In this review of the human cerebro-cerebellar system, the focus is on the possible contributions of the cerebellum to cognitive and language functions. The role of the cerebellum in these human functions has tended to be obscured by the traditional preoccupation with the motor functions of the cerebellum, which have been widely observed in other vertebrates as well. In the human brain, some phylogenetically new parts evolved and enlarged in the cerebellum, concomitantly with the enlargement of association areas in the cerebral cortex. Anatomical evidence and behavioral evidence combine to suggest that this enlarged cerebellum contributes not only to motor function but also to some sensory, cognitive, linguistic, and emotional aspects of behavior. The anatomical evidence derives from the modularity of the cerebellum, whose cortical nerve cells are organized into longitudinal micro-modules, which are arrayed perpendicular to the cortical surface and parallel to each other. The number of these micro-modules increased when the cerebellum enlarged, which enlarged the computing capabilities of the network. (From principles underlying the processing of information, it is known that when modules with modest processing capabilities are assembled in large numbers in parallel, the resulting network can achieve remarkably powerful computing capabilities.) Such cerebellar computing capabilities can be utilized in the different areas of the cerebral cortex to which the cerebellum sends signals. The cerebellar output connections convey signals through the thalamus to the cerebral cortex in segregated channels of communication, which preserve the modularity of the cerebellum. Through these channels, modules in the lateral cerebellum can send signals to new cognitive and language areas of the cerebral cortex, such as Broca's area in the prefrontal cortex. The anatomy of the human cerebro-cerebellar system therefore suggests that the cerebellum can contribute to the learning not only of motor skills but also of some cognitive and language skills. Supporting this anatomical evidence is the mounting behavioral evidence, obtained both in normal brains and in clinical studies, which indicates that the lateral cerebellum is indeed involved in some cognitive and language functions.
