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Vaughan G Macefield - One of the best experts on this subject based on the ideXlab platform.
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Vestibular modulation of muscle sympathetic nerve activity assessed over a 100 fold frequency range of sinusoidal Galvanic Vestibular Stimulation
Journal of Neurophysiology, 2019Co-Authors: Natasha Singh, Elie Hammam, Vaughan G MacefieldAbstract:Vestibulosympathetic reflexes have been documented in experimental animals and humans. Here we show that sinusoidal Galvanic Vestibular Stimulation, a means of selectively exciting Vestibular affer...
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low frequency Galvanic Vestibular Stimulation evokes two peaks of modulation in skin sympathetic nerve activity
Experimental Brain Research, 2012Co-Authors: Elie Hammam, Vaughan G Macefield, Tye DawoodAbstract:We have previously shown that sinusoidal Galvanic Vestibular Stimulation (sGVS), delivered bilaterally at 0.2–2.0 Hz, evokes a potent entrainment of sympathetic outflow to muscle and skin. Most recently, we showed that Stimulation at 0.08–0.18 Hz generates two bursts of modulation of muscle sympathetic nerve activity (MSNA), more pronounced at 0.08 Hz, which we interpreted as reflecting bilateral projections from the Vestibular nuclei to the medullary nuclei responsible for the generation of MSNA. Here, we test the hypothesis that these very low frequencies of sGVS modulate skin sympathetic nerve activity (SSNA) in a similar fashion. SSNA was recorded via tungsten microelectrodes inserted into the left common peroneal nerve in 11 awake-seated subjects. Bipolar binaural sGVS (±2 mA, 100 cycles) was applied to the mastoid processes at 0.08, 0.13 and 0.18 Hz. As with MSNA, cross-correlation analysis revealed two bursts of modulation of SSNA for each cycle of Stimulation but, unlike MSNA, this modulation was equally pronounced at all frequencies. These results further support our conclusion that bilateral sGVS causes cyclical modulation of the left and right Vestibular nerves and a resultant modulation of sympathetic outflow that reflects the summed activity of bilateral projections from the Vestibular nuclei onto, in this case, the primary output nuclei responsible for SSNA—the medullary raphe. Furthermore, these findings emphasise the role of the Vestibular system in the control of skin sympathetic outflow, and the cutaneous expression of motion sickness: pallor and sweat release. Indeed, Vestibular modulation of SSNA was higher in those subjects reporting nausea than in those who did not report nausea during this low-frequency sGVS.
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Vestibular and pulse related modulation of skin sympathetic nerve activity during sinusoidal Galvanic Vestibular Stimulation in human subjects
Experimental Brain Research, 2010Co-Authors: Cheree James, Vaughan G Macefield, Alexandra StathisAbstract:We have previously shown that sinusoidal Galvanic Vestibular Stimulation (sGVS), a means of a selectively modulating Vestibular afferent input without affecting other inputs, can cause partial entrainment of muscle sympathetic nerve activity (MSNA). Given that motion sickness causes sweating and pallor, we tested the hypothesis that sGVS also entrains skin sympathetic nerve activity (SSNA), but that the optimal frequencies are closer to those associated with slow postural changes (0.2 Hz). SSNA was recorded via tungsten microelectrodes inserted into the common peroneal nerve in 11 awake-seated subjects. Bipolar binaural sinusoidal GVS (±2 mA, 200 cycles) was applied to the mastoid processes at frequencies of 0.2, 0.5, 0.8, 1.1, 1.4, 1.7 and 2.0 Hz. All subjects reported strong postural illusions of ‘rocking in a boat’ or ‘swaying in a hammock’. Sinusoidal GVS caused a marked entrainment of SSNA at all frequencies. Measured as the modulation index, Vestibular modulation ranged from 81.5 ± 4.0% at 0.2 Hz to 76.6 ± 3.6% at 1.7 Hz; it was significantly weaker at 2.0 Hz (63.2 ± 5.4%). Interestingly, pulse-related modulation of SSNA, which is normally weak, increased significantly during sGVS but was stronger at 0.8 Hz (86.2 ± 2.0%) than at 0.2 Hz (69.3 ± 8.3%), the opposite of the pattern seen with Vestibular modulation of MSNA. We conclude that Vestibular inputs can entrain the firing of cutaneous sympathetic neurones and increase their normally weak pulse-related rhythmicity.
