Vestibulo-Ocular Reflex Is Modulated by Noisy Galvanic Vestibular Stimulation

Abstract

We investigated whether noisy galvanic vestibular stimulation (nGVS) modulates the vestibulo-ocular reflex (VOR) and whether this effect is correlated with the effect of nGVS on body sway. Thirty healthy young adults participated. The video head impulse test (vHIT) was used to estimate the ratio of eye motion velocity/head motion velocity to VOR-gain. The gain 60 ms after the start of head motion (VOR-gain-60 ms) and regression slope (RS) (i.e., gain in eye and head motion; VOR-gain-RS) were calculated. The total path length of the foot center of pressure (COP-TL) during upright standing was calculated to estimate body sway. Noisy Galvanic Vestibular Stimulation at 0.2, 0.6, 1.2 mA, or sham stimulation (direct current: 0 mA) was delivered to the bilateral mastoid process in random order during vHIT and COP measurements. Application of nGVS at 0.2 mA significantly reduced VOR-gain-RS, while application of nGVS at 0.6 mA significantly increased COP-TL. Vestibulo-ocular reflex-gain-60 ms differed significantly between 0.2 and 1.2 mA. There was no significant correlation between COP-TL and VOR-related parameters. These findings suggest that nGVS at 0.2 mA inhibits the VOR, while nGVS at 0.6 mA increases body sway during upright standing, although there may be no relationship between the respective effects in healthy individuals.

Scoping out noisy galvanic vestibular stimulation: a review of the parameters used to improve postural control

“…In contrast Matsugi et al (2022) found that nGVS significantly reduced rather than increased the video head impulse test (vHIT) gain to horizontal head impulses, indicating suppression of the VOR with nGVS. The reasons for these contradictory results are not clear.…”

“…The varying nature of study designs and the sensory conditions utilized during assessment make it difficult to draw credible conclusions between studies ( Matsugi et al, 2020 ; McLaren et al, 2022 ). Of the current amplitudes set at a group level, 200 μA demonstrated significantly reduced postural sway in two studies ( Inukai et al, 2020a ; Nooristani et al, 2021 ), and no change in a further study ( Matsugi et al, 2022 ); 400 μA provided noted improvements in balance in four studies ( Inukai et al, 2018a , b , 2020b , c ) with no effect in one study. At 1,000 and 1,200 μA, the results were variable; balance improved in one study ( Inukai et al, 2018b ), deteriorated in one study ( Matsugi et al, 2020 ) but had no effect ( Nooristani et al, 2019b ; Matsugi et al, 2022 ), or had limited effect ( Nooristani et al, 2019a ) in three other studies.…”

“…While some studies have found the greatest benefit of nGVS was demonstrated with the eyes closed, eliminating the influence of the VOR on balance ( McLaren et al, 2022 ), and others have found no effect of the visual condition ( Matsugi et al, 2020 ), in most real-life situations the stabilizing role of the VOR for vision plays a critical role in balance and postural control. However, to date we do not have evidence that a change in postural control with nGVS is associated with a the change in the VOR ( Matsugi et al, 2022 ).…”

“…Ten studies set amplitude at a group level. One study used a 1,200 μA amplitude ( Matsugi et al, 2022 ), four studies used a 1,000 μA amplitude ( Inukai et al, 2018b ; Nooristani et al, 2019a , b ; Matsugi et al, 2020 ), one at 600 μA ( Matsugi et al, 2022 ), five studies have used a set amplitude of 400 μA ( Inukai et al, 2018a , b , 2020a , b , c ), and three studies 200 μA ( Inukai et al, 2020a ; Nooristani et al, 2021 ; Matsugi et al, 2022 ). The varying nature of study designs and the sensory conditions utilized during assessment make it difficult to draw credible conclusions between studies ( Matsugi et al, 2020 ; McLaren et al, 2022 ).…”

“…The reasons for these contradictory results are not clear. As the frequency band of the nGVS stimulus in Matsugi et al (2022) was not disclosed, and they used set amplitudes, there could be parameter based differences. Also, in both Matsugi et al (2022) and Serrador et al (2018) , young healthy subjects demonstrated no change in ocular counter roll response to nGVS ( Serrador et al, 2018 ) or vHIT ( Matsugi et al, 2022 ).…”