A little while ago, we published a paper that showed, in people with complex regional pain syndrome, that when they moved their hand and watched it through a magnifying lens, it hurt more than when they just looked at. Moreover, the increase in pain was less when they looked through a minifying lens (don’t see too many of those around though do you!). Well, just as you were getting ready to invest in a big fat minimiser2000, this study from University College London seems to turn it all upside down. Or inside out. We are very grateful to Flavia Mancini et al for agreeing to tell us about their experiment. How to interpret it? Well I am not sure, but Flavia herself makes a sensible suggestion. Clearly, put away the minimiser2000 and the magnifierXT, and leave us to do a few more experiments. Stay tuned…
By Flavia Mancini:
Simply looking at your body reduces the pain experienced when a hot object touches the skin. Also the visual appearance of the body matters: the level of pain depends on how large the hand looked – the larger the hand the greater the effect of pain reduction.
The research has been published in the journal Psychological Science, by scientists from UCL (University College London) and the University of Milano-Bicocca, Italy.
The experiment
During the experiment, 18 healthy volunteers had a heat probe placed on their left hand. The probe temperature was gradually increased, and participants stopped the heat by pressing a foot pedal as soon as they began to feel pain. This provides a measure of pain threshold.
We used a set of mirrors to manipulate what the participants saw during the experiment. Participants always looked towards their left hand, but they either saw their own hand, or a wooden object appearing at the hand’s location.
We found that simply viewing the hand reduced acute pain levels: the pain threshold was about 3°C higher when looking at the hand, compared to when looking at another object. Next, we used concave and convex mirrors to show the hand as either enlarged or reduced in size.
When the hand was seen as enlarged, participants tolerated even greater levels of heat from the probe before reporting pain. When the hand was seen as smaller than its true size, participants reported pain at lower temperatures than when viewing the hand at its normal size.
Interpretation
Our findings suggest that the image the brain forms of our own body has a strong effect on the experienced level of pain, revealing an interaction between parts of the brain that process vision and areas that process pain. The perceived size of the body can modulate these interactions. It is important to note that effect of perceived size of the body is different in acute and chronic pain, as shown by previous research. This might be due to plasticity changes that occur in the brain in chronic pain syndromes.
Clinical implications
Many psychological therapies for acute pain focus on the painful stimulus, for example by changing expectations, or by teaching distraction techniques. However, thinking beyond the stimulus that causes pain, to the body itself, may lead to novel clinical treatments in the future.
About Flavia
Flavia Mancini is a cognitive neuroscientist interested in mechanisms underlying perception. She investigates multisensory interactions in perception of touch and pain, using a combination of different methods: psychophysics, EEG, TMS, and fMRI. A short overview of her research can be found here. Flavia is currently based in London, at the Institute of Cognitive Neuroscience at UCL, working under the supervision of Patrick Haggard. She is completing my PhD studies in Milano, at the University of Milano-Bicocca, under the supervision of Giuseppe Vallar and Emanuela Bricolo.
Reference
Mancini F, Longo MR, Kammers MP, & Haggard P (2011). Visual Distortion of Body Size Modulates Pain Perception. Psychological science : a journal of the American Psychological Society / APS PMID: 21303990