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frequency dependent modulation of muscle sympathetic nerve activity by sinusoidal Galvanic Vestibular Stimulation in human subjects
Experimental Brain Research, 2009Co-Authors: Tarandeep Grewal, Vaughan G Macefield, Cheree JamesAbstract:We have previously demonstrated that selective modulation of Vestibular inputs, via sinusoidal Galvanic Vestibular Stimulation (GVS) delivered at 0.5–0.8 Hz, can cause partial entrainment of muscle sympathetic nerve activity (MSNA). Given that we had seen interaction between the dynamic Vestibular input and the normal cardiac-locked MSNA rhythm, we tested the hypothesis that frequencies of GVS remote from the cardiac frequency would cause a greater modulation of MSNA than those around the cardiac frequency. Bipolar binaural sinusoidal GVS (±2 mA, 200 cycles) was applied to the mastoid processes in 11 seated subjects at frequencies of 0.2, 0.5, 0.8, 1.1, 1.4, 1.7 and 2.0 Hz. In all subjects, the Stimulation evoked robust Vestibular illusions of “rocking in a boat” or “swinging from side to side.” Cross-correlation analysis revealed a cyclic modulation of MSNA at all frequencies, with the modulation index being similar between 1.1 Hz (78.5 ± 3.7%) and 2.0 Hz (77.0 ± 4.3%). However, Vestibular modulation of MSNA was significantly stronger at 0.2 Hz (93.1 ± 1.7%) and significantly weaker at 0.8 Hz (67.2 ± 1.8%). The former suggests that low-frequency changes in Vestibular input, such as those associated with postural changes, preferentially modulate MSNA; the latter suggests that Vestibular inputs compete with the stronger baroreceptor inputs operating at the cardiac rhythm (~0.8 Hz), with Vestibular modulation of MSNA being greater when this competition with the baroreceptors is reduced.
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modulation of muscle sympathetic bursts by sinusoidal Galvanic Vestibular Stimulation in human subjects
Experimental Brain Research, 2006Co-Authors: Leah R Bent, Philip S Bolton, Vaughan G MacefieldAbstract:There is controversy as to whether the vestibulosympathetic reflexes demonstrated in experimental animals actually exist in human subjects. While head-down neck flexion and off-vertical axis rotation can increase muscle sympathetic nerve activity (MSNA) in awake subjects, we recently showed that bipolar Galvanic Vestibular Stimulation (GVS) does not. However, it is possible that our stimuli (2 mA, 1 s)-although capable of causing strong postural and occulomotor responses-were too brief. To address this issue we activated Vestibular afferents using continuous sinusoidal (0.5-0.8 Hz, 60-100 cycles, +/-2 mA) bipolar binaural GVS in 11 seated subjects. Sinusoidal GVS evoked robust Vestibular illusions of "rocking in a boat" or "swinging from side to side." Cross-correlation analysis revealed a cyclic modulation of MSNA ranging from 31 to 86% across subjects (mean +/- SE 58 +/- 5%), with total MSNA increasing by 156 +/- 19% (P = 0.001). Furthermore, we documented de novo synthesis of sympathetic bursts that were coupled to the sinusoidal input, such that two bursts-rather than the obligatory single burst-could be generated within a cardiac interval. This demonstrates that the human Vestibular apparatus exerts a potent facilitatory influence on MSNA that potentially operates independently of the baroreceptor system.
Marianne Dieterich - One of the best experts on this subject based on the ideXlab platform.
