 Multiple models of basal ganglia circuits and function have been proposed, however there have been questions raised about the strict divisions of the direct and indirect pathways, their possible overlap and regulation.The circuitry model has evolved since the first proposed model in the 1990s by DeLong in the parallel "processing model", in which the cortex and substantia nigra pars compacta project into the dorsal striatum giving rise to an inhibitory indirect and excitatory direct pathway.Generally, the basal ganglia circuitry is divided into five pathways