Electroencephalographic sensorimotor rhythms are modulated in the acute phase following focal vibration in healthy subjects

Few minutes of focal vibration (FV) on limb muscles can improve motor control in neurological (stroke, Parkinson) patients for unknown underlying neurophysiological mechanisms. Here we hypothesized that in healthy volunteers this FV would increase excitability in the primary sensorimotor cortex (S1-M1) during an isometric contraction of the stimulated muscle. The design included an initial control condition with no FV stimulation (Baseline) as well as three short experimental sessions of FV and a Sham (fake) session in a pseudo-random order. In the Baseline condition and immediately after those sessions, electroencephalographic (EEG) activity was recorded during a mild isometric muscle contraction of the right arm. Alpha and beta motor-related EEG power desynchronization (MRPD) at C4 and C3 electrodes overlying Rolandic regions were used as an index of the cortical excitation in S1-M1. Results showed that, compared to the Baseline (no FV) or Sham stimulation, the first two FV sessions showed a cumulative increase in alpha (but not beta) MRPD at C3 electrode, suggesting a specific effect of vibration on the excitability of contralateral S1-M1 generating EEG "mu" rhythms. FV over limb muscles modulates neurophysiological oscillations enhancing excitability of contralateral S1-M1 in healthy volunteers. The proposed mechanism may explain the clinical effects of vibratory rehabilitation in neurological patients with motor deficits.