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Galvanic Vestibular Stimulation Improves Spatial Cognition After Unilateral Labyrinthectomy in Mice
'Frontiers Media SA', 2021Co-Authors: Thanh Tin Nguyen, Gi-sung Nam, Jin-ju Kang, Gyu Cheol Han, Ji-soo Kim, Marianne DieterichAbstract:Objectives: To investigate the deficits of spatial memory and navigation from unilateral Vestibular deafferentation (UVD) and to determine the efficacy of Galvanic Vestibular Stimulation (GVS) for recovery from these deficits using a mouse model of unilateral labyrinthectomy (UL).Methods: Thirty-six male C57BL/6 mice were allocated into three groups that comprise a control group and two experimental groups, UVD with (GVS group) and without GVS intervention (non-GVS group). In the experimental groups, we assessed the locomotor and cognitive behavioral function before (baseline) and 3, 7, and 14 days after surgical UL, using the open field (OF), Y maze, and Morris water maze (MWM) tests. In the GVS group, the Stimulations were applied for 30 min daily from postoperative day (POD) 0–4 via the electrodes inserted subcutaneously close to both bony labyrinths.Results: Locomotion and spatial cognition were significantly impaired in the mice with UVD non-GVS group compared to the control group. GVS significantly accelerated recovery of locomotion compared to the control and non-GVS groups on PODs 3 (p < 0.001) and 7 (p < 0.05, Kruskal–Wallis and Mann–Whitney U tests) in the OF and Y maze tests. The mice in the GVS group were better in spatial working memory assessed with spontaneous alternation performance and spatial reference memory assessed with place recognition during the Y maze test than those in the non-GVS group on POD 3 (p < 0.001). In addition, the recovery of long-term spatial navigation deficits during the MWM, as indicated by the escape latency and the probe trial, was significantly better in the GVS group than in the non-GVS group 2 weeks after UVD (p < 0.01).Conclusions: UVD impairs spatial memory, navigation, and motor coordination. GVS accelerated recoveries in short- and long-term spatial memory and navigation, as well as locomotor function in mice with UVD, and may be applied to the patients with acute unilateral Vestibular failure
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functional mri of Galvanic Vestibular Stimulation with alternating currents at different frequencies
NeuroImage, 2005Co-Authors: Thomas Stephan, Thomas Brandt, Erich Schneider, Marianne Dieterich, Angela Deutschlander, Annina Nolte, Martin WiesmannAbstract:Abstract Functional MRI was performed in 28 healthy volunteers to study the effects of Galvanic Vestibular Stimulation with alternating currents (AC-GVS) of different frequencies on brain activation patterns. The aims of this study were (1) to identify specific areas within the Vestibular cortical network that are involved in the processing of frequency-specific aspects by correlation analyses, (2) to determine the optimal frequency for Stimulation of the Vestibular system with respect to perception, and (3) to analyze whether different frequencies of AC-GVS are mediated in different cortical areas or different sites within the Vestibular cortex. AC-GVS was performed using sinusoidal Stimulation currents with an amplitude of ±2.5 mA, and frequencies of 0.1 Hz, 0.3 Hz, 0.8 Hz, 1.0 Hz, 2.0 Hz, and 5.0 Hz were applied. Regardless of the applied Stimulation frequency, AC-GVS elicited activations within a network of multisensory areas similar to those described in earlier studies using direct currents. No mapping of different Stimulation frequencies to different cortical locations was observed. Additional activations of somatosensory cortex areas were observed during Stimulation with 5 Hz only. The strongest Vestibular sensations were reported during Stimulation with 1 Hz and 2 Hz. Correlation analyses between blood oxygenation level dependent (BOLD) signal changes and Stimulation frequency revealed a positive dependency in areas of the supramarginal gyrus, posterolateral thalamus, cerebellar vermis, posterior insula, and in the hippocampal region/uncus. These regions represent areas involved in the processing of Vestibular information for head and body orientation in space.
