Reinforcement Learning is Impaired in the Sub-acute Post-stroke Period

Background: In humans, most spontaneous recovery from motor impairment after stroke occurs in the first 3 months. Studies in animal models show higher responsiveness to training over a similar time-period. Both phenomena are often attributed to a milieu of heightened plasticity, which may share some mechanistic overlap with plasticity associated with normal motor learning. Objective: Given that neurorehabilitation approaches are frequently predicated on motor learning principles, here we asked if the sensitivity of trial-to-trial learning for 2 kinds of motor learning processes often involved during rehabilitation is also enhanced early post-stroke. In a cross-sectional design, we compared (1) reinforcement and (2) error-based learning in 2 groups: 1 tested within 3 months after stroke (early group, N = 35) another tested more than 6 months after stroke (late group, N = 30). These 2 forms of motor learning were assessed with variations of the same visuomotor rotation task. Critically, motor execution was matched between the 2 groups. Results: Reinforcement learning was impaired in the early but not the late group, whereas error-based learning was unimpaired in either group. These findings could not be attributed to differences in baseline execution, cognitive impairment, gender, age, or lesion volume and location. Discussion: The presence of a deficit in reinforcement motor learning in the first 3 months after stroke has important implications for rehabilitation. Conclusion: It might be necessary to either increase reinforcement feedback given early after stroke, increase the dose of rehabilitation to compensate, or delay onset of rehabilitation approaches that may rely on reinforcement, for example, constraint-induced movement therapy, and instead emphasize other forms of motor training in the subacute time period.