Noisy Galvanic Vestibular Stimulation Research Articles

Effect of noisy galvanic vestibular stimulation in community-dwelling elderly people: a randomised controlled trial

BackgroundBalance disorders are a risk factor for falls in the elderly. Although noisy galvanic vestibular stimulation (nGVS) has been reported to improve balance in young people, randomised control trials targeting community-dwelling elderly people have not been conducted to date. We aimed to assess the influence of nGVS on COP sway in the open-eye standing posture among community-dwelling elderly people in a randomised controlled trial.MethodsA randomised controlled trial of 32 community-dwelling elderly people randomly assigned to control (sham stimulation) and an nGVS groups. All participants underwent centre of pressure (COP) sway measurements while standing with open eyes at baseline and during stimulation. The control group underwent sham stimulation and the nGVS group underwent noise stimulation (0.4 mA; 0.1–640 Hz).ResultsIn the nGVS group, sway path length, mediolateral mean velocity and anteroposterior mean velocity decreased during stimulation compared with baseline (P < 0.01). The effect of nGVS was large in participants with a high COP sway path length at baseline, but there was no significant difference in COP sway in the control group.ConclusionsWe conclude that nGVS decreases the COP sway path length and mean velocity of community-dwelling elderly people when standing with open eyes. This suggests that nGVS could be effective for treating balance dysfunction in the elderly.

Effects of galvanic vestibular stimulation with white and pink noise on upright standing sway for healthy adults

It has been reported that the noisy galvanic vestibular stimulation (n-GVS) could improve upright body sway in healthy subjects. It is unclear which sort of noise is appropriate for n-GVS. Our study aimed to investigate the effects of n-GVS with white and pink noise for upright standing sway in healthy adults. Seventeen healthy adults (11 men; age = 21.9 ± 1.6 years) were instructed to stand on a force plate with foamed rubber and wore an eye-mask and ear-muffs. Center of pressure (CoP) displacement was measured for 60-s with 1000 Hz sampling. We generated the 30-s white and pink noise and added this to the galvanic vestibular stimulation. We applied the n-GVS to the participants and stimulus intensities were 30, 50, 70, 90, and 110% of each participant's electric sensory threshold level (10 conditions: 2 noise × 5 intensities). Right side anode n-GVS was applied via both mastoids 30-s after the measurement was started. We used the anteroposterior (AP) and mediolateral (ML) direction of standard deviations (SD) and total length (LNG) of CoP displacement as measurement variables. Each condition's variable was represented as a percentage value based on the initial 30-s measurement data (pre-n-GVS). We compared these variables with two-way repeated measures Anovas and t -test as post-hoc test (significance level was 5%). In the AP- and ML-LNG, significant intensity effects were observed with ANOVAs (both of P < 0.05). Conversely, there were no main effects and interactions in the AP- and ML-SD. In the AP-LNG, the 90% intensity condition showed significantly smaller values compared to 50, 70, and 110% in the pink noise. We found that the n-GVS improved the CoP displacement length but not the width and the optimal stimulus intensity was at around 90% of the sensory threshold level with pink noise.

Noisy vestibular stimulation improves vestibulospinal function in patients with bilateral vestibulopathy.

To examine the mechanism underlying previously reported ameliorating effects of noisy galvanic vestibular stimulation (GVS) on balance performance in patients with bilateral vestibulopathy (BVP) and determine those patients (incomplete versus complete vestibular loss) that might benefit from this intervention. Vestibulospinal reflex thresholds were determined in 12 patients with BVP [2 with complete loss (cBVP) and 10 with residual function (rBVP)]. Patients were stimulated with 1Hz sinusoidal GVS of increasing amplitudes (0-1.9mA). Coherence between GVS input and stimulation-induced body motion was determined and psychometric function fits were subsequently used to determine individual vestibulospinal reflex thresholds. The procedure was repeated with an additional application of imperceptible white noise GVS (nGVS). All patients with rBVP but none with cBVP exhibited stimulation-induced vestibulospinal reflex responses with a mean threshold level of 1.26 ± 0.08mA. Additional nGVS resulted in improved processing of weak subthreshold vestibular stimuli (p = 0.015) and thereby effectively decreased the vestibulospinal threshold in 90% of patients with rBVP (mean reduction 17.3 ± 3.9%; p < 0.001). The present findings allow to identify the mechanism by which nGVS appears to stabilize stance and gait performance in patients with BVP. Accordingly, nGVS effectively lowers the vestibular threshold to elicit balance-related reflexes that are required to adequately regulate postural equilibrium. This intervention is only effective in the presence of a residual vestibular functionality, which, however, applies for the majority of patients with BVP. Low-intensity noise stimulation thereby provides a non-invasive treatment option to optimize residual vestibular resources in BVP.

