Basal Ganglia
The basal ganglia include the caudate nucleus, putamen, globus pallidus, and amygdaloid nucleus. The substantia nigra and subthalamic nucleus are closely tied to the basal ganglia, but reside in the brainstem and diencephalon, respectively. The amygdaloid nuclear complex is the oldest phylogenetically and is known as the archistriatum. It is located beneath the uncus in the temporal lobe and is a part of the limbic system. The caudate and putamen make up the neostriatum and are inhibitory in their projections, whereas the globus pallidus (paleostriatum) is excitatory. The putamen and globus pallidus together are also known as the lentiform nucleus. This inhibitory/excitory system creates a feedback loop which originates in the cerebral cortex, projects to the basal ganglia, on to the thalamus and back to the cortex. Lesions here cause various movement disorders, the most familiar of which are Huntington's Chorea resulting from caudate degeneration, and Parkinson's disease resulting from substantia nigra degeneration. Lesions of the globus pallidus produce a paucity of movement, and lesions of the subthalamic nucleus produce what is known as hemiballismus, which is a violent swinging of the extremities.