More on Pain and Illusions

One of the main themes of this blog is that therapies attempting to treat chronic pain should target the brain for change, not just the body. Some recent studies based around sensory tricks or illusions provide further compelling evidence in support of this idea.

1. Big hand, small pain

In the first study, researchers placed heat probes in the left hands of eighteen participants. Then they turned up the heat. Participants were allowed to “get out of the kitchen” as soon as they began to feel pain.

During the experiment, participants looked toward their left hand. However, the scientists used a set of mirrors to manipulate what the participants saw – some saw their own hand while others saw a wooden object in the same location. The participants who looked at their own hand had greater heat tolerance than those who looked at the wooden object, and withstood an extra 3°C of heat.

The study also compared the heat tolerance of participants looking at a hand that was made to appear either larger or smaller than its normal size. The participants looking at the seemingly enlarged hand had greater pain tolerance than those looking at the smaller hand.

The scientists believe that the visual information affected pain processing by influencing the brain’s maps of the skin and associated body parts. Flavia Mancini, one of the authors of the study, said: “the image that the brain forms of our own body has a strong effect on the experienced level of pain. Moreover, the way the body is represented influences the level of pain experienced.” Yes. More evidence that we can treat pain in the brain without doing anything to the body at all.

The part of this study that I found particularly interesting is that the participants with the best pain tolerance were the ones who had the most sensory information about the painful area, not the least. This is perhaps evidence that greater awareness of the body might be a good way to reduce pain. Further, it runs directly counter to the common notion that we should attempt to distract ourselves from awareness of body parts that are in pain.

Perhaps this shouldn't be too surprising considering that sensory signals from the body can effectively compete with danger signals (nociception) for attention in the brain. The greater the flow of sensory information, the less pain will result from the nociceptive information. This is why you can reduce pain from an owie by rubbing it. Perhaps what this study shows is that looking at the owie is another way to do the same thing. Of course if the owie is really nasty looking this might make things worse, as I have noticed with my four year old (and myself.)

Professor Patrick Haggard gives a specific example of how this idea might play out in a specific context: “when a child goes to the doctor for a blood test, we tell them it will hurt less if they don’t look at the needle. Our results suggest that they should look at their arm, but they should try to avoid seeing the needle, if that is possible!” Isn't it nice to see a researcher talking about the implications of his study, not as a starting point to cash in on developing some new drugs, but as a way to comfort kids getting a shot?

2. Small hand, small pain

In the second study, scientists were able to cut the pain of hand osteoarthritis in half by subjecting the painful hands to some interesting illusions. These were created with some software that uses computer manipulated video images, combined with actual pulling or pushing on the hand, to fool the brain into believing the hand is stretching or shrinking. (For some idea on how this might work see here.)

Scientists got the idea for the study after showing the illusions to members of the public for entertainment. One of the participants noticed that the illusion completely eliminated the arthritis pain in her hand. This prompted a study which recruited twenty volunteers with arthritic pain in the hands or fingers. The researchers compared the participants’ pain levels with and without the shrinking/stretching illusion. The illusion cut pain levels in half.

The practical value of the actual pain relief method employed here is obviously limited, because it is rather inconvenient to walk around all day attached to a computer creating weird illusions in various body parts. Perhaps someday we can enjoy these and other benefits when our computer overlords create for us a Matrix-like reality. For now, the findings from the study open up some interesting inquiries into the potential that manipulating the self image has for pain relief. For now, I’ll stick with the Feldenkrais Method as my self image manipulator of choice.