Systematic review: Resting state functional MRI as a biomarker for non-invasive brain stimulation in upper limb...

Stroke is a leading cause of adult-onset disability. Non-invasive brain stimulation (NIBS) techniques such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and transcutaneous vagus nerve stimulation (tVNS) may improve arm weakness after stroke. Resting-state functional MRI (rs-fMRI) and near-infrared spectroscopy (rs-fNIRS) assess brain connectivity. Identifying the effect of NIBS on rs-fMRI/rs-fNIRS may illuminate the post-stroke recovery process. This systematic review assesses NIBS effects on clinical and rs-fMRI/rs-fNIRS outcomes in stroke survivors with arm weakness.

Systematic searches were conducted in EMBASE and MEDLINE. Articles involving adults with arm weakness from stroke, treated with more than one session of NIBS (TMS/tDCS/tVNS) and reporting clinical and rs-fMRI/rs-fNIRS outcomes at baseline and post-intervention were included. The Cochrane Risk of Bias tool was used to assess the methodological quality of included studies. Data extraction and narrative synthesis were performed.

Twelve articles containing 393 participants were included. Nine studies assessed TMS, two studies assessed tDCS, and one study used dual-mode stimulation (TMS and tDCS). All studies showed significant improvements in clinical measures of arm function compared to baseline following NIBS. All studies showed changes in functional connectivity post-intervention. Enhanced interhemispheric connectivity, particularly between primary motor cortices, was positively correlated with functional outcomes.

Both TMS and tDCS are promising adjunctive therapies for arm weakness post-stroke. Rs-fMRI, particularly interhemispheric connectivity, may provide a valid biomarker of restitution of function with NIBS. Future research should involve.