Effect of reversible inactivation of the ipsilesional motor cortex on manual dexterity. Effects of reversible inactivation, by infusion of muscimol, of the ipsilesional M1 hand area on the manual dexterity scores for the ipsilesional (left) hand and the contralesional (right) hand. The manual dexterity scores (ordinate) are the number of pellets successively grasped using the precision grip (opposition of thumb and index finger) in the modified Brinkman board task in 45 sec. All inactivation sessions took place post-lesion at time points indicated in the method section. The manual dexterity score was established before ("B") and after ("A") the infusion of muscimol, separately for the vertical and horizontal wells. Two inactivation sessions were conducted in Mk1 and only one in the two other monkeys. The stars are for scores equal to zero, in other words when muscimol infusion completely abolished the corresponding performance. The drop of all scores to zero after infusion ("A" bars) for the right hand demonstrates the efficacy of the inactivation. See text for more detailed description of the results. The star in the session "before muscimol" for Mk2 indicates that this animal did not recover any ability to grasp pellets in the horizontal slots.