Synergistic effects of action observation and object affordance on cortical excitability during BCI-triggered motor imagery in stroke: a randomized, within-subject, 2 × 2 factorial study protocol.

BACKGROUND: Brain-computer interfaces (BCI) using motor imagery (MI) offer promising rehabilitation potential for upper limb function in stroke survivors. Conventional paradigms rely on abstract visual feedback, which may lack ecological validity and could limit neural recruitment. Action observation (AO) and object affordance (OA) independently modulate motor cortical excitability via the mirror neuron system and canonical neural pathways. However, their potential synergistic effects in enhancing BCI performance have not been systematically investigated. We propose a novel "Phygital" intervention integrating dynamic visual cues (AO) with static environmental cues (OA) to potentially enhance cortical excitability and support motor rehabilitation.

METHODS: We employed a randomized within-subject 2 × 2 factorial design to disentangle dynamic and static visuomotor components during grasping MI. Participants include subacute stroke survivors with hemiplegia and age-matched healthy controls. Four conditions will be tested: (A) Baseline (pureMI), (B) AO (video-guided imagery), (C) OA (object-focused imagery), and (D) Synergy (simultaneous AO and OA). A 32-channel electroencephalography quantified event-related desynchronization (ERD) in mu and beta bands over sensorimotor cortex. Surface electromyography monitored muscle quiescence. Significant task-related ERD triggered a soft robotic hand exoskeleton to deliver time-locked proprioceptive feedback, closing the sensorimotor loop.

HYPOTHESIS: We hypothesize that congruent simultaneous presentation of AO and OA cues will produce a significant AO × OA interaction in sensorimotor ERD. Specifically, the facilitatory effect of AO on ERD is expected to be greater when OA is present than when OA is absent. This interaction is also expected to be accompanied by improved BCI performance compared with the single-cue conditions.

SIGNIFICANCE: By anchoring MI to tangible physical targets within a digital sensorimotor loop, this protocol bridges covert motor planning and real-world interaction. Findings will elucidate visuomotor integration mechanisms and inform development of ecologically valid, high-efficacy BCI rehabilitation strategies.

CLINICAL TRIAL REGISTRATION: https://www.chictr.org.cn/showproj.html?proj=292325, Chinese Clinical Trial Registry, ChiCTR2500111192, prospectively registered on October 27, 2025.