Sensorimotor Cortex Activation during Mirror Therapy in Healthy Right-Handed Subjects: A Study with Near-Infrared Spectroscopy

Abstract

Abstract.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.

Mirror Observation of Finger Action Enhances Activity in Anterior Intraparietal Sulcus: A Functional Magnetic Resonance Imaging Study

“…In addition, Garry et al 10) used TMS to demonstrate that mirror-image observation of the unilateral moving hand enhanced the excitability of the M1 ipsilateral to the moving hand in healthy subjects. Similar results were obtained in another study using functional magnetic resonance imaging (fMRI) 11) . These results suggest the possibility that mirror therapy optimizes neuroplasticity and promote recovery from paralysis in brain-injured patients 10) .…”

Reflections on Mirror Therapy

“…The primary motor cortex (M1) ipsilateral to the active (reflected) hand, that is, M1 projecting to the unseen hand behind the mirror, is considered the final common pathway for the beneficial effect of MVF according to various studies. A complete reversal of lateralization when moving a limb that is reflected by a mirror (ie, the ipsilateral side taking over control), as put forward by some, 53,56,59 is unlikely; however, there is accumulating evidence that MVF decreases the motor threshold and enhances corticospinal output of the ipsilesional M1 in stroke patients. 55,63,[65][66][67][68] This is probably mediated through a reduction in interhemispheric inhibition (from contralateral/lesional to ipsilateral/lesional) 63 and/or a reduction of intracortical inhibition.…”

“…37-47 MEG was the neuroimaging modality in 5 article, 48-52 EEG in 4, 53-56 PET in 2, 57,58 and NIRS in 2. 59,60 Nine studies investigated the effect of MVF on cortical activation with TMS 47,61-68 ; 1 study used both TMS and fMRI. 47 In Tables 1 to 4, the included articles and their methodologies are listed according to modality.…”

Effects of mirror training on motor performance in healthy individuals: a systematic review and meta-analysis

“…Although motor performance of the non-dominant hand was usually evaluated by MTr-induced dominant hand performance, similar behavioural effects of MTr can be observed in the dominant hand by training with the non-dominant hand 18 52 53. However, Imai et al 54 surmised that the effects of MTr were more pronounced in the non-dominant hand when the opposite hand moved. Further studies are needed due to insufficient research in this setting.…”