The quest to understand bimanual coordination.

Many skillful manipulations engage both hands for goal achievement. Whereas the goal is planned consciously and achieved quasi-invariantly, the articulators are mobilized automatically, but in a flexible manner (Lashley's principle of motor equivalence). In brain disorders affecting hand functions, adaptive mechanisms are mobilized to improve goal achievement. Thus, chronic cerebellar patients were found to initiate a bimanual drawer task with marked intermanual desynchronization as compared to control subjects. This was partly compensated for, however, by adjusting the kinematics as the individual limbs move toward the goal, thereby improving the initial desynchronization. Adaptive strategies rarely correct deficits completely, however. Bimanual movement patterns, either in-phase or anti-phase are relatively stable in healthy human subjects, whereas brain pathology may preferentially impair the anti-phase pattern. This is the case in patients with acquired pathology of the corpus callosum, thereby suggesting that this structure is important for maintaining temporally independent limb and hand movements.