Effect of task-specific training on functional recovery and corticospinal tract plasticity after stroke

Purpose: To determine the optimal timing of rehabilitation and its role in corticospinal tract (CST) plasticity after stroke. Methods: Rats were subjected to photothrombotic infarct. The large stroke (LS) and small stroke (SS) groups were subdivided and task-specific training (TST) was initiated at 1, 5, or 14 days poststroke. Behavioral tests were performed at 2, 7, 14, 21, 28, and 35 days poststroke. The differences of axonal sprouting in the cortex, red nucleus, cerebral peduncle, and pyramid level were compared by immunohistochemistry. Results: SS groups with TST starting at 1 day and 5 days showed significantly better recovery in the behavioral tests. LS group with TST starting at 5 days showed better recovery, while those with TST starting at 1 day showed worse recovery. Contralesional axonal sprouting was increased in both groups with TST starting at 5 days. However, it was decreased in the LS group with TST starting at 1day. Transcallosal axonal sprouting from the contralesional motor cortex was increased in the LS group with TST starting at 5 days. Conclusions: Functional recovery after stroke may vary, depending on the lesion size and the timing of rehabilitation. The underlying mechanism may involve contralesional CST plasticity and transcallosal axonal sprouting.