Neuroscience of Bodily Self-Consciousness

We review recent research about human subjectivity and self-consciousness that has focused on cognitive psychology and neuroimaging of bodily self-consciousness. Multidisciplinary research on the fields of neurology, cognitive neuroscience and virtual reality opens new avenues to investigate brain mechanisms underlying a fundamental sense of the bodily self. Clinical evidence for the implication of right temporo-parietal junction for bodily self-consciousness has received support by studies in which virtual-reality based own body illusions are evoked in healthy participants to study the underlying processes. A series of experiments will be reviewed in which it was shown that the experiences of self-location, self-identification and the first-person perspective can be manipulated experimentally and rely on the integration of multisensory stimuli (touch, vision, proprioception, vestibular information). Specific protocols are available to predictably influence the different aspects of bodily self consciousness. We predict that the understanding of fundamental brain mechanisms of bodily self-consciousness will lead to unprecedented empirical insights that are of broad relevance for science, virtual reality, engineering, the humanities, as well as medicine and psychotherapy.

Flight of mind: Sensorimotor and multisensory embodiment with aviation robotics, flight simulator, and virtual reality

Myeong Seop Song

Normally, humans experience an 'I' as residing in one's body and as the agent of one's actions. In other words, the self is experienced as being inside the body (self-location), as having a body (self-identification), and as being able to control the person's body (agency). Over the last decade, research in cognitive neuroscience has revealed that vestibular signals contribute to such aspects of the embodied self. On the other hand, the influences of embodiment on vestibular sensations have received scant attention. In my thesis, I highlight how changes in multisensory and sensorimotor embodiment impact vestibular sensations. For this purpose, I merged technologies from photorealistic virtual reality (VR), aviation robotics such as a drone, flight simulator, haptics with knowledge of cognitive neuroscience about embodiment and bodily self-consciousness (BSC). The multidisciplinary approaches provide new paradigms to modulate embodiment and investigate related vestibular sensations based on multisensory and sensorimotor mechanisms of BSC. Also, the approaches reveal the relationship between embodiment and vestibular sensations. In Study 1, we have objectively shown the possibility of the duplication of the self by measuring peripersonal space (PPS). To this aim, we provided participants with real-time feedback from a drone-mounted camera that autonomously followed them while they responded to multisensory stimuli on their body and in their environment and walked forward. Our results demonstrate that this setup induces two spatially distinct PPSs in healthy participants: reaction times for visuotactile stimuli were faster around both the physical body and the observed body. In Studies 2 & 3, we have added a photorealistic avatar and a haptic vest to a robotic flight simulator to enable and investigate personalized immersive flight experiences in healthy humans. Study 2 showed that modulations of embodiment using sensorimotor stimulation resulted in enhanced subjective flying experience, better piloting performance, and learning. In Study 3, we showed that multisensory - visual and tactile - stimulation could further increase embodiment and improve piloting performance. Furthermore, in both studies, we found a positive relationship between embodiment and flight sensations. In Studies 4 & 5, we developed a new multisensory body scanning technology platform to induce and investigate one of the most common experiences in which the center of awareness is dissociated from the physical body: out-of-body experiences (OBEs). OBEs represent an interesting link between embodiment and vestibular sensations as they are characterized by embodiment of an elevated aerial position and perspective in space that is commonly associated with prominent sensations of floating, elevation, and flight. In this study, we have investigated how several sensorimotor and audio-visual stimulation conditions affect subjective sensations of disembodiment, floating, lightness as well as behavioral measures of self-location. In conclusion, my work developed new paradigms to investigate embodiment, BSC, and vestibular processing. My work revealed the influence of embodiment on vestibular sensations and applied these insights between embodiment and vestibular sensations to the field of field engineering by combining state-of-the-art technologies with knowledge of BSC with broad implications for robotics, neuroscience, of immersive VR, as well as experiential

EPFL2020

Multisensory interactions in peripersonal space and their contributions to bodily self-consciousness

