Task-based fMRI assessment of rTMS over the primary motor cortex in poststroke hemiparetic upper extremity rehabilitation: A systematic review

Background: Repetitive transcranial magnetic stimulation (rTMS) delivered to the primary motor cortex (M1) is a well-established interventional modality promoting poststroke hemiparetic upper extremity recovery. Functional magnetic resonance imaging (fMRI) is a reliable technique that can be used to investigate the neural mechanism of stroke recovery. The objective of this review is to evaluate the impact of M1-rTMS on poststroke brains, measured by task-based fMRI, and to investigate the relationship between brain activation and poststroke hemiparetic upper extremity recovery facilitated by M1-rTMS. Methods: PubMed, EMBASE, Web of Science, and the Cochrane Library were searched from Jan 2000 to Jan 2024. Two independent researchers screened the literature, extracted data, and qualitatively summarized the fMRI findings from the included studies. Results: Thirteen studies involving 374 poststroke patients are included in this review. During hemiparetic hand movement, 5 out of 10 studies reported increased activation in the ipsilesional M1 following Low frequency-rTMS over the contralesional M1. These activations were represented in both the stimulated M1 and in the sensorimotor networks. Three studies found increased lateralization of brain activation towards the ipsilesional M1 to be positively correlated with motor improvements after stroke and one study found decreased bilateral M1–M1 inhibition to be positively correlated with improved motor performance. Conclusions: Task-based fMRI extends the modulatory effect of rTMS over the M1 in poststroke hemiparetic upper extremity recovery. The treatment mechanism of M1-rTMS is in line with the re-establishment of bi-hemispheric balance, which is correlated with upper extremity recovery after stroke.