The significance of foliation and fissuration of cerebellar cortex. The cerebellar folium as a fundamental unit of sensorimotor integration.

I propose the general hypothesis that each individual folium in the cerebellum is an integrative module that is involved in unique sets of sensorimotor transactions. Although the basic types of operations carried out by cerebellar cortex may be similar in all folia, the mosaic of afferent sources, intrinsic organization and efferent destinations appear to be unique for each folium. I believe that this conception is supported by: 1) comparative data which illustrate species-typical folial patterns, 2) neuroanatomical data which reveal not only different structural features of folial crowns and fundi, but differential afferent and efferent connectivity of different folia as well, 3) physiological data, which demonstrate unique patterns of afferent activity in different folia, and especially by 4) ontogenetic data which establish that each folial crown expands and differentiates into an architecturally distinct cortical entity. Taken together, all these lines of evidence suggest that the numbers and patterns of folia exhibited by the cerebellar cortex of different mammals are morphological indicators of differential organization of sensorimotor control functions in each animal. Even intraspecific individual variations in folial number, size and pattern may signify structural-functional determinants of some individual differences in sensorimotor transactions. Since so little research has addressed the many testable ideas embodied in these general hypotheses, it seems to me that neuroscientists have a long way to go to clarify how the many different folia and lobules of cerebellar cortex actually function in the common, everyday, orderly, dynamic and ongoing reflex, postural, learned and deliberate behavioral sequences that characterize the normal behavioral repertoires of different animals. The enormous advances in understanding brought forth by the extensive research and writings of Professor Brodal and his colleagues have expanded our horizons to avail us of an enormous range of new vistas into cerebellar functional morphology. It is now the task of neurobiologists to explore these diverse new domains in ever greater depth and detail.