Activity in superior colliculus during rubber hand illusion unravel network articulating body-part and full-body illusions processing: An fMRI study

The experimental investigation of bodily self-consciousness assumes that body-part and full-body representations can be selectively assessed through body-part and full-body illusions as the rubber hand illusion (RHi) and the induced out-of-body experience (OBE), respectively. Nevertheless, we demonstrated in a previous work that induction of a body-part illusion is accompanied by the induction of a full-body illusion. In the current study we investigate the neuronal underpinnings of this link between body-part and full-body illusions. We used the traditional RHi paradigm in a functional magnetic resonance imaging (fMRI) study. Activity at the ipsilateral superior colliculus (SC) correlated with the illusion. This activation pattern is observed in hemispatial neglect, suggesting that the implication of superior colliculus in body-part illusion may underpin a correlated full-body illusion. To test this hypothesis, we applied a psychophysiological interaction (PPI) analysis aiming to unravel the connectivity of the superior colliculus during RHi. We observed a significant connectivity of ipsilateral superior colliculus with brain structures previously implicated in both body-part and full-body illusions, the bilateral primary somatosensory cortex, implicated with body-part illusions; the right temporoparietal junction (TPJ), associated with full-body illusions; the bilateral ventral premotor cortex (vPM), implicated both in body-part and full-body illusions; and the right fusiform body area (FBA), implicated in full-body representation. Altogether, our findings suggest that multisensory integration of bodily signals at the superior colliculus play a major role in emergence of bodily self-consciousness in humans, affecting both body-part and full-body representations.