Long-Term Effect of VR-based Brain-Computer Interfaces Training in Brain Activity and Clinical Outcome: A Study with Chronic Stroke Patients

Restorative Brain-Computer Interfaces (BCIs) can provide an alternative non-muscular channel for stroke patients who lack volitional movement by reinforcing the modulation of sensorimotor rhythms through motor-imagery (MI). MI practice can be augmented through embodied proprioceptive feedback delivered by virtual reality (VR). Nonetheless, detailed information concerning the impact of embodied VR-BCI training in clinical outcome is still largely missing. This paper investigates the long-term effect of VR-BCI training in brain activity patterns measured through electroencephalography (EEG), functional magnetic resonance imaging (fMRI) and clinical scales through the Fugl-Meyer Assessment (FMA) pre-, post- intervention. Four chronic stroke patients underwent a 3-week MI-BCI longitudinal intervention, performing a bimanual rowing task (NeuRow) in VR involving MI and motor observation. From the EEG, the Event-related Desynchronization (ERD) and lateralization indices were extracted from the Mu band (8-12 Hz), and from the MR imaging, the activation from the primary motor (M1) and supplementary motor (SMA) regions of interest (ROIs) was analyzed during MI. Finally, the BCI performance was computed from the BCI training session. Results show that all patients induced significantly the Mu ERD power, however, the affected side showed reduced ERD compared to baseline during the contralateral MI. Significant ERD differences originating from both the lesioned and the healthy hemisphere were found when comparing post- with pre- intervention in all patients, and decreasing ERD was found for patients with no clinical improvement. Patients with decreased lateralization of ERD had no improvement of the FMA score. Activity within ipsilesional M1 and SMA is correlated with the FMA score. Overall, current results show that stroke patients in the chronic phase can modulate their brain activity patterns using MI in an embodied VR-BCI task, with specific patient differences between brain activity and clinical outcome. Nonetheless, only patients with increased ERD lateralization showed clinical improvement.