POSTURAL AND SYNERGIC CONTROL FOR 3-DIMENSIONAL MOVEMENTS OF REACHINGAND GRASPING

1. A fundamental question about motor control is related to the nature of the representations used by the nervous system to program the move ment. Theoretically, arm displacement can be encoded either in task (e xtrinsic) or in joint (intrinsic) space. 2. The present study investig ated the organization of complex movements consisting of reaching and grasping a cylindrical object presented along different orientations i n space. In some trials, object orientation was suddenly modified at m ovement onset. 3. At a static level, the final limb angles were highly predictable despite the wide range of possible postures allowed by ar ticular redundancy. Moreover, when object orientation was unexpectedly modified at movement onset, the final angular configuration of the li mb was identical to that obtained when the object was initially presen ted along the orientation reached after the perturbation. 4. At a dyna mical level, a generalized synergy was observed, and tight correlation s were noted between all joint angles implicated in the movement with the exception of elbow flexion. For this joint angle, which did not va ry monotonically, strong partial correlations were however observed be fore and after movement reversal. 5. These results suggest that natura l movements are mostly carried out in joint space by postural transiti ons.