Noisy Galvanic Stimulation Improves Roll-Tilt Vestibular Perception in Healthy Subjects

It has recently been demonstrated that noisy galvanic vestibular stimulation (nGVS) delivered as imperceptible white noise can improve balance control via the induction of stochastic resonance. However, it is unclear whether these balance improvements are accompanied by simultaneous enhancement to vestibular motion perception. In this study, 15 healthy subjects performed 8 quiet-stance tasks on foam with eyes closed at 8 different nGVS amplitudes ranging from 0 mA (baseline) to 0.5 mA. The nGVS amplitude that improved balance performance most compared to baseline was assigned as the optimal nGVS amplitude. Optimal nGVS amplitudes could be determined for 13 out of 15 subjects, who were included in the subsequent experimental procedures. The effect of nGVS delivered at the determined optimal intensity on vestibular perceptual thresholds was examined using direction-recognition tasks on a motion platform, testing roll rotations at 0.2, 0.5, and 1.0 Hz, both with active and sham nGVS stimulations. nGVS significantly reduced direction-recognition thresholds compared to the sham condition at 0.5 and 1.0 Hz, while no significant effect of nGVS was found at 0.2 Hz. Interestingly, no correlation was found between nGVS-induced improvements in balance control and vestibular motion perception at 0.5 and 1 Hz, which may suggest different mechanisms by which nGVS affects both modalities. For the first time, we show that nGVS can enhance roll vestibular motion perception. The outcomes of this study are likely to be relevant for the potential therapeutic use of nGVS in patients with balance problems.

Galvanic Vestibular Stimulation (GVS) Augments Deficient Pedunculopontine Nucleus (PPN) Connectivity in Mild Parkinson's Disease: fMRI Effects of Different Stimuli.

Falls and balance difficulties remain a major source of morbidity in Parkinson's Disease (PD) and are stubbornly resistant to therapeutic interventions. The mechanisms of gait impairment in PD are incompletely understood but may involve changes in the Pedunculopontine Nucleus (PPN) and its associated connections. We utilized fMRI to explore the modulation of PPN connectivity by Galvanic Vestibular Stimulation (GVS) in healthy controls (n = 12) and PD subjects even without overt evidence of Freezing of Gait (FOG) while on medication (n = 23). We also investigated if the type of GVS stimuli (i.e., sinusoidal or stochastic) differentially affected connectivity. Approximate PPN regions were manually drawn on T1 weighted images and 58 other cortical and subcortical Regions of Interest (ROI) were obtained by automatic segmentation. All analyses were done in the native subject's space without spatial transformation to a common template. We first used Partial Least Squares (PLS) on a subject-by-subject basis to determine ROIs across subjects that covaried significantly with the voxels within the PPN ROI. We then performed functional connectivity analysis on the PPN-ROI connections. In control subjects, GVS did not have a significant effect on PPN connectivity. In PD subjects, baseline overall magnitude of PPN connectivity was negatively correlated with UPDRS scores (p < 0.05). Both noisy and sinusoidal GVS increased the overall magnitude of PPN connectivity (p = 6 × 10−5, 3 × 10−4, respectively) in PD, and increased connectivity with the left inferior parietal region, but had opposite effects on amygdala connectivity. Noisy stimuli selectively decreased connectivity with basal ganglia and cerebellar regions. Our results suggest that GVS can enhance deficient PPN connectivity seen in PD in a stimulus-dependent manner. This may provide a mechanism through which GVS assists balance in PD, and may provide a biomarker to develop individualized stimulus parameters.

