Cerebellar contributions to reach adaptation and learning sensory consequences of action

Abstract

When we use a novel tool, the motor commands may not produce the expected outcome. In healthy individuals, with practice the brain learns to alter the motor commands. This change depends critically on the cerebellum as damage to this structure impairs adaptation. However,itis unclear precisely what the cerebellum contributes to the processofadaptationinhuman motor learning. Isthe cerebellum crucial forlearningtoassociate motor commandswith novelsensoryconsequences,calledforwardmodel,oristhecerebellum important for learningto associate sensory goals with novel motor commands, called inverse model? Here, we compared performance ofcerebellar patients and healthy controls in a reaching task with a gradual perturbation schedule. This schedule allowed both groups to adapt their motor commands. Following training,we measured two kinds ofbehavior:inone case, people were presented with reach targets near the direction in which they had trained. The resulting generalization patterns of patients and controls were similar, suggesting comparable inverse models.Inthe second case, participants reached withouta target and reported the location of their hand. In controls, the pattern of change in reported hand location was consistent with simulation results of a forward model that had learned to associate motor commands with new sensory consequences. In patients, this change was significantly smaller. Therefore, in our sample of patients, we observed that while adaptation of motor commands can take place despite cerebellar damage, cerebellar integrity appears critical for learning to predict visual sensory consequences of motor commands. © 2012 the authors.