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comparison of human ocular torsion patterns during natural and Galvanic Vestibular Stimulation
Journal of Neurophysiology, 2002Co-Authors: Erich Schneider, Stefan Glasauer, Marianne DieterichAbstract:Galvanic Vestibular Stimulation (GVS) is reported to induce interindividually variable tonic ocular torsion (OT) and superimposed torsional nystagmus. It has been proposed that the tonic component results from the activation of otolith afferents. We tested our hypothesis that both the tonic and the phasic OT are mainly due to semicircular canal (SCC) Stimulation by examining whether the OT patterns elicited by GVS can be reproduced by pure SCC Stimulations. Using videooculography we measured the OT of six healthy subjects while two different stimuli with a duration of 20 s were applied: 1 ) transmastoidal GVS steps of 2 mA with the head in a pitched nose-down position and 2 ) angular head rotations around a combined roll-yaw axis parallel to the gravity vector with the head in the same position. The Stimulation profile was individually scaled to match the nystagmus properties from GVS and consisted of a sustained velocity step of 4–12°/s on which a velocity ramp of 0.67–2°/s2 was superimposed. Since blinks were reported to induce transient torsional eye movements, the subjects were also asked to blink once 10 s after stimulus onset. Analysis of torsional eye movements under both conditions revealed no significant differences. Thus we conclude that both the tonic and the phasic OT responses to GVS can be reproduced by pure rotational Stimulations and that the OT-related effects of GVS on SCC afferents are similar to natural Stimulations at small amplitudes.
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comparison of human ocular torsion patterns during natural and Galvanic Vestibular Stimulation
Journal of Neurophysiology, 2002Co-Authors: Erich Schneider, Stefan Glasauer, Marianne DieterichAbstract:Galvanic Vestibular Stimulation (GVS) is reported to induce interindividually variable tonic ocular torsion (OT) and superimposed torsional nystagmus. It has been proposed that the tonic component ...
Martin J Mckeown - One of the best experts on this subject based on the ideXlab platform.
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Galvanic Vestibular Stimulation data analysis and applications in neurorehabilitation
IEEE Signal Processing Magazine, 2021Co-Authors: Aiping Liu, Martin J Mckeown, Soojin Lee, Xun Chen, Jane Z WangAbstract:A rapidly aging population worldwide has spurred interest in developing new strategies to cope with neural declines and neurodegenerative disorders. Noninvasive brain Stimulation (NIBS) is increasingly being used to explore functional mechanisms of the brain and induce the therapeutic modulation of behavior, cognition, and emotion. Galvanic Vestibular Stimulation (GVS), a safe and well-tolerated NIBS technique, is capable of modulating activity in various cortical and subcortical areas involved in Vestibular and multisensory processing. A key facet of GVS is that the resultant effects may, in part, be a function of the individual being treated and the stimulus waveform that is delivered. Yet, most GVS studies have utilized the same generic stimulus, chosen from a reduced repertoire of candidates, across all subjects. The future use and, ultimately, clinical adoption of this technology will rely on contributions from the signal processing community to customize stimuli that are optimized for their effect and to exert maximum influence on brain imaging biomarkers. We provide a signal processing-focused overview of the current GVS state of the art in neurorehabilitation, including general Stimulation design, concurrent analysis with neuroimaging data, and suggestions for future directions.
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Galvanic Vestibular Stimulation improves subnetwork interactions in parkinson s disease
Journal of Healthcare Engineering, 2021Co-Authors: Aiping Liu, Jane Z Wang, Soojin Lee, Jiayue Cai, Saurabh Garg, Jowon L Kim, Maria Zhu, Xun Chen, Martin J MckeownAbstract: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.
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current perspectives on Galvanic Vestibular Stimulation in the treatment of parkinson s disease
Expert Review of Neurotherapeutics, 2021Co-Authors: Soojin Lee, Aiping Liu, Martin J MckeownAbstract:Introduction: Galvanic Vestibular Stimulation (GVS) is a noninvasive technique that activates Vestibular afferents, influencing activity and oscillations in a broad network of brain regions. Several studies have suggested beneficial effects of GVS on motor symptoms in Parkinson's Disease (PD).Areas covered: A comprehensive overview of the Stimulation techniques, potential mechanisms of action, challenges, and future research directions.Expert opinion: This emerging technology is not currently a viable therapy. However, a complementary therapy that is inexpensive, easily disseminated, customizable, and portable is sufficiently enticing that continued research and development is warranted. Future work utilizing biomedical engineering approaches, including concomitant functional neuroimaging, have the potential to significantly increase efficacy. GVS could be explored for other PD symptoms including orthostatic hypotension, dyskinesia, and sleep disorders.