Effect of noisy galvanic vestibular stimulation on center of pressure sway of static standing posture

BackgroundThe vestibular system is involved in the control of standing balance. Galvanic vestibular stimulation (GVS) is a noninvasive technique that can stimulate the vestibular system. In recent years, noisy GVS (nGVS) using noise current stimulation has been attempted, but it has not been clarified whether it affects postural sway in open-eye standing. ObjectiveThe purpose of this study was to clarify the influence of nGVS on the center of pressure (COP) sway measurement in open-eye standing postural control and identify the responders of nGVS. MethodsnGVS (0.1–640 Hz) was delivered at 0.4 and 1.0 mA over the bipolar mastoid. COP sway root mean square area, sway path length, medio-lateral (ML) mean velocity, and antero-posterior (AP) mean velocity before and during nGVS in an open-eye standing posture was measured. ResultsnGVS at 0.4 and 1.0 mA significantly reduced sway path length, mean velocity. The stimulation effect of nGVS was also large in subjects with a long sway path. For subjects with high COP sway of Baseline, nGVS was effective even with stimulation for a short duration (5 s). ConclusionsThese findings suggest that nGVS improves postural sway in an open-eye standing posture among young subjects.

Noisy galvanic vestibular stimulation: an emerging treatment option for bilateral vestibulopathy.

Patients with bilateral vestibulopathy (BVP) suffer from persistent imbalance during standing and walking as well as an impaired gaze stabilization during head movements. Disabilities associated with BVP severely compromise patients' daily activities and are often linked to an increased risk of falls. Currently, the only established treatment option in BVP is physical therapy. However, treatment effects of physical therapy in BVP are most often limited and many patients do not adequately recover performance. Therefore, a number of technical therapeutic approaches are being explored that either try to substitute lost vestibular sensation with a congruent stimulation of other sense modalities or to artificially mimic vestibular function by means of an implantable vestibular prosthesis. Besides, attempts have recently been made to augment and optimize residual vestibular function in patients with BVP using an imperceptible noisy galvanic vestibular stimulation (nGVS). This approach is based on the natural phenomenon of stochastic resonance, wherein the signal processing in sensory systems can be improved by adding an appropriate level of noise to the system. Promising first study outcomes of nGVS treatment in patients with BVP indicate the feasibility of a future non-invasive sensory prosthetic device for BVP rehabilitation. This paper gives an overview about recent research on nGVS treatment in patients with BVP and discusses future research perspectives in this field.

Effect of Noisy Galvanic Vestibular Stimulation on Ocular Vestibular-Evoked Myogenic Potentials to Bone-Conducted Vibration.

Galvanic vestibular stimulation (GVS) delivered as zero-mean current noise (noisy GVS) has been shown to improve static and dynamic postural stability probably by enhancing vestibular information. The purpose of this study was to examine the effect of an imperceptible level noisy GVS on ocular vestibular-evoked myogenic potentials (oVEMPs) in response to bone-conducted vibration (BCV). oVEMPs to BCV were measured during the application of white noise GVS with an amplitude ranging from 0 to 300 µA [in root mean square (RMS)] in 20 healthy subjects. Artifacts in the oVEMPs caused by GVS were reduced by inverting the waveforms of noisy GVS in the later half of the stimulus from the one in the early half. We examined the amplitudes of N1 and N1-P1 and their latencies. Noisy GVS significantly increased the N1 and N1-P1 amplitudes (p < 0.05) whereas it had no significant effects on N1 or P1 latencies (p > 0.05). Noisy GVS had facilitatory effects in 79% of ears. The amplitude of the optimal stimulus was 127 ± 14 µA, and it increased the N1 and N1-P1 amplitude by 75.9 ± 15% and 47.7 ± 9.1%, respectively, as compared with 0 µA session (p < 0.05). Noisy GVS can increase the amplitude of oVEMPs to BCV in healthy subjects probably via stochastic resonance. The results of the present study suggest that noisy GVS may improve static and dynamic postural stability by enhancing the function of the vestibular afferents.

Vection Latency Is Reduced by Bone-Conducted Vibration and Noisy Galvanic Vestibular Stimulation

