Pain experience can be modulated at different levels of processing and is influenced by higher cognitive function like attention and expectations. It has been shown recently that looking at one’s own hand, but not at a neutral object or another person’s hand, induces analgesic effects while receiving acute painful stimulation (Longo, et al., 2009).
The sense of body ownership is not considered a static construct, and experimental evidence suggests that it results from multisensory integration occurring in the brain. Several studies demonstrate that it is possible to extend one’s own body representation to different external objects such as a prosthetic hand, but also entire bodies (Full Body Illusion – FBI). The FBI can be induced by means of congruent visuo-tactile stimulation at the trunk of one’s body and an observed avatar, inducing self-identification with the virtual or fake body (Lenggenhager et al., 2007). We investigated whether this illusory self-identification with the alien body can reduce the physiological response to pain, similar to viewing one’s own body.
In two experiments, we collected Skin Conductance Responses (SCR) – i.e. an index of autonomic nervous system activation – to painful stimuli delivered to the participants’ hand while they viewed either the body of an avatar, a non-body object (control object), or a body avatar with scrambled body parts (control body) that were stroked in congruent or incongruent fashion.
We found reduced SCRs to painful stimuli when participants observed the anatomical body avatar being stroked in the same way with their back that were associated with higher ratings of self-identification with the avatar, and these reduced responses were recordable already during the pain anticipation phase. Moreover we observed a negative correlation between self-identification ratings and SCR, signifying that a greater degree of self-identification with the avatar was associated with larger decreases in SCR. Our physiological results corroborate earlier studies reporting elevated pain thresholds when seeing a body part or when self-identifying with a virtual body, but extend these data as we not only showed that visual analgesia is tuned by bodily self-consciousness, but also that this modulates anticipatory levels of pain processing. This means that the analgesic effect induced by the vision of owned body is effective before the contact of the nociceptive stimulus suggesting that it impacts the cognitive aspects of the pain experience more than the analysis of the nociceptive information. However this physiological reduced response did not correspond to a reduced experience of pain in our experiment, as we did not observe reductions in explicit pain ratings in both experiments, possibly suggesting that a subjective reduced experience of pain is harder to achieve by means of bodily illusions. This might be because the experience of ownership felt under illusory conditions is heterogeneous and, generally speaking, less strong than the feeling of ownership felt for one’s own body. We can speculate that the physiological changes that follow the presentation of a threatening stimulus dissociate from the conscious experience of pain. Although the physiological response may precede a modulation of conscious experience of pain it may also occur without any behavioural correlate.
Summing up, our data hint that pain processing shares functional mechanisms with self-identification, suggesting that the body representation might be an interface for the efficient and safe interaction with the world around us.
About Daniele
Daniele Romano (1984) had just defended his PhD thesis in experimental psychology, linguistics and cognitive neuroscience at the University of Milano-Bicocca (January 2014). He completed his bachelor studies in Psychology in Milan, followed by a master degree in Neuropsychology. He undertook his PhD at University of Milano-Bicocca under the supervision of Angelo Maravita, spending also part of this period at the LNCO directed by Olaf Blanke, studying the interactions between the sense of ownership and the processing of painful stimuli.
His current research interests include the study of pain processing in patients with deranged body representation (Somatoparaphrenia, Xenomelia, Alien Hand, Anosognosia), and the mechanisms underlying the Mirror Box Therapy.
Here is the link to Daniele’s published studies.
References
Lenggenhager B, Tadi T, Metzinger T, & Blanke O (2007). Video ergo sum: manipulating bodily self-consciousness. Science, 317 (5841), 1096-9 PMID: 17717189
Longo MR, Betti V, Aglioti SM, & Haggard P (2009). Visually induced analgesia: seeing the body reduces pain. J Neurosci, 29 (39), 12125-30 PMID: 19793970
Romano D, Pfeiffer C, Maravita A, & Blanke O (2014). Illusory self-identification with an avatar reduces arousal responses to painful stimuli. Behav Brain Res, 261, 275-81 PMID: 24412686