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Galvanic Vestibular Stimulation Effects on EEG Biomarkers of Motor Vigor in Parkinson's Disease
'Frontiers Media SA', 2021Co-Authors: Alireza Kazemi, Martin J Mckeown, Soojin Lee, Maryam S. MirianAbstract:Background: Impaired motor vigor (MV) is a critical aspect of Parkinson's disease (PD) pathophysiology. While MV is predominantly encoded in the basal ganglia, deriving (cortical) EEG measures of MV may provide valuable targets for modulation via Galvanic Vestibular Stimulation (GVS).Objective: To find EEG features predictive of MV and examine the effects of high-frequency GVS.Methods: Data were collected from 20 healthy control (HC) and 18 PD adults performing 30 trials total of a squeeze bulb task with sham or multi-sine (50–100 Hz “GVS1” or 100–150 Hz “GVS2”) stimuli. For each trial, we determined the time to reach maximum force after a “Go” signal, defined MV as the inverse of this time, and used the EEG data 1-sec prior to this time for prediction. We utilized 53 standard EEG features, including relative spectral power, harmonic parameters, and amplitude and phase of bispectrum corresponding to standard EEG bands from each of 27 EEG channels. We then used LASSO regression to select a sparse set of features to predict MV. The regression weights were examined, and separate band-specific models were developed by including only band-specific features (Delta, Theta, Alpha-low, Alpha-high, Beta, Gamma). The correlation between MV prediction and measured MV was used to assess model performance.Results: Models utilizing broadband EEG features were capable of accurately predicting MV (controls: 75%, PD: 81% of the variance). In controls, all EEG bands performed roughly equally in predicting MV, while in the PD group, the model using only beta band features did not predict MV well compared to other bands. Despite having minimal effects on the EEG feature values themselves, both GVS stimuli had significant effects on MV and profound effects on MV predictability via the EEG. With the GVS1 stimulus, beta-band activity in PD subjects became more closely associated with MV compared to the sham condition. With GVS2 stimulus, MV could no longer be accurately predicted from the EEG.Conclusions: EEG features can be a proxy for MV. However, GVS stimuli have profound effects on the relationship between EEG and MV, possibly via direct vestibulo-basal ganglia connections not measurable by the EEG
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Frequency-Specific Effects of Galvanic Vestibular Stimulation on Response-Time Performance in Parkinson's Disease
'Frontiers Media SA', 2021Co-Authors: Paul F. Smith, Martin J Mckeown, Soojin Lee, Won Hee LeeAbstract: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
Sergei B. Yakushin - One of the best experts on this subject based on the ideXlab platform.
