Effects Of Galvanic Vestibular Stimulation Research Articles

Exploration of effects of galvanic vestibular stimulation on circadian rhythms and its associations with sleep and spatial memory in patients with breast cancer: The ICANSLEEP-2 protocol.

Patients with breast cancer (BC) exhibit circadian rhythm disruptions, mainly of rest-activity rhythm (RAR), of which sleep is an essential component, and cortisol rhythm. Sleep complaints such as insomnia and cognitive impairments are prevalent in BC. In general population, sleep is known to contribute greatly to cognition. Thus, improving RAR (and particularly sleep) could help limiting cognitive impairments in BC patients. It has recently been suggested that, in addition to its essential role in spatial memory, the vestibular system contributes to RAR synchronization. Its stimulation could therefore limit both sleep disturbances and spatial memory deficits in BC. The main aim of the ICANSLEEP-2 study is to assess the effects of galvanic vestibular stimulation (GVS) on circadian rhythms. The secondary aim is to assess whether GVS improves sleep and spatial memory in BC patients. Two groups with insomnia complaints (Insomnia Severity Index > 7) will be included: a patients' group with BC (n = 50) and a healthy control group without history of cancer (n = 25). There will be two assessment sessions, before and after 2 weeks of GVS. Patients will be randomly assigned to either a GVS group or a sham group (noneffective stimulation). Controls will receive GVS. GVS effects will be quantified and compared between groups. Assessments will include actigraphy, salivary cortisol, polysomnography, a cognitive test battery (including a computer-based task for spatial memory) and validated questionnaires (for psychological functioning and sleep complaints). Current methods for improving sleep in BC have had controversial outcomes regarding sleep structure. We expect GVS to offer a new mean of directly targeting RAR disruptions in BC patients, with beneficial effects on sleep structure. Given the crucial impact of sleep on cognitive functioning, notably spatial memory, improving sleep of BC patients should enhance their cognitive functioning. This study received ethical approval from the Ile de France IV institutional review board on 19 April 2022 (no. ID-RCB: 2022-A00437-36). The findings yielded by this protocol will be presented at various conferences and in peer-reviewed journals. NCT05414357.

Effects of galvanic vestibular stimulation on postural righting reactions in hemiplegia

Patients with post-stroke hemiplegia often exhibit reduced ability to maintain sitting balance, a crucial factor for predicting prognosis. Galvanic vestibular stimulation (GVS) influences postural control by stimulating vestibular organ. Although several studies have focused on GVS in static postures, no studies have demonstrated the influence of GVS on righting reactions. Therefore, we aimed to investigate the effects of GVS on postural righting reactions in seated patients with stroke-induced hemiplegia. Using a vertical board (VB), righting reactions were induced by tilting the VB at 10° after patients sat for 1 min. Patients adjusted their bodies until feeling vertical upon prompt. Twenty-two left hemiplegic patients with cerebrovascular disease participated, divided into two groups undergoing right cathode GVS (RC-GVS) followed by left cathode GVS or vice versa, preceded by sham stimulation. Centre of pressure and the joint angle were measured. During the postural righting reactions towards the paralysed side, RC-GVS enhanced the righting reactions and moved the mean position on the x-axis (COPx) to the right and the mean position on the y-axis (COPy) to the front. During the postural righting reaction towards the right side, RC-GVS induced resistance against the righting reaction, COPx was deflected to the right, COPy was deflected backward, and the angle of the neck tilt increased. The findings revealed that GVS with anodal stimulation on the paralysed side could promote righting reactions in patients with post-stroke hemiplegia. Significance StatementThe study findings suggest that using the contralesional placement of the anode promotes righting reactions, and galvanic vestibular stimulation can induce joint movements in the neck and trunk by polarising it to act as resistance against righting reactions.

Effect of galvanic vestibular stimulation applied at the onset of stance on muscular activity and gait cycle duration in healthy individuals.

