The feeling of being inside one’s own body is not as self-evident as one might think. In a new study from Sweden’s Karolinska Institutet, neuroscientists created an out-of-body illusion in participants placed inside a brain scanner. They then used the illusion to perceptually ‘teleport’ the participants to different locations in a room and show that the perceived location of the bodily self can be decoded from activity patterns in specific brain regions.
The sense of owning one’s body and being located somewhere in space is so fundamental that we usually take it for granted. To the brain, however, this is an enormously complex task that requires continuous integration of information from our different senses in order to maintain an accurate sense of where the body is located with respect to the external world. Studies in rats have shown that specific regions of the brain contain GPS-like ‘place cells’ that signal the rat’s position in the room – a discovery that was awarded the 2014 Nobel Prize in Physiology or Medicine. To date, however, it remains unknown how the human brain shapes our perceptual experience of being a body somewhere in space, and whether the regions that have been identified in rats are involved in this process.
In a new study, published in the scientific journal Current Biology, the scientists created an out-of-body illusion in fifteen healthy participants placed inside a brain scanner. In the experiment, the participants wore head-mounted displays and viewed themselves and the brain scanner from another part of the room. From the new visual perspective, the participant observes the body of a stranger in the foreground while their physical body is visible in the background, protruding from the bore of the brain scanner. To elicit the illusion, the scientist touches the participant’s body with an object in synchrony with identical touches being delivered to the stranger’s body, in full view of the participant.
“In a matter of seconds, the brain merges the sensation of touch and visual input from the new perspective, resulting in the illusion of owning the stranger’s body and being located in that body’s position in the room, outside the participant’s physical body,” says Arvid Guterstam, lead author of the present study.
Different places in the scanner room
In the most important part of the study, the scientists used the out-of-body illusion to perceptually ‘teleport’ the participants between different places in the scanner room. They then employed pattern recognition techniques to analyze the brain activity and show that the perceived self-location can be decoded from activity patterns in specific areas in the temporal and parietal lobes. Furthermore, the scientists could demonstrate a systematic relationship between the information content in these patterns and the participants’ perceived vividness of the illusion of being located in a specific out-of-body position.
To elicit the out-of-body illusion, the participants viewed a stranger’s body, lying in the corner of the room, being touched while they received identical touches on their real body (hidden from view). To examine whether the illusion actually worked, the scientists would threaten the stranger’s body with a knife and measure the participants’ stress response. The results showed that the knife threat lead to increased skin sweating and level of neural activity in fear centers of the brain during periods when the illusion was experienced compared to when it was broken, suggesting that the brain interpreted the stranger’s body as one’s own. Conversely, when the scientists threatened the participants’ real body with a large rubber sledgehammer, experiencing the illusion was associated with a lower stress response; as if the seen physical body belonged to someone else. Photo credit: Arvid Guterstam.
“The sense of being a body located somewhere in space is essential for our interactions with the outside world and constitutes a fundamental aspect of human self-consciousness,” says Arvid Guterstam. “Our results are important because they represent the first characterization of the brain areas that are involved in shaping the perceptual experience of the bodily self in space.”
One of the brain regions from which the participants’ perceived self-location could be decoded was the hippocampus – the structure in which the Nobel Prize awarded ´’place cells’ have been identified.
“This finding is particularly interesting because it indicates that place cells are not only involved in navigation and memory encoding, but are also important for generating the conscious experience of one’s body in space,” says principal investigator Henrik Ehrsson, professor at the Department of Neuroscience, Karolinska Institutet.
Funding: This study was made possible by funding from amongst others the Swedish Research Council, the James McDonnell Foundation, and Riksbankens Jubileumsfond.
Source: Katarina Sternudd – Karolinska Institute
Image Source: Image credited to Malin Björnsdotter/Arvid Guterstam
Video Source: The video is credited to Arvid Guterstam and is available at the karolinskainstitutet YouTube page
Original Research: Abstract for “Posterior Cingulate Cortex Integrates the Senses of Self-Location and Body Ownership” by Arvid Guterstam, Malin Björnsdotter, Giovanni Gentile, and H. Henrik Ehrsson in Current Biology. Published online April 30 2015 doi:10.1016/j.cub.2015.03.059
Abstract
Posterior Cingulate Cortex Integrates the Senses of Self-Location and Body Ownership
Highlights
•We used an out-of-body illusion to perceptually teleport participants during fMRI
•Self-location could be decoded from parieto-cingulate-hippocampal activity
•Ownership of a seen full body was associated with premotor-intraparietal activity
•The posterior cingulate plays a key role in merging self-location and body ownership
Summary
The senses of owning a body and being localized somewhere in space are two key components of human self-consciousness. Despite a wealth of neurophysiological and neuroimaging research on the representations of the spatial environment in the parietal and medial temporal cortices, the relationship between body ownership and self-location remains unexplored. To investigate this relationship, we used a multisensory out-of-body illusion to manipulate healthy participants’ perceived self-location, head direction, and sense of body ownership during high-resolution fMRI. Activity patterns in the hippocampus and the posterior cingulate, retrosplenial, and intraparietal cortices reflected the sense of self-location, whereas the sense of body ownership was associated with premotor-intraparietal activity. The functional interplay between these two sets of areas was mediated by the posterior cingulate cortex. These results extend our understanding of the role of the posterior parietal and medial temporal cortices in spatial cognition by demonstrating that these areas not only are important for ecological behaviors, such as navigation and perspective taking, but also support the perceptual representation of the bodily self in space. Our results further suggest that the posterior cingulate cortex has a key role in integrating the neural representations of self-location and body ownership.
“Posterior Cingulate Cortex Integrates the Senses of Self-Location and Body Ownership” by Arvid Guterstam, Malin Björnsdotter, Giovanni Gentile, and H. Henrik Ehrsson in Current Biology. Published online April 30 2015 doi:10.1016/j.cub.2015.03.059
