The effect of different observation modalities in motor imagery: immersive virtual reality produces stronger...

Objective. The combination of action observation and motor imagery (AO + MI) has emerged as a promising neurorehabilitation strategy to promote sensorimotor plasticity without real movement, making it particularly valuable for individuals whose motor capacity is limited or absent. Improving AO + MI protocols requires understanding whether different observation stimuli engage the sensorimotor system to varying degrees, as the quality of cortical activation during each training trial may directly influence cumulative neuroplastic outcomes. The growing accessibility of immersive technologies such as virtual reality head-mounted displays and robotic agents opens new possibilities for enriching the observation component of AO + MI, yet the neurophysiological impact of these modalities relative to conventional video approaches remains largely unexplored. Therefore, this study aimed to determine how the observation modality influences the activation of the sensorimotor cortex during synchronous AO + MI.Approach. This study investigated the effects of three observation modalities: immersive virtual reality (iVR), two-dimensional video and real-world observation of a robotic agent, on sensorimotor cortical engagement, using event-related desynchronization (ERD) as a neurophysiological marker. Electroencephalographic signals were recorded from fifteen healthy participants across three sessions, one per modality, while they observed a humanoid robot performing arm movements and simultaneously engaged in motor imagery of the same movements. ERD was computed for alpha and beta frequency bands over eight electrodes covering frontocentral, central, and centroparietal regions.Main Results. Statistical analyses revealed significant modality-dependent differences in sensorimotor cortical engagement across multiple frequency bands, electrode locations, and movement types. iVR consistently elicited the strongest desynchronization, with robust effects in the beta band over frontocentral and right centroparietal regions, and in the alpha band over the right central motor cortex.Significance. These results demonstrate that the modality of action observation significantly shapes sensorimotor cortical engagement during AO + MI. Our findings also support the integration of iVR as a neurophysiological grounded tool for optimizing AO + MI-based neurorehabilitation protocols and brain-computer interface applications.