Distinct illusory own-body perceptions caused by damage to posterior insula and extrastriate cortex

Recent research in cognitive neuroscience using virtual reality, robotic technology and brain imaging has linked self-consciousness to the processing and integration of multisensory bodily signals. This work on bodily self-consciousness has implicated the temporo-parietal, premotor and extrastriate cortex and partly originated in work on neurological patients with different disorders of bodily self-consciousness. One class of such disorders is autoscopic phenomena, which are defined as illusory own-body perceptions, during which patients experience the visual illusory reduplication of their own body in extrapersonal space. Three main forms of autoscopic phenomena have been defined. During autoscopic hallucinations, a second own body is seen without any changes in bodily self-consciousness. During out-of-body experiences, the second own body is seen from an elevated perspective and location associated with disembodiment. During heautoscopy, subjects report strong self-identification with the second own body, often associated with the experience of existing at and perceiving the world from two places at the same time. Although it has been proposed that each autoscopic phenomenon is associated with different impairments of bodily self-consciousness, past research on neurological patients and the development of experimental paradigms for the study of bodily self-consciousness has focused on out-of-body experiences and the association with temporo-parietal cortex. Here, we performed quantitative lesion analysis in the-to date-largest group of patients with autoscopic hallucination and heautoscopy and compared the location of brain damage with those of control patients suffering from complex visual hallucinations. We found that heautoscopy was associated with lesions to the left posterior insula, and that autoscopic hallucinations were associated with damage to the right occipital cortex. Autoscopic hallucination and heautoscopy were further associated with distinct symptoms and deficits. The present data suggest that the autoscopic hallucination is a visuo-somatosensory deficit implicating extrastriate cortex and is, despite the visual hallucination of the own body, not associated with major deficits in bodily self-consciousness. Based on the symptoms and deficits in patients with heautoscopy and the implication of the left posterior insula, we suggest that abnormal bodily self-consciousness during heautoscopy is caused by a breakdown of self-other discrimination regarding affective somatosensory experience due to a disintegration of visuo-somatosensory signals with emotional (and/or interoceptive) bodily signals. These brain mechanisms are distinct from those described for out-of-body experiences. The present data extend previous models of autoscopic phenomena and provide clinical evidence for the importance of emotional and interoceptive signal processing in the posterior insula in relation to bodily self-consciousness.

Turning Body and Self Inside Out

Lukas Heydrich

What is the self? This major philosophical question has been considered too complex to be studied in neuroscience. However, during the last 20 years, researchers from different disciplines within the cognitive neurosciences have started investigating the neural correlates of self-consciousness, using a range of behavioural paradigms and functional imaging techniques. Where as many researchers have studied highorder representational aspects of self-consciousness, such as language (i.e. the use of the self-referential pronoun "I" or "Me"), converging evidence suggests that the most basic sense of self, e.g. the sensation that we possess a stable and coherent representation of our body, that we identify with our body and that we perceive the self as being located within the bodily boundaries (e.g. bodily self-consciousness), is due to integration of bodily signals from different exteroceptive sensory modalities (vision, touch, proprioception). Others have highlighted the importance signals related to internal signals (homeostasis, interoception) for self-consciousness. Using lesion analysis, we could demonstrate a causal link between damage to the right temporo-parietal junction and an altered state of bodily self-consciousness, e.g out-of-body experiences. This was confirmed using functional magnetic resonance imaging, multisensory exteroceptive conflicts and virtual reality: if healthy participants perceived themselves as "disembodied", activity in the same cortical region (i.e. temporo-parietal junction) was systematically modulated. Moreover, we were able to demonstrate in a second line of experiments that interoceptive signals can be used to systematically alter bodily self-consciousness and somatosensory processing, extending previous paradigms that focused exclusively on exteroceptive signals. This was strengthened by our finding that the left posterior insula, repeatedly linked to the representation and integration of internal and external bodily signals, is implicated in another state of altered bodily self-consciousness, e.g. heautoscopy. Our results demonstrate that bodily self-consciousness is based on a neural network that represents and integrates both external and internal signals from the body.

EPFL2012

Multisensory and sensorimotor origins of the sense of self

Polona Pozeg

Cognitive neuroscience has increasingly focused on studying the subject, i.e. the self, of conscious experience. In order to be the subject of an experience, we generally experience owning a physical body, being located within that body, and being able to distinguish the body and its actions from others. These pre-reflective experiences are based on brain mechanisms of multisensory and sensorimotor integration. In this thesis I investigated how our sense of self, in particular the senses of body ownership and of agency, depend on multimodal bodily signals. I achieved this by using approaches developed by cognitive neuroscience to study how the sense of self relates to the processing of bodily signals: creating bodily illusions with multisensory conflicts through the use of virtual reality and robotics. The first part of this thesis describes the investigation of the sense of body ownership in healthy subjects and in spinal cord injury patients, achieved by inducing conflicts between tactile information and visual feedback. The research presented in the second part of the thesis is centered on the experience of self-touch. There, I have first investigated how the manipulation of reference frames influences the perception of the illusion of self-touch, and second, how active self-touch influences the sense of body ownership. Lastly, in the third part of the thesis, I investigated how experimentally induced multisensory and sensorimotor conflicts perturb the sense of self in healthy subjects and induce experiences similar to certain symptoms observed in neurological and psychiatric disorders. I show that particular conflicts between bodily signals not only affect body perception and sense of agency for motor actions but also propagate to higher levels and influence even the sense of agency for mental representations in healthy subjects. Finally, I discuss my results and their relation to existing knowledge on bodily self-consciousness and position them in a broader picture of our current understanding of the self.

EPFL2016

Body ownership and embodiment: vestibular and multisensory mechanisms

Olaf Blanke, Pär Halje, Christophe Lopez

Body ownership and embodiment are two fundamental mechanisms of self-consciousness. The present article reviews neurological data about paroxysmal illusions during which body ownership and embodiment are affected differentially: autoscopic phenomena (out-of-body experience, heautoscopy, autoscopic hallucination, feeling-of-a-presence) and the room tilt illusion. We suggest that autoscopic phenomena and room tilt illusion are related to different types of failures to integrate body-related information (vestibular, proprioceptive and tactile cues) in addition to a mismatch between vestibular and visual references. In these patients, altered body ownership and embodiment has been shown to occur due to pathological activity at the temporoparietal junction and other vestibular-related areas arguing for a key importance of vestibular processing. We also review the possibilities of manipulating body ownership and embodiment in healthy subjects through exposition to weightlessness as well as caloric and galvanic stimulation of the peripheral vestibular apparatus. In healthy subjects, disturbed self-processing might be related to interference of vestibular stimulation with vestibular cortex leading to disintegration of bodily information and altered body ownership and embodiment. We finally propose a differential contribution of the vestibular cortical areas to the different forms of altered body ownership and embodiment.