What is the role of the cerebellum in motor learning and cognition?

The exact role of the cerebellum in motor learning and cognition is controversial. Nonetheless, recent ideas and facts have prompted an attempt at building and testing a more unified and coherent conceptualization. This article will suggest that the cerebellum might indeed participate in both motor control and cognition, and in motor adaptation, motor learning, and procedural learning. The proposed process would entail stimulus-response linkage through trial and error learning, and would consist of groupings of single-response elements-motor and cognitive-into large combinations. After practice, the occurrence of a sensory or experiential `context' would automatically trigger the combined response. The parallel fiber is the proposed agent of stimulus-response linkage and of combining the response elements. The attempt here is to focus on the role of the parallel fiber as a possible combiner of downstream motor and cognitive elements.