Studies of the illusory sense of self-motion elicited by a moving visual surround (‘vection’) have revealed key insights about how sensory information is integrated. Vection usually occurs after a delay of several seconds following visual motion onset, whereas self-motion in the natural environment is perceived immediately. It has been suggested that this latency relates to the sensory mismatch between visual and vestibular signals at motion onset. Here, we tested three techniques with the potential to reduce sensory mismatch in order to shorten vection onset latency: noisy galvanic vestibular stimulation (GVS) and bone conducted vibration (BCV) at the mastoid processes, and body vibration applied to the lower back. In Experiment 1, we examined vection latency for wide field visual rotations about the roll axis and applied a burst of stimulation at the start of visual motion. Both GVS and BCV reduced vection latency by two seconds compared to the control condition, whereas body vibration had no effect on latency. In Experiment 2, the visual stimulus rotated about the pitch, roll, or yaw axis and we found a similar facilitation of vection by both BCV and GVS in each case. In a control experiment, we confirmed that air-conducted sound administered through headphones was not sufficient to reduce vection onset latency. Together the results suggest that noisy vestibular stimulation facilitates vection, likely due to an upweighting of visual information caused by a reduction in vestibular sensory reliability.

ノイズ前庭電気刺激を利用した両側前庭障害患者の体平衡機能改善

The peripheral vestibular organs sense angular and linear accelerations of the head, and help to maintain gaze and posture during head movements through the vestibulo-ocular and vestibulo-spinal reflexes. Bilateral vestibular dysfunction causes persistent imbalance and oscillopsia while moving the body or the head, and so far no effective treatments have been found for this condition except vestibular rehabilitation. We used noisy galvanic vestibular stimulation (noisy GVS), which was delivered as zero-mean current noise, of an imperceptible amplitude to improve postural performance in patients with bilateral vestibular dysfunction. We demonstrated that the application of noisy GVS for 30 sec significantly improved postural performance as measured by stabilometry in patients with bilateral vestibulopathy. We then examined the effect of noisy GVS on locomotion, and showed that it significantly increased the gait velocity and stride length, but significantly decreased the stride time in patients with vestibulopathy. Furthermore, to examine the effect of noisy GVS on vestibular function, we examined the effects of noisy GVS on ocular vestibular evoked myogenic potentials (oVEMP) in response to bone-conducted vibration (BCV). The noisy GVS increased the amplitude of oVEMP responses without affecting the latencies of oVEMP responses, suggesting that noisy GVS improves static and dynamic postural stability by enhancing the function of the vestibular afferents. Finally, we tested the long-term effects of noisy GVS on postural stability in elderly adults, and showed that noisy GVS can lead to a postural stability improvement that lasts for several hours after the cessation of the stimulus, probably via neuroplasticity. This newly discovered effect could contribute to an increase in the application of noisy GVS in appropriate patients.

Noisy galvanic vestibular stimulation induces a sustained improvement in body balance in elderly adults.

Vestibular dysfunction causes postural instability, which is prevalent in the elderly. We previously showed that an imperceptible level of noisy galvanic vestibular stimulation (nGVS) can improve postural stability in patients with bilateral vestibulopathy during the stimulus, presumably by enhancing vestibular information processing. In this study, we investigated the after-effects of an imperceptible long-duration nGVS on body balance in elderly adults. Thirty elderly participants underwent two nGVS sessions in a randomised order. In Session 1, participants received nGVS for 30 min twice with a 4-h interval. In Session 2, participants received nGVS for 3 h. Two-legged stance tasks were performed with eyes closed while participants stood on a foam rubber surface, with and without nGVS, and parameters related to postural stability were measured using posturography. In both sessions, the postural stability was markedly improved for more than 2 h after the cessation of the stimulus and tended to decrease thereafter. The second stimulation in Session 1 caused a moderate additional improvement in body balance and promoted the sustainability of the improvement. These results suggest that nGVS can lead to a postural stability improvement in elderly adults that lasts for several hours after the cessation of the stimulus, probably via vestibular neuroplasticity.

Noisy galvanic vestibular stimulation enhances spatial memory in cognitive impairment-induced by intracerebroventricular-streptozotocin administration

