It has long been known that stimulation of the appropriate part of the cerebral cortex will give rise to rhythmic, serially repeated movements of mastication. As a result of early experimental work the existence of an intercalary subcortical center was postulated in the reaction. This center was thought to receive the impulses from the cortex and transform them into the rhythmic series which bring about the movements involved in eating. Evidence both from electrical stimulation and from experiments in which degeneration was employed pointed to the substantia nigra as being such a center.
The corticifugal pathway for reaction of mastication was first traced through the internal capsule by Réthi1 in the rabbit. By sectioning the brain and stimulating the exposed end with faradic current he obtained rhythmic masticatory movements as far caudally as the subthalamic region; below that level he obtained only a steady closure of the jaws. He