The caudate nucleus is one of three basic structures that make up the basal ganglia, along with the putamen and globus pallidus. Also, in conjunction with the thalamus and two related structures (the substantia nigra and subthalamic nucleus), the caudate nucleus constitutes a system that is responsible largely for voluntary movement. While this system has long been associated with motor processes due primarily to the basal ganglia’s role in Parkinson's disease, there is mounting evidence that the structures that make up the basal ganglia—the caudate nucleus included—play important roles in various other nonmotor functions as well. Organizationally, the interplay between the basal ganglia and various regions in the brain is best described as a series of cortico-striatal loops, in which the striatum receives axons from the cortex (along with the putamen, the caudate nuclei are the main input regions for the basal ganglia), processes the information, then relays this back to distinct cortical regions (hence the name cortico-striatal). The caudate plays an important role in three of these loops: the oculomotor, dorsolateral, and ventral/orbital circuits. In a related way then, the caudate nucleus has been implicated with voluntary movement, learning, memory, sleep, and social behavior.