The after effects of motor cortex rTMS depend on the state of contraction when rTMS is applied

To test whether the after effects of 5 Hz focal rTMS over the primary motor cortex are modulated by the state of muscle contraction when the rTMS is applied.

Ten healthy volunteers gave informed consent to the studies. Fifty stimuli at active motor threshold intensity were applied at 5 Hz to the forearm motor area during 10% MVC isometric wrist flexion, 10% MVC wrist extension and at rest. Short interval intracortical inhibition (SICI: interstimulus intervals of 2-5 ms) and intracortical facilitation (interstimulus intervals of 7 and 10 ms) were recorded at rest before and after rTMS from flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles with surface electrodes.

rTMS during wrist flexion decreased SICI in the FCR whereas SICI was increased if rTMS was given during wrist extension. The opposite was true in ECR: SICI was increased if rTMS was applied during wrist flexion, whereas it was reduced if rTMS was given during wrist extension. rTMS applied at rest produced a small overall decrease of SICI in FCR and ECR but this was not individually significant in the FCR. The 10 s wrist flexion without any rTMS did not have any effect on SICI.

The after effects of motor cortex rTMS can be selectively modulated by the pattern of muscle contraction.