Neurological and Robot-Controlled Induction of an Apparition

Abstract

Tales of ghosts, wraiths, and other apparitions have been reported in virtually all cultures. The strange sensation that somebody is nearby when no one is actually present and cannot be seen (feeling of a presence, FoP) is a fascinating feat of the human mind, and this apparition is often covered in the literature of divinity, occultism, and fiction. Although it is described by neurological and psychiatric patients and healthy individuals in different situations, it is not yet understood how the phenomenon is triggered by the brain. Here, we performed lesion analysis in neurological FoP patients, supported by an analysis of associated neurological deficits. Our data show that the FoP is an illusory own-body perception with well-defined characteristics that is associated with sensorimotor loss and caused by lesions in three distinct brain regions: temporoparietal, insular, and especially frontoparietal cortex. Based on these data and recent experimental advances of multisensory own-body illusions, we designed a master-slave robotic system that generated specific sensorimotor conflicts and enabled us to induce the FoP and related illusory own-body perceptions experimentally in normal participants. These data show that the illusion of feeling another person nearby is caused by misperceiving the source and identity of sensorimotor (tactile, proprioceptive, and motor) signals of one's own body. Our findings reveal the neural mechanisms of the FoP, highlight the subtle balance of brain mechanisms that generate the experience of "self" and "other," and advance the understanding of the brain mechanisms responsible for hallucinations in schizophrenia.

The bodily self: Insights from clinical and experimental research

“…Other disorders, being more complex, involve varied disturbances of multimodal and vestibular integration, notably at the left posterior insula regarding heautoscopy [74], the insula and a fronto-temporo-parietal network for the feeling of a presence [75], and the right temporo-parietal junction for out-ofbody experiences [76].…”

Self-Awareness: The Neural Signature of Disturbed Self-Monitoring

“…Consistent with this suggestion, hallucinating schizophrenics show deficits in tasks that require self-monitoring [8]. A paper in this issue of Current Biology [9] now reports important findings suggesting that the strange sensation that somebody is nearby (and typically behind) when no one is actually present and hence cannot be seen -the 'feeling of presence' -is caused by misperceiving the source and identity of sensorimotor signals of one's own body.…”

“…Lesion analysis in neurological patients suggests that the feeling of presence results from focal brain interferences to three brain regions, namely temporo-parietal, insular, and particularly fronto-parietal cortex, and that its origin is typically, albeit not exclusively, epileptic [9]. On the basis of these findings, Blanke et al [9] hypothesized that distorted sensorimotor processing may underlie feeling of presence also in healthy subjects.…”

“…On the basis of these findings, Blanke et al [9] hypothesized that distorted sensorimotor processing may underlie feeling of presence also in healthy subjects. Compatible with this hypothesis, using a sensorimotor robot, Blanke et al [9] were able to reliably induce a feeling of presence in healthy subjects via the generation of conflicting sensorimotor signals, incompatible with physical self-touch. The study provides insights into the functional brain processes that underlie the apparition of an alien agent, an experience that shares important aspects with positive first-rank symptoms in schizophrenia.…”

“…Blanke et al [9] collected, over more than fifteen (!) years, twelve neurological patients who experience the feeling of presence.…”