Brain Activity Changes Induced by Transcranial Direct Current Stimulation in Post-Stroke Motor Recovery: A Narrative Review

Brain activity can be assessed using electroencephalography (EEG) through measures such as power spectral density (PSD), functional connectivity, the brain symmetry index (BSI), and event-related brain responses. Transcranial direct current stimulation (tDCS) is an adjunctive intervention for post-stroke motor rehabilitation using different montages, including ipsilesional anodal, contralesional cathodal, and bilateral M1 stimulation. However, EEG-derived neurophysiological responses associated with motor recovery following tDCS have not been comprehensively reviewed. A PubMed search from 2000 to 2025 identified 12 studies investigating the effects of tDCS on oscillatory activity and 3 studies examining event-related brain responses. Five studies evaluated tDCS alone (without rehabilitation), whereas 10 investigated tDCS combined with rehabilitation. For tDCS alone, ipsilesional anodal stimulation (anode over the ipsilesional M1 and cathode over the contralateral supraorbital area) and bilateral M1 stimulation (anode over the ipsilesional M1 and cathode over the contralesional M1) showed similar trends toward enhancing high-frequency power and functional connectivity, whereas contralesional cathodal stimulation tended to reduce beta band connectivity. For tDCS combined with rehabilitation, PSD findings were inconsistent; however, BSI and event-related desynchronization (ERD) following ipsilesional anodal stimulation consistently showed increased high-frequency activity associated with motor improvement. ERD enhancements were also observed following bilateral M1 stimulation. Overall, heterogeneity in EEG analytical methods likely contributes to inconsistent findings. Nevertheless, current evidence suggests that ipsilesional anodal and bilateral M1 stimulation may upregulate high-frequency activity in individual with stroke. Future systematic studies integrating standardized EEG analyses with clinical outcomes across different tDCS montages are needed to establish EEG-based guidelines for post-stroke motor rehabilitation.