Abstract

Obsessions and compulsions frequently accompany motor and vocal tics in Gilles de la Tourette syndrome (GTS). The occurrence of motor tics and compulsions helps to understand the neurobiological foundation of repetitive behavior patterns. Based on a review of the literature and our own studies in GTS, we suggest that simple motor tics are caused by a stimulus-dependent disinhibition of stereotypies encoded in the head of the caudate, while more complex compulsions are associated with a serotonergic disinhibition of frontocortical-striatal circuits in GTS and obsessive-compulsive disorder. These findings indicate that obsessions and compulsions do not simply result from a lack of cortical control of phylogenetically primitive behavior patterns. Rather, an activation of the orbitofrontal cortex seems to be essential for the induction of anxiety and the disinhibition of subcortical stereotypies. The neurobiological findings may help to clarify why compulsions differ from cultural rituals. Cultural rituals are performed cyclically, represent important social conflicts and are usually not accompanied by fear or anxiety. Obsessions, on the other hand, seem to be generated in a self perpetuating cycle of cortico-subcortical activation and are associated with anxiety and ineffective repetition of stereotypies.