Pain while you are out of your body—A new approach to pain relief? Commentary on a paper by Hänsel et al. (2011)

A great deal of attention has been given lately to illusions of body ownership. Experiments that involve the illusory ownership over an artificial body (Blanke et al., 2002), arm (Botvinick and Cohen, 1998) or finger (Walsh et al., 2011) have revealed much about the physiological underpinnings of these illusions, including which brain areas are involved (see Tsakiris, 2010 for review). Bodily illusions occur in a range of clinical conditions, including, but not limited to, chronic pain (Moseley et al., 2008b). For example, people with complex regional pain syndrome of one arm can perceive that their affected arm is bigger than it really is (Moseley, 2005; Lewis et al., 2007), and people with back pain can feel that their back is ‘missing’ (Moseley, 2008a). Indeed, the large body of literature in this area has led to a proposal that a network of homeostatic and multisensory brain areas form a ‘cortical body matrix’ – a dynamic neural representation that integrates sensory data, from across several frames of reference, with physiological regulation of the body, and which subserves our sense of where and who, physically, we are (Moseley et al., 2011). Relevant to this is a recent paper by Hänsel et al. (2011), published in this issue, in which they investigate, in healthy volunteers, pressure pain thresholds during an out of body illusion. Hänsel et al. assessed pressure pain threshold on the index finger under four different conditions. The experimental condition involved an established method to induce an out of body experience. By synchronous stroking on the back of both the mannequin and the participant while the participant watches a rearview of the mannequin through a head mounted display, the participant quickly feels as though they can actually sense the stroking on the mannequin and therefore, they are standing outside of themselves (Lenggenhager et al., 2007). This method of inducing the illusion can be considered a third person approach, whereas others use a first person approach by tapping the mannequin and the participant on the chest, within the first-person field of view (Ehrsson, 2007). In the Hänsel et al. experiment, there were three control conditions – asynchronous stroking of the mannequin and the participant (which does not induce the illusion) and two identical conditions but with a panel or ‘object’ instead of a mannequin. The authors predicted that pressure pain thresholds would be higher during the illusion, or synchronous stroking condition, than they were during the other conditions. That is, they predicted that the illusion would have an analgesic effect. I suspect that, with