Cerebellar Transcranial Magnetic Stimulation Disrupts Vestibular Reflexes in Standing Balance

Abstract

Despite its seemingly effortless execution, standing balance is a complex task maintained by the integration of sensory feedback from visual, somatosensory (muscle, skin, joint receptors), and vestibular (inner ear) systems. The vestibular system provides feedback about head acceleration and can be manipulated experimentally by passing an electrical current percutaneously through the mastoid processes. The cerebellum plays an important role in standing balance by integrating sensory feedback to refine activity in postural muscles. A recent study has shown that experimentally depressing cerebellar activity with repetitive transcranial magnetic stimulation can influence postural sway and muscle reflex responses following electrical vestibular stimulation. The aim of this study was to investigate the impact of acute cerebellar stimulation on vestibular muscle reflex responses in different head positions during standing balance. We applied a novel combination of stochastic electrical vestibular stimulation (SVS, ±2.5 mA, 0–20 Hz) and single‐pulse cerebellum transcranial magnetic stimulation (TMS, 60% maximum stimulator output) on fifteen healthy adults (6 males, 9 females; 21–32 years old) in two head positions: head forward and head right. Muscle reflexes were recorded bilaterally with surface electromyography (EMG) from lower leg (soleus and medial gastrocnemius) and neck (sternocleidomastoid) muscles. Time‐based cumulant density and frequency‐based coherence analyses were used to evaluate the relationship between the SVS and evoked EMG responses one second before (Pre) and one second after (Post) cerebellar TMS. 50 TMS pulses were delivered per head position. Preliminary analysis performed on left medial gastrocnemius (LMG) head right data indicated a significant reduction in the short latency (SL, P = 0.0377) and medium latency (ML, P < 0.0001) reflexes following cerebellar TMS (Fig. 1). In addition, a significant drop in the coherence between the SVS and LMG Pre to Post was found using a difference of coherence test. These findings support the cerebellum to be an important center for the integration of vestibular feedback for the control of standing balance.Support or Funding InformationMount Royal University Faculty of Science and TechnologyFigure 1