Gaze-stabilization exercise (GSE) is often conducted in vestibular rehabilitation, but its effect on vestibular function in postural control is not clear. We investigated whether GSE affects vestibular function during static upright standing and vestibulospinal reflex (VSR) in healthy young adults. First, the center of pressure of the total trajectory length (CoP-L) was measured before each GSE task or control (only standing) task (pre), immediately after (post), and 10 min after (post10) in the static standing position on foam rubber with the eyes open or closed (EC). Second, the H-reflex on the soleus muscle was measured after the onset of ipsilateral anodal galvanic vestibular stimulation before and after a GSE or a control task to estimate the amount of VSR induced by electrical vestibular input. CoP-L for the pre, post, and post10 control tasks and the GSE in EC did not differ significantly; the CoP-L for the post and post10 tasks in EC were significantly lower than that for the pretask. The H-reflex was inhibited by galvanic vestibular stimulation in the pre-GSE tasks. The inhibition increased after GSE, but not during control tasks. These findings suggest that GSE immediately improves the postural stability required for vestibular function and can be mediated by VSR improvements.

Objective: This study aimed to investigate whether galvanic vestibular stimulation with stochastic noise (nGVS) modulates the body sway and muscle activity of the lower limbs, depending on visual and somatosensory information from the foot using rubber-foam.Methods: Seventeen healthy young adults participated in the study. Each subject maintained an upright standing position on a force plate with/without rubber-foam, with their eyes open/closed, to measure the position of their foot center of pressure. Thirty minutes after baseline measurements under four possible conditions (eyes open/closed with/without rubber-foam) performed without nGVS (intensity: 1 mA, duration: 40 s), the stimulation trials (sham-nGVS/real-nGVS) were conducted under the same conditions in random order, which were then repeated a week or more later. The total center of pressure (COP) path length movement (COP-TL) and COP movement velocity in the mediolateral (Vel-ML) and anteroposterior (Vel-AP) directions were recorded for 30 s during nGVS. Furthermore, electromyography activity of the right tibial anterior muscle and soleus muscle was recorded for the same time and analyzed.Results: Three-way analysis of variance and post-hoc multiple comparison revealed a significant increment in COP-related parameters by nGVS, and a significant increment in soleus muscle activity on rubber. There was no significant effect of eye condition on any parameter.Conclusions: During nGVS (1 mA), body sway and muscle activity in the lower limb may be increased depending not on the visual condition, but on the foot somatosensory condition.

We investigated whether cerebellar transcranial magnetic stimulation (C-TMS) facilitates the excitability of the ipsilateral soleus motoneuron pool in resting humans, and whether the facilitation is modulated by a task that promotes cerebellar activity. A test tibial nerve stimulus evoking the H-reflex from the right soleus muscle was delivered before or after conditioning C-TMS in prone individuals. The amplitude of the H-reflex was significantly increased at conditioning-test interstimulus intervals of 110, 120, and 130 ms. Furthermore, we revealed that this facilitation effect was inhibited while the individuals tapped their right index finger. These findings indicate that C-TMS facilitates spinal motoneuronal excitability with an ∼100 ms latency in resting humans, and that this cerebellar spinal facilitation is modulated by a task that might increase cerebellar activity. Cerebellar spinal facilitation could thus be useful for assessing the excitability of the cerebellum, or the cerebellar output to spinal motoneurons.