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what does Galvanic Vestibular Stimulation actually activate
Frontiers in Neurology, 2012Co-Authors: Bernard Cohen, Sergei B. YakushinAbstract:Luigi Galvani spent 20 years conducting experiments to demonstrate electrical conductivity of nerves and muscles before publishing his major treatise on the subject in 1791 (Galvani, 1791). His personal friend and professional nemesis Count Alessandro Volta held a respectful but opposing view, that nerve and muscle tissues simply serve as passive conductors, and he built the first “voltaic” battery in an attempt to prove his point. Ultimately it appears that they were both partially correct, and the same bioelectric potentials sought by Galvani and debunked by Volta continue to be used in present day because they are an easy, non-invasive approach to activate the Vestibular nerve(s). Yet, debate continues in contemporary medicine and science regarding the exact effect of Galvanic Stimulation on the nervous system. Galvanic Vestibular Stimulation (GVS) has been used to activate fibers of the Vestibular nerve in humans and experimental animals by applying 0.1–4 mA DC currents through the skin over the mastoid processes (for reviews, see Fitzpatrick and Day, 2004; Curthoys, 2009). Steps of current are used most often, causing continuous activation of the entire Vestibular nerve, particularly those fibers with irregular spontaneous firing rates (Goldberg et al., 1984; Minor and Goldberg, 1991). This Stimulation excites a wide range of central Vestibular neurons, including those related to both the semicircular canals and the otolith organs (Wilson et al., 1979; Peterson et al., 1980; Ezure et al., 1983; Courjon et al., 1987). However, despite this non-selective activation, it appears that only otolith-related behavioral responses are induced. Human subjects experience sensations of rocking or pitching, head and/or body tilt, and have ocular torsion – all characteristics of otolith system activation (Zink et al., 1997; Watson et al., 1998; Severac Cauquil et al., 2003; Macdougall et al., 2005; Bent et al., 2006). They do not experience sensations of rotation and do not 4display ocular nystagmus, which would occur if the semicircular canals were continuously stimulated (Mach, 1875; Cohen et al., 1965; Guedry, 1974). This apparent paradox has engendered considerable controversy: does GVS primarily or exclusively activate the otolith system, or does it activate both the otolith and semicircular canal systems equivalently? The preponderance of physiological data support the view that GVS is primarily an otolithic stimulus. A variant of GVS utilizing binaurally applied sinusoidal currents (sinusoidal GVS, sGVS) was introduced by Macefield and colleagues (Bent et al., 2006; Grewal et al., 2009; James and Macefield, 2010; James et al., 2010), and has proven to be a potent technique for inducing muscle sympathetic nerve activity (MSNA) in the legs of humans. MSNA causes peripheral vasoconstriction, which maintains adequate blood supply to the brain upon standing. This orthostatic response is clearly associated with the otolith system (Yates, 1992; Woodring et al., 1997; Kerman et al., 2003). When sGVS is applied to anesthetized rats, it can also induce sudden decreases in blood pressure and heart rate that resemble human vasovagal syncope (Cohen et al., 2011). Similar sustained drops in blood pressure have been shown in alert and anesthetized rats after linear acceleration (Zhu et al., 2007). sGVS also evokes frequency-dependent postural sway in standing subjects, further supporting the idea that the stimulus primarily activates the otolith system (Lau et al., 2003). Functional anatomical studies have also contributed to the controversy regarding the neural effect(s) of GVS. These investigations have utilized GVS to induce activation of the immediate early gene c-fos, and to visualize its protein product c-Fos, which accumulates in the nuclei of activated neurons. Steps of GVS applied unilaterally to rodents result in bilateral c-Fos expression near the ventricular wall in the medial Vestibular nucleus (MVN), with muted expression in the inferior Vestibular nucleus (IVN) and no c-Fos accumulation in the superior or lateral Vestibular nuclei (SVN and LVN, respectively; Kaufman and Perachio, 1994; Marshburn et al., 1997; Abe et al., 2009). In this Frontiers Special Topic, Holstein and colleagues report that sGVS in rats results in c-Fos accumulation in some neurons in caudal IVN, in cells of the parasolitary nucleus, in neurons throughout MVN, and in cells located in a small medial wedge in caudal SVN. There were no activated neurons in the portions of the Vestibular nuclear complex (VNC) that participate directly in the horizontal and vertical vestibulo-ocular reflexes, or the vestibulo-spinal postural