Postural electromyographic responses in the arm and leg following galvanic vestibular stimulation in man

Abstract

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 degrees 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 +/- 5.2 ms) 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.(ABSTRACT TRUNCATED AT 250 WORDS)

The medium latency muscle response to a vestibular perturbation is increased after depression of the cerebellar vermis

“…GVS alters the firing of the peripheral vestibular afferents and elicits the sensation of imbalance, which consequently evokes a postural sway response (Britton et al., 1993; Coats & Stoltz, 1969; Fitzpatrick, Burke, & Gandevia, 1994; Lund & Broberg, 1983). GVS also produces a well‐documented reflex response in the muscles that are used to maintain balance.…”

“…GVS also produces a well‐documented reflex response in the muscles that are used to maintain balance. The typical response is observed in the soleus muscle as a biphasic modulation comprised of two distinct parts, a short latency (SL; 40–70 ms after stimulus onset) response and a medium latency (ML; 70–140 ms) response (Britton et al., 1993). …”

“…The ML response has been shown to be related to the postural sway (Britton et al., 1993; Fitzpatrick et al., 1994) and can be modulated by sensory input such as vision and somatosensory feedback (Britton et al., 1993; Lund & Broberg, 1983; Muise, Lam, & Bent, 2012; Welgampola & Colebatch, 2001). Welgampola and Colebatch (2001) found a decrease in the magnitude of the ML response when they provided vision or enabled the use of additional somatosensory feedback (touch).…”

“…In contrast, the function of the SL is not as fully understood. One group of researchers has shown the response magnitude could be decreased by additional sensory input (Welgampola & Colebatch, 2001), however, the majority agree that the SL response remains unchanged across conditions of increased or decreased sensory contribution (Britton et al., 1993; Fitzpatrick et al., 1994; Muise et al., 2012). …”

“…There has been much discussion around the nature of the SL and ML responses, including the specific origin of the responses (e.g., semicircular canals or otolith organs); whether they have a common descending pathway (e.g., vestibulospinal or reticulospinal tract) and if the responses are modulated by other cortical structures (Britton et al., 1993; Cathers, Day, & Fitzpatrick, 2005; Fitzpatrick et al., 1994; Mian, Dakin, Blouin, Fitzpatrick, & Day, 2010). Based on the latency of the ML response, and its ability to be modified by sensory input, it has been hypothesized that this vestibular reflex response could be modulated by the cerebellum (Cathers et al., 2005), a structure where sensory input converges for comparison and integration (Apps & Garwicz, 2005; Chadderton, Schaefer, Williams, & Margrie, 2014; Wiestler, McGonigle, & Diedrichsen, 2011).…”