Unisensory and Multisensory Processing in the Integration of Bodily Information: An EEG Study Using the Rubber Hand Illusion.

Abstract

Multisensory integration (MSI) is crucial to interact adaptively with our environment and create a coherent representation of the body. Body illusion techniques, such as the rubber hand illusion, provide useful tools to study MSI since they produce a conflict between different sensory modalities and alter body perception. While previous research revealed that body illusions modulate neural activity in unisensory and multisensory cortical areas during multisensory stimulation, cortical activity during unisensory stimulation has barely been studied. The present EEG study investigated brain mechanisms involved in MSI using unisensory (visual, tactile) and multisensory (visuotactile) stimulation. Alpha- and beta-band power, as well as functional connectivity, were assessed in 36 subjects during visual, tactile, and visuotactile stimulation in the rubber hand illusion paradigm and a control condition. The illusion was associated with widespread reductions in alpha and beta power, alongside increased beta-band connectivity between unisensory and multisensory cortical regions. Notably, alpha-band effects revealed cross-modal influences: visual stimulation modulated activity in somatosensory regions, while tactile stimulation affected occipital areas. Unisensory stimulation also elicited beta connectivity changes across modalities, with visual input enhancing sensorimotor coupling and tactile input increasing connectivity involving visual regions. The subjective strength of the illusion was associated with beta power reductions during visual stimulation, linking neural modulation to individual perceptual experience. These findings demonstrate that the illusory state is characterized by a global reconfiguration of sensory processing, extending beyond multisensory contexts and shaping unisensory processing through cross-modal interactions.