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 day1 and day 2. Interestingly, at 1 Hz and 20 Hz rTMS, the modulatory effect produced by rTMS was greater on day 2. However, there was no significant change in corticospinal excitability following 10 Hz rTMS neither on day 1 nor day 2.


CONCLUSIONS
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.
Maeda
F
F
Laboratory for Magnetic Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave. KS452, Boston, USA.
Keenan
J P
JP
Tormos
J M
JM
Topka
H
H
Pascual-Leone
A
A
D000328:Adult; D019054:Evoked Potentials, Motor / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology* / Q000528:radiation effects; D011712:Pyramidal Tracts / Q000502:physiology* / Q000528:radiation effects; D012016:Reference Values; D012044:Regression Analysis; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation