The basal ganglia (basal nuclei) have been regarded traditionally as a motor control system. Lesions in the basal ganglia almost always result in movement disorders. Recently, these structures have been found to influence other emotionally related behaviors. Research on the behavioral influence of the basal ganglia was prompted by the repeated observation that emotional and cognitive dysfunctions frequently accompany movement disorders of basal ganglia origin. In some cases, psychiatric manifestations precede the onset of motor symptoms. With the advent of neuroimaging techniques, investigation into the anatomy and metabolic physiology of these structures in the awake behaving human has revealed intriguing behavioral relationships.

Motor activity is controlled by the intricate interaction of three major systems: the cerebral cortex, the cerebellum, and the basal ganglia. The few milliseconds that intervene between thought and action are crucial for our adjustment in modern society. Understanding the structures that influence those few milliseconds, such as the basal ganglia, will help unravel some of the mysteries of human behavior. It is interesting that the main input to the basal ganglia comes from the cerebral cortex and that its output returns (via the thalamus) to the frontal cortex (motor, premotor, and prefrontal cortex). The frontal cortex, including the prefrontal areas, thus mediates and plays a significant role in the various functions of the basal ganglia.

Originally the basal ganglia were described as a group of cerebral (telencephalic) nuclei. These classical basal ganglia included the caudate nucleus, putamen, globus pallidus, claustrum, and amygdala.