This scientific commentary refers to ‘Enhanced habit formation in Gilles de la Tourette syndrome’, by Delorme et al. (doi:10.1093/brain/awv307). Tourette syndrome is characterized by the presence of tics, which have a fluctuating, waxing and waning course, and are typically exacerbated by stress, anxiety, excitement, anger or fatigue. Tics are known to diminish when an individual is absorbed in an activity, concentrating, focused or pleased. Studies have also shown that tics can occur during sleep, although understandably patients fail to report their presence. Further, many individuals with tics, especially older children and adults, describe a sensory phenomenon (premonitory urge), such as a tension, impulse, tingle, or feeling located in the relevant body part, prior to the tic. Although it has been suggested that tics should be considered a habitual disorder (Singer, 2013), the presence of a premonitory urge, and its reduction by the performance of tics, may lead some to consider tics to be a goal-directed, rather than habitual behaviour. Moreover, it is unclear whether the occurrence of tics in all stages of sleep should modify their acceptance as a habit-based disorder. In this issue of Brain , Delorme and co-workers explore the strength of habit formation and its underlying structural connectivity in medicated and unmedicated subjects with Tourette syndrome (Delorme et al. , 2016). In order to study human goal-directed and habitual behaviours in the laboratory, investigators have developed instrumental learning paradigms, which test the flexibility of the individual to adjust their behaviour to changes in outcome values. The paradigm used by Delorme et al. has been utilized in previous studies, and is considered sufficiently sensitive. The data obtained indicate that unmedicated subjects with Tourette syndrome have a greater reliance on habitual control systems than either healthy controls or medicated subjects. Several concerns, however, pertain to a lack …