.001; High: p = 0.035) in two groups; (2) decreased ML1 of two groups (AIS: ps < 0.01; HC: ps < 0.05) and medial-lateral impulses in patients with AIS (Low: p = 0.013; High: p = 0.015) during obstacle negotiation. Additionally, the rates of change in ML1 and medial-lateral impulses among patients with AIS were significantly higher than that of HC, indicating that stochastic GVS demonstrated a greater effect of decreasing ML1 and medial-lateral impulses in AIS. Stochastic GVS ameliorated kinetic performance of patients with AIS during obstacle negotiation, and its potential mechanism may involve the induction of stochastic resonance phenomenon to enhance vestibular perception. Our study offered stochastic GVS as a novel approach to target vestibular-related postural instability in AIS.

Noisy galvanic vestibular stimulation induces stochastic resonance in vestibular perceptual thresholds assessed efficiently using confidence reports

In sensory perception, stochastic resonance (SR) refers to the application of noise to enhance information transfer, allowing for the sensing of lower-level stimuli. Previously, subjective-assessments identified SR in vestibular perceptual thresholds, assessed using a standard two alternative (i.e., binary), forced-choice task, when applying noisy Galvanic Vestibular Stimulation (nGVS). However, this required extensive testing of at least 100 binary trials to yield sufficiently precise thresholds at each of several nGVS amplitudes, leading to confounds of fatigue, sleepiness, learning, etc. stalling the study of vestibular SR. To mitigate this, we explore confidence reporting, which via a confidence signal detection (CSD) model may much more efficiently identify SR (i.e., with fewer trials), if SR exists in CSD thresholds. To test this, Y-translation thresholds were tested with 100 trials at each nGVS amplitude (0 or sham, 0.1, 0.2, 0.3 and 0.4 mA peak-to-peak). To objectively identify SR, we applied a machine learning classification algorithm trained on simulated datasets. We found significant evidence of SR exhibition using CSD thresholds (p = 0.0025), with six of 10 subjects classified as exhibiting SR. Next, we considered fewer trials, finding the false positive rate of SR identification to be better using CSD thresholds with as few as 50 trials, when compared to 100 binary trials. Applying the CSD model to our subject's data with a subset of their trials found similar classifications of SR exhibition as with 100 binary trials. We demonstrate CSD thresholds exhibit SR, proving a means of better and much more efficiently identifying SR.

Effects of individually calibrated white and pink noise vestibular stimulation on standing balance of young healthy adults

Imperceptible noisy galvanic vestibular stimulation (nGVS) improves standing balance due to the presence of stochastic resonance (SR). There is, however, a lack of consensus regarding the optimal levels and type of noise used to elicit SR like dynamics. We aimed to confirm the presence of SR behavior in the vestibular system of young healthy adults by examining postural responses to increasing amplitudes of white and pink noise stimulation scaled to individual cutaneous perceptual threshold. Forty (40) healthy young participants (19 males, 25.1 ± 5.6 years) were randomly divided into a group that received nGVS with white (WHITE group) or pink noise (PINK group). Participants performed a cutaneous perceptual threshold detection task followed by 8 trials of quiet standing and eyes closure (60s) with nGVS applied during the last 30s. Balance stabilization was quantified in the ratio of the stimulus versus pre-stimulus Centre of Pressure (CoP) 90% ellipse area, Root Mean Square (RMS) and mean velocity. Cutaneous perceptual threshold was similar across groups. Group analysis confirmed that the mean CoP velocity increased across nGVS intensities, particularly for the PINK group while the other two variables remained unchanged. Single subject analysis indicated that 55% of WHITE and 30% of PINK group participants showed an SR-like response judged by three experts. Results are puzzling with respect to the presence of SR-like response dynamics in young healthy adults and highlight the need for further research using individual calibrated stimulus intensities. White noise seems more effective than pink noise in revealing an SR-like response to nGVS.

Neural interference effects on lateral vestibulospinal tract excitability by noisy galvanic vestibular stimulation

OBJECTIVE

Noisy galvanic vestibular stimulation (GVS) using weak random noise waveforms enhances postural stability by modulating vestibular-related neural networks. This study aimed to investigate the neural interference mechanisms of noisy GVS on lateral vestibulospinal tract (LVST) excitability.

METHODS

Twenty-six healthy volunteers were randomly divided into two groups: balance training combined with noisy GVS and sham GVS. Participants performed 10-minute balance training while standing on a soft foam surface with their eyes closed while adapting to each electrical stimulus. LVST excitability was assessed by measuring the soleus H-reflex following square-wave pulse GVS. Postural stability was measured by assessing the center of foot pressure sway while standing on a foam surface with eyes closed.

RESULTS

The noisy GVS group showed significantly increased post-intervention H-reflex amplitude. The sham GVS group showed no significant difference in H-reflex amplitude pre- and post-intervention. The average sway velocity in the noisy and sham GVS groups significantly decreased in the medial-lateral direction of the center of foot pressure.

CONCLUSIONS

Noisy GVS may enhance LVST excitability and decrease body sway via vestibular system interference during holding upright, which relies heavily on vestibular sensations.

SIGNIFICANCE

These findings may help understand the neural mechanisms of noisy GVS in neurorehabilitation.

Human perception of self-motion and orientation during galvanic vestibular stimulation and physical motion

Galvanic vestibular stimulation (GVS) is an emergent tool for stimulating the vestibular system, offering the potential to manipulate or enhance processes relying on vestibular-mediated central pathways. However, the extent of GVS's influence on the perception of self-orientation pathways is not understood, particularly in the presence of physical motions. Here, we quantify roll tilt perception impacted by GVS during passive whole-body roll tilts in humans (N = 11). We find that GVS systematically amplifies and attenuates perceptions of roll tilt during physical tilt, dependent on the GVS waveform. Subsequently, we develop a novel computational model that predicts 6DoF self-motion and self-orientation perceptions for any GVS waveform and motion by modeling the vestibular afferent neuron dynamics modulated by GVS in conjunction with an observer central processing model. This effort provides a means to systematically alter spatial orientation perceptions using GVS during concurrent physical motion, and we find that irregular afferent dynamics alone best describe resultant perceptions.

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.

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.

Low-intensity vestibular noise stimulation improves postural symptoms in progressive supranuclear palsy

BACKGROUND

Postural imbalance and falls are an early disabling symptom in patients with progressive supranuclear palsy (PSP) of multifactorial origin that may involve abnormal vestibulospinal reflexes. Low-intensity noisy galvanic vestibular stimulation (nGVS) is a non-invasive treatment to normalize deficient vestibular function and attenuate imbalance in Parkinson's disease. The presumed therapeutic mode of nGVS is stochastic resonance (SR), a mechanism by which weak sensory noise stimulation can enhance sensory information processing.

OBJECTIVE

To examine potential treatment effects of nGVS on postural instability in 16 patients with PSP with a clinically probable and [18F]PI-2620 tau-PET-positive PSP.

METHODS

Effects of nGVS of varying intensity (0-0.7 mA) on body sway were examined, while patients were standing with eyes closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal sway reductions at intermediate nGVS intensities to be indicative of SR. An established SR-curve model was fitted on individual patient outcomes and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR.

