Origin of Motor Reactions Produced by Electrical Stimulation of the Cerebral Cortex

Since the discoveries of Hitzig (1870), knowledge of the functions of the cerebral cortex has been vastly increased. The methods of extirpation of various parts and areas of the cortex and of electrical and chemical stimulation have yielded and still yield valuable information. Notwithstanding this remarkable progress, insight is still lacking into many fundamental problems. One of the principal reasons for this obscurity is undoubtedly the stupendous complexity of the structure of the cortex, concerning which even modern histologic methods warrant only a vague surmise. I refer here especially to the complexity of the cortex in cross-section, in a direction perpendicular to the surface. One finds here, more or less distinctly in various regions of the cortex, an arrangement of the myriads of nerve cell bodies in a few layers. A fundamental subdivision in six layers is nowadays generally accepted. This arrangement is suggestive of separation and difference in function;