Can simultaneous bilateral movement involve the undamaged hemisphere in reconstruction of neural networks damaged by stroke?

Normalization of upper limb movement remains a difficult problem for a significant subpopulation of hemiplegic stroke patients. Clinical observations prompted investigation of a novel approach using simultaneous identical bilateral movements performed independently. We briefly report 12 controlled single-case experiments using multiple-baseline designs across three separate grasp/reach activities. Unilateral performance tests with the hemiplegic arm using the bilaterally trained actions demonstrated clinically and statistically significant improvements in movement patterns. These improvements were specific to the trained movement and well maintained. Using recent literature we develop a theoretical model proposing that bilateral simultaneous movement promotes interhemispheric disinhibition likely to allow reorganization by sharing of normal movement commands from the undamaged hemisphere. Disinhibition may also encourage recruitment of undamaged neurones to construct new task-relevant neural networks. The potential contribution of spared ipsilateral pathways in the damaged hemisphere, indirect corticospinal pathways and ipsilateral pathways from the undamaged hemisphere is discussed.