Neuromodulatory effects of offline low-frequency repetitive transcranial magnetic stimulation of the motor cortex: A functional magnetic resonance imaging study.

Repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) can modulate cortical excitability and is thought to influence activity in other brain areas. In this study, we investigated the anatomical and functional effects of rTMS of M1 and the time course of after-effects from a 1-Hz subthreshold rTMS to M1. Using an "offline" functional magnetic resonance imaging (fMRI)-rTMS paradigm, neural activation was mapped during simple finger movements after 1-Hz rTMS over the left M1 in a within-subjects repeated measurement design, including rTMS and sham stimulation. A significant decrease in the blood oxygen level dependent (BOLD) signal due to right hand motor activity during a simple finger-tapping task was observed in areas remote to the stimulated motor cortex after rTMS stimulation. This decrease in BOLD signal suggests that low frequency subthreshold rTMS may be sufficiently strong to elicit inhibitory modulation of remote brain regions. In addition, the time course patterns of BOLD activity showed this inhibitory modulation was maximal approximately 20 minutes after rTMS stimulation.