Basal Ganglia: Internal Organization

The basal ganglia are a group of highly interconnected nuclei involved in a variety of functions, including movement and cognition. The dorsal component, which is primarily related to motor and associative functions, consists of the striatum, external segment of the globus pallidus, subthalamic nucleus, and the internal segment of the globus pallidus and substantia nigra pars reticulata. The latter two structures are the output nuclei of the basal ganglia whereas the striatum is the principal input structure. The major inputs to the basal ganglia arise in the cerebral cortex and thalamus and are carried by the corticostriatal and the thalamostriatal pathways. This information is processed in the striatum and transmitted by various routes to the output nuclei. The basal ganglia then influence behavior by these structures projecting to thalamus and thence to the cortex, or to other subcortical structures involved in movement. Overlying this feed-forward system is feedback from dopamine neurons in the substantia nigra pars compacta that modulates the flow of cortical and thalamic information through the basal ganglia.