Is there a correlation between functional recovery of manual dexterity after motor cortex lesion and initial motor...

A cohort of 13 adult macaques offered a unique opportunity to collect over several years manual dexterity data, from an initial learning phase in intact animals to a terminal phase of functional recovery after unilateral lesion of primary motor cortex (M1). Manual dexterity was assessed daily using the modified Brinkman Board task, yielding a total score given by the number of food pellets retrieved by one or the other hand from vertical and horizontal slots. A motor learning curve slope was established during the initial learning phase before reaching a stable performance with the dominant hand. Later, following contralateral M1 lesion, the manual dexterity score dropped to zero, before a progressive spontaneous functional recovery occurred, reaching a unique plateau of usually incomplete recovery. A recovery curve slope was calculated. In six of the 13 monkeys, a treatment aimed at enhancing the functional recovery of manual dexterity was applied, yielding a second plateau of recovery added to the first spontaneous recovery plateau. A recovery curve slope was also calculated for the second plateau. The hypothesis that steep initial motor learning is correlated with rapid and efficient functional recovery after M1 lesion was tested. In contradiction to this hypothesis, the data showed an inverse correlation with decreasing recovery curve slopes as a function of increasing learning curve slopes. This result suggests that the mechanisms underlying initial motor learning may be different from those mobilized for functional recovery after M1 lesion.