There are several anatomical connections between vestibular system and brain areas construct spatial memory. Since subliminal noisy galvanic vestibular stimulation (GVS) has been demonstrated to enhance some types of memory, we speculated that application of noisy GVS may improve spatial memory in a rat model of intracerebroventricular streptozotocin (ICV-STZ)-induced cognitive impairment. Moreover, we attempted to determine the effect of repeated exposure to GVS on spatial memory performance. The spatial memory was assessed using Morris water maze test. The groups received 1 (ICV-STZ/GVS-I) or 5 (ICV-STZ/GVS-II) sessions, each lasting 30min, of low amplitude noisy GVS, or no GVS at all (Control, ICV-saline, ICV-STZ/noGVS). Hippocampal morphological changes investigated with cresyl violet staining and the immediate early gene product c-Fos, as a neuronal activity marker, was measured. Hippocampal c-Fos positive cells increased in both GVS stimulated groups. We observed significantly improved spatial performance only in ICV-STZ/GVS-II group. Histological evaluation showed normal density in ICV-STZ/GVS-II group whereas degeneration observed in ICV-STZ/GVS-I group similar to ICV-STZ/noGVS. The results showed the improvement of memory impairment after repeated exposure to GVS. This effect may be due in part to frequent activation of the vestibular neurons and the hippocampal regions connected to them. Our current study suggests the potential role of GVS as a practical method to combat cognitive decline induced by sporadic Alzheimer disease.

Noise-Enhanced Vestibular Input Improves Dynamic Walking Stability in Healthy Subjects.

White noise galvanic vestibular stimulation (GVS) is thought to enhance the sensitivity of vestibular organs. To examine the effects of noise-enhanced vestibular input on the walking performance in healthy subjects walking with eyes closed. Walking performance of 17 healthy subjects (mean age 28.8 ± 1.7 years) at slow, preferred, and fast speeds was examined during three different conditions: (1) walking with eyes open (EO) as baseline condition, (2) walking with eyes closed and sham noisy GVS (EC), and (3) walking with eyes closed and non-zero amplitude noisy GVS set to 80% of the individual sensory threshold for GVS (EC-GVS). Ten gait parameters were examined: stride time, stride length, base of support, swing time percentage, double support time percentage as well as gait asymmetry, bilateral phase coordination and the coefficient of variation (CV) of stride time, stride length and base of support. Noisy GVS improved stride time CV by 36% (p < 0.034), stride length CV by 31% (p < 0.037), base of support CV by 14% (p < 0.009), and bilateral phase coordination by 23% (p < 0.034). The ameliorating effects of noisy GVS on locomotion function were primarily observable during slow walking speeds. Noise-enhanced vestibular input is effective in improving locomotion function and is accompanied by a subjectively felt improvement of walking balance. It predominantly targets the variability and bilateral coordination characteristics of the walking pattern, which are critically linked to dynamic walking stability. Noisy GVS might present an effective treatment option to improve walking performance in patients with bilateral vestibular dysfunction.

P33. Noisy galvanic vestibular stimulation improves dynamic walking stability in healthy subjects

Introduction We examined the effect of galvanic vestibular stimulation (GVS) delivered as zero-mean white noise current (noisy GVS) on the walking performance in healthy subjects. Methods The walking performance of 15 healthy subjects (mean age 23.0±1.3 years) at slow, preferred and fast walking speed was examined during two different conditions: (1) walking with eyes closed and zero amplitude sham noisy GVS, and (2) walking with eyes closed and non-zero amplitude noisy GVS set to 80% of the individual sensory threshold for GVS. We examined 10 gait parameters: stride time, stride length, base of support, swing time percentage, double support time percentage as well as the CV of stride time, stride length and base of support, gait asymmetry and bilateral phase synchronization. Results Noisy GVS significantly improved stride time CV by 34% ( p p p p p Conclusion Noisy GVS is effective in improving locomotion function in healthy subjects. It predominantly targets the variability and bilateral coordination characteristics of the walking pattern, which are critically linked to dynamic walking stability. The predominant impact of noisy GVS during slow walking supports the principle of a speed-depended role of sensory feedback in locomotion control.

Synergistic effects of noisy galvanic vestibular stimulation and oral L-dopa in improving manual tracking performance in Parkinson’s disease

Sub-threshhold, noisy, galvanic vestibular stimulation (nGVS), has been recently suggested as a potential treatment for some of the motor aspects of Parkinson’s disease (PD), possibly by modulating ongoing brain rhythms [1]. L-dopa medication, the principal pharmacotherapy for PD, also affects brain rhythms [2], and responsiveness to L-dopa medication is a good predictor of the effectiveness of Deep Brain Stimulation (DBS), a known surgical treatment for PD. However, the use of nGVS as treatment of PD will only be practical if it can be shown that further improvement in motor performance can still occur when subjects are already optimally managed with medication.

