Multisensory mechanisms of body ownership and self-location

Having an accurate sense of the spatial boundaries of the body is a prerequisite for interacting with the environment and is thus essential for the survival of any organism with a central nervous system. Every second, our brain receives a staggering amount of information from the body across different sensory channels, each of which features a certain degree of noise. Despite the complexity of the incoming multisensory signals, the brain manages to construct and maintain a stable representation of our own body and its spatial relationships to the external environment. This natural “in-body” experience is such a fundamental subjective feeling that most of us take it for granted. However, patients with lesions in particular brain areas can experience profound disturbances in their normal sense of ownership over their body (somatoparaphrenia) or lose the feeling of being located inside their physical body (out-of-body experiences), suggesting that our “in-body” experience depends on intact neural circuitry in the temporal, frontal, and parietal brain regions. The question at the heart of this thesis relates to how the brain combines visual, tactile, and proprioceptive signals to build an internal representation of the bodily self in space. Over the past two decades, perceptual body illusions have become an important tool for studying the mechanisms underlying our sense of body ownership and self-location. The most influential of these illusions is the rubber hand illusion, in which ownership of an artificial limb is induced via the synchronous stroking of a rubber hand and an individual’s hidden real hand. Studies of this illusion have shown that multisensory integration within the peripersonal space is a key mechanism for bodily self-attribution. In Study I, we showed that the default sense of ownership of one’s real hand, not just the sense of rubber hand ownership, also depends on spatial and temporal multisensory congruence principles implemented in fronto-parietal brain regions. In Studies II and III, we characterized two novel perceptual illusions that provide strong support for the notion that multisensory integration within the peripersonal space is intimately related to the sense of limb ownership, and we examine the role of vision in this process. In Study IV, we investigated a fullbody version of the rubber hand illusion—the “out-of-body illusion”—and show that it can be used to induce predictable changes in one’s sense of self-location and body ownership. Finally, in Study V, we used the out-of-body illusion to “perceptually teleport” participants during brain imaging and identify activity patterns specific to the sense of self-location in a given position in space. Together, these findings shed light on the role of multisensory integration in building the experience of the bodily self in space and provide initial evidence for how representations of body ownership and self-location interact in the brain. LIST OF SCIENTIFIC PUBLICATIONS I. Gentile, Guterstam, Brozzoli, Ehrsson (2013) Disintegration of multisensory signals from the real hand reduces default limb self-attribution: an fMRI study. The Journal of Neuroscience. II. Guterstam, Zeberg, Özçiftci, Ehrsson (2016) The magnetic touch illusion: a perceptual correlate of visuo-tactile integration in peripersonal space. Cognition. III. Guterstam, Gentile, Ehrsson (2013) The Invisible Hand Illusion: Multisensory Integration Leads to the Embodiment of a Discrete Volume of Empty Space. Journal of Cognitive Neuroscience. IV. Guterstam & Ehrsson (2012) Disowning one's seen real body during an out-of-body illusion. Consciousness and Cognition. V. Guterstam, Björnsdotter, Gentile, Ehrsson (2015) Posterior Cingulate Cortex Integrates the Senses of Self-Location and Body Ownership. Current Biology. LIST OF ADDITIONAL PUBLICATIONS Guterstam, Petkova, Ehrsson (2011) The illusion of owning a third arm. PLoS ONE. Van der Hoort, Guterstam, Ehrsson (2011). Being Barbie: the size of one's own body determines the perceived size of the world. PLoS ONE. Guterstam, Björnsdotter, Bergouignan, Li, Gentile, Ehrsson (2015) Decoding illusory selflocation from activity in the human hippocampus. Frontiers in Human Neuroscience. Guterstam, Abdulkarim, Ehrsson (2015). Illusory ownership of an invisible body reduces autonomic and subjective social anxiety responses. Scientific Reports.