Inter-lateral Referral of Sensation in Health and Disease Using a Mirror Illusion—A Scoping Review

OBJECTIVE: Perception of touch is expected at the location where it is applied. However, there are indications that being touched may be perceived on the contralateral side when seen as a reflection in a mirror at midline. Such inter-lateral referral of sensation (RS) lacks evidence, as mirror therapy research usually focusses on movement-based techniques. This study aimed to map out existing research across disciplines regarding the effect of RS in health and disease, and to understand whether there is rehabilitation potential in RS. METHOD: A scoping review was conducted to map out concepts and keywords across disciplines interested in this topic, using keywords in several languages, and a wide range of databases and additional sources. RESULTS: The review revealed mostly cross-sectional experiments and included over 486 participants: healthy, or with stroke, complex regional pain syndrome, amputation, nerve graft surgery or radial fracture. Procedures varied regarding stimulation tool, time and location, with two stimulating replacements, one the face and one a variety of areas. Response rates ranged from 0 to 100%. In general, RS was regarded as a phenomenon or even as a predictor of maladaptive neuroplasticity. There was little research into using RS stimulation as a modulatory tool to improve sensory perception. CONCLUSIONS: RS challenges the understanding of touch perception and elicits a range of questions regarding neuro-processing. A modulatory approach using RS has not been described, requires investigation and, if promising, development as an intervention.