Action observation in the modification of postural sway and gait: Theory and use in rehabilitation.

The discovery of cortical neurons responsive to both the observation of another individual's movement and one's own physical movement has spurred scientists into utilising this interplay for rehabilitation. The idea that humans can quickly transfer motor programmes or refine existing motor strategies through observation has only recently gained interest in the context of gait rehabilitation but may offer significant promise as an adjunctive therapy to routine balance training. This review is the first dedicated to action observation in postural control or gait in healthy individuals and patients. The traditional use of action observation in rehabilitation is that the observer has to carefully watch pre-recorded or physically performed actions and thereafter imitate them. Using this approach, previous studies have shown improved gait after action observation in stroke, Parkinson's disease and knee or hip replacement patients. In healthy subjects, action observation reduced postural sway from externally induced balance perturbations. Despite this initial evidence, future studies should establish whether patients are instructed to observe the same movement to be trained (i.e., replicate the observed action(s)) or observe a motor error in order to produce postural countermeasures. The best mode of motor transfer from action observation is yet to be fully explored, and may involve observing live motor acts rather than viewing video clips. Given the ease with which action observation training can be applied in the home, it offers a promising, safe and economical approach as an adjunctive therapy to routine balance training.