reflexes. These studies reflect the same apparent contradiction evident in human physiological investigations: if GVS activates the entire Vestibular nerve, why are activated neurons restricted to non-vestibulo-ocular and vestibulo-spinal regions? The most likely explanation for this discrepancy derives from a report by Courjon et al. (1987) in which a wide variety of central Vestibular neurons were activated by Galvanic Stimulation. Units that responded to rotation promptly habituated, while those units that were non-responsive to rotation, which were presumably otolith units, continued to fire in response to GVS. We propose that this canal-specific response habituation underlies the apparent inconsistency between the global Vestibular activation by GVS and the otolith-predominant neural and behavioral responses. Moreover, the c-Fos localization findings can be further interpreted in this light, since c-Fos protein is not manifest in neurons that are tonically inhibited (Chan and Sawchenko, 1994). Many Vestibular neurons that participate in vestibulo-ocular and vestibulo-spinal reflexes receive formidable direct inhibition from cerebellar Purkinje cells and/or inhibitory commissural and intra-VNC fibers (for review, see Holstein, 2011). These neurons are not likely to express c-Fos protein, even though they may initially be activated by sGVS. Further still, while neurons that receive predominantly excitatory input and some cells under conditions of release from tonic inhibition show c-Fos expression in response to appropriate stimuli, other disinhibited neurons do not express c-Fos induction (for review, see Kovacs, 2008), and c-Fos is rarely observed in large motor neurons of the brainstem (Chan and Sawchenko, 1994). As a result, vestibulo-ocular, vestibulo-spinal, and vestibulo-colic motor neurons present in subregions of the VNC should not be expected to accumulate c-Fos protein. On the basis of this analysis, we conclude that while sGVS does indeed activate the entire Vestibular nerve, only the otolith system expresses a persistent behavioral and neural response due to the habituation of the canal-related units and the attendant inhibition of Vestibular neuronal populations. It is likely that the habituation of the semicircular canal induced activity originates in the cerebellum, but this remains to be determined.
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Fos expression in neurons of the rat vestibulo-autonomic pathway activated by sinusoidal Galvanic Vestibular Stimulation
Frontiers Media S.A., 2012Co-Authors: Sergei B. Yakushin, Giorgio P. Martinelli, Gay R. Holstein, Victor L. Friedrich, Dmitri Eogorodnikov, Bernard EcohenAbstract:The Vestibular system sends projections to brainstem autonomic nuclei that modulate heart rate and blood pressure in response to changes in head and body position with regard to gravity. Consistent with this, binaural sinusoidal Galvanic Vestibular Stimulation (sGVS) in humans causes vasoconstriction in the legs, while low frequency (0.02-0.04 Hz) sGVS causes a rapid drop in heart rate and blood pressure in anesthetized rats. We have hypothesized that these responses occur through activation of vestibulo-sympathetic pathways. In the present study, c-Fos protein expression was examined in neurons of the Vestibular nuclei and rostral ventrolateral medullary region (RVLM) that were activated by low frequency sGVS. We found c-Fos-labeled neurons in the spinal, medial and superior Vestibular nuclei (SpVN, MVN and SVN, respectively) and the parasolitary nucleus. The highest density of c-Fos-positive Vestibular nuclear neurons was observed in MVN, where immunolabeled cells were present throughout the rostro-caudal extent of the nucleus. C-Fos expression was concentrated in the parvocellular region and largely absent from magnocellular MVN. C-Fos-labeled cells were scattered throughout caudal SpVN, and the immunostained neurons in SVN were restricted to a discrete wedge-shaped area immediately lateral to the IVth ventricle. Immunofluorescence localization of c-Fos and glutamate revealed that approximately one third of the c-Fos-labeled Vestibular neurons showed intense glutamate-like immunofluorescence, far in excess of the stain reflecting the metabolic pool of cytoplasmic glutamate. In the RVLM, which receives a direct projection from the Vestibular nuclei and sends efferents to preganglionic sympathetic neurons in the spinal cord, we observed an approximately 3-fold increase in c-Fos labeling in the sGVS-activated rats. We conclude that localization of c-Fos protein following sGVS is a reliable marker for sGVS-activated neurons of the vestibulo-sympathetic pathway
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Sinusoidal Galvanic Vestibular Stimulation (sGVS) induces a vasovagal response in the rat