RESULTS

We found nGVS-induced reductions of body sway compatible with SR in 9 patients (56%) with optimal improvements of 31 ± 10%. In eight patients (50%), nGVS-induced sway reductions exceeded the minimal clinically important difference (improvement: 34 ± 5%), indicative of strong SR.

CONCLUSION

nGVS yielded clinically relevant reductions in body sway compatible with the exhibition of SR in vestibular sensorimotor pathways in at least half of the assessed patients. Non-invasive vestibular noise stimulation may be thus a well-tolerated treatment strategy to ameliorate postural symptoms in PSP.

Exploring the Potentials of Wearable Technologies in Managing Vestibular Hypofunction

The vestibular system is dedicated to gaze stabilization, postural balance, and spatial orientation; this makes vestibular function crucial for our ability to interact effectively with our environment. Vestibular hypofunction (VH) progresses over time, and it presents differently in its early and advanced stages. In the initial stages of VH, the effects of VH are mitigated using vestibular rehabilitation therapy (VRT), which can be facilitated with the aid of technology. At more advanced stages of VH, novel techniques that use wearable technologies for sensory augmentation and sensory substitution have been applied to manage VH. Despite this, the potential of assistive technologies for VH management remains underexplored over the past decades. Hence, in this review article, we present the state-of-the-art technologies for facilitating early-stage VRT and for managing advanced-stage VH. Also, challenges and strategies on how these technologies can be improved to enable long-term ambulatory and home use are presented.

Impaired vestibular function associated with orthostatic hypotension in patients with multiple system atrophy

BACKGROUND

Orthostatic hypotension (OH) is one of the most common symptoms in patients with multiple system atrophy (MSA). Vestibular system plays an important role in blood pressure regulation during orthostatic challenges through vestibular-sympathetic reflex. The current study aimed to investigate the relationship between vestibular function and OH in patients with MSA.

METHODS

Participants with MSA, including 20 with OH (mean age, 57.55 ± 8.44 years; 7 females) and 15 without OH (mean age, 59.00 ± 8.12 years; 2 females) and 18 healthy controls (mean age, 59.03 ± 6.44 years; 8 females) were enrolled. Cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) tests were conducted to evaluate vestibular function.

RESULTS

Patients with MSA presented with significantly higher rate of absent cVEMPs (57.1% vs 11.1%, p = 0.001) and oVEMPs (25.7% vs 0, p = 0.021) than controls. MSA patients with OH showed more absent cVEMPs (75.0% vs 11.1%, Bonferroni corrected p < 0.001) and oVEMPs (40.0% vs 0, Bonferroni corrected p = 0.003) than controls. Patients with OH also showed higher rate of absent cVEMPs than those without OH (33.3%, Bonferroni corrected p = 0.014).

CONCLUSIONS

Our results demonstrated that impairment of vestibular function was associated with MSA, particularly in those with OH. Absent VEMPs may be a potential marker for MSA severity. Our findings suggest that impaired vestibular function is involved in OH development and may serve as an intervention target.

The VertiGO! Trial protocol: A prospective, single-center, patient-blinded study to evaluate efficacy and safety of prolonged daily stimulation with a multichannel vestibulocochlear implant prototype in bilateral vestibulopathy patients

BACKGROUND

A combined vestibular (VI) and cochlear implant (CI) device, also known as the vestibulocochlear implant (VCI), was previously developed to restore both vestibular and auditory function. A new refined prototype is currently being investigated. This prototype allows for concurrent multichannel vestibular and cochlear stimulation. Although recent studies showed that VCI stimulation enables compensatory eye, body and neck movements, the constraints in these acute study designs prevent them from creating more general statements over time. Moreover, the clinical relevance of potential VI and CI interactions is not yet studied. The VertiGO! Trial aims to investigate the safety and efficacy of prolonged daily motion modulated stimulation with a multichannel VCI prototype.

METHODS

A single-center clinical trial will be carried out to evaluate prolonged VCI stimulation, assess general safety and explore interactions between the CI and VI. A single-blind randomized controlled crossover design will be implemented to evaluate the efficacy of three types of stimulation. Furthermore, this study will provide a proof-of-concept for a VI rehabilitation program. A total of minimum eight, with a maximum of 13, participants suffering from bilateral vestibulopathy and severe sensorineural hearing loss in the ear to implant will be included and followed over a five-year period. Efficacy will be evaluated by collecting functional (i.e. image stabilization) and more fundamental (i.e. vestibulo-ocular reflexes, self-motion perception) outcomes. Hearing performance with a VCI and patient-reported outcomes will be included as well.

DISCUSSION

The proposed schedule of fitting, stimulation and outcome testing allows for a comprehensive evaluation of the feasibility and long-term safety of a multichannel VCI prototype. This design will give insights into vestibular and hearing performance during VCI stimulation. Results will also provide insights into the expected daily benefit of prolonged VCI stimulation, paving the way for cost-effectiveness analyses and a more comprehensive clinical implementation of vestibulocochlear stimulation in the future.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT04918745. Registered 28 April 2021.

Mechanisms underlying treatment effects of vestibular noise stimulation on postural instability in patients with bilateral vestibulopathy

BACKGROUND

Previous studies indicate that imbalance in patients with bilateral vestibulopathy (BVP) may be reduced by treatment with low-intensity noisy galvanic vestibular stimulation (nGVS).

OBJECTIVE

To elucidate the potential mechanisms underlying this therapeutic effect. In particular, we determined whether nGVS-induced balance improvements in patients are compatible with stochastic resonance (SR)-a mechanism by which weak noise stimulation can paradoxically enhance sensory signal processing.

METHODS

Effects of nGVS of varying intensities (0-0.7 mA) on body sway were examined in 19 patients with BVP standing with eye closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal sway reductions at intermediate nGVS intensities to be indicative of SR. An established SR curve model was fitted on individual patient outcomes, and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR.

RESULTS

nGVS-induced reductions of body sway compatible with SR were found in 12 patients (63%) with optimal improvements of 31 ± 21%. In 10 patients (53%), nGVS-induced sway reductions exceeded the minimally important clinical difference (optimal improvement: 35 ± 21%), indicative of strong SR. This beneficial effect was more likely in patients with severe vestibular loss (i.e. lower video head impulse test gain; R = 0.663; p = 0.002) and considerable postural imbalance (baseline body sway; R = 0.616; p = 0.005).

CONCLUSIONS

More than half of the assessed patients showed robust improvements in postural balance compatible with SR when treated with nGVS. In particular, patients with a higher burden of disease may benefit from the non-invasive and well-tolerated treatment with nGVS.

Electrical stimulation of the peripheral and central vestibular system

PURPOSE OF REVIEW

Electrical stimulation of the peripheral and central vestibular system using noninvasive (galvanic vestibular stimulation, GVS) or invasive (intracranial electrical brain stimulation, iEBS) approaches have a long history of use in studying self-motion perception and balance control. The aim of this review is to summarize recent electrophysiological studies of the effects of GVS, and functional mapping of the central vestibular system using iEBS in awake patients.

RECENT FINDINGS

The use of GVS has become increasingly common in the assessment and treatment of a wide range of clinical disorders including vestibulopathy and Parkinson's disease. The results of recent single unit recording studies have provided new insight into the neural mechanisms underlying GVS-evoked improvements in perceptual and motor responses. Furthermore, the application of iEBS in patients with epilepsy or during awake brain surgery has provided causal evidence of vestibular information processing in mostly the middle cingulate cortex, posterior insula, inferior parietal lobule, amygdala, precuneus, and superior temporal gyrus.

