This anatomical arrangement seems to indicate that the peripheral substance, and not the central mass, is the point of motor stimulation and the seat of sensitive impressions. It is everywhere admitted that the brain is the organ of thought and will; but for a long time it was believed that the central mass was the important portion, and the convolutions were disregarded. Hippocrates thought they were only a gland. Malpighi and Vieussens thought the same. Ruysch, from their vascularity, considered them as a simple sanguinous network, and Boerhaave and Haller adopted this conclusion. Vic d'Azyr was the first to examine their structure; then came Baillarger, Ehrenberg, Purkinje, Meynert, Luys, Betz, and Charcot, who revealed their precise anatomy. As to their physiology. Gall taught that intelligence is a function of the convolutions; Desmoulins added that the degree of intelligence is in proportion to their number and depth; and Broca, taking the ideas and facts of Dax and Bouillaud, announced the first discovered localization—that of articulate language in the third left frontal convolution.
In 1870 two German scientists, Fritsch and Hitzig, passed a current of electricity across the head and behind the ears of a living subject, which caused movements of the eyes. They referred these movements to stimulation of the gray matter of the convolutions, and set about the verification of their hypothesis. From their experiments they drew the three following fundamental propositions: 1. There are in the head convolutions that may be excited by electricity, and this excitation is followed by the production of determinate movements—depending upon the point excited; other parts being excited without producing movements. 2. The points, which under stimulation induce action in such and such muscular groups, occupy a very limited portion of the cerebral surface. 3. The extirpation of such a point of the surface, known to be a center of distinct movements, paralyzes these movements.
The theory of cerebral localization assumes as proved that there is in the brain a peripheral portion devoted to the production of movements—a motor region; and another where stimulation is not followed by movements—a non-motor region. It further assumes that the motor region may be subdivided into a certain number of small tracts, definitely circumscribed, each of which presides over the movements of a certain muscular group and this group alone. Ferrier, stalling with these conclusions, proceeded with the research, and seems to have established—that the convolutions, in man as well as in the lower animals, may be separated into three regions: the anterior, devoted to intellectual functions; the middle portion, charged with the motor innervation of the body; and a sensitive region where are received the impressions made upon the sense-organs by the external world. To show how Ferrier reaches and justifies these conclusions is the object of this article.
