Repetitive transcranial magnetic stimulation of motor cortex after stroke: a focused review

Repetitive Transcranial Magnetic Stimulation (rTMS) is known to modulate cortical excitability and has thus been suggested to be a therapeutic approach for improving the efficacy of rehabilitation for motor recovery after stroke. In addition to producing effects on cortical excitability, stroke may affect the balance of transcallosal inhibitory pathways between motor primary areas in both hemispheres: the affected hemisphere (AH) may be disrupted not only by the infarct itself but also by the resulting asymmetric inhibition from the unaffected hemisphere, further reducing the excitability of the AH. Conceptually, therefore, rTMS could be used therapeutically to restore the balance of interhemispheric inhibition after stroke. rTMS has been used in two ways: low-frequency stimulation (≤1 Hz) to the motor cortex of the unaffected hemisphere to reduce the excitability of the contralesional hemisphere or high-frequency stimulation (>1 Hz) to the motor cortex of the AH to increase excitability of the ipsilesional hemisphere. The purpose of this systematic review is to collate evidence regarding the safety and efficacy of high-frequency rTMS to the motor cortex of the AH. The studies included investigated the concurrent effects of rTMS on the excitability of corticospinal pathways and upper-limb motor function in adults after stroke. This review suggests that rTMS applied to the AH is a safe technique and could be considered an effective approach for modulating brain function and contributing to motor recovery after stroke. Although the studies included in this review provide important information, double-blinded, sham-controlled Phase II and Phase III clinical trials with larger sample sizes are needed to validate this novel therapeutic approach.