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Finis J, Enticott PG, Pollok B, M√ľnchau A, Schnitzler A, Fitzgerald PB (2013) Repetitive transcranial magnetic stimulation of the supplementary motor area induces echophenomena. Cortex, 49(7):1978-1982    
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Abstract
Apart from tics, echopraxia or echophenomena (EP), i.e., automatic imitation of observed movements, are common in patients with Gilles de la Tourette syndrome (TS). The supplementary motor area (SMA) has been shown to be overactive before the onset of tics in these patients, and it is possible that this area might also play a key role in the generation of echopraxia. We wondered whether EP can also be evoked in healthy controls (HC) by modifying neural activity of this cortical region. To this end, we modulated activity of the SMA in 30 HC by repetitive transcranial magnetic stimulation (rTMS) in an attempt to induce EP. We used both 5 Hz (which can temporarily increase neural activity) and 1 Hz (which disrupts or reduces cortical activity) rTMS. Video clips were presented to 30 HC before and after stimulation. Each clip showed one single movement, either a tic of a TS patient or a spontaneous movement of a HC. During the whole presentation, participants were videotaped in order to detect EP. Video films of participants' responses were rated by two independent raters with respect to EP frequency. Our results reveal an increase of EP following 5 Hz stimulation but no effect following 1 Hz stimulation. This finding implies that the SMA is a relay mediating EP