Cerebellar Repetitive Transcranial Magnetic Stimulation and Noisy Galvanic Vestibular Stimulation Change Vestibulospinal Function

Abstract

Background: The cerebellum strongly contributes to vestibulospinal function, and the modulation of vestibulospinal function is important for rehabilitation. As transcranial magnetic stimulation (TMS) and electrical stimulation may induce functional changes in neural systems, we investigated whether cerebellar repetitive TMS (crTMS) and noisy galvanic vestibular stimulation (nGVS) could modulate vestibulospinal response excitability. We also sought to determine whether crTMS could influence the effect of nGVS. Methods: Fifty-nine healthy adults were recruited; 28 were randomly allocated to a real-crTMS group and 31 to a sham-crTMS group. The crTMS was conducted using 900 pulses at 1 Hz, while the participants were in a static position. After the crTMS, each participant was allocated to either a real-nGVS group or sham-nGVS group, and nGVS was delivered (15 min., 1 mA; 0.1-640 Hz) while patients were in a static position. The H-reflex ratio (with/without bilateral bipolar square wave pulse GVS), which reflects vestibulospinal excitability, was measured at pre-crTMS, post-crTMS, and post-nGVS. Results: We found that crTMS alone and nGVS alone have no effect on H-reflex ratio but that the effect of nGVS was obtained after crTMS. Conclusion: crTMS and nGVS appear to act as neuromodulators of vestibulospinal function.

The Effects of Stochastic Galvanic Vestibular Stimulation on Body Sway and Muscle Activity

“…Rubber foam can make somatosensory input from feet unreliable and also generates mechanical consequences for balance control (Horak et al, 1990 ; Macedo et al, 2015 ), and vestibular contribution to postural control can be increased (Fujimoto et al, 2009 ). nGVS can modulate the threshold of the vestibular response (Kwan et al, 2019 ) against the signals from head movements and the excitability of the vestibulospinal response (Matsugi et al, 2020 ). Therefore, one possible mechanism of increment of body sway by nGVS (1 mA), if the stimulus intensity is in supratidal, is the increase in the threshold of the vestibulospinal response for postural control because the contaminating intensive noise stimulation generally disturbs signal detection (Fallon et al, 2004 ).…”

“…Figure 1A shows the stimulation setup, and Figure 1B shows the typical waveform of nGVS. nGVS was conducted in almost the same way as in a previous study (Inukai et al, 2018b ; Matsugi et al, 2020 ). nGVS was delivered via Ag/AgCl surface electrodes affixed to the right and left mastoid processes.…”

“…DC-STIMULATOR PLUS (Eldith, NeuroConn GmbH, Ilmenau, Germany) was used to deliver random noise galvanic stimulation to the primary vestibular nerve. For nGVS in the “noise” stimulation mode, a random level of current was generated for every sample (sample rate 1,280 samples/s) (Moliadze et al, 2012 ; Inukai et al, 2018b ; Matsugi et al, 2020 ). The intensity was set to 1 mA in this mode.…”

“…Furthermore, it has been reported that stochastic electrical stimulation of the vestibular nerve improves the postural balance in young people (Inukai et al, 2018b ), elderly people (Fujimoto et al, 2016 ; Inukai et al, 2018a ) and patients with vestibular disorders (Fujimoto et al, 2018 ), with long aftereffects. Noise GSV (nGVS) (Wuehr et al, 2017 ) can modulate the threshold of motor responses from vestibular inputs (Wuehr et al, 2017 ) in a posture-dependent manner (Matsugi et al, 2020 ), resulting in improvements in balance (Fujimoto et al, 2016 , 2018 ; Inukai et al, 2018b ). One possible rationale for changes in the motor threshold is stochastic resonance, in which the addition of low-intensity noise affects the nonlinear systems, which induces a response against signals that are buried in natural noise within neural systems (Mcdonnell and Ward, 2011 ).…”

“…Square-wave pulse GVS induces muscle contractions (Fitzpatrick et al, 1994 ; Ali et al, 2003 ) and modulates spinal motoneuron pool excitability (Matsugi et al, 2017 , 2020 ; Okada et al, 2018 ). Therefore, nGVS may increase muscle activity for postural control.…”