The basal ganglia work in concert with cortex to orchestrate and execute planned, motivated behaviors requiring motor, cognitive, and limbic circuits. Its main driving force is cortex as indicated by a massive projection from all cortical areas. Historically, the basal ganglia are best known for their motor functions. This functional association was driven in large part by the neuropathology in the neurodegenerative disorders effecting the control of movement, such as that found in Parkinson's Disease (PD) and Huntington's Chorea. In addition, while receiving input from wide areas of cortex, basal ganglia pathways were thought to return primarily to motor cortex. In further support of role of the basal ganglia in the control of movement, animal studies demonstrated several roles in motor and in sensory-motor integration.

While its role in movement is clear, our concepts of basal ganglia function has dramatically changed in the last 20 years, from a purely motor or sensory-motor one to a more complex and complicated set of functions that mediate the full range of goal directed behaviors. Thus, in addition to its involvement in the expression of goal directed behaviors through movement, the basal ganglia is also involved in the development of the substrates that lead to movement. In other words, the elements that drive actions, including emotions, motivation, and cognition. Indeed, regions within each of the basal ganglia nuclei have been identified as serving not only a sensory-motor function, but also limbic and cognitive ones as well. Ventral regions of the basal ganglia play a key role in reward and reinforcement and are important in the development of addictive behaviors and habit formation. More central basal ganglia areas are involved in cognitive functions such as procedural learning; and working memory tasks. Diseases affecting mental health, including schizophrenia, drug addiction, and obsessive compulsive disorder, are linked to pathology in the basal ganglia, albeit, the ventral basal ganglia. This is in contrast to diseases that interfere with motor control and primarily affect the dorsal basal ganglia. Thus, the role of the basal ganglia in cognitive and emotional behaviors is now as well accepted as is its role in motor control.

Although several new theories of general function have emerged from the enormous progress in understanding the anatomy, physiology, and behaviors associated with the basal ganglia, the actual role of the basal ganglia in executing goal-directed behaviors remains elusive. What is clear from the recent progress is that this set of subcortical nuclei work in tandem with cortex (particularly frontal cortex) via a complex cortico-basal ganglia network to develop and carry out complex behaviors. The present review describes the organization of the primate basal ganglia from the perspective of cortical function, in carrying out goal-directed actions. In some situations, when necessary, data is also presented from rodent work. We have integrated, whenever possible, the anatomical data with physiological and behavioral findings, thus emphasizing the functional organization of this complex network.