Repetitive transcranial magnetic stimulation in the treatment of dystonia

First described by Barker et al. (5) to study central motor pathways, TMS has been extensively used to investigate the pathophysiology of movement disorders (6), mostly dystonia and Parkinson’s disease (7-9). Over the last decade, increasing interest in this technology has focused around the possibility of modulating the excitability of the brain, and specifically the motor areas (10). By means of repetitive TMS (rTMS), a train of pulses applied to a brain area, is able to inhibit to facilitate cortical excitability, depending on the frequency of stimulation. Low-frequency rTMS (<1 Hz) decreases cortical excitability, whereas highfrequency stimulation (>5 Hz) increases it (10-12); the duration of the after effects of rTMS depends on the duration and intensity of the stimulation (13). Functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies suggest that rTMS induces changes of cortical excitability and potentially reorganizes brain networks (14). Indeed, it has been shown that rTMS, not only affects the target region, but may also influence remote brain areas interconnected with the stimulation site, such as dorsal premotor cortex (dPMC), supplementary motor area (SMA), and subcortical structures (15).