Locomotion requires the complex involvement of the spinal and supraspinal systems. So far, the role of vestibular input in gait has been assessed mainly with respect to gait stability. The noninvasive technique of galvanic vestibular stimulation (GVS) has been reported to decrease gait variability and increase gait speed, but the extent of its effect on spatiotemporal gait parameters is not fully known. Objective: Characterize vestibular responses during gait and determine the influence of GVS on cycle duration in healthy young participants. Methods: Fifteen right-handed individuals participated in the study. Electromyography (EMG) recordings of the bilateral soleus (SOL) and tibialis anterior muscles (TA) were performed. First, to determine stimulation intensity, an accelerometer placed on the vertex recorded the amplitude of the head tilts evoked by the GVS (1-4 mA, 200 ms) to establish a motor threshold (T). Second, while participants walked on a treadmill, GVS was applied at the onset of the stance phase during the treadmill gait with an intensity of 1 and 1.5 T with the cathode behind the right (RCathode) or left ear (LCathode). EMG traces were rectified, averaged (n = 30 stimuli), and analyzed. Latency, duration, and amplitude of vestibular responses as well as the mean duration of the gait cycles were measured. Results: GVS mainly induced long-latency responses in the right SOL, right TA and left TA. Only short-latency responses were triggered in the left SOL. Responses in the right SOL, left SOL and left TA were polarity dependent, being facilitatory with RCathode and inhibitory with LCathode, whereas responses in the right TA remained facilitatory regardless of the polarity. With the RCathode configuration, the stimulated cycle was prolonged compared with the control cycle at both 1 and 1.5 T, due to prolonged left SOL and TA EMG bursts, but no change was observed in right SOL and TA. With LCathode, GVS did not modify the cycle duration. Conclusion: During gait, a brief, low-intensity GVS pulse delivered at the right stance onset induced mainly long-latency polarity-dependent responses. Furthermore, a RCathode configuration increased the duration of the stimulated gait cycle by prolonging EMG activity on the anodic side. A similar approach could be explored to influence gait symmetry in individuals with neurological impairment.

The effect of galvanic vestibular stimulation on the movement-related cortical potential in Parkinson’s disease

The effect of galvanic vestibular stimulation on the movement-related cortical potential in Parkinson’s disease

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.

Galvanic vestibular stimulation to counteract leans illusion: comparing step and ramped waveforms

Leans is a common type of Spatial Disorientation (SD) illusion that causes pilots to be confused about the position of the aircraft during a flight. This illusion could lead to serious adverse effects and even flight mishaps. Therefore, an effective means to deal with leans is crucial for flight safety. This study aims to investigate the effects of Galvanic Vestibular Stimulation (GVS) technology with different waveforms as a tool to mitigate the negative effects of leans. 20 Air Force pilots participated in leans-induced flight simulation experiment with three GVS conditions (without-GVS, step-GVS, ramped-GVS). Bank angle error, subjective SD, perceived strength, and annoyance were measured as the dependent variables. Analysis revealed that step-GVS and ramped-GVS yielded lower bank angle errors and subjective SD than without-GVS. In addition, annoyance ratings were lower for ramped-GVS than step-GVS. This study suggests that GVS has the potential to be utilised as a counteracting tool to cope with leans. Practitioner summary: Galvanic Vestibular Stimulation (GVS) can be utilised as a tool to counteract the detrimental effects of leans illusion, specifically the ramped style GVS, considering that it is less annoying and distracting for the pilots. In general, GVS induces a roll sensation that can offset the false sensation caused by the leans, which can potentially help maintain flight safety and avoid spatial disorientation-related accidents. Abbreviations: SD: spatial disorientation; GVS: galvanic vestibular stimulation; MSSQ: motion sickness susceptibility questionniare; SSQ: simulator sickness questionnaire; BLE: bluetooth low energy; PCB: printed circuit board; RPM: revolution per minute

Effects of Galvanic Vestibular Stimulation on Subjective Visual Vertical and Sitting Balance in Patients with Stroke

ObjectiveThis study aimed to examine the effects of galvanic vestibular stimulation (GVS) on visual vertical cognition and sitting balance in stroke patients. Materials and MethodsPatients with unilateral supratentorial infarction and hemorrhagic lesions and healthy controls were recruited. Bipolar GVS was performed through the bilateral mastoid processes with an 1.5-mA electric current. Each participant received three stimulation patterns: right anode-left cathode, left anode-right cathode, and sham. The subjective visual vertical (SVV) and center of gravity positions in the sitting posture were measured in three groups of participants: patients with right hemisphere lesions, patients with left hemisphere lesions, and in healthy controls. Changes in the SVV and center of gravity positions before and during galvanic vestibular stimulation were assessed. ResultsIn each group, eight individuals were recruited for SVV measurements and nine individuals for center of gravity measurements. We found changes due to polarity of stimulation on the SVV and mediolateral changes in the center of gravity in the sitting position of patients with stroke, while there was no significant difference between groups or interaction of the two factors (polarity vs. group). ConclusionChanges in the visual vertical cognition and sitting balance occur during GVS in patients with stroke. GVS is a potential tool for ameliorating balance dysfunction in patients with stroke.

