Inducing neuroplasticity in the human motor system by transcranial magnetic stimulation: from pathophysiology to a therapeutic option in movement disorders

Objective: Stimulation frequency has been considered themost important factor in conventional repetitive transcranial magnetic stimulation (rTMS) for determining the direction of after effects on corticospinal excitability. Here, we examined the functional relevance of breaks during high-frequency subthreshold rTMS for the induction of facilitatory after effects. Methods: The after effects on corticospinal excitability of a standard 5 Hz rTMS protocol in a block design were compared to a continuous rTMS protocol using the same number of pulses. In addition the effect of current direction both for rTMS and single pulse TMS was included in the study design. Results: While 5 Hz rTMS in a standard block design induces facilitatory after effects on corticospinal excitability, the continuous protocol does not induce facilitation but rather inhibition. In our study only rTMS using an initially posterior–anterior current direction in the brain leads to significant neuroplastic effects at all. Conclusions: Breaks during conventional high-frequency rTMS are a crucial factor determining the direction of induced neuroplastic changes. Significance: These results contribute to theunderstanding of rTMS-inducedneuroplasticity andare important for the design of rTMS protocols both for experimental and clinical studies. 2009 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.