The cerebellum is critical for adaptation, which can be defined as learning of a forward model to reduce sensory prediction errors (Shadmehr et al., 2010). The difference between the role of the cerebellum for limb movements, where it has no access to motor neurons, versus in the case of eye movements, where the cerebellum could also potentially act as a controller, needs further investigation (Medina, 2011). The role of the BG remains contentious but almost all the studies we reviewed tested some kind of sequence task and can be subsumed under

the idea of action selection and instrumental conditioning. A current idea is that the BG injects variability for exploration and then as the best movement is converged upon, variability selleck kinase inhibitor is reduced and stereotypy and automatization ensue (Costa, 2011). Quality of movement execution, i.e., motor skill, is not explained by this framework and has not been the focus of these studies, although in a few SCH 900776 supplier studies, striatal lesions have been shown to impair tasks that can be considered tests of motor skill (Costa et al., 2004 and Wächter et al., 2010). Motor skill, faster and more precise movements compared to baseline, has been surprisingly understudied, compared to either adaptation or selection

of sequential actions, but to the degree that it has been studied, M1 appears to be a necessary structure. The implication Cell press of this framework is that skill may be a late development evolutionarily. Adaptation and learning to select the right actions from a hard-wired repertoire of synergies might suffice both for the vast majority of animals and for eye movements

in primates. Where to go from here? One fruitful direction would be for investigators using particular model systems with particular behavioral tasks to take a look across at their colleagues, predicated on the assumption that anatomical homology allows for experimental and conceptual borrowings. Of particular interest is to ask how error-based and reward-based processes combine during motor learning, especially as anatomical connections between the cerebellum and the basal ganglia have recently been described (Hoshi et al., 2005). We finish with a few suggestions for future directions: (1) rodent models could potentially be developed that combine the finer-grained kinematic analysis of the rat reach-and-grasp task (Whishaw et al., 2008) with a sequential action selection requirement. (2) Human and primate studies of sequence learning could pay closer attention to movement quality as well as sequence order, i.e., start to study motor skill with quantitative kinematic analysis. Suggestions (1) and (2) could help characterize the precise nature of the interaction between the BG and M1 during skill learning. (3) Rodent models of limb adaptation could be developed.