The role of emotion on body ownership and Rubber Hand Illusion: an EEG-NIRS study

Objective: Rubber hand illusion (RHI) is a well-known phenomenon where the wrong attribution of tactile sensations to a rubber hand placed in front of a subject lead to the embodiment of such external object in the subject's body schema. However, the depth of such integration within the body schema and its affective undertones are still understudied. In order to investigate the extent to which an embodied rubber hand can be processed as part of one's own body, we implemented the classic RHI paradigm with an additional affective stimulation by presenting an adverse stimulus next to the rubber hand. Participants and methods: The illusion was induced in healthy subjects by repeatedly and simultaneously stimulating with two brushes the real hidden hand and the rubber hand for three minutes. The study included three experimental stimulation sessions. Half of the subjects was presented with the adverse stimulus after the first illusion-inducing stimulation, while the other half experienced the adverse condition after the second stimulation session, to control for potential habituation effects. Results: During the entire study we also recorded cortical activity by EEG and fNIRS (functional Near-Infrared Spectroscopy). EEG data showed the involvement of temporal-parietal areas during RHI after the emotional stimulation, as marked by an increase of delta power. fNIRS hemodynamic data pointed at the involvement of left frontal areas during adverse condition. Conclusions: Evidences suggest that exposure to an adverse stimulus - though involving an embodied external object - might influence subsequent re-embodiment and body ownership processes and its cortical correlates.