RECEIVING AREAS OF THE TACTILE, AUDITORY, AND VISUAL SYSTEMS IN THE CEREBELLUM

IT IS AN established and universally recognized fact that the cerebellum is a place of convergence of impulses from proprioceptors located throughout the body. The great emphasis placed on this fact, the tacit assumption that the spinocerebellar tracts convey only impulses of proprioceptive origin, and the nature of signs and symptoms resulting from cerebellar deficit doubtless have combined to discourage serious experimental examination of the possibility that impulses from other groups of receptors also pass to this organ. Yet a number of considerations warrant the hypothesis that at least some classes of exteroceptors possess a cerebellar representation. The present investigation was begun when the following facts were considered together: (i) tactile impulses are relayed by the nuclei gracilis and cuneatus to the thalamus and thence to the cerebral cortex, and (ii) these same nuclei, according to many workers, send fibers to the cerebellum by way of the external arcuate fibers. Since there is no good reason for supposing that all impulses carried from the nuclei of the posterior columns by the external arcuate system originate only in proprioceptors, it seemed reasonable to attempt to determine whether impulses from tactile end-organs pass to the cerebellum. The success which has attended recent attempts to map areas of sensory projection in the brain by recording evoked potential changes led us to use this method. It soon was found that the application of an appropriate tactile stimulus to the region of the foot of a cat evokes discrete potential changes in definite cerebellar areas. The extension of this original observation enabled .on of us to secure evidence of the existence of a topical projecti of the cutaneous tactile system to the cerebellum. certain parts