Mirror Neuron Applications on Motor Recovery in Stroke Patients: A Systematic Review

Abstract
Background: Mirror neurons represent a variety of neurons that fire when the subject executes a motor act or observes others making the same action. A lot of therapeutic applications based on the existence of mirror neurons are widely used today in the field of stroke rehabilitation.
Objectives: To summarize the best evidence of the effec-tiveness of mirror neuron applications for improving motor function, activities of daily living, spasticity, pain, visuospatial neglect, sensation, quality of life and muscle power in the stroke patients.
Methods: We searched the following electronic databases: Pubmed (October 2017), Cochrane Library (November 2017) and PEDro (November 2017). We also checked the reference lists. We included Randomized Controlled Trials (RCTs) that compare mirror neuron applications (mirror therapy, motor imagery/mental practice, action observation therapy or virtual reality reflection therapy) with conventional physical or occupational therapy for patients after stroke. Then we selected the trials that match the inclusion criteria, and we assessed the methodological quality of studies and extracted data. Finally, we analyzed the results by pooling the data of change scores between pre- and post-intervention through calculation of the overall Standardized Mean Differences (SMDs) with 95% Confidence Interval (CI).
Results: We included 44 studies with a total of 1792 participants. Of the 44 studies, 4 interventions based on mirror neurons were studied. Firstly, mirror therapy may have a significant effect on motor function of the upper extremity; however, effects on motor function are influenced by the variation of mirror therapy, activities of the unaffected limb showed greater effect than bilateral activities. We found limited evidence for improving walking ability. Secondly, motor imagery/mental practice showed a significant improve-ment on the motor function specially for the lower extremity functions. Thirdly, we found limited evidence of action ob-servation therapy in improving motor function of the upper extremity, walking ability. Finally, we included only one study that used virtual reality reflection therapy in stroke rehabili-tation, so we didn't include it in the pool analysis.
Conclusion: There is an evidence from the included RCTs on the effectiveness of mirror therapy on improving motor function of the upper extremity. Additionally, we found a significant positive effect of mental practice on motor function specially the walking ability. And there was a poor evidence on the effects of action observation on motor recovery in patients after stroke. However, much more studies should be conducted to assess the benefits of virtual reality reflection therapy.