If you’ve ever heard of stories in which people report having an ‘out of body experience’ (OBE) during a traumatic incident like a car crash you might be able to guess why there could be a link between OBEs and chronic pain. Some scientists have suggested that the very vivid hallucination that is an OBE can sometimes serve an adaptive function by helping trauma victims to psychologically distance themselves from the pain and trauma of an accident. We recently used an illusion a bit like an OBE in our laboratory to see whether it might lessen the pain that individuals with chronic pain experience [5].
Our participants – eighteen people who suffered from a range of chronic pain conditions from sciatica to osteoarthritis and back pain – were asked to take part in a very strange setup: sitting on a chair, wearing virtual reality goggles that were linked to a video camera filming them from behind (!) You can see a video of the setup here:
While they sat, the experimenter tapped and stroked their backs and the participants viewed their own (virtual) body (via the VR goggles), in a location in front of them. This generated what is known as a ‘full body’ or ‘out of body’ illusion: a multisensory body illusion that has been used in several studies since 2007 [1-3]. It creates, in most participants, the strange experience that one’s self is no longer located in one’s body, but rather at a location somewhere between one’s real body and where the virtual body is seen. Participants also identify with the virtual body more when the tapping and stroking is viewed in real time.
To find out if the illusion could cause a reduction in pain intensity we measured it – using the McGill Pain questionnaire – before and after the illusion conditions (when the stroking is viewed in real time) and the control conditions (when a recording was viewed and the participants were stroked ‘asynchronously’). Pain intensity was reduced by 37% in the illusion conditions! This is what might be termed a ‘clinically useful’ analgesic effect. What we don’t yet know though, is how long-lasting this reduction in pain is, or whether something like this could feasibly be used to aid the management of chronic pain conditions.
As for what explains the reduction in pain intensity, we can only speculate at this stage. There is growing evidence that at least some types of chronic pain are closely linked to the [aberrant] multisensory representation of the body. By further perturbing this representation with the multisensory conflict inherent in the full body illusion, pain intensity is reduced. Our findings resonate with a number of previous studies that have shown how the high-level integration of multisensory body signals can impact on physiology and possibly homeostasis, e.g., the finding by Moseley’s group that the related rubber hand illusion causes a small reduction in hand temperature [4, and see 6]. As we now know, both acute and chronic pain perception can also be affected by changes in multisensory integration induced by body illusions. In some ways, perhaps, we should not be surprised by this. Where there is pain, there is always some body in pain. If the brain representations of the spatial extent or location of that body are made ‘fuzzy’ by body illusions (or brain damage), the experience of pain in that body may also be altered: sometimes for the worse, sometimes for the better.
About James Pamment
James is currently an Assistant Clinical Psychologist at the Oliver Zangwill Centre in Ely, UK, and has a research interest in pain perception and management. James studied psychology at Anglia Ruskin University where he devised and ran the study described above as part of his final year research project, after seeing one of Jane’s lectures on body illusions.
Link to James talking about the research in more detail here.
About Jane Aspell
Jane is a cognitive neuroscientist and she has published several studies involving the full body illusion paradigm. Her research investigates multisensory – exteroceptive and interoceptive – contributions to bodily self-consciousness. Jane read Biological Sciences at Oxford before studying for a PhD on multisensory integration at Newcastle. Following a postdoc back at Oxford, she worked at EPFL, Switzerland, before returning to the UK. Jane is currently Senior Lecturer in the Psychology Department at Anglia Ruskin University, Cambridge, UK.
More on Jane Aspell’s published research here.
References
[1] Aspell, J.E., Heydrich, L., Marillier, G., Tom Lavanchy, T., Herbelin, B. and Blanke, O., 2013. Turning body and self inside out: visualized heartbeats alter bodily self-consciousness and tactile perception. Psychological Science, 24(12), pp.2445-2453.
[2] Ehrsson, H. (2007). The Experimental Induction of Out-of-Body Experiences. Science 317, 1048
[3] Lenggenhager, B., Tadi, T., Metzinger, T., and Blanke, O. (2007). Video Ergo Sum: Manipulating Bodily Self-Consciousness. Science 317, 1096-1099.
[4] Moseley, G.L., Olthof, N., Venema, A., Don, S., Wijers, M., Gallace, A., and Spence, C. (2008). Psychologically induced cooling of a specific body part caused by the illusory ownership of an artificial counterpart. Proceedings of the National Academy of Sciences 105, 13169-13173.
[5] Pamment, J. & Aspell, J.E., 2016. Putting pain out of mind with an ‘out of body’ illusion. European Journal of Pain 21(2): 334-342.
[6] Salomon, R., Lim, M., Pfeiffer, C., Gassert, R., and Blanke, O. (2013). Full body illusion is associated with widespread skin temperature reduction. Frontiers in behavioral neuroscience
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