OBJECTIVE

Stimulation frequency has been considered the most 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 5Hz 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 5Hz 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 the understanding of rTMS-induced neuroplasticity and are important for the design of rTMS protocols both for experimental and clinical studies.