Vibration stimulation during non-fatiguing tonic contraction induces outlasting neuroplastic effects

The objective was to explore if vibration superposed to tonic contraction induces plastic changes in the contra- and ipsilateral motor cortex. Healthy subjects (n=12) abducted the right index finger with a force 5% of maximal voluntary contraction (MVC) against the lever of a torque motor while a 60 Hz vibration stimulus of 10 min was delivered. Motor evoked potentials (MEPs) after single and paired-pulse transcranial magnetic stimulation (TMS) were recorded from the first dorsal interosseous muscle of right and left hand pre, during, post and 30 min post-stimulation. The TMS assessments were employed with tonic contraction alone (TONIC) and with superposed vibrostimulation (VIBRO), each for the ipsi- and contralateral cortex separately. In the contralateral cortex: resting motor threshold (rMT) decreased, MEP amplitudes increased, short-interval intracortical inhibition (SICI) reduced and intracortical facilitation (ICF) increased post VIBRO, while no changes occurred post TONIC. In the ipsilateral cortex: rMT decreased, MEP amplitude increased and SICI reduced during TONIC, while no changes occurred post TONIC, during and post VIBRO. Vibration superposed to tonic contraction, induces lasting (30 min) plastic changes, whereas contraction alone caused no outlasting effects. Mainly intrinsic intracortical mechanisms are involved because spinal adaptation could be excluded (F-wave assessments). These findings have a therapeutic potential in the functional recovery of motor deficits with robot-aided devices.