Subthreshold, noisy galvanic vestibular stimulation affects submovements in manual tracking tasks in Parkinson’s disease

s / Brain Stimulation 8 (2015) 395e411 401 through direct or indirect approach has shown promising results in relieving tinnitus in both human and animal subjects. Among the structures stimulated include the cochlear nucleus, auditory cortex, basal ganglion, and prefrontal cortex. However, there remains a large variability in therapeutic effects across different brain stimulation modalities. In order to achieve effective therapy, our lab has established animalmodels of brain stimulation to suppress tinnitus. We have been searching for optimal stimulation strategies and to delineate the underlyingmechanisms of brain-stimulation-induced tinnitus suppression. In this conference, I will present the latest development on tinnitus suppression through brain stimulation and discuss the underlying mechanisms and technological development.

Multifaceted effects of noisy galvanic vestibular stimulation on manual tracking behavior in Parkinson's disease.

Parkinson’s disease (PD) is a neurodegenerative movement disorder that is characterized clinically by slowness of movement, rigidity, tremor, postural instability, and often cognitive impairments. Recent studies have demonstrated altered cortico-basal ganglia rhythms in PD, which raises the possibility of a role for non-invasive stimulation therapies such as noisy galvanic vestibular stimulation (GVS). We applied noisy GVS to 12 mild-moderately affected PD subjects (Hoehn and Yahr 1.5–2.5) off medication while they performed a sinusoidal visuomotor joystick tracking task, which alternated between 2 task conditions depending on whether the displayed cursor position underestimated the actual error by 30% (‘Better’) or overestimated by 200% (‘Worse’). Either sham or subthreshold, noisy GVS (0.1–10 Hz, 1/f-type power spectrum) was applied in pseudorandom order. We used exploratory (linear discriminant analysis with bootstrapping) and confirmatory (robust multivariate linear regression) methods to determine if the presence of GVS significantly affected our ability to predict cursor position based on target variables. Variables related to displayed error were robustly seen to discriminate GVS in all subjects particularly in the Worse condition. If we considered higher frequency components of the cursor trajectory as “noise,” the signal-to-noise ratio of cursor trajectory was significantly increased during the GVS stimulation. The results suggest that noisy GVS influenced motor performance of the PD subjects, and we speculate that they were elicited through a combination of mechanisms: enhanced cingulate activity resulting in modulation of frontal midline theta rhythms, improved signal processing in neuromotor system via stochastic facilitation and/or enhanced “vigor” known to be deficient in PD subjects. Further work is required to determine if GVS has a selective effect on corrective submovements that could not be detected by the current analyses.

Noisy vestibular stimulation improves body balance in bilateral vestibulopathy

To examine the effect of an imperceptible level of galvanic vestibular stimulation (GVS), delivered as zero-mean current noise (noisy GVS), on postural performance in healthy subjects as well as in patients with bilateral peripheral vestibular dysfunction. White noise GVS with an amplitude ranging from 0 to 1,000 μA was applied in 21 healthy subjects and 11 patients with bilateral vestibular dysfunction. Two-legged stance tasks were performed with the eyes closed during a 60-second period, which consisted of a baseline period without stimulation and a stimulation period with GVS. We examined 3 parameters: the velocity, the envelopment area, and the root mean square (RMS) of the center of pressure. White noise GVS improved all 3 parameters in 76% of healthy subjects. The amplitude of the optimal stimulus was 281 ± 40 μA, and it improved the velocity, area, and RMS by 18.4% ± 2%, 37.9% ± 3.5%, and 20.4% ± 2.2%, respectively (p < 0.01). The GVS improved all 3 parameters in 91% of patients. The amplitude of the optimal stimulus was 456 ± 82 μA, and it improved the velocity, area, and RMS by 29.4% ± 4.9%, 45.6% ± 4.7%, and 22% ± 3.3%, respectively (p < 0.01). Noisy GVS is effective in improving postural stability in healthy subjects as well as in patients with bilateral vestibular dysfunction. This study provides Class IV evidence that in patients with bilateral vestibular dysfunction, an imperceptible level of noisy GVS may improve postural stability.

