Tics as a model of over-learned behavior-imitation and inhibition of facial tics

Tics are the defining feature in Tourette syndrome and can be triggered by watching tics or single voluntary movements. This automatic imitation of movements referred to as "echopraxia" has been ascribed to a failure in top-down inhibition of imitative response tendencies. Alternatively, it could be interpreted in the context of automatic overlearned behavior. To this end, we investigated 18 Tourette patients aged 28.22 years (9.44 standard deviation; 16 male) and 24 healthy controls (mean age 29.21 years [9.1 standard deviation]; 17 male) using an adapted version of an action-interference paradigm.

Patients were asked to respond to 2 different auditory tones with either a facial movement that was part of their tic repertoire (tic-like movement), or a facial movement that was not (nontic movement). Simultaneously, behaviorally irrelevant videos of the 2 same facial movements were presented, which were either compatible or incompatible with the movement executed by the patient. Movements in healthy controls were matched to those in the patients.

Healthy participants responded faster in compatible than in incompatible trials. Tourette patients showed the same effect for nontic movements. However, their responses were equally fast in incompatible and compatible trials when the movement they were asked to execute was a tic-like movement. Error rates did not differ between the groups.

The results suggest that tic-like movements do not occur as a consequence of a failure to inhibit motor output. Instead, tics might be considered highly overlearned behavior that can be triggered without interference by external, incompatible movement stimuli. © 2016 International Parkinson and Movement Disorder Society.