Modulation of corticospinal excitability by repetitive transcranial magnetic stimulation

Objective: Repetitive transcranial magnetic stimulation (rTMS) is able to modulate the corticospinal excitability and the effects appear to last beyond the duration of the rTMS itself. Different studies, employing different rTMS parameters, report different modulation of corticospinal excitability ranging from inhibition to facilitation. Intraindividual variability of these effects and their reproducibility are unclear. Methods: We examined the modulatory effects of rTMS to the motor cortex at various frequencies (1, 10, 20 Hz) and at different time-points in twenty healthy volunteers. Results: We observed significant inhibition of MEPs following 1 Hz rTMS and significant facilitation of MEPs following 20 Hz rTMS for both day 1 and day 2. Interestingly, at 1 Hz and 20 Hz rTMS, the modulatory effect produced by rTMS was greater an day 2. However, there was no significant change in corticospinal excitability following 10 Hz rTMS neither on day I nor day 2. Conclusion: Our findings raise questions as to how stimulation parameters should be determined when conducting studies applying rTMS on multiple days, and in particular, studies exploring rTMS as a treatment modality in neuropsychiatric disorders. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.