Voluntary tic suppression and the normalization of motor cortical beta power in Gilles de la Tourette syndrome: an EEG study

Gilles de la Tourette syndrome (GTS) is a neurological condition characterized by motor and vocal tics. Previous studies suggested that this syndrome is associated with abnormal sensorimotor cortex activity at rest, as well as during the execution of voluntary movements. It has been hypothesized that this abnormality might be interpreted as a form of increased tonic inhibition, probably to suppress tics; however, this hypothesis has not been tested so far. The present study was designed to formally test how voluntary tic suppression in GTS influences the activity of the sensorimotor cortex during the execution of a motor task. We used EEG to record neural activity over the contralateral sensorimotor cortex during a finger movement task in adult GTS patients, in both free ticcing and tic suppression conditions; these data were then compared with those collected during the same task in age-matched healthy subjects. We focused on the levels of activity in the beta frequency band, which is typically associated with the activation of the motor system, during three different phases: a pre-movement, a movement, and a post-movement phase. GTS patients showed decreased levels of beta modulation with respect to the healthy controls, during the execution of the task; however, this abnormal pattern returned to be normal when they were explicitly asked to suppress their tics while moving. This is the first demonstration that voluntary tic suppression in GTS operates through the normalization of the EEG rhythm in the beta frequency range during the execution of a voluntary finger movement.