Disowning pain with binoculars

My second article for the Scientific American Mind Matters website is online now. This one is about the recent study which demonstrated that distorting the body image alters pain perception - specifically, it was found that using inverted binoculars to make the hand look smaller than it actually was led to a reduction in the pain and swelling induced by movement in patients with chronic pain. 

It is not clear why this happens, but the findings obviously have major implications for pain management. One explanation put forward by the authors is that this simple manipulation caused the subjects to "disown" their hands; the hand feels less like a part of their own body, because it appears to be further away than normal, and so painful stimuli originating from it are reduced.

This, and several other studies which investigate the phenomenon of body ownership, are in my opinion among the most interesting research findings to be published this year. Both of the others were conducted by Henrik Ehrsson's group at the Karolinska Institute. One showed that amputees can be made to experience a rubber hand as their own, so that they can sense the tactile stimuli applied to it. This could eventually lead to the development of prosthetic limbs which provide accurate sensory feedback to the user and therefore feel realistic.

The second study from Ehrsson's group is about the body swap illusion. Here, participants could be made to experience someone else's body, or that of a mannequin, as their own, simply by seeing it from a first-person perspective, while at the same time seeing their own body from the third-person perspective and having identical stimuli applied simultaneously to both.

All of three studies point to the hitherto unrecognized - and somewhat surprising - notion that visual information can easily override the other types of sensory information entering the brain to modulate tactile sensations. In other words, altering the visual perception of one's own body can have significant effects on how one's body feels.

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You can experience all this strange stuff without any special equipment:
Using the index finger it is possible to experience the fact that the mind can bend pain sensation. If you hold your index finger about 23 inches from your nose and look straight ahead, you should see a double vision of your finger: a real and a phantom one. Now touch the tip of the index finger with the other hand. You will feel the sensation of touch both in the real and phantom fingers. Along these lines, if you gently pinch or pinprick the fingertip you will feel the pain and discomfort in the real and phantom index fingers.
A variation of this party trick is to hold a pen horizontally about 23 inches away from the nose, with the tip, firmly pressed against the tip of the index finger of the opposite hand (also held horizontally). Look straight ahead. You should be able to see an imaginary object, half fingerhalf pen, hanging between the tip of the pen and the tip of the index finger. Press the tip of the pen firmly against the index finger until you feel discomfort / pain. This pain will be felt both at the tip of the imaginary object as well as the real index finger.
(From Lederman E.2005 The science and Practice of manual therapy, Elsevier)