What Does Galvanic Vestibular Stimulation Actually Activate: Response

et al., 2012). The sense of roll is consistent with a host of other studies using GVS (Fitzpatrick et al., 1994; Inglis et al., 1995; Day et al., 1997; Zink et al., 1997; Day and Cole, 2002; Scinicariello et al., 2002/2003; Wardman et al., 2003a,b; see Fitzpatrick and Day, 2004 for review). Modeled on this research, we used 2–3 mA currents in lightly anesthetized rats and found strong activation of the sympathetic nervous system and vasovagal responses, but not tonic deviations of the eyes (Cohen et al., 2011). We have also stimulated the vestibular nerve with trains of pulses to activate MSNA in humans (Voustianiouk et al., 2006), sometimes utilizing currents of 5 mA. MSNA was facilitated, but ocular deviations were never induced. The semicircular canals can exert a powerful influence on eye movements through the vestibulo-ocular reflex. Head turns induce eye movements with velocities of up to 400°/s (Atkin and Bender, 1968), and with response characteristics up to 20 Hz (Grossman et al., 1988; Tabak and Collewijn, 1994; Armand and Minor, 2001). Furthermore, a change in body temperature of only 7°C during caloric stimulation with either air or water readily induces nystagmus with slow phase velocities of 30–40°/s in monkeys (Arai et al., 2002) and 10–20°/s in humans (M. Dai, personal communication). Thus, at best, the semicircular canal activation induced using strong GVS by Curthoys and MacDougall, which produced average slow phase eye velocities of 5°/s, was weak and functionally inconsequential. The question of function is particularly relevant in this regard. The semicircular canals stabilize gaze in space during head What does galvanic vestibular stimulation actually activate: response