Effect of galvanic vestibular stimulation on axial symptoms in Parkinson's disease.

Postural imbalance, abnormal axial posture, and axial rigidity are the characteristic features of Parkinson’s disease (PD), and they are referred to as axial symptoms. The symptoms are difficult to manage since they are often resistant to both L-DOPA and deep brain stimulation. Hence, other treatments that can improve Parkinsonian axial symptoms without adverse effects are required. Vestibular dysfunction occurs in PD since neuropathological changes and reflex abnormalities are involved in the vestibular nucleus complex. Galvanic vestibular stimulation (GVS), which activates the vestibular system, is a noninvasive method. This review aimed to assess the clinical effect of GVS on axial symptoms in PD. To date, studies on the effects of GVS on postural instability, anterior bending posture, lateral bending posture, and trunk rigidity and akinesia in PD had yielded interesting data, and none of the patients presented with severe adverse events, and the others had mild reactions. GVS indicated a possible novel therapy. However, most included a small number of patients, and the sample sizes were not similar in some studies that included controls. In addition, there was only one randomized controlled clinical trial, and it did not perform an objective evaluation of axial symptoms. In this type of research, vestibular contributions to balance should be distinguished from others such as proprioceptive inputs or nonmotor symptoms of PD.

The Differential Effects of Acute Right- vs. Left-Sided Vestibular Deafferentation on Spatial Cognition in Unilateral Labyrinthectomized Mice.

This study aimed to investigate the disparity in locomotor and spatial memory deficits caused by left- or right-sided unilateral vestibular deafferentation (UVD) using a mouse model of unilateral labyrinthectomy (UL) and to examine the effects of galvanic vestibular stimulation (GVS) on the deficits over 14 days. Five experimental groups were established: the left-sided and right-sided UL (Lt.-UL and Rt.-UL) groups, left-sided and right-sided UL with bipolar GVS with the cathode on the lesion side (Lt.-GVS and Rt.-GVS) groups, and a control group with sham surgery. We assessed the locomotor and cognitive-behavioral functions using the open field (OF), Y maze, and Morris water maze (MWM) tests before (baseline) and 3, 7, and 14 days after surgical UL in each group. On postoperative day (POD) 3, locomotion and spatial working memory were more impaired in the Lt.-UL group compared with the Rt.-UL group (p < 0.01, Tamhane test). On POD 7, there was a substantial difference between the groups; the locomotion and spatial navigation of the Lt.-UL group recovered significantly more slowly compared with those of the Rt.-UL group. Although the differences in the short-term spatial cognition and motor coordination were resolved by POD 14, the long-term spatial navigation deficits assessed by the MWM were significantly worse in the Lt.-UL group compared with the Rt.-UL group. GVS intervention accelerated the vestibular compensation in both the Lt.-GVS and Rt.-GVS groups in terms of improvement of locomotion and spatial cognition. The current data imply that right- and left-sided UVD impair spatial cognition and locomotion differently and result in different compensatory patterns. Sequential bipolar GVS when the cathode (stimulating) was assigned to the lesion side accelerated recovery for UVD-induced spatial cognition, which may have implications for managing the patients with spatial cognitive impairment, especially that induced by unilateral peripheral vestibular damage on the dominant side.

Galvanic vestibular stimulation with low intensity improves dynamic balance.

BackgroundDynamic balance is associated with fall risk. The aim of this study is to explore the effects of galvanic vestibular stimulation with very low intensity direct current (dcGVS) on dynamic balance.MethodologyWe used a rocker force platform for assessing the dynamic balance performance. Center-of-pressure (COP) coordinates were acquired and decomposed to rambling (RA) and trembling (TR). We measured sway parameters, including length, average speed, and average range, affected by dcGVS at 0.01 mA with eyes open (EO) and eyes closed (EC).ResultsWe assessed 33 young healthy subjects and found that all sway parameters were shorter in the EO condition, indicating a better dynamic balance performance. dcGVS significantly improved the dynamic balance performance both in EO and EC conditions. All the sway parameters in COP in EO were significantly shorter than those in EC, indicating a better dynamic balance performance in EO. In EO, RA had greater improvement rates than TR. In EC, only average speed had a greater improvement rate in RA, whereas length and average range had greater improvement rates in TR. These results indicate a different modulation model between EO and EC.ConclusionThese findings indicate that very low intensity dcGVS improved the sway parameters of dynamic balance in young healthy subjects. Moreover, our results suggest different dynamic balance control models between having EO and EC. The mechanisms of these phenomena caused by very low intensity dcGVS require further investigation.

