The interaction between training and plasticity in the poststroke brain

Recovery after stroke can occur either via reductions in impairment or through compensation. Studies in humans and nonhuman animal models show that most recovery from impairment occurs in the first 1-3 months after stroke as a result of both spontaneous reorganization and increased responsiveness to enriched environments and training. Improvement from impairment is attributable to a short-lived sensitive period of postischemic plasticity defined by unique genetic, molecular, physiological, and structural events. In contrast, compensation can occur at any time after stroke. Here, we address both the biology of the brain's postischemic sensitive period and the difficult question of what kind of training (task-specific vs. a stimulating environment for self-initiated exploration of various natural behaviors) best exploits this period. Data suggest that three important variables determine the degree of motor recovery from impairment: the timing, intensity, and approach to training with respect to stroke onset; the unique postischemic plasticity milieu; and the extent of cortical reorganization. Future work will need to further characterize the unique interaction between types of training and postischemic plasticity, and find ways to augment and prolong the sensitive period using pharmacological agents or noninvasive brain stimulation.