Cortex 2016 Apr 23;77:24-37. Epub 2016 Jan 23.
Department of Paediatric and Adult Movement Disorders and Neuropsychiatry, Institute of Neurogenetics, University of Lübeck, Germany.
Premonitory urges are a cardinal feature in Tourette syndrome and are commonly viewed as the driving force of tics, building up before and subsiding after the execution of tics. Although the urge-tic interplay is one of the most preeminent features in Tourette syndrome, the temporal relationship between tics and urges has never been examined experimentally, mainly due to the lack of an appropriate assessment tool. We investigated the temporal relationship between urge intensity and tics in 17 Tourette patients and between urge intensity and eye blinks in 16 healthy controls in a free ticcing/blinking condition and a tic/blink suppression condition. For this purpose, an urge assessment tool was developed that allows real-time monitoring and quantification of urge intensity. Compared to free ticcing/blinking, urge intensity was higher during the suppression condition in both Tourette patients and healthy controls, while tics and blinks occurred less frequently. The data show that urge intensity increases prior to tics and decreases after tics in a time window of approximately ±10 sec. Tic suppression had a significant effect on the shape of the urge distribution around tics and led to a decrease in the size of the correlation between urge intensity and tics, indicating that tic suppression led to a de-coupling of tics and urges. In healthy controls, urges to blink were highly associated with eye blink execution, albeit in a narrower time frame (∼±5 sec). Blink suppression had a similar effect on the urge distribution associated with eye blinks as tic suppression had on the urge to tic in Tourette patients. These results corroborate the negative reinforcement model, which proposes that tics are associated with a relief in urges, thereby perpetuating ticcing behaviour. This study also documents similarities and differences between urges to act in healthy controls and urges to tic in Tourette syndrome.