Contribution of therapeutic strategies for understanding the Tourette syndrome

Motion is a behavior involving a motor act programmed and executed in a particular cognitive and emotional context. Deep structures of the brain, including the basal ganglia, appear to play a crucial role in the integration of these three kinds of cortex information (motion, cognition, emotion). Through its organization, the basal ganglia system enables learning and memorization of behavioral sequences, which can then be executed as routines. Their dysfunctions seem to be associated with many psychopathological situations. Thus, tics in Tourette's syndrome (TS) can be seen as a control routines defect that may result from wiring anomaly between the cortex and the basal ganglia. By precisely targeting deep brain circuits implicated in psychiatric disorders, deep brain stimulation (DBS) offers hope for the alleviation of severe illnesses resistant to drug therapies and provides a novel tool to investigate the neuroanatomic and physiological bases of certain disorders, including Obsessive-Compulsive Disorder (OCD) and TS, for which early results indicate positive therapeutic outcomes, even during the long-term follow-up. The pathophysiologies of OCD and of TS share dysfunctions of the associative and limbic circuits running between cortical and sub-cortical structures. Recent pathophysiological hypotheses suggest that TS symptoms result from a dysfunction of the basal ganglia circuitry, notably of the ventral striatum. These data are consistent with the supposed function of cortico-basal ganglia circuits in habit learning and routine performance of habits. Based on early reports indicating that high-frequency stimulation of structures along the cortico-basal ganglia axis might be effective in alleviating TS symptoms, DBS is being tested across the world at several nodes of this circuit, including the pallidum, and thalamus. Increasing our knowledge of the functional organization of the cortico-basal ganglia circuits and of their dysfunction in pathological repetitive behaviors would certainly contribute to better define the surgical therapeutic targets, thereby improving available treatments.