SUMMARY

Recent studies have established that GVS evokes robust and parallel activation of both canal and otolith afferents that is significantly different from that evoked by natural head motion stimulation. Furthermore, there is evidence that GVS can induce beneficial neural plasticity in the central pathways of patients with vestibular loss. In addition, iEBS studies highlighted an underestimated contribution of areas in the medial part of the cerebral hemispheres to the cortical vestibular network.

Changes in vestibular-related responses to combined noisy galvanic vestibular stimulation and cerebellar transcranial direct current stimulation

Vestibular nuclei and cerebellar function comprise vestibular neural networks that control vestibular-related responses. However, the vestibular-related responses to simultaneous stimulation of these regions are unclear. This study aimed to examine whether the combination of noisy galvanic vestibular stimulation (nGVS) and cerebellar transcranial direct current stimulation (ctDCS) using a complex transcranial electrical stimulation device alters vestibular-dominant standing stability and vestibulo-ocular reflex (VOR) function. The center of foot pressure (COP) sway and VOR of participants (28 healthy, young adults) were assessed under four conditions of transcranial electrical stimulation using nGVS and ctDCS. The COP was calculated with the participant standing on a soft-foam surface with eyes closed using a force plate to evaluate body sway. VOR measurements were collected via passive head movements and fixation on a target projected onto the front wall using a video head impulse test (vHIT). VOR gain was calculated in six directions using a semicircular canal structure based on the ratio of eye movement to head movement. The nGVS + ctDCS and nGVS + sham ctDCS conditions decreased COP sway compared to the sham nGVS + ctDCS and sham nGVS + sham ctDCS conditions. No significant differences were observed in the main effect of stimulation or the interaction of stimulation and direction on the vHIT parameters. The results of this study suggest that postural stability may be independently affected by nGVS. Our findings contribute to the basic neurological foundation for the clinical application of neurorehabilitation using transcranial electrical stimulation of the vestibular system.

Repetitive Low-Intensity Vestibular Noise Stimulation Partly Reverses Behavioral and Brain Activity Changes following Bilateral Vestibular Loss in Rats

Low-intensity noisy galvanic vestibular stimulation (nGVS) can improve static and dynamic postural deficits in patients with bilateral vestibular loss (BVL). In this study, we aimed to explore the neurophysiological and neuroanatomical substrates underlying nGVS treatment effects in a rat model of BVL. Regional brain activation patterns and behavioral responses to a repeated 30 min nGVS treatment in comparison to sham stimulation were investigated by serial whole-brain 18F-FDG-PET measurements and quantitative locomotor assessments before and at nine consecutive time points up to 60 days after the chemical bilateral labyrinthectomy (BL). The 18F-FDG-PET revealed a broad nGVS-induced modulation on regional brain activation patterns encompassing biologically plausible brain networks in the brainstem, cerebellum, multisensory cortex, and basal ganglia during the entire observation period post-BL. nGVS broadly reversed brain activity adaptions occurring in the natural course post-BL. The parallel behavioral locomotor assessment demonstrated a beneficial treatment effect of nGVS on sensory-ataxic gait alterations, particularly in the early stage of post-BL recovery. Stimulation-induced locomotor improvements were finally linked to nGVS brain activity responses in the brainstem, hemispheric motor, and limbic networks. In conclusion, combined 18F-FDG-PET and locomotor analysis discloses the potential neurophysiological and neuroanatomical substrates that mediate previously observed therapeutic nGVS effects on postural deficits in patients with BVL.

Post-activation depression of the Hoffman reflex is not altered by galvanic vestibular stimulation in healthy subjects

The comprehension of the neural elements interacting in the spinal cord affected by vestibular input will contribute to the understanding of movement execution in normal and pathological conditions. In this context, Hoffman's reflex (H-reflex) has been used to evaluate transient excitability changes on the spinal cord descending pathways. The post-activation depression (P-AD) of the H-reflex consists of evoking consecutive responses (>1 Hz) provoking an amplitude depression, which has been shown to diminish in pathological conditions (i.e., spasticity, diabetic neuropathy). Galvanic Vestibular Stimulation (GVS) is a non-invasive method that activates the vestibular afferents and has been used to study the excitability of the H-reflex applied as a conditioning pulse. To our knowledge, there are no reports evaluating the P-AD during and after GVS. Our primary aim was to determine if GVS alters the P-AD evoked by stimulating the tibial nerve at 0.1, 1, 5, and 10 Hz, recording in the gastrocnemius and soleus muscles. Direct current stimulation of 2.0 ± 0.6 mA with the cathode ipsilateral (Ipsi) or contralateral (Contra) to the H-reflex electrode montage was applied bilaterally over the mastoid process in 19 healthy subjects. The P-AD's immediate post-GVS response (P Ipsi, P Contra) was also analyzed. Secondarily, we analyzed the excitability of the H-reflex during GVS. Responses evoked at 0.1 Hz with GVS, post-GVS, and a Control (no GVS) condition were used for comparisons. Our results show that P-AD persisted in all subjects despite increased excitability induced by GVS: statistical significance was found when comparing P-AD at 1, 5, and 10 Hz with the corresponding condition (Control, Ipsi, P Ipsi, Contra, P Contra) at 0.1 Hz (p < 0.001). Additionally, the increase in excitability produced by GVS was quantified for the first H-reflex of each P-AD stimulation frequency. The percentage change for all GVS conditions surpassed the Control by at least 20%, being statistically significant for Contra compared to Control (p < 0.01). In summary, although GVS increases the excitability of the vestibulospinal pathway at a premotor level, the neural inhibitory mechanism present in P-AD remains unaltered in healthy subjects.

The Neural Basis for Biased Behavioral Responses Evoked by Galvanic Vestibular Stimulation in Primates

Noninvasive electrical stimulation of the vestibular system in humans has become an increasingly popular tool with a broad range of research and clinical applications. However, common assumptions regarding the neural mechanisms that underlie the activation of central vestibular pathways through such stimulation, known as galvanic vestibular stimulation (GVS), have not been directly tested. Here, we show that GVS is encoded by VIIIth nerve vestibular afferents with nonlinear dynamics that differ markedly from those predicted by current models. GVS produced asymmetric activation of both semicircular canal and otolith afferents to the onset versus offset and cathode versus anode of applied current, that in turn produced asymmetric eye movement responses in three awake-behaving male monkeys. Additionally, using computational methods, we demonstrate that the experimentally observed nonlinear neural response dynamics lead to an unexpected directional bias in the net population response when the information from both vestibular nerves is centrally integrated. Together our findings reveal the neural basis by which GVS activates the vestibular system, establish that neural response dynamics differ markedly from current predictions, and advance our mechanistic understanding of how asymmetric activation of the peripheral vestibular system alters vestibular function. We suggest that such nonlinear encoding is a general feature of neural processing that will be common across different noninvasive electrical stimulation approaches.SIGNIFICANCE STATEMENT Here, we show that the application of noninvasive electrical currents to the vestibular system (GVS) induces more complex responses than commonly assumed. We recorded vestibular afferent activity in macaque monkeys exposed to GVS using a setup analogous to human studies. GVS evoked notable asymmetries in irregular afferent responses to cathodal versus anodal currents. We developed a nonlinear model explaining these GVS-evoked afferent responses. Our model predicts that GVS induces directional biases in centrally integrated head motion signals and establishes electrical stimuli that recreate physiologically plausible sensations of motion. Altogether, our findings provide new insights into how GVS activates the vestibular system, which will be vital to advancing new clinical and biomedical applications.

