Crossed effects of muscle vibration on motor-evoked potentials

Objectives: Muscle vibration (MV) to a forearm muscle augments motor-evoked potentials (MEPs) following transcranial magnetic stimulation (TMS) and th e underlying mechanism involves cortical structures. Although MV-induced co rtical activation is bilateral, the effects of MV on MEPs in contralateral muscles have not been investigated. Methods: Low-amplitude MV (80 Hz, amplitude 0.5 mm, duration 4 s), subthres hold for the tonic vibration reflex, was applied to the right extensor carp i radialis muscle (ECR). MEPs were elicited (0.5, 3 and 5 s after MV onset) in the left and right ECR and flexor carpi radialis muscle (FCR) by TMS (1 20% of threshold at rest) to the left and right hemisphere, respectively. Results: During MV of right ECR the left ECR revealed a slight non-signific ant augmentation of MEPs. In contrast, the left FCR showed a gradual depres sion of MEPs with ongoing MV and at 3 s the reduction of MEPs was significa nt. The time course of MEP changes in left FCR correlated with the facilita tion of the vibrated right ECR. Post-vibration MEPs at 1 s after the offset of MV were still significantly decreased. Conclusions: The study demonstrates crossed effects of MV on motor cortex e xcitability, suggesting transcallosal MEP modulation. (C) 2001 Elsevier Sci ence Ireland Ltd. All rights reserved.