P 256. Augmented set-shifting in Parkinson’s disease with noisy Galvanic Vestibular Stimulation

Introduction Cognitive impairment and executive dysfunction, in addition to overt motor deficits, are common in Parkinson’s disease (PD). Perseveration of behavioural paradigms in PD reflects cognitive inflexibility ( Cools, 2001 ) and is related to the inability to stop and switch motor paradigms ( Stoffers, 2001 ). Noisy Galvanic Vestibular Stimulation (GVS) is a technique that has improved motor metrics in PD ( Samoudi et al., xxxx , Yamamoto, xxxx ). Widespread vestibular areas-both cortical and subcortical-are activated by GVS ( Lopez and Blanke, 2011 ), perhaps explaining the positive effects of GVS on PD motor symptoms and also on cognitive effects, such as enhancing visual memory recall ( Wilkinson, 2008 ). Objectives We investigated whether noisy GVS has effects on PD switching abilities in a set-shifting motor task. Unlike other switching paradigms (e.g., Wisconsin Card Sorting Task), our task does not additionally depend on other cognitive components such as working memory and rule learning, thereby predicting a more sensitive measure of switching abilities per se. Materials and methods We tested 4 patients with mild to moderate PD (Hoehn and Yahr stages: 1–2), and 4 healthy age-matched control subjects. All PD patients were asked to stop taking dopaminergic medication at least 12 h prior to the study. Subjects performed 8 trials of a sinusoidal visual tracking task which alternated between 2 modes depending upon whether the displayed cursor position underestimated the actual error by 30% (’Better’) or overestimated by 200% (’Worse’). The switching was covert, unbeknownst to the subject. Either a subthreshold, noisy GVS (0.1–10 Hz, 1/f-type power spectrum) or sham current was applied during each trial in a pseudorandom order. Using Multiple Model Adaptive Estimation (MMAE) ( Oishi, 2010 ), we were able to predict which type of performance mode (‘Better’ or ‘Worse’) the subject was applying to the task. The MMAE algorithm essentially determines the likelihood a subject is behaving in a given ‘Better’ or ‘Worse’ performance mode at specific time stamps throughout a given trial. Results Noisy GVS had no significant effect on the switching detection frequency in control subjects ( Fig. 1 ). PD patients off medication demonstrated notably less switching than control subjects. Patients also responded to GVS delivery with significantly greater frequencies of switching (p = 0.02, Fig. 1 ). Conclusion Noisy GVS increased overall switching behaviour in PD patients without any effect on healthy control subjects, suggesting that Vestibular Stimulation may be able to influence cognitive flexibility deficits in PD. However, further work is needed to see if GVS can, in fact, also result in excessive switching between motor programs.

Noisy Galvanic Vestibular Stimulation Modulates the Amplitude of EEG Synchrony Patterns

Noisy galvanic vestibular stimulation has been associated with numerous cognitive and behavioural effects, such as enhancement of visual memory in healthy individuals, improvement of visual deficits in stroke patients, as well as possibly improvement of motor function in Parkinson’s disease; yet, the mechanism of action is unclear. Since Parkinson’s and other neuropsychiatric diseases are characterized by maladaptive dynamics of brain rhythms, we investigated whether noisy galvanic vestibular stimulation was associated with measurable changes in EEG oscillatory rhythms within theta (4–7.5 Hz), low alpha (8–10 Hz), high alpha (10.5–12 Hz), beta (13–30 Hz) and gamma (31–50 Hz) bands. We recorded the EEG while simultaneously delivering noisy bilateral, bipolar stimulation at varying intensities of imperceptible currents – at 10, 26, 42, 58, 74 and 90% of sensory threshold – to ten neurologically healthy subjects. Using standard spectral analysis, we investigated the transient aftereffects of noisy stimulation on rhythms. Subsequently, using robust artifact rejection techniques and the Least Absolute Shrinkage Selection Operator regression and cross-validation, we assessed the combinations of channels and power spectral features within each EEG frequency band that were linearly related with stimulus intensity. We show that noisy galvanic vestibular stimulation predominantly leads to a mild suppression of gamma power in lateral regions immediately after stimulation, followed by delayed increase in beta and gamma power in frontal regions approximately 20–25 s after stimulation ceased. Ongoing changes in the power of each oscillatory band throughout frontal, central/parietal, occipital and bilateral electrodes predicted the intensity of galvanic vestibular stimulation in a stimulus-dependent manner, demonstrating linear effects of stimulation on brain rhythms. We propose that modulation of neural oscillations is a potential mechanism for the previously-described cognitive and motor effects of vestibular stimulation, and noisy galvanic vestibular stimulation may provide an additional non-invasive means for neuromodulation of functional brain networks.