Sensory Referral for Rehabilitation? Scoping review of the literature, exploratory within-person randomized mixed-methods experiment with healthy subjects and feasibility study in chronic stroke

Clinical observation of touch, watched in a mirror at midline (sensory referral, SR) restoring sensory function 12 years post stroke is the basis of this thesis.

A scoping review of the multi-disciplinary literature identified studies in health and disease on 486 participants. SR response rates varied between 0 and 100%, and were highest in Complex Regional Pain Syndrome or when rubber hands were stimulated in preference to participant’s own. Though procedures differed between studies, SR response was regarded as a phenomenon, even as a predictor of maladaptive neuroplasticity, but rarely as a tool to improve sensory perception.

To understand who responds, how and when, and whether there are unwanted effects, a mixed methods study was conducted, mirror-stimulation of 47 healthy participants between 20 and 83 years-old on their hands and feet, and rubber replacements. Eight cycles were randomised by order of testing. Voice recordings showed quality and development of SR. Response rate was 76.6% on at least two occasions, mean intensity 5.19 on the numeric rating scale (NRS), and significantly more often in extraverts who were open to experience. However, some responded with elicited numbness (a negative response), raising the question whether the brain defaults towards normal in disease. As SR developed over time and through dwelling on responding locations, the subsequent stroke feasibility trial provided scope for increasing stimulation time.

Chronic stroke patients recruited from England and Germany reflected a similar SR response rate (5 of 6 experienced SR), with sensory perception even improving in the non-responder. However, whether an engagement with the illusion is sufficient, and whether improvement is higher compared to a control group, requires further study.

Presence of a SR response through visual illusion offers new approaches in rehabilitation and demonstrates potential therapeutic access to the sensory system.