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.

To investigate whether gaze stabilization exercises (GSEs) improve eye and head movements and whether low-frequency cerebellar repetitive transcranial magnetic stimulation (rTMS) inhibits GSE trainability. 25 healthy adults (real rTMS, n = 12; sham rTMS, n = 13) were recruited. Real or sham rTMS was performed for 15 min (1 Hz, 900 stimulations). The center of the butterfly coil was set 1 cm below the inion in the real rTMS. Following stimulation, 10 trials of 1 min of a GSE were conducted at 1 min intervals. In the GSE, the subjects were instructed to stand upright and horizontally rotate their heads according to a beeping sound corresponding to 2 Hz and with a gaze point ahead of them. Electrooculograms were used to estimate the horizontal gaze direction of the right eye, and gyroscopic measurements were performed to estimate the horizontal head angular velocity during the GSE trials. The percentage change from the first trial of motion range of the eye and head was calculated for each measurement. The percent change of the eye/head range ratio was calculated to assess the synchronous changes of the eye and head movements as the exercise increased. Bayesian two-way analysis of variance showed that cerebellar rTMS affected the eye motion range and eye/head range ratio. A post hoc comparison (Bayesian t-test) showed evidence that the eye motion range and eye/head range ratio were reduced in the fifth, sixth, and seventh trials compared with the first trial sham stimulation condition. GSEs can modulate eye movements with respect to head movements, and the cerebellum may be associated with eye–head coordination trainability for dynamic gazing during head movements.

[Purpose] The aim of this study was to investigate whether gaze stabilization exercise derives sensory reweighting of vestibular for upright postural control. [Subjects and Methods] Twenty-three healthy volunteers participated in this study. The center of pressure of the total trajectory length was measured before (pre), immediately after (post), and 10 min after (post10) gaze stabilization exercise, in the static standing position, with the eyes open or closed, on the floor or on foam rubber. The sensory contribution values of the visual, somatosensory, and vestibular systems were calculated using center of pressure of the total trajectory length value in these measuring conditions. [Results] The center of pressure of the total trajectory length on foam rubber in post and post10 were significantly lower than that in the pre. The sensory contribution values of vestibular in post10 stages were significantly higher than that in pre-stage. [Conclusion] Gaze stabilization exercise can improve the static body balance in a condition that particularly requires vestibular function. The possible mechanism involves increasing sensory contribution of the vestibular system for postural control by the gaze stabilization exercise, which may be useful to derive sensory reweighting of the vestibular system for rehabilitation.

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.

Previously, we reported that cerebellar transcranial magnetic stimulation (C-TMS) facilitates spinal motoneuronal excitability in resting humans. In this study, we aimed to characterize the descending pathway that is responsible for the C-TMS-associated cerebellar spinal facilitation. We evaluated the effect of C-TMS on ipsilateral soleus Ia presynaptic inhibition (PSI) and reciprocal inhibition (RI) because the vestibulospinal and reticulospinal tracts project from the cerebellum to mediate spinal motoneurons via interneurons associated with PSI. PSI and RI were measured with a soleus H-reflex test following operant conditioning using electrical stimulation of the common peroneal nerve. C-TMS was delivered before test tibial nerve stimulation with conditioning-test interstimulus intervals of 110 ms. C-TMS did not generate motor-evoked potentials, and it did not increase electromyography activity in the ipsilateral soleus muscle, indicating that C-TMS does not directly activate the corticospinal tract and motoneurons. However, C-TMS facilitated the ipsilateral soleus H-reflex and reduced the amount of soleus Ia PSI, but not RI. These findings indicate that C-TMS may facilitate the excitability of the spinal motoneuron pool via the vestibulospinal or reticulospinal tracts associated with PSI. Cerebellar spinal facilitation may be useful for assessing the functional connectivity of the cerebellum and vestibular nuclei or reticular formation.

This study aimed to investigate whether cerebellar transcranial magnetic stimulation (C-TMS) affected the cortical silent period (cSP) induced by TMS over the primary motor cortex (M1) and the effect of interstimulus interval (ISI) on cerebellar conditioning and TMS to the left M1 (M1-TMS). Fourteen healthy adult participants were instructed to control the abduction force of the right index finger to 20% of the maximum voluntary contraction. M1-TMS was delivered during this to induce cSP on electromyograph of the right first dorsal interosseous muscle. TMS over the right cerebellum (C-TMS) was conducted prior to M1-TMS. In the first experiment, M1-TMS intensity was set to 1 or 1.3 × resting motor threshold (rMT) with 20-ms ISI. In the second experiment, the intensity was set to 1 × rMT with ISI of 0, 10, 20, 30, 40, 50, 60, 70, or 80 ms, and no-C-TMS trials were inserted. In results, cSP was significantly shorter in 1 × rMT condition than in 1.3 × rMT by C-TMS, and cSP was significantly shorter for ISI of 20–40 ms than for the no-C-TMS condition. Further, motor evoked potential for ISI40-60 ms were significantly reduced than that for ISI0. Thus, C-TMS may reduce cSP induced by M1-TMS with ISI of 20–40 ms.