The Cerebellum: A Summary of Functional Localization *

The cerebellum of man and higher animals is a vast organ whose functions have proved peculiarly difficult to analyze. All are agreed that it is essential for orderly volitional movement, yet its mode of action remains still a matter of challenging uncertainty. As early as 1824, Flourens stated that removal of the cerebellum did not disturb mental activity or sensory perception, but he fully described the character of the disturbances in movement which follow ablation of the cerebellum, pointing out, among other things, that the gait of a decerebellated animal is similar to that occurring in alcoholic intoxication. Indeed, the staggering, tremor, and slurring of speech observed after cerebellar injury in man led Flourens to suggest that the primary seat of the action of alcohol was in the cerebellum. Actually very little has been added to his vivid description of the motor disturbances produced by cerebellar lesions; but Flourens was obliged to leave, as indeed we must leave, many of the fundamental problems unsolved. It would be incorrect, however, to imply that no progress has been made since his time, for progress, especially in the last several years, has been rapid and the time seems ripe for a critical review of recent work. Attention during the last thirty years has been largely concentrated upon the problem of functional localization within the cerebellum. In 1906, Bolk published his well-known book on the mammalian cerebellum, in which he concluded that specific muscle groups in the body are regulated by discrete morphological units within the cerebellum; according to his schema, the lobulus simplex subserved the neck muscles, the posterior lobe the lower extremity, the "formatio vermicularis" the tail, etc. Many attempts have been made to elaborate this attractive hypothesis, but opinion has come to