Experimental Brain Research, 2011Co-Authors: Bernard Cohen, Yongqing Xiang, Theodore Raphan, Giorgio P. Martinelli, Dmitri Ogorodnikov, Gay R. Holstein, Sergei B. YakushinAbstract:Blood pressure (BP) and heart rate (HR) were studied in isoflurane-anesthetized Long-Evans rats during sinusoidal Galvanic Vestibular Stimulation (sGVS) and sinusoidal oscillation in pitch to characterize Vestibular influences on autonomic control of BP and HR. sGVS was delivered binaurally via Ag/AgCl needle electrodes inserted over the mastoids at stimulus frequencies 0.008–0.4 Hz. Two processes affecting BP and HR were induced by sGVS: 1) a transient drop in BP (≈15–20 mmHg) and HR (≈3 beat*s^−1), followed by a slow recovery over 1–6 min; and 2) inhibitory modulations in BP (≈4.5 mmHg/g) and HR (≈0.15 beats*s^−1/g) twice in each stimulus cycle. The BP and HR modulations were approximately in-phase with each other and were best evoked by low stimulus frequencies. A wavelet analysis indicated significant energies in BP and HR at scales related to twice and four times the stimulus frequency bands. BP and HR were also modulated by oscillation in pitch at frequencies 0.025–0.5 Hz. Sensitivities at 0.025 Hz were ≈4.5 mmHg/g (BP) and ≈0.17 beat*s^−1/g (HR) for pitches of 20–90°. The tilt-induced BP and HR modulations were out-of-phase, but the frequencies at which responses were elicited by tilt and sGVS were the same. The results show that the sGVS-induced responses, which likely originate in the otolith organs, can exert a powerful inhibitory effect on both BP and HR at low frequencies. These responses have a striking resemblance to human vasovagal responses. Thus, sGVS-activated rats can potentially serve as a useful experimental model of the vasovagal response in humans.
Ian S Curthoys - One of the best experts on this subject based on the ideXlab platform.
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what Galvanic Vestibular Stimulation actually activates
Frontiers in Neurology, 2012Co-Authors: Ian S CurthoysAbstract:In a recent paper in Frontiers Cohen et al. (2012) asked “What does Galvanic Vestibular Stimulation actually activate?” and concluded that Galvanic Vestibular Stimulation (GVS) causes predominantly otolithic behavioural responses. In this Perspective paper we show that such a conclusion does not follow from the evidence. The evidence from neurophysiology is very clear: Galvanic Stimulation activates primary otolithic neurons as well as primary semicircular canal neurons (Kim and Curthoys, 2004). Irregular neurons are activated at lower currents. The answer to what behaviour is activated depends on what is measured and how it is measured, including not just technical details, such as the frame rate of video, but the exact experimental context in which the measurement took place (visual fixation vs total darkness). Both canal and otolith dependent responses are activated by GVS.
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effects of Galvanic Vestibular Stimulation on cognitive function
Experimental Brain Research, 2012Co-Authors: Ian S CurthoysAbstract:Although imaging studies suggest activation of cortical areas by Vestibular input, there is little evidence of an adverse effect of non-veridical Vestibular input on cognitive function. To test the hypothesis that degraded Vestibular afferent input adversely affects cognition, we compared performance on a cognitive test battery in a group undergoing suprathreshold bilateral bipolar Galvanic Vestibular Stimulation (GVS) with a control group receiving no GVS or subthreshold Stimulation. The battery consisted of six cognitive tests as follows: reaction time, dual tasking, Stroop, mental rotation, perspective-taking and matching-to-sample, as well as a simple visuomotor (manual tracking) task. Subjects performed the test battery before, during and after suprathreshold GVS exposure or subthreshold Stimulation. Suprathreshold GVS significantly increased error rate for the match-to-sample and perspective-taking tasks relative to the subthreshold group, demonstrating a negative effect of non-veridical Vestibular input in these specific cognitive tasks. Reaction time, dual tasking, mental rotation and manual tracking were unaffected by GVS exposure. The adverse effect of suprathreshold GVS on perspective taking but not mental rotation is consistent with imaging studies, which have demonstrated that egocentric mental transformations (perspective taking) occur primarily in cortical areas that receive Vestibular input (the parietal–temporal junction and superior parietal lobule), whereas object-based transformations (mental rotation) occur in the frontoparietal region. The increased error rate during the match-to-sample task is likely due to interference with hippocampal processing related to spatial memory, as suggested by imaging studies on Vestibular patients.
