Challenging Marr’s theory of the cerebellum

Introduction to motor learning theory There have been successive attempts to understand the relationships between the structure, function, and dynamics in neuronal circuits (Arbib et al., 1998) in the hope of explaining behavior. At different times these attempts have been based on the available experimental data and conceptual tools and have been synthesized into various theories and models. One of the most famous is Marr’s theory of the cerebellum, the so-called motor learning theory (MLT; Marr, 1969), which was developed in the late 1960s and has since then dominated the view of how the cerebellum might function. To be fair we must say that the MLT was extended by Albus two years later (Albus, 1971) and then further developed by Ito in the subsequent decades (Ito, 1972; Ito, 1984; Ito, 1993, 2006, 2008). Thus, it is appropriate to consider it as the Marr–Albus–Ito theory. The MLT was based purely on statistical connectivity rules, so that, unavoidably, it did not take into account the myriad biological parameters that are now considered critical to guarantee cerebellar network functioning. Therefore, over the years Marr’s theory has been repeatedly challenged by new experimental findings and concepts. In this chapter, I analyze the major aspects of the MLT, how it has been challenged experimentally, and how it has contributed to our understanding of the structure–function relationship of the cerebellar circuit and the adaptive behaviors that are dependent on the cerebellum.