One hour jaw muscle training does not evoke plasticity in the corticomotor control of the masseter muscle

Transcranial magnetic stimulation (TMS) has been used to assess corticomotor control of jaw muscles, but few studies have examined cortical plasticity of the masticatory system and potential modification by jaw muscle training.

To determine if a 1-h jaw muscle training task would be sufficient to induce signs of neuroplastic changes in the corticomotor excitability of the masseter muscle.

Corticomotor excitability was assessed by changes in electromyographic activity evoked by TMS in 15 healthy participants. Motor evoked potentials (MEPs) recorded in the masseter and the first dorsal interosseos (FDI - as a control) muscle were assessed at four time points: at baseline, immediately after the 1-h training, 1h after training and 1 day follow-up (n=7). MEPs were assessed by stimulus-response curves and corticomotor mapping.

All participants successfully performed the task (mean success rate: 47.0±4.1%) which increased significantly during the 1-h training. However, no significant effect of jaw muscle training on masseter and FDI MEPs or corticomotor maps were observed.

The present finding showed that 1-h jaw muscle training is insufficient to evoke neuroplastic changes in corticomotor excitability. The potential for training-induced neuroplasticity may vary among different cranial muscles which may have therapeutic consequences.