Functional brain correlates for premovement planning and compensatory adjustments in rapid aimed movement

The distinction between pre-movement planning and feedforward adjustments has been considered crucial to an understanding of the neural control of goal-directed movement. Rapid and accurate responses without manifest discontinuities are controlled by parallel neural processes that concurrently provide for trajectory planning and feedforward updating as the response unfolds. However, the functional neural substrates associated with these parallel 'paths' have yet to be determined. The purpose of this dissertation was to provide evidence for a functional neural distinction between these two motor control processes. Numerous reports identify a role for the cerebellum in pre-movement planning, while sensorimotor (SM) areas appear to support the execution of ongoing adjustments to the movement trajectory. To test these hypotheses, the performance of six subjects with unilateral SM area stroke were compared to that of matched control subjects and 5 subjects with unilateral cerebellar stroke were compared to that of matched control subjects under conditions of a timed-response movement paradigm. Subjects rapidly flexed or extended the forearm to targets presented in either a fixed (predictable condition) or a random sequence (unpredictable condition). Subjects with SM area stroke used the limb ipsilateral to the side of the SM lesion. Subjects with cerebellar stroke used the limb that was contralateral to the side of the cerebellar lesion. Time to prepare the response was manipulated by varying the time of target presentation relative to an auditory cue for movement initiation. Kinematic analysis and multiple regression were used to determine the effect of pre-movement planning and trajectory updating on end-point accuracy. Both the subjects with SM area strokes and those with cerebellar strokes were significantly less accurate than their matched controls. Overall, the source of the inaccuracy for individuals with SM area strokes was largely the result of a deficiency in the performance of feedforward compensatory adjustments. In contrast, deficits in pre-movement planning accounted for the inaccuracy for individuals with cerebellar strokes. These results suggest a role for SM areas in feedforward updating while the cerebellum has substantial involvement in the planning of goal-directed aiming tasks.