Noisy galvanic vestibular stimulation improves vestibular perception in bilateral vestibulopathy

BACKGROUND

Patients with bilateral vestibulopathy (BVP) suffer from impaired vestibular motion perception that is linked to deficits in spatial memory and navigation.

OBJECTIVE

To examine the potential therapeutic effect of imperceptible noisy galvanic vestibular stimulation (nGVS) on impaired vestibular perceptual performance in BVP.

METHODS

In 11 patients with BVP (mean age: 54.0 ± 8.3 years, 7 females), we initially determined the nGVS intensity that optimally stabilizes balance during a static posturographic assessment. Subsequently, effects of optimal nGVS vs. sham stimulation on vestibular motion perception were examined in randomized order. Vestibular perceptual performance was determined as direction recognition thresholds for head-centered roll tilt motion on a 6DOF motion platform in the absence of any visual or auditory motion cues.

RESULTS

For each patient, an nGVS intensity that optimally stabilized static balance compared to sham stimulation could be identified (mean 0.36 ± 0.16 mA). nGVS at optimal intensity resulted in lowered vestibular perceptual thresholds (0.94 ± 0.30 deg/s) compared to sham stimulation (1.67 ± 1.11 deg/s; p = 0.040). nGVS-induced improvements in vestibular perception were observed in 8 of 11 patients (73%) and were greater in patients with poorer perceptual performance during sham stimulation (R = - 0.791; p = 0.007).

CONCLUSIONS

nGVS is effective in improving impaired vestibular motion perception in patients with BVP, in particular in those patients with poor baseline perceptual performance. Imperceptible vestibular noise stimulation might thus offer a non-invasive approach to target BVP-related impairments in spatial memory, orientation, and navigation.

Impact of episodic and chronic vestibular disorders on health-related quality of life and functioning-results from the DizzyReg patient registry

PURPOSE

Vertigo and dizziness belong to the most frequent syndromes in the primary, secondary and tertiary setting and can be divided into vertigo with episodic or chronic persistent complaints. Episodic vertigo (EVS) is characterized by recurrent attacks of vertigo or dizziness with intermittent symptom-free periods, while chronic vertigo (CVS) presents with persistent vertigo. It is still not completely understood how EVS or CVS affect health-related quality of life (HRQoL) and functioning.

METHODS

Data originates from the DizzyReg patient registry, an ongoing prospective clinical patient registry situated at tertiary clinic at the university hospital, Munich. HRQoL and functioning was measured by self-report. CVS and EVS was categorized after comprehensive neuro-otological work-up in line with the diagnostic guidelines. Association of CVS and EVS was assessed with multivariable linear regression models adjusting for potential risk factors and confounders.

RESULTS

The study included 548 patients (57% female, mean age 51.35). Patients with EVS were significantly younger (48.5 vs. 59.6 years) and were more often female (60 vs. 49%). EVS patients reported significantly better functioning (42.1 vs. 47.8) and HRQoL (63.87 vs. 58.08) than CVS patients. The effect was stable after adjusting for potential confounders.

CONCLUSION

This is the first study to show worse HRQoL in patients with CVS compared to EVS. The results of the study underpin the experience from clinical practice that mobility and balance control are especially important for patients with CVS.

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.

[Bilateral peripheral vestibulopathy]

Bilateral vestibulopathy is a relatively widespread and at the same time rarely diagnosed cause of chronic postural instability. Numerous toxic factors, dysmetabolic, autoimmune and neurodegenerative processes can lead to this condition. The main clinical manifestations of bilateral vestibulopathy are balance disorders and visual disturbances (oscillopsia), which can significantly increase the risks of falls in such patients. In addition, cognitive and affective disorders, which also reduce the quality of life in patients with bilateral vestibulopathy, have been described and actively studied in recent years. The diagnosis of bilateral vestibulopathy is based on the results of a clinical neurovestibular study, including a dynamic visual acuity test and a Halmagyi test. A video head impulse test, a bithermal caloric test and a sinusoidal rotation test are used as instrumental methods confirming the dysfunction of the peripheral vestibular system. However, they are still not widespread in neurological practice. Treatment of bilateral vestibulopathy is reduced to vestibular rehabilitation. Encouraging results have been obtained in a number of studies using galvanic vestibular stimulation and the use of vestibular implants. In addition, cognitive rehabilitation methods are currently being developed, which presumably can also improve compensation for bilateral vestibular loss.

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

People with Parkinson's disease (PD) develop postural imbalance and falls. Galvanic Vestibular Stimulation (GVS) may potentially improve postural balance in humans and hence reduce falls in PD. This systematic review and meta-analysis investigate the effects of GVS on postural balance in PD. Six separate databases and research registers were searched for cross-over design trials that evaluated the effects of GVS on postural balance in PD. We used standardized mean difference (Hedges' g) as a measure of effect size in all studies. We screened 223 studies, evaluated 14, of which five qualified for the meta-analysis. Among n = 40 patients in five studies (range n = 5 to 13), using a fixed effects model we found an effect size estimate of g = 0.43 (p < 0.001, 95% CI [0.29,0.57]). However, the test for residual heterogeneity was significant (p < 0.001), thus we used a random effects model and found a pooled effect size estimate of 0.62 (p > 0.05, 95% CI [- 0.17, 1.41], I2 = 96.21%). Egger's test was not significant and thus trim and funnel plot indicated no bias. To reduce heterogeneity, we performed sensitivity analysis and by removing one outlier study (n = 7 patients), we found an effect size estimate of 0.16 (p < 0.05, 95% CI [0.01, 0.31], I2 = 0%). Our meta-analysis found GVS has a favourable effect on postural balance in PD patients, but due to limited literature and inconsistent methodologies, this favourable effect must be interpreted with caution.

Combining vestibular rehabilitation with noisy galvanic vestibular stimulation for treatment of bilateral vestibulopathy

OBJECTIVE

Noisy galvanic vestibular stimulation (nGVS) has been shown to partly restore vestibular function and to stabilize stance and gait in patients with incomplete bilateral vestibulopathy (BVP). Here, we examined potential synergistic effects of nGVS when combined with standardized vestibular rehabilitation training (VRT).

METHODS

23 patients with confirmed BVP received a 30-min vestibular rehabilitation training (VRT) program three times a week for 2 weeks. The intervention group (n = 12) was stimulated with nGVS (at individually determined optimal amplitudes) during training, whereas the control group (n = 11) received zero-amplitude nGVS (sham stimulation) during training. Outcome measurements assessed at baseline, after 2 weeks of training, and at 2-week follow-up included quantitative posturography, instrumented gait analysis, Timed Up and Go Test (TUG), Functional Gait Assessment (FGA), and clinical scores related to quality of life and balance confidence.

RESULTS

After 2 weeks of VRT, all patients showed moderate improvement in balance. Irrespective of nGVS treatment, performance improved in the TUG (p < 0.013), and in the FGA (p < 0.040). Furthermore, base of support when walking with closed eyes was reduced after 2-week training (p < 0.003). Postural sway did not change. There was no difference between groups and thereby no evidence for an additional influence of nGVS on the VRT treatment effects.

