EMG responses in the soleus muscles evoked by unipolar galvanic vestibular stimulation (original) (raw)
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EMG responses evoked by the termination of galvanic (DC) vestibular stimulation: ‘off-responses’
Clinical Neurophysiology, 2003
Objective: Vestibular responses in soleus electromyography (EMG) evoked by the sudden onset of galvanic (DC) stimulation ('on-responses') have been described in detail previously. The aim of the present study was to describe responses in soleus triggered by the termination of galvanic stimulation ('off-responses'). Methods: In 10 healthy human subjects, we studied responses to transmastoid (bilateral) stimuli of 200 ms and 2 s average duration and 3 or 4 mA intensity. We obtained both on-and off-responses using the same raw data. EMG activity was recorded onto tape while current pulses of systematically varying duration were delivered. Averaged on-responses were obtained by triggering from the beginning of the current pulses. Averaged off-responses were obtained by triggering from the termination of the current pulses. Results: Short-latency (SL) and medium latency (ML) off-responses were both obtained in all but one study. The SL and the ML components of the off-responses were present and had similar latencies and amplitudes, but opposite excitability, to the on-responses obtained with the same stimuli. Conclusions: Off-responses to galvanic vestibular stimulation can be recorded from soleus EMG. Our findings imply that vestibular SL and ML reflex responses in the legs are dependent on the change in the rate of vestibular nerve discharge, not its absolute level. Both on-and off-responses have properties appropriate to a role in maintaining body stability.
Experimental Brain Research, 1998
The aim of this study was to demonstrate, if possible, vestibulospinal reflex responses in soleus using a stimulus known to be capable of exciting vestibular afferents, namely 100-dB (NHL) clicks. We were able to show short-latency electromyographic (EMG) responses after clicks in five of eight normal subjects, and then we compared these responses with those after transmastoid galvanic stimulation (12 normal subjects). Stimulation of the side towards which the head was rotated (i.e. the side facing backwards) with either clicks or the cathode (anode applied to the opposite side) gave an initial excitatory response in soleus, while click or cathodal stimulation of the opposite side (i.e. the side facing forwards) gave an initial inhibitory response. Onset latencies and modulation with changes in postural task were identical for both click-and galvanic-evoked responses. In addition, there was a significant correlation between the amplitudes of the responses in soleus after click and galvanic stimulation (R 2 =0.72). These similarities suggest that the earliest reflex responses in soleus after clicks and galvanic stimulation may be mediated by a common central pathway. In contrast, there was no correlation between the amplitudes of responses evoked by 100-dB clicks in soleus and those evoked by the same stimulus in the sternocleidomastoid. We conclude that vestibular activation by clicks can evoke reflex responses in lower-limb muscles and these responses have similar characteristics to the earliest responses evoked by galvanic vestibular stimulation.
Experimental Brain Research, 1993
Application of a small (around 1 mA), constant electric current between the mastoid processes (galvanic stimulation) of a standing subject produces enhanced body sway in the approximate direction of the ear behind which the anode is placed. We examined the electromyographic (EMG) responses evoked by such stimulation in the soleus and in the triceps brachii muscles. For soleus, subjects stood erect, with their eyes closed, leaning slightly forward. The head was turned approximately 90° to the right or left relative to the feet. In averaged records (n=40), current pulses of 25 ms or longer modulated the EMG in a biphasic manner: a small early component (latency 62±2.4 ms, mean ± SEM) was followed by a larger late component (latency 115±5.2ms) of opposite sign, which was appropriate to produce the observed body sway. The early component produced no measurable body movement. Lengthening the duration of the stimulus pulse from 25 to 400 ms prolonged the late component of the response but had little effect on the early component. Short- and long-latency EMG responses were also evoked in the triceps brachii muscle if subjects stood on a transversely pivoted platform and had to use the muscle to maintain their balance in the anteroposterior plane by holding a fixed handle placed by the side of their hip. The latency of the early component was 41±2.6 ms; the latency of the late component was 138±4.3 ms and was again of appropriate sign for producing the observed body sway. Galvanic stimulation evoked no comparable responses in either triceps brachii or soleus muscles if these muscles were not being used posturally. The responses were most prominent if vestibular input provided the dominant source of information about postural stability, and were much smaller if subjects lightly touched a fixed support or opened their eyes. The difference in latency between the onset of the early component of the response in arm and leg muscles suggests that this part of the response uses a descending pathway which conducts impulses down the spinal cord with a velocity comparable with that of the fast conducting component of the corticospinal tract. The late component of the EMG response occurs earlier in the leg than the arm. We suggest that it forms part of a patterned, functional response which is computed independently of the early component.
Motor Control, 2013
The integration of vestibular and somatosensory information for the control of lower limb musculature remains elusive. To determine whether a subthreshold vestibular input influences the cutaneous evoked response, the isometric EMG activity in the posturally inactive soleus muscles of 13 healthy, seated subjects was collected. Vestibular afferents were activated using galvanic vestibular stimulation (GVS; 1.8–2.5mA, 500ms), while percutaneous electrical stimulation was delivered to the distal tibial nerve (11ms train of 3 × 1.0 ms pulses, 200Hz) to activate foot sole skin afferents. GVS elicited responses in soleus both independently and when combined with cutaneous stimulation. The responses to the combined sensory input showed an interaction between the two sensory modalities to influence muscle activation. Of note is the presence of significant muscle modulation in the combined condition, where subthreshold vestibular inputs altered the outcome of the cutaneous reflex response. T...
