A certain person knew somebody who almost died. During the event, the person was able to see his/her own body, from above, lying in bed, inert. This, a classical out-of-body experience, refers to the sensation that a person’s consciousness seems to become detached from the body, watching the scene from a third-person perspective.
Phenomena as this one are generally called body transfer illusions. These illusions can also involve the altered perception of a body part, as for instance an arm. You can try it at home – it’s called the rubber hand illusion. The recipe is surprisingly intuitive: make someone believe that their body is in front of them, while truly, it isn’t there.
Inducing the body transfer illusion
To experiment with such a body transfer illusion, let’s start by calling a good friend. Take a (large) mirror or wood plank and put it straight on a table. One of your hands goes in front of the mirror (with your face) and the other hand, behind the mirror, where you cannot see it. Instead, put a rubber hand in the table (make sure to cover its “forearm” as if there were a sleeve). Now, ask your friend to stroke your fingers and the rubber hand’s finger simultaneously. Slowly but surely you will be getting the feeling that the rubber hand is also your hand!
The described perceptual with the rubber-hand can be extended to your whole body, as studied by Olaf Blanke’s team in Switzerland – linking body part illusions with out-of-body experiences. Through the use of virtual reality, the Blanke lab has been able to transfer whole-body perception into a virtual human body.
In a series of studies about first person experience of body transfer in virtual reality, participants entering a virtual reality environment experienced physical stimulation (like arm or back stroking), in both their own body and their “virtual self”. In those experiments, the participant’s perception of their body was successfully transferred into their virtual equivalent, sufficiently to generate a body transfer illusion.
Such an out-of-body-experience has been also reported as a result of deep brain stimulation studies, as far back as the nineteen-forties but also in more recent times. In such conditions, researchers were able to repeatedly induce an out-of-body experience by the repeated electrical stimulation of the tempo-parietal junction (TPJ), a brain area that is commonly related to body-related processing.
While one of the most basic questions that we can ask ourselves is ‘where am I?’, the answer to this question remains largely unaddressed. Illusions as those described are in fact a great tool to study how the brain creates a sense of body ownership. They are, as well, an approach to study how perception arises from the interaction of multiple sensory inputs (multi-sensory perception).
While we perceive ourselves to be inside our body, how do we perceive our body? We recognize our own hand by receiving information about its muscles, tendons or surface temperature, the vestibular system or by visual and auditory feedback. This implies that, to perceive our hand, hence its ownership, a required step is the integration of multi-sensory inputs.
While the association between tempo-parietal junction (TPJ) stimulation and the induction of the out of body experience was first reported in 1941, its revival in scientific research can only be explained by the advances in neural engineering approaches. Think about your favorite technology. How would you use it to probe brain mechanisms? Can you think about probing conscious experience?
Out-of-body experiences and the study of consciousness
In fact, out-of-body experiences are considered a door to the study of consciousness. As often mentioned by Susan Blackmore: an awareness of your own body requires awareness of yourself and of your surroundings. So, what can we learn about consciousness and awareness by probing the limits of our perception? While consciousness remains an enigma, an unresolved puzzle, current technologies are becoming a crucial tool in probing the neural mechanisms of consciousness.
However, recent advances do not only aim to probe mechanisms. Instead, they also aim to restore consciousness in clinical situations. For instance: can technology facilitate recovery of a coma patient? This extremely challenging goal is addressed at the Luminous project, an H2020 FetOpen project coordinated by Starlab.
The basic idea with such neural/engineering approach is that in probing the brain with technology, we can also probe the perception of consciousness. In that way, one can thus understand its biological basis. Because, after all, is consciousness strictly biological? Learn more about that in this video or in this podcast.
This post was originally written by Luminous team member Marta Castellano, and published at the Neuroelectrics website blog. It has been reproduced here with permission with some edition for the sake of clarity and adaptation to the format.
Tempo-parietal junction representation picture was reproduced with permission from the original article.
Patient picture taken from the Luminous archives.