Mirror-induced visual illusion and its application in stroke rehabilitation

Abstract

Stroke is among the common causes of death and disability globally. Hemiparesis secondary to stroke is commonly reported and results in reduced quality of life and decrease participation in the activities of daily living. Mirror-induced visual illusion (MVI) achieved via mirror therapy is widely adopted to enhance motor recovery among stroke survivors. Facilitation of neural activity in the ipsilesional primary motor cortex (M1) which is known to modulate motor planning and execution has been found during MVI. However, the ipsilesional motor facilitation during MVI without movements of the associated body part requires further investigation. The aims of this thesis entail examining the neural processes modulating MVI, the contribution of kinaesthetic motor imagery in MVI and the effect of manipulating fingertapping complexity and image clarity on top-down motor facilitation and visuo-motor memory during MVI paradigm. The thesis is composed of four studies; Critical review, Activation likelihood estimation (ALE) meta-analysis, pilot behavioural study and an observation study using the functional near infrared spectroscopy (fNIRS). The critical review and the activation likelihood estimation (ALE) meta-analysis adopted systematic review processes with qualitative and quantitative analytical approaches respectively, to identify the most frequently reported neural substrates of MVI and to review evidence supporting the role of kinaesthetic motor imagery in the MVI processes. Both reviews indicated involvement of the various neural substrates in the MVI paradigm, including; M1, primary somatosensory cortex, precuneus and the cerebellum, which have been shown to mediate the mental processes of kinaesthetic motor imagery. Specifically, the ALE meta-analysis indicated complete lateralization of neural activity towards the ipsilateral hemisphere in the visual-related areas, such as cuneus, middle occipital gyrus, fusiform gyrus and lingual gyrus, indicating the influence of MVI in early visual perception processes. The reviewed studies indicated the potential benefits of manipulating the task and contents of the mirror image for better response in the neural system during MVI. Therefore, the main study of this thesis examined if altering the complexity of finger-tapping task and clarity of mirror image would enhance top-down-motor facilitation and visuo-motor memory demand in the MVI paradigm. The main study was a cross-sectional observation study using functional near infrared spectroscopy (fNIRS) among fifteen stroke survivors [mean age(standard deviation) = 60.9(6.8) years] and eighteen healthy volunteers [61.11(7.4) years]. Findings of the study indicated statistically significant higher motor facilitation at the ipsilesional/ipsilateral M1 during complex finger-tapping task with blurred mirror image (complex+blurred condition) in comparison with simple finger-tapping task with clear mirror image (simple+clear condition) in the two groups (p=0.03). Higher statistically significant motor facilitation [F=5.08; p=0.03; partial eta squared=0.14] was reported among the stroke survivors in comparison with healthy volunteers. Likewise, higher statistically significant visuo-motor memory demand [F=7.71; p<0.01; partial eta squared=0.20] was reported among the stroke survivors in comparison with healthy volunteers. Enhancement of motor activity in the ipsilesional hemisphere among chronic stroke survivors could be achieved by manipulating the finger tapping complexity and clarity of mirror images in the MVI paradigm. Future study should examine whether such gains in the motor activity would result in enhanced functional output using randomized controlled trial design.

Date of Award	12 Apr 2021
Original language	English
Awarding Institution	Department of Rehabilitation Sciences
Supervisor	Stanley John Winser (Chief supervisor)