Not Exactly Rocket Science

Pain in the eye of the beholder

Blogging on Peer-Reviewed ResearchIt goes without saying that we are capable of noticing changes to our bodies, but it’s perhaps less obvious that the way we perceive our bodies can affect them physically. The two-way nature of this link, between physicality and perception, has been dramatically demonstrated by a new study of people with chronic hand pain. Lorimer Moseley at the University of Oxford found that he could control the severity of pain and swelling in an aching hand by making it seem larger or smaller.

Moseley recruited 10 patients with chronic pain in one of their arms and asked them to perform a series of ten hand movements at a set intensity and to a set pace. The volunteers had to watch their arms as they went through the motions. On some trials, they did so unaided, but on others, they viewed their arms through a pair of binoculars that doubled their size, a pair of clear-glass binoculars that did not magnify at all, or a pair of inverted binoculars that shrunk the image. 

On each trial, Moseley asked the recruits to rate their pain on a visual sliding scale. He found that they were in greater pain after they had moved their arms – no surprise there. But the amount of pain they felt depended on how large their arm appeared to them. They experienced the greatest degree of extra pain when they saw magnified views of their arms, and took the longest amount of time to return to normal. Perhaps more surprisingly, the “minified” images actually evoked less pain than normal.

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You could argue that this was nothing more than a cute psychological effect, but changing the perceived size of the volunteers’ arms also evoked physical changes. Moseley measured the circumference of the volunteers’ fingers as they moved them about. Again, those who saw a magnified image had the most extreme swelling and those who saw the shrunken versions had less swelling. All of these changes were statistically significant.

Moseley isn’t clear why this effect happens, although he suggests that making things more visually apparent could also make them more sensitive to touch. After all, some studies have found that it’s possible to heighten someone’s sense of touch by magnifying their view of the area they’re touching. Alternatively, the sight of a bigger and more swollen limb could fool the brain into evoking the type of pain response that it would normally use to signal imminent danger.  And scientists have even suggested that a mere conflict between what we see and what we feel can cause localised pain and swelling.

For now, that’s all speculation, but Moseley is especially interested in the fact that he could soothe the degree of pain and swelling in a limb, simply by making it look smaller. That could certainly have clinical merit, so it’s worth understanding why it happens. Moseley suggests that people may feel less ownership over their own body parts, if they seem smaller than expected. Indeed, in a study he published earlier this year, he used an illusion to convince volunteers that an artificial limb actually belonged to them and, as a result, the temperature in their actual arm fell. 

Reference: Moseley GL, Parsons TJ and Spence C. 2008. Visual distortion of a limb modulates the pain and swelling evoked by movement. Current Biology 18: R1047

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Comments

  1. #1 Freidenker
    November 27, 2008

    Spectacular read. The article itself is fascinating. I want to say something rather OT that bugs me about science journalism in Israel as opposed to the kind of writing on your blog.
    In short, science journalism here sucks. You have utter non-experts (and not even informed laymen) doing the science section, and the end result is garbled and disinterested descriptions of scientific fields that, if written by informed writers, can actually reach out to the public.

    The flip side is that scientists who write about science are usually not that good at writing, and eventually, the only to find good science news and articles is by blogging abroad. :/

  2. #2 Jivlain
    November 27, 2008

    Clearly this is to allow us all to avoid dying every time we stubbed our toes.

  3. #3 Robert V Sobczak
    November 27, 2008

    What the mind harbors the body manifests … or one of its corollaries. Now, it would have been a fool proof test had they given the “large hand” group a placebo, and the other a pain killer. (That’s a joke). Nice post as usual, always thought provoking.

  4. #4 Scriptor Senex
    November 28, 2008

    As a chronic pain sufferer I found that fascinating. I wonder if staring at a small photo of myself might help? (And I’m only half joking – I’ll try anything!)

  5. #5 Jon D
    November 28, 2008

    I’m trying to think how this could be practically applied to relieve pain, but I cant get very far past giving people glasses with lenses which make things look smaller.

    I wonder if this could be extended to people imagining their hands are smaller than they are?
    Next time I slam my fingers in a drawer I’ll let you know how I go

    Anyway, its always interesting learning more about how our brains work!

  6. #6 Ed Yong
    November 28, 2008

    It’s interesting isn’t it? It’s one of those studies where there surely must be some practical value, but it’ll take a more creative mind than me to work out what it is. I agree with Jon though – the main interest for me is in learning that it happens and trying to work out why.

  7. #7 MissPrism
    November 28, 2008

    Cool! It reminds me of those weird studies on phantom limbs that Ramachandran writes about.

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