Giving people the illusion of teleporting around a room has revealed how the brain constructs our sense of self. The findings may aid treatments for schizophrenia and asomatognosia – a rare condition characterised by a lack of awareness of a part of one’s body.
As we go about our daily lives, we experience our body as a physical entity with a specific location. For instance, when you sit at a desk you are aware of your body and its rough position with respect to objects around you. These experiences are thought to form a fundamental aspect of self-consciousness.
Arvid Guterstam, a neuroscientist at the Karolinska Institute in Stockholm, Sweden, and his colleagues wondered how the brain produces these experiences. To find out, Guterstam’s team had 15 people lie in an fMRI brain scanner while wearing a head-mounted display. This was connected to a camera on a dummy body lying elsewhere in the room, enabling the participants to see the room – and themselves inside the scanner – from the dummy’s perspective.
A member of the team then stroked the participant’s body and the dummy’s body at the same time. This induced the out-of-body experience of owning the dummy body and being at its location.
Here… no, here
The experiment was repeated with the dummy body positioned in different parts of the room, allowing the person to be perceptually teleported between the different locations, says Guterstam. All that was needed to break the illusion was to touch the participant’s and the dummy’s bodies at different times.
By comparing brain activity when the participants were and weren’t in the grip of the illusion, and while they were perceptually in different parts of the room, the team were able to identify which parts of the brain control our sense of body ownership and self-location.
One region appeared to combine the two: the posterior cingulate cortex, a region deep in the middle of the brain, towards the back of your head.
We normally discover a lot about brain function by studying people who have had a stroke, but the cingulate cortex is located in between stroke-prone areas and is rarely affected itself. “This means we know little about its function,” says Guterstam. “It’s a very mysterious area.”
The cingulate cortex was already linked with emotion formation, memory and learning, and abnormal activity here has been linked to depression and schizophrenia. “It’s interesting to see it does so much more,” says Guterstam.
Floating in space
As expected, the parietal lobe and premotor cortex were also involved in generating the teleporting illusion. “These parts of the brain are known for integrating information from different senses to build higher representations of the body,” says Guterstam. Other areas, known to house specialised place and grid cells that help us navigate, were also active during the illusion.
“In the long run, if we can figure out how the brain constructs the sense of body in space, it will give us clues as to what goes on in disorders such as schizophrenia – where there are disturbances of self-perception and other disorders where the sense of body is changed in some way,” says Guterstam.
His team would also like to investigate what happens in the brain during other out-of-body illusions. The classic one occurs when people report seeing themselves from above. “The physical body is rotated so that even though you’re lying on your back, you’re viewing yourself from above,” says Guterstam. “It involves an interesting sense of rotation in respect to gravitational experience.”