Out of body experiences – neural engineering informs brain sciences

https://www.sciencedirect.com/science/article/pii/S2468451118300333

Someone knew someone who almost died. And when that happened, this person was able to see their own body, from above, lying in that bed. Inert. This, a classical out-of-body experience (Figure 1A), refers to the sensation that a person’s consciousness seems to become detached from the body, taking remote viewing position. Generally called body transfer illusions, these illusions can also involve the altered perception of a body part, like 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. Let’s start by calling a good friend. Take a (large) mirror or wood plank and put it straight on a table (see Figure 1B). 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 as if there was a sleeve). Now, ask your friend to stroke your fingers and the rubber’s hand finger simultaneously. Slowly but surely you will be getting the feeling that your hand in fact your hand.

 

Figure 1A. Image by Rad el Baluvar via wikimedia.

 

Figure 1B via Flickr.

 

This perceptual trick that we did with the rubber-hand can be extended to your whole body, as studied by Olaf Blanke’s team in Germany – linking body part illusions with out-of-body experiences. Through the use of virtual reality, the Blanke lab has been able transfer whole-body perception into a virtual human body. In a series of studies presented in [1], participants entering a virtual reality environment experienced physical stimulation (like arm or back stroking), in both their own body and their virtual self, standing just in front. This time, the participant’s perception of their body was successfully transferred into their virtual equivalent, sufficiently to generate a body transfer illusion. Such out-body-experience has been also reported as a result of the deep brain stimulation [2,3]. This time, 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 [4].

 

While one of the basic questions that we can make about ourselves is ‘where am I?’ the answer remains largely unaddressed. These illusions are in fact a great tool to study how the brain creates a sense of body ownership, as well as an approach to study how perception arises from the interaction of multiple sensory inputs (multi-sensory perception). While we perceive ourselves 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 the visual and auditory feedback. This implies that, to perceive our hand and thus, its ownership, a required step is the integration of multi-sensory inputs. While this association between tempo-parietal junction (TPJ) stimulation and the induction of the out of body experience was first reported in 1941, its revival into the scientific research can only be explained by the advancements 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?

 

In fact, out of body experiences are considered a door for the study of consciousness, as often mentioned by Susan Blackmore: an awareness of your own body requires awareness of your self and your surroundings. 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. But recent advancements do not only aim to probe mechanisms, but also instead, aim to restore consciousness in clinical situations – 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 this neural-engineering approach is that in probing the brain with technology, we can also probe the perception of consciousness and thus, understand its biological basis. After all, is consciousness strictly biological? Learn more here or here.

References:

[1] Slater, M., Spanlang, B., Sanchez-Vives, M. V., & Blanke, O. (2010). First person experience of body transfer in virtual reality. PloS one5(5), e10564.

[2] Jasper, H., & Erickson, T. C. (1941). Cerebral blood flow and pH in excessive cortical discharge induced by metrazol and electrical stimulation. Journal of Neurophysiology4(5), 333-347.

[3] Blanke, O., Ortigue, S., Landis, T., & Seeck, M. (2002). Neuropsychology: stimulating illusory own-body perceptions. Nature419(6904), 269.

[4] Blanke, O., Mohr, C., Michel, C. M., Pascual-Leone, A., Brugger, P., Seeck, M., … & Thut, G. (2005). Linking out-of-body experience and self processing to mental own-body imagery at the temporoparietal junction. Journal of Neuroscience25(3), 550-557.

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