Anterior and posterior callosal contributions to simultaneous bimanual movements of the hands and fingers

In order to study the role of the corpus callosum in two-handed coordinatio n we tested callosotomy subjects while they attempted to initiate simultane ous discrete movements with both hands. We observed four split-brain patien ts, including one pre- and post-operatively, as well as normal and epilepti c control subjects. Split-brain patients made button presses that were less synchronous than either normal or epileptic controls. Although split-brain patients' average performance did not always differ from control subjects, callosotomy resulted in a 3-fold increase in the variability with which 's imultaneous' movements were initiated. The one subject tested pre- and post -callosotomy showed distinct changes in movement initiation synchrony after both the anterior and the posterior stages of the surgery, These changes s uggest that anterior and posterior callosal fibres may make unique contribu tions to bimanual synchronization, depending on whether responses are self- initiated or in reaction to a visual stimulus. This study demonstrates that neural communication across anterior and posterior fibres of the corpus ca llosum strongly influences the temporal precision of bimanual coordination. Specifically, callosal transmission affects the degree of bilateral synchr ony with which simple simultaneous hand and finger movements are initiated.