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 鈥� a rare condition characterised by a lack of awareness of a part of one鈥檚 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.
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, a neuroscientist at the Karolinska Institute in Stockholm, Sweden, and his colleagues wondered how the brain produces these experiences. To find out, Guterstam鈥檚 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 鈥� and themselves inside the scanner 鈥� from the dummy鈥檚 perspective.
A member of the team then stroked the participant鈥檚 body and the dummy鈥檚 body at the same time. This induced the out-of-body experience of owning the dummy body and being at its location.
Here鈥� 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鈥檚 and the dummy鈥檚 bodies at different times.
By comparing brain activity when the participants were and weren鈥檛 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. 鈥淭his means we know little about its function,鈥� says Guterstam. 鈥淚t鈥檚 a very mysterious area.鈥�
The cingulate cortex was already linked with emotion formation, memory and learning, and abnormal activity here has been linked to depression and schizophrenia. 鈥淚t鈥檚 interesting to see it does so much more,鈥� says Guterstam.
Floating in space
As expected, the parietal lobe and premotor cortex were also involved in generating the teleporting illusion. 鈥淭hese parts of the brain are known for integrating information from different senses to build higher representations of the body,鈥� says Guterstam. Other areas, known to house specialised place and grid cells that help us navigate, were also active during the illusion.
鈥淚n 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 鈥� where there are disturbances of self-perception and other disorders where the sense of body is changed in some way,鈥� 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. 鈥淭he physical body is rotated so that even though you鈥檙e lying on your back, you鈥檙e viewing yourself from above,鈥� says Guterstam. 鈥淚t involves an interesting sense of rotation in respect to gravitational experience.鈥�
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