Sensorimotor cortex activation during mirror therapy in healthy right-handed subjects: A study with near-infrared spectroscopy

Clinical studies have shown that functional motor recovery after stroke may be facilitated by mirror therapy (MT). However, its underlying mechanism is uncertain. In this study, we examined brain activation during unilateral hand movement in 5 right-handed healthy subjects (1 male and 4 females) with or without viewing a mirror reflection of the moving hand (MT). We measured the changes in the concentration of oxygenated hemoglobin in the primary sensorimotor cortex (SMC) using near-infrared spectroscopy. We calculated the laterality index (LI) using the extent of activation in the right and left SMCs. The LIs (+/- standard error of mean) during right hand grasping without and with MT were 0.17 +/- 0.11 (left SMC predominance) and -0.42 +/- 0.24 (right SMC predominance), respectively (p < 0.05). However, there was no significant difference in LIs during left hand grasping without and with MT (0.02 +/- 0.05 and 0.08 +/- 0.05, respectively). The findings suggest that MT is more effective when it is used for dominant right hand movement, and this phenomenon may be the related to the different manipulability between the dominant and non-dominant hands.