The medium latency muscle response to a vestibular perturbation is increased after depression of the cerebellar vermis

INTRODUCTION: Galvanic vestibular stimulation (GVS) is able to evoke distinct responses in the muscles used for balance. These reflexes, termed the short (SL) and medium latency (ML) responses, can be altered by sensory input; decreasing in size when additional sensory cues are available. Although much is known about these responses, the origin and role of the responses are still not fully understood. It has been suggested that the cerebellum, a structure that is involved in postural control and sensory integration, may play a role in the modulation of these reflexes. METHODS: The cerebellar vermis was temporarily depressed using continuous theta burst stimulation and SL, ML and overall vestibular electromyographic and force plate shear response amplitudes were compared before and after cerebellar depression. RESULTS: There were no changes in force plate shear amplitude and a non-significant increase for the SL muscle response (p = .071), however, we did find significant increases in the ML and overall vestibular muscle response amplitudes after cerebellar depression (p = .026 and p = .016, respectively). No changes were evoked when a SHAM stimulus was used. DISCUSSION: These results suggest that the cerebellar vermis plays a role in the modulation of vestibular muscle reflex responses to GVS.