Involving people with Parkinson's disease in the co-design a trial investigating the effect of Galvanic Vestibular Stimulation on balance

Purpose: Parkinson's disease is the second most common neurodegenerative disease, and the most common neurodegenerative movement disorder worldwide. Symptoms commonly impact an individual's balance, increasing the likelihood of falling. It is thought that Galvanic Vestibular Stimulation (GVS) may improve balance and postural responses in PD however there has been limited work exploring the optimal frequency of intervention. PPI was completed with patients/carers regarding project design and feedback on proposed study documentation. This ensured that the project/documentation were designed appropriately before applying for ethical approval and committing funding.

Effects of Galvanic Vestibular Stimulation on Visual Verticality and Standing Posture Differ Based on the Polarity of the Stimulation and Hemispheric Lesion Side in Patients With Stroke.

Introduction: There is growing evidence supporting the relationship of vertical misperception and poor balance control with asymmetrical standing posture in patients with stroke. Although the vestibular system has been shown to be responsible for vertical misperception and balance disorders, the effect of galvanic vestibular stimulation (GVS) on both vertical misperception and postural asymmetry after stroke remains elusive. The aim of this study was to investigate the effects of GVS on visual verticality and postural asymmetry after stroke and to clarify whether the effects differ depending on the polarity of the stimulation and hemispheric lesion side.Methods: We measured the subjective visual vertical (SVV) and body weight distribution on each foot in an upright stance in 24 patients with a hemispheric stroke (10 with a left hemisphere lesion and 14 with a right hemisphere lesion) and nine age-matched healthy controls. During the measurements, bipolar GVS (1.5 mA) was applied over the bilateral mastoid processes in three stimulation conditions: contralesional-anodal and ipsilesional-cathodal vestibular stimulation, ipsilesional-anodal and contralesional-cathodal vestibular stimulation, and no stimulation. To examine whether GVS modulates visual verticality and standing posture, SVV and weight-bearing in the three conditions were analyzed.Results: During no stimulation, the SVV deviated to the contralesional side in patients with a right hemisphere lesion, while more weight-bearing was observed on the ipsilesional limb than on the contralesional limb in both patient groups than in the controls. The SVV was modulated by reversing the polarity of GVS in all the groups when the cathodal stimulus side was either ipsilateral or contralateral to the lesion while the ipsilesional-cathodal vestibular stimulation reduced weight-bearing asymmetry in only the patients with a right hemisphere lesion.Conclusions: These findings demonstrate that the effects of GVS on the SVV and standing posture differ depending on the polarity of GVS and the hemispheric lesion side. Patients with a right hemisphere lesion have difficulty maintaining their preferred standing posture under visual verticality modulation evoked by GVS. The application of GVS may clarify whether the vestibular system has neural redundancy after stroke to suppress any effects of the stimulation, including modulation of the visual verticality, on balance.

Frequency-Specific Effects of Galvanic Vestibular Stimulation on Response-Time Performance in Parkinson's Disease.

Background: Galvanic vestibular stimulation (GVS) is being increasingly explored as a non-invasive brain stimulation technique to treat symptoms in Parkinson's disease (PD). To date, behavioral GVS effects in PD have been explored with only two stimulus types, direct current and random noise (RN). The interaction between GVS effects and anti-parkinsonian medication is unknown. In the present study, we designed multisine (ms) stimuli and investigated the effects of ms and RN GVS on motor response time. In comparison to the RN stimulus, the ms stimuli contained sinusoidal components only at a set of desired frequencies and the phases were optimized to improve participants' comfort. We hypothesized GVS motor effects were a function of stimulation frequency, and specifically, that band-limited ms-GVS would result in better motor performance than conventionally used broadband RN-GVS.Materials and Methods: Eighteen PD patients (PDMOFF/PDMON: off-/on-levodopa medication) and 20 healthy controls (HC) performed a simple reaction time task while receiving sub-threshold GVS. Each participant underwent nine stimulation conditions: off-stimulation, RN (4–200 Hz), ms-θ (4–8 Hz), ms-α (8–13 Hz), ms-β (13–30 Hz), ms-γ (30–50 Hz), ms-h1 (50–100 Hz), ms-h2 (100–150 Hz), and ms-h3 (150–200 Hz).Results: The ms-γ resulted in shorter response time (RPT) in both PDMOFF and HC groups compared with the RN. In addition, the RPT of the PDMOFF group decreased during the ms-β while the RPT of the HC group decreased during the ms-α, ms-h1, ms-h2, and ms-h3. There was considerable inter-subject variability in the optimum stimulus type, although the frequency range tended to fall within 8–100 Hz. Levodopa medication significantly reduced the baseline RPT of the PD patients. In contrast to the off-medication state, GVS did not significantly change RPT of the PD patients in the on-medication state.Conclusions: Using band-limited ms-GVS, we demonstrated that the GVS frequency for the best RPT varied considerably across participants and was >30 Hz for half of the PDMOFF patients. Moreover, dopaminergic medication was found to influence GVS effects in PD patients. Our results indicate the common “one-size-fits-all” RN approach is suboptimal for PD, and therefore personalized stimuli aiming to address this variability is warranted to improve GVS effects.

