The Basal Nuclei

Voluntary movement is essential to the well-being of living animals. Such behaviors are accomplished by signals that direct the actions of individual muscles. Although these signals originate in the cerebral cortex, they are modulated by a variety of subcortical structures. One such group of structures is the basal nuclei and their functionally associated cell groups. Classically, motor systems have been divided into pyramidal and extrapyramidal on the basis of whether the pathway is mediated by corticofugal neurons (pyramidal) or by the basal nuclei, cerebellum, or pathways originating in brainstem (extrapyramidal). However, this distinction is overly simplistic if not inaccurate. Consequently, it is not used here. The basal nuclei are involved in a wide variety of motor and affective behaviors, in sensorimotor integration, and in cognitive functions.