Petr Grivaz

What is the relevance of the body and body-transformed sensory information for subjective experience? In the last two decades, paradigms from cognitive neuroscience have demonstrated that the subjective sensations of possessing a body (body ownership, BO), of being located in space (self-location) and being directed at the world (first-person perspective, 1PP), crucially rely on and can be manipulated by exposure to conflicting sensory information in so called bodily illusions. These aspects of subjective experience that are attached to the body, or bodily self-consciousness (BSC), are therefore malleable in healthy participants and accessible to experimental manipulations. BSC is argued to rely on multisensory integration mechanisms within the space directly surrounding the body (i.e. the peripersonal space, PPS). Amply supported by behavioral evidence, data from the brain is sparse. To help elucidate, in terms of neural activity, the relationship between PPS and an aspect of BSC, namely BO, in the first part of my thesis, I will present the results from an fMRI study and a meta-analysis, whereby I globally show that visual and tactile information presented within PPS is processed predominantly within the fronto-parietal and temporo-parietal regions of the brain whereas BO is processed in fronto-parietal and insular regions. Critically, both PPS and BO processing converges only in the left superior parietal cortex (intraparietal sulcus and area 2), thus suggesting both a level of neural integration and dissociation. The subjective 1PP is also argued to rely on multisensory mechanisms and in particular vestibular signals, but the underlying behavioral and neural mechanisms remain largely unexplored. Thus, in the second part of my thesis, I present a behavioral study and a clinical case report. In the prior, we exposed healthy subjects in a supine posture to touch on their backs and synchronous or asynchronous touch on the back of an observed avatar. We further simulated visual gravity using virtual balls falling either in the same or opposite direction with respect to the pull of physical gravity. In line with our expectations, the latter biased the direction of the 1PP to that suggested by the visual gravity (thus subjects reported looking downwards). The visual gravity information also interacted with the synchrony of stroking to affect 1PP and a more frequent downward 1PP was associated with a higher self-elevation rating. Also in line with the idea that BSC and in particular the 1PP relies on multisensory (in particular visuo-vestibular) integration, in the clinical case report we describe a male patient with peripheral vestibulopathy experiencing out-of-body experiences, who fails to integrate visual and vestibular information and is sensitive to visuo-tactile conflicts in bodily illusions. The results from my thesis collectively reinforce the current view that BSC can be manipulated by and thus crucially relies on multisensory mechanisms within PPS as shown both behaviorally for 1PP and in terms of neural correlates for BO. The results also suggest that different combinations of sensory stimuli manipulate most effectively these aspects, with synchronous visuo-tactile stroking affecting BO whereas asynchronous visuo-tactile stroking and vestibular information affecting 1PP. Apprehending better these mechanisms will be an important milestone to understanding how sensory information shapes subjective experience.

EPFL2017

Early and late activity in somatosensory cortex reflects changes in bodily self-consciousness: An evoked potential study

Jane Aspell, Olaf Blanke, Estelle Palluel

How can we investigate the brain mechanisms underlying self-consciousness? Recent behavioural studies on multisensory bodily perception have shown that multisensory conflicts can alter bodily self-consciousness such as in the "full body illusion" (FBI) in which changes in self-identification with a virtual body and tactile perception are induced. Here we investigated whether experimental changes in self-identification during the FBI are accompanied by activity changes in somatosensory cortex by recording somatosensory-evoked potentials (SEPs). To modulate self-identification, participants were filmed by a video camera from behind while their backs were stroked, either synchronously (illusion condition) or asynchronously (control condition) with respect to the stroking seen on their virtual body. Tibial nerve SEPs were recorded during the FBI and analysed using evoked potential (EP) mapping. Tactile mislocalisation was measured using the crossmodal congruency task. SEP mapping revealed five sequential periods of brain activation during the FBI, of which two differed between the illusion condition and the control condition. Activation at 30-50ms (corresponding to the P40 component) in primary somatosensory cortex was stronger in the illusion condition. A later activation at ∼110-200ms, likely originating in higher-tier somatosensory regions in parietal cortex, was stronger and lasted longer in the control condition. These data show that changes in bodily self-consciousness modulate activity in primary and higher-tier somatosensory cortex at two distinct processing steps. We argue that early modulations of primary somatosensory cortex may be a consequence of (1) multisensory integration of synchronous vs. asynchronous visuo-tactile stimuli and/or (2) differences in spatial attention (to near or far space) between the conditions. The later activation in higher-tier parietal cortex (and potentially other regions in temporo-parietal and frontal cortex) likely reflects the detection of visuo-tactile conflicts in the asynchronous condition.

2012