Background: Mirror therapy (MT) is becoming an alternative rehabilitation strategy for various conditions, including stroke. Although recent studies suggest the positive benefit of MT in chronic stroke motor recovery, little is known about its neural mechanisms.
Purpose: To identify functional brain changes induced by a single MT intervention in ischemic stroke survivors, assessed by both transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI).
Materials and methods: TMS and fMRI were used to investigate 15 stroke survivors immediately before and after a single 30-min MT session.
Results: We found statistically significant increase in post-MT motor evoked potential (MEP) amplitude (increased excitability) from the affected primary motor cortex (M1), when compared to pre-MT MEP. Post-MT fMRI maps were associated with a more organized and constrained pattern, with a more focal M1 activity within the affected hemisphere after MT, limited to the cortical area of hand representation. Furthermore, we find a change in the balance of M1 activity toward the affected hemisphere. In addition, significant correlation was found between decreased fMRI β-values and increased MEP amplitude post-MT, in the affected hemisphere.
Conclusion: Our study suggests that a single MT intervention in stroke survivors is related to increased MEP of the affected limb, and a more constrained activity of the affected M1, as if activity had become more constrained and limited to the affected hemisphere.
Keywords: Mirror therapy; functional magnetic resonance imaging; ischemic stroke; stroke rehabilitation; transcranial magnetic stimulation.