Visual guidance modulates hemispheric asymmetries during an interlimb coordination task.

The cerebral hemispheres of humans exhibit functional asymmetries. It is generally thought that the left hemisphere contributes to higher order planning of demanding motor tasks, while the right hemisphere plays an important role in processing visual or proprioceptive stimuli and controls spatial attention. Few studies have directly investigated which aspects of motor control increase the involvement of right-lateralized areas. We used fMRI to examine hemispheric lateralization during unilateral motor coordination of the wrist and ankle performed either with the left or right body side, and either with or without visual guidance. Visual guidance was provided such that the spatial position of a cursor directly informed subjects about the mode and quality of the coordination pattern. Activation was only considered lateralized for a specific condition if it was significantly stronger in one hemisphere than the other, independent of which body side performed the task. We found that task performance with visual guidance mainly engaged a right-lateralized occipital-temporoparietal network and the inferior frontal gyrus, a circuit known to integrate visual and proprioceptive information to guide movements in space. Importantly, this lateralized activation was only observed when visual guidance was provided, but not when movements were performed without visual guidance or when subjects passively watched a similar visual stimulus without moving their limbs. We argue that the functional lateralization of right visuomotor areas was a direct consequence of performing this motor task in the presence of visual guidance, i.e., visuospatial information was integrated with somatosensory guidance to produce well coordinated hand-foot movements.