a smoothly executed, goal-directed behavior. Although the anatomical pathways appear to be generally topographic from cortex through basal ganglia circuits and there are some physiological correlates to the functional domains of the striatum, there are major points that argue against a strict parallel processing system. A number of studies show that these pathways are not as segregated as once thought.13,120-123 The dendrites and axons of the striatal interneurons often cross functional boundaries and have been suggested to be one mechanism that integrates information across regions. The fact that adjacent areas overlap in function is not surprising. Many cortical areas are tightly linked to the immediately adjacent cortex. Nonetheless, the interface between functional circuits increases with the complexity of interconnections within the intrinsic basal ganglia circuitry and with the compression of pathways to successively smaller structures.14,124
