Functional synchronization in repetitive bimanual prehension movements.

To examine the mechanisms of functional bimanual synchronization in goal-directed movements, we studied the movement kinematics of motorically unimpaired subjects while they performed repetitive prehension movements (either unimanually or bimanually) to small food items. Compared to unimanual conditions, bimanual movement execution yielded a significantly prolonged mouth contact phase. We hypothesized that this threefold prolongation led to a proper functional synchronization of the movement onsets of both hands at the beginning of each new movement cycle. That these temporal adjustments occurred in the movement phase with maximal haptic input points to the importance of sensory feedback for bimanual coordination. These results are discussed with respect to the important role of sensory feedback in the timing of coordinated bimanual movements. Furthermore, we propose that time-based coordinating schemas, which are implemented by the cerebellum and the posterior parietal cortex using sensory feedback, underlie functional inter-limb coordination.