Mirror-Induced Visual Illusion of Hand Movements: A Functional Magnetic Resonance Imaging Study

Objective: To identify neural networks associated with the use of a mirror to superimpose movement of 1 hand on top of a nonmoving contralateral hand (often referred to as mirror therapy or mirror-induced visual illusion). Design: A functional magnetic resonance imaging (fMRI) study of mirror-induced visual illusion of hand movements using a blocked design in a 1.5T magnetic resonance imaging scanner. Neural activation was compared in a no-mirror experiment and a mirror experiment. Both experiments consisted of blocks of finger tapping of the right hand versus rest. In the mirror experiment, movement of the left hand was simulated by mirror reflection of right hand movement. Setting: University medical center. Participants: Eighteen healthy subjects. Interventions: Not applicable. Main Outcome Measures: Differences in fMRI activation between the 2 experiments. Results: In the mirror experiment, we found supplementary activation compared with the no-mirror experiment in 2 visual areas: the right superior temporal gyrus (STG) and the right superior occipital gyrus. Conclusions: In this study, we found 2 areas uniquely associated with the mirror-induced visual illusion of hand movements: the right STG and the right superior occipital gyrus. The STG is a higher-order visual region involved in the analysis of biological stimuli and is activated by observation of biological motion. The right superior occipital gyrus is located in the secondary visual cortex within the dorsal visual stream. In the literature, the STG has been linked with the mirror neuron system. However, we did not find activation within the frontoparietal mirror neuron system to support further a link with the mirror neuron system. Future studies are needed to explore the mechanism of mirror induced visual illusions in patient populations in more detail.