Galvanic Vestibular Stimulation effects on LSTM-based EEG neuro-markers of Motor Vigor in Parkinson's Disease

Galvanic Vestibular Stimulation effects on LSTM-based EEG neuro-markers of Motor Vigor in Parkinson's Disease

Effects of Galvanic Vestibular Stimulation on Vestibular Compensation in Unilaterally Labyrinthectomized Mice.

Objectives: To investigate the ameliorating effects of sinusoidal galvanic vestibular stimulation (GVS) on vestibular compensation from unilateral vestibular deafferentation (UVD) using a mouse model of unilateral labyrinthectomy (UL).Methods: Sixteen male C57BL/6 mice were allocated into two groups that comprise UL groups with GVS (GVS group, n = 9) and without GVS intervention (non-GVS group, n = 7). In the experimental groups, we assessed vestibulo-ocular reflex (VOR) recovery before (baseline) and at 3, 7, and 14 days after surgical unilateral labyrinthectomy. In the GVS group, stimulation was applied for 30 min daily from postoperative days (PODs) 0–4 via electrodes inserted subcutaneously next to both bony labyrinths.Results: Locomotion and VOR were significantly impaired in the non-GVS group compared to baseline. The mean VOR gain of the non-GVS group was attenuated to 0.23 at POD 3 and recovered continuously to the value of 0.54 at POD 14, but did not reach the baseline values at any frequency. GVS intervention significantly accelerated recovery of locomotion, as assessed by the amount of circling and total path length in the open field tasks compared to the non-GVS groups on PODs 3 (p < 0.001 in both amount of circling and total path length) and 7 (p < 0.01 in amount of circling and p < 0.001 in total path length, Mann–Whitney U-test). GVS also significantly improved VOR gain compared to the non-GVS groups at PODs 3 (p < 0.001), 7 (p < 0.001), and 14 (p < 0.001, independent t-tests) during sinusoidal rotations. In addition, the recovery of the phase responses and asymmetry of the VOR was significantly better in the GVS group than in the non-GVS group until 2 weeks after UVD (phase, p = 0.001; symmetry, p < 0.001 at POD 14).Conclusion: Recoveries for UVD-induced locomotion and VOR deficits were accelerated by an early intervention with GVS, which implies that GVS has the potential to improve vestibular compensation in patients with acute unilateral vestibular failure.

Against the leans: Overcoming spatial disorientation through galvanic vestibular stimulation

Leans illusion is a type of Spatial Disorientation (SD) that pilots often experience which can adversely affect flight performance. For pilots’ flight safety, research on how to effectively overcome SD such as leans illusion is important. The purpose of this study is to identify the overcoming effect of Galvanic Vestibular Stimulation (GVS) technology on leans illusion. Twenty-one Air Force pilots participated in a flight simulation experiment where leans illusion was induced through a specialized SD simulator. In the with-GVS condition, GVS was given during the roll-out phase. Data was analyzed using roll angle error and subjective SD scales by two conditions (with-GVS, without-GVS). Results showed that both the roll angle error and the subjective SD scale scores were found to be lower in the with-GVS condition than in the without-GVS condition. This study suggests that the use of GVS technology can potentially contribute in overcoming leans illusion.

