Temporal control of a bimanual task in patients with cerebellar dysfunction.

The objective of the study was to investigate whether temporal control during a goal-directed bimanual action is disturbed in cerebellar patients. The task was to open a drawer with one hand and to reach and grasp a small object with the other hand. Interlimb coupling was determined at start and end positions. Cerebellar patients as compared to normal subjects showed an increased offset for initiating the hand movements which denotes the involvement of the cerebellum for organizing the components underlying the bimanual task. The reduced simultaneity was caused by a delayed movement onset of the grasping (non-leading) hand as compared to the pulling hand. Lack of vision increased the degree of desynchronization for the patients at the start position, indicating that they depended on external cues for organizing the temporal coordinates of the combined motion pattern. At the goal, the magnitude of temporal offset was similar/smaller than at movement onset which can be related to feedforward mechanisms that are used to anticipate the limbs' end positions. These results confirm the role of the cerebellum for planning the temporal ordering of movement sequences into a synergic action.