Impaired direction and extent specification of aimed arm movements in humans with stroke-related brain damage

The role of sensorimotor (S-M) areas in the specification of kinematic para meters for aiming movements was studied by comparing the performance of six subjects with unilateral stroke to that of matched control subjects. Rapid arm movements were made to one of four targets by rotating the forearm in a short (20 degrees) or long (45 degrees) are of motion. Thus, the four tar gets represented two directions (flexion or extension) and two extents (sho rt or long). Subjects with stroke used the arm ipsilateral to the side of t he lesion. A timed-response paradigm was used to dissociate response initia tion and specification. Subjects initiated movements in concert with the la st of four regularly timed tones. A visual cue of the designated target was presented during the preparation interval (400-0 ms) before the last tone. Targets were presented in a fixed sequence (predictable condition) or a ra ndom sequence (unpredictable condition). No significant differences in perf ormance were found between stroke and control groups in the predictable con dition. in the unpredictable condition, subjects with stroke produced more direction errors and were less accurate in extent than the control subjects . As specification time increased to 400 ms, the frequency of direction err ors attenuated less for stroke than for control groups, but the reduction i n magnitude of extent errors was similar for the two groups. When specifica tion was minimal (i.e., <100 ms), default responses were distributed equall y between directions and clustered around the short extent. Further, wrong direction responses did not converge on the designated extent as specificat ion time increased. This pattern of findings is consistent with a view of p arameterization of planning and executing movements, in which direction and extent can be specified in parallel. Our results suggest that ipsilateral S-M areas contribute to the specification of an optimal motor program, part icularly when imperative programming of unimanual goal-directed aiming move ments is required.