EEG Biomarkers During Upper-Limb Action Observation Therapy for Stroke Rehabilitation: A Scoping Review

Stroke often leads to persistent upper-limb motor impairments that limit activities of daily living. Action observation (AO) therapy holds promise for priming residual motor pathways even when voluntary movement is minimal. This scoping review aimed to identify EEG-derived indicators of cortical engagement during upper-limb AO therapy after stroke, examine how these neural metrics relate to motor outcomes, and summarize methodological variability across studies.

Following PRISMA-ScR guidelines, six databases were searched, yielding 386 records. Twenty-two studies met inclusion criteria by combining upper-limb AO paradigms with EEG outcomes and motor assessments. Data were extracted on AO task characteristics, EEG acquisition and processing, biomarker definitions, and associations with behavioral measures.

Across paradigms, sensorimotor event-related desynchronization (ERD) in the mu (8-13 Hz) and beta (13-30 Hz) bands consistently indexed activation of action observation network. Multi-week AO therapy interventions produced sustained increases in mu/beta ERD, beta-band connectivity, and fast-to-slow spectral power ratios. These neural changes frequently correlated with improvements in Fugl-Meyer Assessment scores, dexterity tests, and functional performance. Furthermore, AO-driven brain-computer interface paradigms and combined AO and motor imagery elicited robust cortical and functional gains, underscoring the potential of EEG-guided, closed-loop AO therapies.

EEG provides reproducible, temporally precise biomarkers of AO-induced cortical engagement and motor recovery in stroke rehabilitation. Nonetheless, heterogeneity in AO protocol and stimulus design hampers cross-study comparability. Future work should standardize protocols and determine reliable biomarkers for real-time AO personalized neurorehabilitation.