Figure 1 provides an overview of the cortico-basal ganglia circuit. The striatum is comprised of the dorsal striatum (DS) and ventral striatum (VS). The VS is a ventral extension of the DS and, based on its connections, cell morphology, and histochemistry, it includes the nucleus accumbens, the medial and ventral portions of the caudate and putamen, the striatal cells of the olfactory tubercle, and the anterior perforated substance.16,17 Afferent projections to the striatum are derived from three major sources: (i) a massive and topographic input from the cerebral cortex; (ii) input from the thalamus; and (iii) and input from the brain stem, primarily from the brain stem dopaminergic cells. Inputs from the cortex and thalamus terminate in a general topographic manner, such that the dorsolateral striatum receives cortical input from sensory-motor areas, central striatum receives input from associative cortical areas, and the ventromedial striatum receives input from limbic areas.14,18-20 The striatum, in turn, projects topographically to the pallidal complex and the substantia nigra (SN), both pars reticulata (SNr), and pars compacta(SNc).21-24
