The basal ganglia differs in size and structure between species. For example the striatum in the rat is not segregated into a distinct caudate nucleus and putamen as it is in primates (Brodal, 1981; Paxinos, 1995). Also, the rat homologue of the internal globus pallidus, the entopeduncular nucleus, is not located in the same position as it is in primates (Brodal, 1981; Paxinos, 1995). Such anatomical differences between species may result in differential effects of basal ganglia surgery or pharmacological manipulations when results from animals are extrapolated to human movement disorders.