Pain in the eye of the beholder
It 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.
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
More on perception:
- Westerners focus on the eyes, East Asians on the nose
- Fearful facial expressions enhance our perception
- The smell of danger – shocks help people discriminate between similar odour
Go Further
Animals
- Cougar travels 1,000 miles in one of longest recorded treksCougar travels 1,000 miles in one of longest recorded treks
- Rare gray whale spotted in the Atlantic—and it's only the beginningRare gray whale spotted in the Atlantic—and it's only the beginning
- Why 'funga' is just as important as flora and faunaWhy 'funga' is just as important as flora and fauna
- Termite fossils prove mating hasn't changed in 38 million yearsTermite fossils prove mating hasn't changed in 38 million years
Environment
- Why the 2024 hurricane season could be especially activeWhy the 2024 hurricane season could be especially active
- Mushroom leather? The future of fashion is closer than you think.Mushroom leather? The future of fashion is closer than you think.
- This deadly fungus is hitchhiking its way across the worldThis deadly fungus is hitchhiking its way across the world
- Why 'funga' is just as important as flora and faunaWhy 'funga' is just as important as flora and fauna
- This exploding mine holds a treasure that may change the worldThis exploding mine holds a treasure that may change the world
History & Culture
- This ancient festival is a celebration of springtime—and a brand new yearThis ancient festival is a celebration of springtime—and a brand new year
- See the story of Jonah and the whale like never beforeSee the story of Jonah and the whale like never before
- This ancient mosaic offers extraordinary insights into the pastThis ancient mosaic offers extraordinary insights into the past
- These are the real dunes that inspired Dune—and you can visit themThese are the real dunes that inspired Dune—and you can visit them
- Meet the only woman privy to the plot to kill Julius CaesarMeet the only woman privy to the plot to kill Julius Caesar
Science
- Women’s bodies are understudied—but that’s starting to changeWomen’s bodies are understudied—but that’s starting to change
- Hundreds of tiny arachnids are likely on your face right nowHundreds of tiny arachnids are likely on your face right now
- What's worse than a hangover? Hangxiety. Here's why it happens.What's worse than a hangover? Hangxiety. Here's why it happens.
Travel
- A guide to Gdansk, Poland's regenerated maritime cityA guide to Gdansk, Poland's regenerated maritime city