CONCLUSION

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.

Comparison of verticality perception and postural sway induced by double temple-mastoidal and bipolar binaural 20 Hz sinusoidal galvanic vestibular stimulation

BACKGROUND

Galvanic vestibular stimulation (GVS) is believed to be one of the most valuable tools for studying the vestibular system. In our opinion, its combined effect on posture and perception needs to be examined more.

OBJECTIVE

The present study was conducted to investigate the effect of a 20 Hz sinusoidal Galvanic Vestibular Stimulation (sGVS) on the body sway and subjective visual vertical (SVV) deviation through two sets of electrode montages (bipolar binaural and double temple-mastoidal stimulation) during a three-stage experiment (baseline, threshold, and supra-threshold levels).

METHODS

While the individuals (32 normal individuals, 10 males, the mean age of 25.37±3.00 years) were standing on a posturography device and SVV goggles were put on, the parameters of the body sway and SVV deviation were measured simultaneously. Following the baseline stage (measuring without stimulation), the parameters were investigated during the threshold and supra-threshold stages (1 mA above the threshold) for 20 seconds. This was done separately for each electrode montage. Then, the results were compared between the three experimental stages and the two electrode montages.

RESULTS

In both electrode montages, "the maximum amplitude" of the mediolateral (ML) and anteroposterior (AP) body sway decreased and increased in the threshold and supra-threshold stages, respectively, compared to the baseline stage. Comparison of the amount of  "amplitude change" caused by each electrode montages showed that the double temple-mastoidal stimulation induced a significantly greater amplitude change in body sway during both threshold and supra-threshold stages (relative to the baseline stage).The absolute mean values of the SVV deviation were significantly different between the baseline and supra-threshold levels in both electrode montages. The SVV deviation in double temple-mastoidal stimulation was a bit greater than that in the bipolar binaural stimulation.

CONCLUSION

Double temple-mastoidal stimulation has induced greater amount of change in the body sway and SVV deviation. This may be due to the more effective stimulation of the otoliths than semicircular canals.

Effects of Low-Intensity Vestibular Noise Stimulation on Postural Instability in Patients with Parkinson's Disease

BACKGROUND

Postural instability is a major disabling factor in patients with advanced Parkinson's disease (PD) and often resistant to treatment. Previous studies indicated that imbalance in PD may be reduced by low-intensity noisy galvanic vestibular stimulation (nGVS).

OBJECTIVE

To investigate the potential mode of action of this therapeutic effect. In particular, we examined whether nGVS-induced reductions of body sway in PD are compatible with stochastic resonance (SR), a mechanism by which weak sensory noise stimulation can paradoxically enhance sensory information transfer.

METHODS

Effects of nGVS of varying intensities (0-0.7 mA) on body sway were examined in 15 patients with PD standing with eye closed on a posturographic force plate. We assumed a bell-shaped response curve with maximal reductions of sway at intermediate nGVS intensities to be indicative of SR. An established SR-curve model was fitted on individual patient outcomes and three experienced human raters had to judge whether responses to nGVS were consistent with the exhibition of SR.

RESULTS

nGVS-induced reductions of body sway compatible with SR were found in 10 patients (67%) with optimal improvements of 23±13%. In 7 patients (47%), nGVS-induced sway reductions exceeded the minimally important clinical difference (optimal improvement: 30±10%), indicative of strong SR. This beneficial effect was more likely in patients with advanced PD (R = 0.45; p = 0.045).

CONCLUSIONS

At least half of the assessed patients showed robust improvements in postural balance compatible with SR when treated with low-intensity nGVS. In particular, patients with more advanced disease stages and imbalance may benefit from the non-invasive and well-tolerated treatment with nGVS.

Effects of Noisy Galvanic Vestibular Stimulation on the Muscle Activity and Joint Movements in Different Standing Postures Conditions

Objective

Noisy galvanic vestibular stimulation (nGVS) is an effective method for stabilizing posture; however, little is known regarding the detailed muscle activity and joint movement in the standing posture. This study aimed to clarify the changes in the lower limb muscle activity and joint angular velocity by nGVS intervention using the simultaneous assessment method of inertial measurement units and surface electromyography (EMG).

Methods

Seventeen healthy participants were assessed for their physical responses under four conditions (standing on a firm surface with eyes-open/eyes-closed, and a foam surface with eyes-open/eyes-closed) without stimulation (baseline) and with stimulation (sham or nGVS). Noise stimuli were applied for 30 s at a level below the perceptual threshold. The body control response was evaluated using EMG activity and angular velocity of the lower limbs.

Result

Regarding the change from baseline for each parameter, there was a significant interactive effect of EMG activity in the muscle type × intervention and EMG activity and angular velocity in the condition × intervention. Post hoc analysis revealed that the angular velocity was significantly decreased in the abduction-adduction direction in the standing on a foam surface with eyes-closed condition compared to that with eyes-open in the nGVS intervention.

Conclusion

Our results suggest that nGVS altered physical responses in different standing postural conditions. The present study is exploratory and therefore the evidence should be investigated in future studies specifically target those muscle activities and joint motion parameters.

The Effect of Galvanic Vestibular Stimulation on Visuospatial Cognition in an Incomplete Bilateral Vestibular Deafferentation Mouse Model

Objectives

To evaluate the efficacy of galvanic vestibular stimulation (GVS) for recovering from the locomotor and spatial memory deficits of a murine bilateral vestibular deafferentation (BVD) model.

Methods

Male C57BL/6 mice (n = 36) were assigned to three groups: bilateral labyrinthectomy with (BVD_GVS group) and without (BVD_non-GVS group) the GVS intervention, and a control group with the sham operation. We used the open field and Y maze, and Morris water maze (MWM) tests to assess locomotor and visuospatial cognitive performance before (baseline) and 3, 7, and 14 days after surgical bilateral labyrinthectomy. For the GVS group, a sinusoidal current at the frequency at 1 Hz and amplitude 0.1 mA was delivered for 30 min daily from the postoperative day (POD) 0 to 4 via electrodes inserted subcutaneously close to both the bony labyrinths.

Results

Short-term spatial memory was significantly impaired in bilaterally labyrinthectomized mice (BVD_non-GVS group), as reflected by decreased spontaneous alternation performance in the place recognition test and time spent in the novel arm and increased same arm return in the Y-maze test, compared with the control. Long-term spatial memory was also impaired, as indicated by a longer escape latency in the hidden platform trial and a lower percentage of time spent in the target quadrant in the probe trial of the MWM. GVS application significantly accelerated the recovery of locomotion and short-term and long-term spatial memory deficits in the BVD mice.

Conclusions

Our data demonstrate that locomotion, short-term, and long-term (at least 2 weeks) spatial memory were impaired in BVD mice. The early administration of sinusoidal GVS accelerated the recovery of those locomotion and spatial memory deficiencies. GVS could be applied to patients with BVD to improve their locomotion and vestibular cognitive functioning.

