Short-duration galvanic vestibular stimulation evokes prolonged balance responses

Abstract

Lee Son GM, Blouin J-S, Inglis JT. Short-duration galvanic vestibular stimulation evokes prolonged balance responses. J Appl Physiol 105: 1210 -1217, 2008. First published July 31, 2008 doi:10.1152/japplphysiol.01398.2006.-The application of galvanic vestibular stimulation (GVS) evokes distinct responses in lower limb muscles involved in the control of balance. The purpose of this study was to investigate the balance and lower limb muscle responses to short-duration GVS and to determine whether these responses are modulated by small changes in center of gravity (CoG) and baseline muscle activity occurring during quiet standing. Twelve subjects stood quietly on a force plate with their feet together and were instructed to look straight ahead. One thousand twenty-four GVS stimuli (4 mA, 20-ms pulses) were delivered bilaterally to the mastoid processes in a bipolar, binaural configuration. Bilateral surface electromyography (EMG) from soleus (Sol) and tibialis anterior (TA) and ground reaction forces were recorded. EMG and force responses were trigger averaged at the onset of the GVS pulse. Short-duration GVS applied during quiet standing with the head facing forward evoked characteristic balance responses and biphasic modulation of all muscles with the same polarity for ipsilateral Sol and TA. The amplitude of the GVS-evoked muscle responses was modulated by both the estimated position of the subject's CoG and the background activation of the recorded muscle. Muscle-dependent modulations of the GVSevoked muscle responses were observed: the Sol responses decreased, while the TA responses increased when the CoG position shifted toward the heels. The well-defined balance responses evoked by short-duration GVS are important to acknowledge when studying the vestibulo-motor responses in healthy subjects and patient populations.vestibulo-motor responses; electromyography; center of pressure THE CONTRIBUTIONS OF VESTIBULAR information in the control of human balance are still being debated. Visual and somatosensory inputs provide the dominant sources of afferent information during stance, while the vestibular system is thought to have a less important role (30). Galvanic vestibular stimulation (GVS), a technique used to probe the vestibular system, has gained attention from researchers studying human balance (5, 6, 8, 9, 14, 15, 26, 29, 36, 37; for review see Ref. 11). GVS alters the firing rates of all vestibular afferents with a preference toward the irregular afferents (12), such that the anode decreases and the cathode increases afferent firing rates (13). In standing humans, binaural, bipolar GVS applied for a long duration (1-2 s) elicits a well-defined biphasic muscle response (4, 9) and a multiphasic center of pressure (CoP) response often identified by lateral sway and tilt toward the side of the anode (8, 21, 28). Short-duration GVS (20 -50 ms) have also been used to evoke vestibulomotor responses in lower and upper limb muscles engaged in balance (4, 40). Such stimuli have been thought to evoke motor respons...

Reduced input from foot sole skin through cooling differentially modulates the short latency and medium latency vestibular reflex responses to galvanic vestibular stimulation

“…Fortunately, there was no significant difference in the level of background EMG between control and iced conditions despite the small increase in CoP deviations that were observed. This further supports our conclusions that the increase in the size of the ML response after icing is related to the decreased skin sensitivity rather than fluctuations in prestimulus EMG (Son et al 2008).…”

“…1; and see Welgampola and Colebatch 2001). To ensure differences between control and ice conditions were not due to background EMG levels (Son et al 2008), pre-stimulus EMG levels were compared between conditions. This was assessed by calculating the area beneath the rectified and smoothed EMG, prior to zeroing the data, in the 50 ms preceding the GVS stimulus onset.…”

Why do oVEMPs become larger when you look up? Explaining the effect of gaze elevation on the ocular vestibular evoked myogenic potential

“…This mechanism causes the size of a reflex to remain constant relative to different levels of muscle activity, and is thought to be due to a change in the population of muscle units being available to change their firing rate in response to an external stimulus. This property is shared by other short-latency vestibular reflexes such as the cervical VEMP and vestibulo-spinal reflexes (Colebatch et al, 1994;Lim et al, 1995;Lee Son et al, 2008) and was earlier described for other proprioceptive reflexes, such as the stretch and H-reflexes (Capaday and Stein, 1987;Gottlieb and Agarwal, 1971;Matthews, 1986). Scaling with background contraction can be expected to occur whenever there is a consistent reflex effect on the motoneuron pool causing frequency modulation of discharge rate (Matthews, 1986).…”

The effect of fear of falling on vestibular feedback control of balance

“…; Son et al. ). These latencies are longer than expected for the presence of direct vestibulospinal connections and are consistent with the additional processes of postural gating and coordinate transformation associated with appendicular balance responses (Fitzpatrick and Day ).…”