Hypothetical cortico-BG circuitry functioning in Tourette syndrome before and after GPi DBS. Cx, cerebral cortex; GPe, external globus pallidum; GPi, internal globus pallidum; SNc, subtantia nigra pars compacta; SNr, substantia nigra pars reticulata; STN, subthalamic nucleus; Str, striatum; Th, thalamus. Illustration adapted from Nambu (2011).