Galvanic Vestibular Stimulation Headset balancing robust and simple administration with subject comfort: A Usability Analysis. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:5063-5066. [PMID: 34892345 DOI: 10.1109/embc46164.2021.9630466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The vestibular system is responsible for spatial orientation and stability. It can be stimulated with a weak electric current, a mechanism known as Galvanic Vestibular Stimulation (GVS). Typical GVS administration involves holding down electrodes on the mastoids either with a strap (or bandage) wrapped around the head or by positioning a self-adhesive electrode at the mastoid location. While the latter approach is simple to administer, it is limited to exposed skin application as hair impedes adhesion. The reduced access area limits total current delivery allowable due to increased skin sensation. Accordingly the former approach is more typically employed but leads to inconsistent and inaccurate electrode placement. As current flow pattern is directly influenced by electrode position, this results in inconsistent stimulation and replicability issues. The primary goal of this study was to test usability and comfort while developing a GVS-specific headset named "Mastoid Adjustable Robust Stimulation (MARS)" compared to a conventional elastic strap. We recruited 10 subjects, 5 operators and 5 wearers, and tested usability using the System Usability Scale (SUS) as well as comfort levels over a typical 20 minute stimulation session. Additional questions were answered by the operators and wearers on visual appeal, interference, slippage, and electrode placement. The results of this testing guided the development of a final version meeting our requirements of robustness, simple to administer, and subject comfort.Clinical Relevance-This study introduces a headset for routine Bilateral-Bipolar GVS administration that is highly usable and ensures both flexible and consistent electrode application over typical approaches.

Noisy Galvanic Vestibular Stimulation Combined With a Multisensory Balance Program in Older Adults With Moderate to High Fall Risk: Protocol for a Feasibility Study for a Randomized Controlled Trial

Background

Reduced mobility and falls are common among older adults. Balance retraining programs are effective in reducing falls and in improving balance and mobility. Noisy galvanic vestibular stimulation is a low-level electrical stimulation used to reduce the threshold for the firing of vestibular neurons via a mechanism of stochastic resonance.

Objective

This study aims to determine the feasibility of using noisy galvanic vestibular stimulation to augment a balance training program for older adults at risk of falls. We hypothesize that noisy galvanic vestibular stimulation will enhance the effects of balance retraining in older adults at risk of falls

Methods

In this 3-armed randomized controlled trial, community dwelling older adults at risk of falling will be randomly assigned to a noisy galvanic vestibular stimulation plus balance program (noisy galvanic vestibular stimulation group), sham plus balance program (sham group), or a no treatment group (control). Participants will attend the exercise group twice a week for 8 weeks with assessment of balance and gait pretreatment, posttreatment, and at 3 months postintervention. Primary outcome measures include postural sway, measured by center of pressure velocity, area and root mean square, and gait parameters such as speed, step width, step variability, and double support time. Spatial memory will also be measured using the triangle completion task and the 4 Mountains Test.

Results

Recruitment began in November 2020. Data collection and analysis are expected to be completed by December 2022.

Conclusions

This study will evaluate the feasibility of using noisy galvanic vestibular stimulation alongside balance retraining in older adults at risk of falls and will inform the design of a fully powered randomized controlled trial.

Trial Registration

New Zealand Clinical Trials Registry (ACTRN12620001172998); https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=379944

International Registered Report Identifier (IRRID)

DERR1-10.2196/32085

Bilateral vestibulopathy decreases self-motion perception

Objective

Current diagnostic criteria for bilateral vestibulopathy (BV) primarily involve measurements of vestibular reflexes. Perceptual self-motion thresholds however, are not routinely measured and their clinical value in this specific population is not yet fully determined. Objectives of this study were (1) to compare perceptual self-motion thresholds between BV patients and control subjects, and (2) to explore patterns of self-motion perception performance and vestibular function in BV patients.

Methods

Thirty-seven BV patients and 34 control subjects were included in this study. Perceptual self-motion thresholds were measured in both groups using a CAREN platform (Motek Medical BV, Amsterdam, The Netherlands). Vestibular function was evaluated (only in BV patients) by the caloric test, torsion swing test, video head impulse test of all semicircular canals, and cervical- and ocular vestibular-evoked myogenic potentials. Differences in thresholds between both groups were analyzed. Hierarchical cluster analysis was performed to visualize patterns between self-motion perception and vestibular function within the group of BV patients.

Results

Perceptual self-motion thresholds were significantly higher in BV patients compared to control subjects, regarding nearly all rotations and translations (depending on the age group) (p ≤ 0.001). Cluster analysis showed that within the group of BV patients, higher perceptual self-motion thresholds were generally associated with lower vestibular test results (significant for yaw rotation, caloric test, torsion swing test, and video head impulse test (p ≤ 0.001)).

Conclusion

Self-motion perception is significantly decreased in BV patients compared to control subjects regarding nearly all rotations and translations. Furthermore, decreased self-motion perception is generally associated with lower residual vestibular function in BV patients.

Trial registration

Trial registration number NL52768.068.15/METC

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-021-10695-3.

Comparison of efficacy of vestibular rehabilitation and noisy galvanic vestibular stimulation to improve dizziness and balance in patients with multiple sclerosis

BACKGROUND

Dizziness and imbalance are common symptoms in patients with multiple sclerosis (PwMS), and rehabilitation interventions varying greatly in effectiveness.

OBJECTIVE

To compare the effectiveness of vestibular rehabilitation therapy (VRT) and noisy galvanic vestibular stimulation (nGVS) on dizziness and balance in PwMS.

METHODS

This was a single-blind, randomized controlled trial. Twenty-four PwMS were randomly divided into groups of VRT, nGVS, and Control. The VRT and the nGVS groups underwent the intervention program. The patients were assessed with the composite score in anteroposterior and lateral directions (CS AP and LAT) obtained by sensory organization test (SOT), Dizziness Handicap Inventory (DHI), and Activities-Specific Balance Confidence Scale (ABC).

RESULTS

The VRT group showed greater improvements in CS AP and LAT, DHI total score, and ABC total score compared with the nGVS group and the control group. No significant difference was found between the nGVS group and the control group. These results were approximately stable at the 4-week follow-up.

CONCLUSIONS

These findings provided evidence for effectiveness of the VRT in improvement of dizziness and balance in PwMS. These improvements were not associated with the nGVS. Further studies are needed to assess the effectiveness of the nGVS on dizziness and balance in PwMS.

[Update on diagnosis and therapy in frequent vestibular and balance disorders]

The 8 most frequent vestibular disorders account for more than 70% of all presentations of vertigo, dizziness, and imbalance. In acute (and mostly non-repetitive) vestibular disorders acute unilateral vestibulopathy and vestibular stroke are most important, in episodic vestibulopathies benign paroxysmal positional vertigo (BPPV), Menière's disease and vestibular migraine, and in chronic vestibular disorders bilateral vestibulopathy/presbyvestibulopathy, functional dizziness and cerebellar dizziness. In the last decade, internationally consented diagnostic criteria and nomenclature were established for the most frequent vestibular disorders, which can be easily applied in clinical practice. The diagnostic guidelines are based on history taking (including onset, duration, course, triggers, accomanying symptoms), clinical examination, and only a few apparative tests (by videooculography and audiometry) for securing the diagnosis. Treatment of vestibular disorders includes physical training (repositioning maneuvers, multimodal balance training) and pharmacological approaches (e.g., corticosteroids, antiepileptics, antidepressants, potassium-canal-blockers, drugs enhancing neuroplasticity). For most drugs, high-level evidence from prospective controlled trials is lacking. In clinical practice, the most frequent vestibular disorders can be treated effectively, thus avoiding chronicity and secondary comorbidity (by immobility, falls or psychiatric disorders such as anxiety or depression).

