Stockolm: 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 of 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.
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.
“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.
This study was made possible by funding from amongst others the
Swedish Research Council, the James McDonnell Foundation, and
Riksbankens Jubileumsfond.
Publication:
'
Posterior Cingulate Cortex Integrates the Senses of Self-location and Body Ownership
', Arvid Guterstam, Malin Björnsdotter, Giovanni Gentile & Henrik Ehrsson,
Current Biology
,
online 30 April 2015,
doi:
http://dx.doi.org/10.1016/j.cub.2015.03.059.
.View a video on YouTube about this research