EFFECTS OF REVERSIBLE INACTIVATION OF THE SUPPLEMENTARY MOTOR AREA (SMA) ON UNIMANUAL GRASP AND BIMANUAL PULL AND GRASP PERFORMANCE IN MONKEYS

The supplementary motor area (SMA) was reversibly inactivated by musci mol microinfusion in two monkeys while they were performing two motor tasks: (1) a delayed conditional bimanual drawer pulling and grasping sequence which was initiated on a self-paced basis; (2) a unimanual re ach and grasp task (modified Kluver board task). Unilateral or bilater al inactivation of the SMA induced a prominent deficit in trial initia tion of bimanual sequential movements, affecting the hand contralatera l to the inactivated side or both hands, respectively. The deficit was a long lasting (10-15 min or more) inability of the monkey to place i ts hand (s) in the ready position on start touch-sensitive pads, a con dition required to initiate the drawer task. However, if after such a deficit period, the experimenter put his hand on the start touch-sensi tive pad to initiate the trial, then the monkey executed the drawer ta sk without obvious motor deficit. SMA inactivation did not affect unim anual reaching and grasping movements in the board task. In contrast t o the SMA, inactivation of other motor areas (primary, premotor dorsal , anterior intraparietal area) did not affect the initiation of moveme nt sequences in the drawer task. These data thus indicate that the SMA plays a crucial and specific role in initiation of self-paced movemen t sequences. However, SMA inactivation did not prevent the monkeys to perform coordinated movements of the two forelimbs and hands, indicati ng that SMA is not necessary for bimanual coordination.