Brain Injury, 2011
Objective: Galvanic vestibular stimulation (GVS) induces polarity-specific activations in the vestibular nerves and upstream in the vestibular and parietotemporal cortices as well as sub-cortical regions. This makes it an attractive technique for cognitive neuromodulation. However, systematic studies regarding adverse effects of GVS are unavailable. Thus, this study assessed adverse effects during and after sub-sensory GVS (mean: 0.6 mA) and GVS with 1.5 mA. Methods: Two hundred and fifty-five GVS sessions delivered to 55 persons with stroke and 30 healthy individuals were analysed using a 34-item-questionnaire including potential symptoms and rating scales for adverse effects. Results: The most frequent symptoms during and after GVS were slight itching (mean: 10.2%) and tingling (mean: 10.7%) underneath the electrodes. Healthy individuals and persons with stroke did not differ in their incidence and rated intensity of adverse effects, nor did persons with or without unilateral spatial neglect. Adverse effects were found more frequently with GVS with 1.5 mA as with sub-sensory GVS. Participants were unable to differentiate real from sham conditions during sub-sensory GVS. Importantly, neither seizures nor vertigo or nausea were observed. Conclusion: Sub-sensory GVS and GVS with 1.5 mA induce very few and mild adverse effects in healthy and persons with stroke and are safe when safety guidelines are followed.
Galvanic and acoustic vestibular stimulation activate different populations of vestibular afferents
Clinical Neurophysiology, 2003
Objective: To deduce whether similar or distinct populations of vestibular afferents are activated by acoustic and galvanic vestibular stimulation by comparing the effectiveness of 'matched' stimuli in eliciting vestibulospinal reflexes. Methods: Twelve subjects (5 men, 7 women) underwent individual 'matching' of 2 ms tone burst and galvanic stimuli, using vestibulocollic reflexes so that corrected reflex amplitudes to tone burst and galvanic stimuli were within 10% of each other. These same intensities were then administered using 20 ms durations to determine whether they were equally effective in evoking vestibulospinal responses. Results: Corrected reflex amplitudes for vestibulocollic responses to tone burst and galvanic stimulation were not significantly different for the right (P ¼ 0:45) or left (P ¼ 0:68) sides. All subjects had vestibulospinal responses to galvanic stimulation (average intensity 4.0 mA for both sides). The short latency (SL) and medium latency (ML) components of the vestibulospinal reflexes were larger after galvanic compared to tone burst stimulation in 11 of 12 subjects (P , 0:01). Conclusions: Despite evoking equal-sized vestibulocollic reflexes, there was a clear dissociation between the magnitude of tone burst and galvanic-induced vestibulospinal reflexes. Galvanic stimulation evoked SL and ML reflexes in all subjects. Tone burst stimuli evoked only small SL reflexes and, in most cases, no ML reflexes. Acoustically-evoked vestibulocollic reflexes are likely to be due to saccular excitation. The limited effectiveness of longer tone burst stimuli to evoke ML vestibulospinal reflexes suggests that saccular afferents have, at most, only a minor role in the production of these reflexes. We conclude that galvanic stimulation is more effective in eliciting vestibulospinal reflexes than tone burst stimulation, and that the two methods activate different populations of vestibular afferents.
Hearing research, 2018
In an attempt to view the effects of the efferent vestibular system (EVS) on peripheral dynamic vestibular function, we have monitored the Vestibular short-latency Evoked Potential (VsEP) evoked by pulses of bone conducted vibration during electrical stimulation of the EVS neurons near the floor of the fourth ventricle in the brainstem of anesthetized guinea pigs. Given the reported effects of EVS on primary afferent activity, we hypothesized that EVS stimulation would cause a slight reduction in the VsEP amplitude. Our results show a substantial (>50%) suppression of the VsEP, occurring immediately after a single EVS current pulse. The effect could not be blocked by cholinergic drugs which have been shown to block efferent-mediated vestibular effects. Shocks produced a short-latency P1-N1 response immediately after the electrical artifact which correlated closely to the VsEP suppression. Ultimately, we have identified that this suppression results from antidromic blockade of the...
Somatosensory influence on postural response to galvanic vestibular stimulation
We investigated how postural responses to galvanic vestibular stimulation were affected by standing on a translating support surface and by somatosensory loss due to diabetic neuropathy. We tested the hypothesis that an unstable surface and somatosensory loss can result in an increase of vestibulospinal sensitivity. Bipolar galvanic vestibular stimulation was applied to subjects who were standing on a force platform, either on a hard, stationary surface or during a backward platform translation (9 cm, 4.2 cm/s). The intensity of the galvanic stimulus was varied from 0.25 to 1mA. The amplitude of the peak body CoP displacement in response to the galvanic stimulus was plotted as a function of stimulus intensity for each individual. A larger increase in CoP displacement to a given increase in galvanic current was interpreted as an increase of vestibulospinal sensitivity. Subjects with somatosensory loss in the feet due to diabetes showed higher vestibulospinal sensitivity than healthy subjects when tested on a stationary support surface. Control subjects and patients with somatosensory loss standing on translating surface also showed increased galvanic response gains compared to stance on a stationary surface. The severity of the somatosensory loss in the feet correlated with the increased postural sensitivity to galvanic vestibular stimulation. These results showed that postural responses to galvanic vestibular stimulus were modified by somatosensory information from the surface. Somatosensory loss due to diabetic neuropathy and alteration of somatosensory input during stance on translating support surface resulted in increased vestibulospinal sensitivity.