Effects of Early versus Late Rehabilitative Training on Manual Dexterity after 1 Corticospinal Tract Lesion in Macaque Monkeys 2 3 Authors and Affiliations 4

26 Dexterous hand movements can be restored with motor rehabilitative training after a 27 lesion of the lateral corticospinal tract (l-CST) in macaque monkeys. To maximize 28 effectiveness, the optimal time to commence such rehabilitative training must be 29 determined. We conducted behavioral analyses and compared the recovery of dexterous 30 hand movements between monkeys in which hand motor training was initiated 31 immediately after the l-CST lesion (early-trained monkeys) and those in which training 32 was initiated 1 month after the lesion (late-trained monkeys). The performance of 33 dexterous hand movements was evaluated by food-retrieving tasks. In early-trained 34 monkeys, the performance evaluated by the success rate in the vertical-slit task, 35 retrieving a small piece of food through a narrow vertical slit, recovered to the level of 36 intact monkeys during the first 1–2 months after lesioning. In late-trained monkeys, the 37 task success rate averaged about 30% even after 3 months of rehabilitative training. We 38 also evaluated the hand performance with the Klüver board task, in which the monkeys 39 retrieved small spherical food pellets from cylindrical wells. Although the success rate 40 of the Klüver board task did not differ between earlyand late-trained monkeys, 41 kinematic movement analysis showed that there was a difference between the groups: 42 the late-trained monkeys with the improved success rate frequently used alternate 43 movement strategies that were different from those used before the lesion. These results 44 suggest that early rehabilitative training after a spinal cord lesion positively influences 45 subsequent functional recovery. 46 47