Influence of the intensity of galvanic vestibular stimulation and cutaneous stimulation on the soleus H-reflex in healthy individuals

Abstract

Modulation of the soleus H-reflex following galvanic vestibular stimulation (GVS) has been used to evaluate vestibulospinal tract function. It is not known whether this modulation is because of vestibular stimulation and/or cutaneous stimulation, and the suitable stimulating intensity of GVS for the modulation is not established. We investigated the influence of GVS intensity and cutaneous stimulation on the soleus H-reflex in healthy adults. We applied cathodal GVS (at 1, 2, and 3 mA) or 3-mA cutaneous stimulation as a conditioning stimulation in a random order to 17 individuals in the prone position with the head facing forward, and we examined the changes in the right soleus H-reflex amplitude. We maintained the interval between the conditioning stimulation's onset and the tibial nerve stimulation evoking the soleus H-reflex constant at 100 ms. The amplitude of all conditioned H-reflexes was significantly larger than that of the unconditioned H-reflexes. The greatest facilitation of the H-reflex occurred when 3-mA GVS was applied. The degree of facilitation of the H-reflex by 3-mA GVS was significantly larger than that produced by the 3-mA cutaneous stimulation. These findings indicate that (a) the facilitation of the soleus motor neuron pool excitability by GVS is derived from both vestibular stimulation and cutaneous stimulation, and (b) the intensity of GVS affects the degree of facilitation. When this technique is used to examine vestibulospinal tract function, no less than 3 mA GVS may be appropriate as the conditioning stimulation.

Assessment of vestibulocortical interactions during standing in healthy subjects

“…Others have observed modulation of H-reflex by GVS at latencies similar to those tested here [35,[62][63][64][65] using a large number of stimuli during prone, sitting or standing positions. In the current protocol, only 10 stimuli were applied to facilitate or inhibit corticospinal pathways.…”

The Effects of Stochastic Galvanic Vestibular Stimulation on Body Sway and Muscle Activity

“…Baseline measurements without nGVS were conducted for 30 min before the nGVS condition was applied in both real and sham trials, meaning baseline measurements were conducted both days. Further, before baseline measurements were acquired, we confirmed that a 3 mA square wave pulse (GVS) (Okada et al, 2018), administered for 200 ms (Matsugi et al, 2017), prompted the body to sway to the anodal side when participants stood with their eyes closed, feet together, and head facing forward (Fitzpatrick and Day, 2004;Matsugi et al, 2017). This was done to test whether they were responders to GVS.…”

“…Square-wave pulse GVS induces muscle contractions (Fitzpatrick et al, 1994;Ali et al, 2003) and modulates spinal motoneuron pool excitability (Matsugi et al, 2017(Matsugi et al, , 2020Okada et al, 2018). Therefore, nGVS may increase muscle activity for postural control.…”

Cerebellar Repetitive Transcranial Magnetic Stimulation and Noisy Galvanic Vestibular Stimulation Change Vestibulospinal Function

“…A bipolar binaural square-wave pulse GVS was delivered via Ag/AgCl surface electrodes affixed to the mastoid processes (Britton et al, 1993;Fitzpatrick et al, 1994;Welgampola and Colebatch, 2001;Ghanim et al, 2009;Lowrey and Bent, 2009;) (right, cathode; left, anode; Figure 4). The GVS consisted of a 200-ms square-wave pulse that was delivered using an electrical isolator (SS-104J, Nihon Kohden, Japan) driven by a stimulator (SEN-3301, Nihon Kohden, Japan); the intensity was set at 3 mA (Fitzpatrick and Day, 2004;Okada et al, 2018).…”

“…Changes in the activities of muscles that maintain postural control can be measured by electromyography (EMG) and the Hoffman reflex (H-reflex) (Iles and Pisini, 1992;Britton et al, 1993;Ali et al, 2003;Matsugi, 2019), which reflect the excitability of the spinal motoneuron pool (Knikou, 2008). Applied to an individual in a static position unaffected by natural body sway, change in the range of joints, or background EMG activity, sqGVS modulates the excitability of the H-reflex in the soleus muscle (Kennedy and Inglis, 2001;Ghanim et al, 2009;Lowrey and Bent, 2009;Okada et al, 2018). These observations indicate that the H-reflex-modulation induced by sqGVS reflects changes in the excitability of the vestibulospinal response.…”