Simple motor tics may be preceded by a premotor potential

Obese st al reported that simple motor ties in Tourette's syndrome were not associated with premotor potentials, which were present when patients mimicked their ties voluntarily, suggesting that spontaneous ties were not generated in the same manner as voluntary movements. Five patients with simple motor ties were studied using a similar paradigm. Premotor potentials were examined during spontaneous ties and during voluntary imitation of the tics. All patients had premotor negativity with the voluntary movements. As in the study of Obese et al, spontaneous ties were not preceded by premotor potentials in three patients. However, premotor negativity was present with spontaneous ties in two patients and resembled the NS' segment of the premotor potential seen with self paced, voluntary movements. A similar premotor potential pattern has been reported with voluntary movements performed in response to external triggering stimuli. In patients with Tourette's syndrome, the eliciting signals could be internal sensations.