The potential of noisy galvanic vestibular stimulation for optimizing and assisting human performance

Noisy galvanic vestibular stimulation (nGVS) is an emerging non-invasive brain stimulation technique. It involves applying alternating currents of different frequencies and amplitudes presented in a random, or noisy, manner through electrodes on the mastoid bones behind the ears. Because it directly activates vestibular hair cells and afferents and has an indirect effect on a variety of brain regions, it has the potential to impact many different functions. The objective of this review is twofold: (1) to review how nGVS affects motor, sensory, and cognitive performance in healthy adults; and (2) to discuss potential clinical applications of nGVS. First, we introduce the technique. We then describe the regions receiving and processing vestibular information. Next, we discuss the effects of nGVS on motor, sensory, and cognitive function in healthy adults. Subsequently, we outline its potential clinical applications. Finally, we highlight other electrical stimulation technologies and discuss why nGVS offers an alternative or complementary approach. Overall, nGVS appears promising for optimizing human performance and as an assistive technology, though further research is required.

Vestibular function modulates the impact of nGVS on postural control in older adults

Previous studies have reported an important relationship between increasing age, vestibular impairment, and increased risk of falls. Recently, noisy galvanic vestibular stimulation (nGVS) has been shown to improve postural control in older adults during and potentially following stimulation. However, this effect of nGVS in older adults has not been examined in interaction with the integrity of the vestibular function. We aimed at determining the effect of nGVS on postural control in older adults with and without vestibular impairment and examining the sustained effect of nGVS as compared with a sham stimulation. Thirty-six older adults were assigned to the nGVS group (n = 24) or the sham group (n = 12). In the nGVS group, 12 participants had normal vestibular function and 12 had vestibular impairment. Static postural control was assessed prior to stimulation, during stimulation, and immediately following 30 min of nGVS. Results showed that nGVS induced a significant improvement in sway velocity (P < 0.001) and path length (P < 0.001) compared with sham stimulation. Furthermore, nGVS induced a significantly greater improvement of sway velocity (P < 0.05) and path length (P < 0.05) in older adults with vestibular impairment compared with older adults with normal vestibular function. Improvements in sway velocity (P < 0.001) and path length (P < 0.001) induced by nGVS were sustained immediately following stimulation. These findings suggest that nGVS improves postural control in older adults, and that the effect of nGVS varies depending on the integrity of the vestibular function. Results also show that nGVS effect on postural control, compared with a sham stimulation, can be sustained after the end of stimulation.NEW & NOTEWORTHY The present study is the first study to investigate the impact of vestibular function on the improvement of postural control induced by nGVS in older adults and to compare the improvement of postural control of older adults with and without vestibular impairment. 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.

Effects of Different Stimulation Conditions on the Stimulation Effect of Noisy Galvanic Vestibular Stimulation

Balance disorders are a risk factor for falls in the elderly population. Balance control involving the complex interaction among nervous, muscular, and sensory systems should be maintained to keep an upright posture and prevent falls. Vestibular sensation is one of the main senses essential for postural control. Noisy galvanic vestibular stimulation (nGVS) is a noninvasive stimulation method for vestibular organs. Recently, it has received increasing attention for the treatment of balance disorders. However, the effect of balance disorders on stimulus effect during the implementation of nGVS remains unknown. Therefore, this study aimed to determine the effects of different floor surface and visual conditions on the stimulus effects of the nGVS intervention. In this study, two experiments were conducted with 24 participants (12 each for Experiments 1 and 2). In Experiment 1, nGVS (0.4 mA; 0.1-640 Hz) was performed in the open-eyes standing position on a solid surface (nGVS condition) and in the closed-eye standing position on a foam rubber (nGVS + foam rubber condition). In Experiment 2, sham stimulation was performed under the same conditions as in Experiment 1, except for nGVS. Center of pressure (COP) sway was measured in all participants with them standing with open eyes at Pre and Post-1 (immediately after the intervention) and Post-2 (10 min after the measurement of post-1). In Experiment 1, under the nGVS condition, COP sway was significantly reduced in Post-1 and Post-2 compared with Pre. However, no significant difference was observed among Pre, Post-1, and Post-2 under the nGVS + foam rubber condition. Furthermore, the intervention effect was significantly greater in the nGVS condition than in the nGVS + foam rubber condition. In contrast, in Experiment 2, the COP sway did not significantly differ among Pre, Post-1, and Post-2 under either condition. Based on the results of this study, nGVS was found to be effective with open-eyes standing on a solid surface.

Modeling Vestibular Compensation: Neural Plasticity Upon Thalamic Lesion

The present study in rats was conducted to identify brain regions affected by the interruption of vestibular transmission and to explore selected aspects of their functional connections. We analyzed, by positron emission tomography (PET), the regional cerebral glucose metabolism (rCGM) of cortical, and subcortical cerebral regions processing vestibular signals after an experimental lesion of the left laterodorsal thalamic nucleus, a relay station for vestibular input en route to the cortical circuitry. PET scans upon galvanic vestibular stimulation (GVS) were conducted in each animal prior to lesion and at post-lesion days (PLD) 1, 3, 7, and 20, and voxel-wise statistical analysis of rCGM at each PLD compared to pre-lesion status were performed. After lesion, augmented metabolic activation by GVS was detected in cerebellum, mainly contralateral, and in contralateral subcortical structures such as superior colliculus, while diminished activation was observed in ipsilateral visual, entorhinal, and somatosensory cortices, indicating compensatory processes in the non-affected sensory systems of the unlesioned side. The changes in rCGM observed after lesion resembled alterations observed in patients suffering from unilateral thalamic infarction and may be interpreted as brain plasticity mechanisms associated with vestibular compensation and substitution. The second set of experiments aimed at the connections between cortical and subcortical vestibular regions and their neurotransmitter systems. Neuronal tracers were injected in regions processing vestibular and somatosensory information. Injections into the anterior cingulate cortex (ACC) or the primary somatosensory cortex (S1) retrogradely labeled neuronal somata in ventral posteromedial (VPM), posterolateral (VPL), ventrolateral (VL), posterior (Po), and laterodorsal nucleus, dorsomedial part (LDDM), locus coeruleus, and contralateral S1 area. Injections into the parafascicular nucleus (PaF), VPM/VPL, or LDDM anterogradely labeled terminal fields in S1, ACC, insular cortex, hippocampal CA1 region, and amygdala. Immunohistochemistry showed tracer-labeled terminal fields contacting cortical neurons expressing the μ-opioid receptor. Antibodies to tyrosine hydroxylase, serotonin, substance P, or neuronal nitric oxide-synthase did not label any of the traced structures. These findings provide evidence for opioidergic transmission in thalamo-cortical transduction.

