Interlimb neural coupling: implications for poststroke hemiparesis.

Interlimb coordination is essential to perform goal-directed daily tasks and purposeful locomotion. The coordination occurs due to spatiotemporal coupling of movements, which also comprises interactions in segmental kinematics, joint dynamics, and muscle activity. Neuroanatomical and neurophysiological linkages at the spinal and brain level are responsible for the coordination. The linkage is termed "neural coupling". According to the task demand, the coupling may occur between two upper limbs or two lower limbs or all four limbs. Central pattern generators play a key role in interlimb coordination by regulating the rhythmic upper and lower limb movements. Neuroanatomically, multiple areas of both cerebral hemispheres via the corpus callosum interact and control the bimanual upper limb movements. There is an interhemispheric synchronization and disinhibition to control the coupled bimanual upper and lower limb movements. Movement of the upper limb also enhances neuromuscular recruitment of the lower limb. In stroke, bimanual motor impairments exist in the form of asymmetry and reduced coordination, which may be related to weakness of the ipsilateral body side lesser than the contralateral side. The aim of the present review was to understand the interlimb coordination and neural coupling and its implication in stroke rehabilitation. The review suggests incorporating the movements of bilateral upper and lower limbs either simultaneously or consecutively for hemiparetic subjects. Further, the conventional and contemporary rehabilitation methods need to be reconsidered while utilizing the coupling concept.