Inhibitory function and sustained attention following galvanic vestibular stimulation in children with attention-deficit/hyperactivity disorder

Background and Aim: In recent years, galvanic vestibular stimulation (GVS) has been used as an effective method in rehabilitation and treat­ment of psychological disorders in children and adults. This study was designed to evaluate the effect of GVS on response inhibition and susta­ined attention in children with attention-deficit/ hyperactivity disorder (ADHD). Methods: Seventeen children with ADHD, within the age range of 9−12 years, participated in this study. All participants were exposed to the go/no-go task. The behavioral outcomes and event-related potentials were recorded at baseline status, in sham condition, and after 20 minutes of exposure to GVS polarities, with an anode on the right mastoid region and a cathode on the left mastoid region. Results: The results showed that there was a sig­nificant difference in reducing the behavioral response of the commission error (p &lt; 0.05). But the reduction in behavioral responses to omission error and reaction time were not significant (p &gt; 0.05). However, regarding ERPs, reduced latencies and increased amplitudes of N2 and P3 waves were observed in GVS intervention, com­pared to the baseline and sham conditions (p &lt; 0.05). Conclusion: The present results indicated the potential of GVS in improving of cognition func­tion in children with ADHD and could help us develop a new strategy for rehabilitation of res­ponse inhibition disorders in the future. Keywords: Galvanic vestibular stimulation; attention-deficit/hyperactivity disorder; go/no-go task; event-related potentials; motor control

Galvanic Vestibular Stimulation Improves Subnetwork Interactions in Parkinson's Disease.

Background Activating vestibular afferents via galvanic vestibular stimulation (GVS) has been recently shown to have a number of complex motor effects in Parkinson's disease (PD), but the basis of these improvements is unclear. The evaluation of network-level connectivity changes may provide us with greater insights into the mechanisms of GVS efficacy. Objective To test the effects of different GVS stimuli on brain subnetwork interactions in both health control (HC) and PD groups using fMRI. Methods FMRI data were collected for all participants at baseline (resting state) and under noisy, 1 Hz sinusoidal, and 70-200 Hz multisine GVS. All stimuli were given below sensory threshold, blinding subjects to stimulation. The subnetworks of 15 healthy controls and 27 PD subjects (on medication) were identified in their native space, and their subnetwork interactions were estimated by nonnegative canonical correlation analysis. We then determined if the inferred subnetwork interaction changes were affected by disease and stimulus type and if the stimulus-dependent GVS effects were influenced by demographic features. Results At baseline, interactions with the visual-cerebellar network were significantly decreased in the PD group. Sinusoidal and multisine GVS improved (i.e., made values approaching those seen in HC) subnetwork interactions more effectively than noisy GVS stimuli overall. Worsening disease severity, apathy, depression, impaired cognitive function, and increasing age all limited the beneficial effects of GVS. Conclusions Vestibular stimulation has widespread system-level brain influences and can improve subnetwork interactions in PD in a stimulus-dependent manner, with the magnitude of such effects associating with demographics and disease status.

Posture influences on vestibulospinal tract excitability

The human vestibulospinal tract has important roles in postural control, but it has been unknown whether vestibulospinal tract excitability is influenced by the body's postures. We investigated whether postures influence the vestibulospinal tract excitability by a neurophysiological method, i.e., applying galvanic vestibular stimulation (GVS) 100ms before tibial nerve stimulation evoking the soleus H-reflex. GVS is a percutaneous stimulation, and it has not been clarified how the cutaneous input from GVS influences the facilitation effect of cathodal GVS on the soleus H-reflex amplitude. In Experiment 1, we evaluated the effects of GVS on the soleus H-reflex amplitude of subjects in the prone, supine, and sitting positions in random order to clarify the differences in the GVS effects among these postures. In Experiment 2, to determine whether the effects of GVS in the supine and sitting positions are due solely to cutaneous input from GVS, we provided GVS and cutaneous stimulations as conditioning stimuli and compared the effects in both postures. Interaction effects between postures and stimulus conditions were observed in both experiments. The facilitation rate of the maximum H-reflex amplitude by GVS in the sitting position was significantly higher than those in the prone and supine positions (Experiment 1). The facilitation rate of GVS was significantly larger than the cutaneous stimulation only in the sitting position (Experiment 2). These results indicate that vestibulospinal tract excitability may be higher in the sitting position than in either lying position (prone and supine), due mainly to the increased need for postural control.

Effect of galvanic vestibular stimulation on arterial pressure dynamics during static and dynamic postural change

Effect of galvanic vestibular stimulation on arterial pressure dynamics during static and dynamic postural change