Effects of early versus late rehabilitative training on manual dexterity after corticospinal tract lesion in macaque monkeys

Dexterous hand movements can be restored with motor rehabilitative training after a lesion of the lateral corticospinal tract (l-CST) in macaque monkeys. To maximize effectiveness, the optimal time to commence such rehabilitative training must be determined. We conducted behavioral analyses and compared the recovery of dexterous hand movements between monkeys in which hand motor training was initiated immediately after the l-CST lesion (early-trained monkeys) and those in which training was initiated 1 mo after the lesion (late-trained monkeys). The performance of dexterous hand movements was evaluated by food retrieval tasks. In early-trained monkeys, performance evaluated by the success rate in a vertical slit task (retrieval of a small piece of food through a narrow vertical slit) recovered to the level of intact monkeys during the first 1-2 mo after the lesion. In late-trained monkeys, the task success rate averaged ∼30% even after 3 mo of rehabilitative training. We also evaluated hand performance with the Klüver board task, in which monkeys retrieved small spherical food pellets from cylindrical wells. Although the success rate of the Klüver board task did not differ between early- and late-trained monkeys, kinematic movement analysis showed that there was a difference between the groups: late-trained monkeys with an improved success rate frequently used alternate movement strategies that were different from those used before the lesion. These results suggest that early rehabilitative training after a spinal cord lesion positively influences subsequent functional recovery.