Role of primary motor cortex in the control of manual dexterity assessed via sequential bilateral lesion in the adult macaque monkey: A case study

From a case study, we describe the impact of unilateral lesion of the hand area in the primary motor cortex (M1) on manual dexterity and the role of the intact contralesional M1 in long-term functional recovery. An adult macaque monkey performed two manual dexterity tasks: (i) “modified Brinkman board” task, assessed simple precision grip versus complex precision grip, the latter involved a hand postural adjustment; (ii) “modified Klüver board” task, assessed movements ranging from power grip to precision grip, pre-shaping and grasping. Two consecutive unilateral M1 lesions targeted the hand area of each hemisphere, the second lesion was performed after stable, though incomplete, functional recovery from the primary lesion. Following each lesion, the manual dexterity of the contralesional hand was affected in a comparable manner, effects being progressively more deleterious from power grip to simple and then complex precision grips. Both tasks yielded consistent data, namely that the secondary M1 lesion did not have a significant impact on the recovered performance from the primary M1 lesion, which took place 5 months earlier. In conclusion, the intact contralesional M1 did not play a major role in the long-term functional recovery from a primary M1 lesion targeted to the hand area.