Finding a Balance: A Systematic Review of the Biomechanical Effects of Vestibular Prostheses on Stability in Humans

The vestibular system is located in the inner ear and is responsible for maintaining balance in humans. Bilateral vestibular dysfunction (BVD) is a disorder that adversely affects vestibular function. This results in symptoms such as postural imbalance and vertigo, increasing the incidence of falls and worsening quality of life. Current therapeutic options are often ineffective, with a focus on symptom management. Artificial stimulation of the vestibular system, via a vestibular prosthesis, is a technique being explored to restore vestibular function. This review systematically searched for literature that reported the effect of artificial vestibular stimulation on human behaviours related to balance, using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) technique. A total of 21 papers matched the inclusion criteria of the literature search conducted using the PubMed and Web of Science databases (February 2019). The populations for these studies included both healthy adults and patients with BVD. In every paper, artificial vestibular stimulation caused an improvement in certain behaviours related to balance, although the extent of the effect varied greatly. Various behaviours were measured such as the vestibulo-ocular reflex, postural sway and certain gait characteristics. Two classes of prosthesis were evaluated and both showed a significant improvement in at least one aspect of balance-related behaviour in every paper included. No adverse effects were reported for prostheses using noisy galvanic vestibular stimulation, however, prosthetic implantation sometimes caused hearing or vestibular loss. Significant heterogeneity in methodology, study population and disease aetiology were observed. The present study confirms the feasibility of vestibular implants in humans for restoring balance in controlled conditions, but more research needs to be conducted to determine their effects on balance in non-clinical settings.

No evidence for after-effects of noisy galvanic vestibular stimulation on motion perception

Noisy galvanic vestibular stimulation (nGVS) delivered at imperceptible intensities can improve vestibular function in health and disease. Here we evaluated whether nGVS effects on vestibular function are only present during active stimulation or may exhibit relevant post-stimulation after-effects. Initially, nGVS amplitudes that optimally improve posture were determined in 13 healthy subjects. Subsequently, effects of optimal nGVS amplitudes on vestibular roll-tilt direction recognition thresholds (DRT) were examined during active and sham nGVS. Ten of 13 subjects exhibited reduced DRTs during active nGVS compared to sham stimulation (p < 0.001). These 10 participants were then administered to 30 mins of active nGVS treatment while being allowed to move freely. Immediately post-treatment , DRTs were increased again (p = 0.044), reverting to baseline threshold levels (i.e. were comparable to the sham nGVS thresholds), and remained stable in a follow-up assessment after 30 min. After three weeks, participants returned for a follow-up experiment to control for learning effects, in which DRTs were measured during and immediately after 30 min application of sham nGVS. DRTs during both assessments did not differ from baseline level. These findings indicate that nGVS does not induce distinct post-stimulation effects on vestibular motion perception and favor the development of a wearable technology that continuously delivers nGVS to patients in order to enhance vestibular function.

Ionic direct current modulation evokes spike-rate adaptation in the vestibular periphery

Recent studies have shown that ionic direct current (iDC) can modulate the vestibular system in-vivo, with potential benefits over conventional pulsed stimulation. In this study, the effects of iDC stimulation on vestibular nerve fiber firing rate was investigated using loose-patch nerve fiber recordings in the acutely excised mouse crista ampullaris of the semicircular canals. Cathodic and anodic iDC steps instantaneously reduced and increased afferent spike rate, with the polarity of this effect dependent on the position of the stimulating electrode. A sustained constant anodic or cathodic current resulted in an adaptation to the stimulus and a return to spontaneous spike rate. Post-adaptation spike rate responses to iDC steps were similar to pre-adaptation controls. At high intensities spike rate response sensitivities were modified by the presence of an adaptation step. Benefits previously observed in behavioral responses to iDC steps delivered after sustained current may be due to post-adaptation changes in afferent sensitivity. These results contribute to an understanding of peripheral spike rate relationships for iDC vestibular stimulation and validate an ex-vivo model for future investigation of cellular mechanisms. In conjunction with previous in-vivo studies, these data help to characterize iDC stimulation as a potential therapy to restore vestibular function after bilateral vestibulopathy.

Questioning the lasting effect of galvanic vestibular stimulation on postural control

Noisy galvanic vestibular stimulation (nGVS) has been shown to enhance postural stability during stimulation, and the enhancing effect has been observed to persist for several hours post-stimulation. However, these effects were observed without proper control (sham condition) and the possibility of experimental bias has not been ruled out. The lasting effect of nGVS on postural stability therefore remains in doubt. We investigated the lasting effect of nGVS on postural stability using a control (sham) condition to confirm or infirm the possibility of experimental bias. 28 participants received either nGVS or a sham stimulation. Static postural control was examined before stimulation, immediately after 30 minutes of nGVS and one-hour post-stimulation. Results showed a significant improvement of sway velocity (p<0.05) and path length (p<0.05) was observed following nGVS, as previously shown. A similar improvement of sway velocity (p<0.05) and path length (p<0.05) was observed in sham group and no significant difference was found between nGVS group and sham group (p>0.05), suggesting that the observed postural improvement in nGVS could be due to a learning effect. This finding suggests the presence of experimental bias in the nGVS effect on postural stability, and highlights the need to use a sham condition in the exploration of the nGVS effect so as to disentangle the direct effect of the electrical stimulation from a learning effect. Furthermore, numerous parameters and populations need to be tested in order to confirm or infirm the presence of a real long-lasting effect of nGVS on postural stability.

Milestones in the development of a vestibular implant

Purpose of review

Bilateral vestibular deficits exist and their prevalence is more important than believed by the medical community. Their severe impact has inspired several teams to develop technical solutions in an attempt to rehabilitate patients. A particularly promising pathway is the vestibular implant. This article describes the main milestones in this field, mainly focusing on work conducted in human patients.

Recent findings

There have been substantial research efforts, first in animals and more recently in humans, toward the development of vestibular implants. Humans have demonstrated surprising adaptation capabilities to the artificial vestibular signal. Today, the possibility of restoring vestibular reflexes, particularly the vestibulo-ocular reflex, and even achieving useful function in close-to-reality tasks (i.e. improving visual abilities while walking) have been demonstrated in humans.

Summary

The vestibular implant opens new perspectives, not only as an effective therapeutic tool, but also pushes us to go beyond current knowledge and well-established clinical concepts.

Balance and mobility in geriatric patients : Assessment and treatment of neurological aspects

BACKGROUND

Personal autonomy in advanced age critically depends on mobility in the environment. Geriatric patients are often not able to walk safely with sufficient velocity. In many cases, multiple factors contribute to the deficit. Diagnostic identification of single components enables a specific treatment.

OBJECTIVE

This article describes the most common neurological causes of imbalance and impaired gait that are relevant for a pragmatic approach for the assessment of deficits in clinical and natural environments taking into account the physiology of balance and gait control, typical morbidities in older people and the potential of innovative assessment technologies.

MATERIAL AND METHODS

Expert opinion based on a narrative review of the literature and with reference to selected research topics.

RESULTS AND DISCUSSION

Common neurological causes of impaired balance and mobility are sensory deficits (reduced vision, peripheral neuropathy, vestibulopathy), neurodegeneration in disorders with an impact on movement control and motoric functions (Parkinsonian syndromes, cerebellar ataxia, vascular encephalopathy) and functional (psychogenic) disorders, particularly a fear of falling. Clinical tests and scores in laboratory environments are complemented by the assessment in the natural environment. Wearable sensors, mobile smartphone-based assessment of symptoms and functions and adopted strategies for analysis are currently emerging. Use of these data enables a personalized treatment. Furthermore, sensor-based assessment ensures that effects are measured objectively.