Watch Your Back: Mirrors Reduce Back Pain

I just read an interesting paper from Lorimer Moseley's group about how looking at your back in the mirror can reduce back pain. The paper describes a simple study where people with back pain were asked to make numerous repetitive provocative movements of the low back under two conditions: one group was able to see their back moving in a mirror, while the other group could not. The group that received visual feedback from the mirror experienced less pain after the movements and for a shorter duration. Now the effects seen in the study were not so dramatic as to suggest that staring at your backside in the mirror all day would be a miracle cure for back pain. But it does raise an interesting question about the mechanism of the effect. Why should looking at your back make it hurt less? The discussion section of the paper provides an interesting analysis of the role of nonthreatening sensory feedback in reducing pain.

Seeing it helps for many things

The authors note that case studies have found that visual feedback can reduce pain in a number of conditions, including phantom limb pain, CRPS, brachial plexus avulsion and fibromyalgia. It is also known that viewing oneself causes a number of physiological responses, including changes in sensory experience, the perceived location of a body part, and increased excitability of motor pathways.

So why does visual feedback reduce pain? The authors offer several potential explanations.

Correcting sensory motor incongruence

The first explanation involves the concept of sensory motor incongruence (as you may have guessed from the title of this section). As I have discussed previously on this blog, there are numerous researchers who believe that pain related to movement may be caused by a discordance between a motor command and the related sensory feedback. The idea is that when the CNS issues a motor command, it makes predictions about the likely sensory feedback. When the prediction is off, the error is considered a threat which provokes pain.

In support of this idea, there is significant research showing that a wide range of painful conditions can be made better and worse by using reducing or increasing sensorimotor incongruence with visual data that is either informative or illusory.

There is also research showing that people with chronic low back pain have disruptions in the way their brains represent the back, including alterations in brain structure. They also have numerous perceptive deficiencies indicating poor mapping of the back, such as decreased lumbar tactile acuity, slow movement in the lumbar spine, difficulty in determining the outline of the back, and deficits in proprioception. These perceptual impairments can be improved by seeing the affected area. Based on this evidence, one might speculate that the pain reduction  seen in the study resulted from visual feedback correcting for poor mapping of the low back, thereby reducing the incongruence between the motor intention and the sensory feedback. (An idea not discussed in the paper is that the improved mapping of the low back helped correct motor errors, thereby reducing nociception.)

Non threatening input

An alternative theory explaining why visual data may reduce pain is that it acts as a non threatening input into the "neuromatrix" which reduces the threat associated with the movement. In other words, even as the brain is receiving nociceptive signals from the back indicating danger in the area, the eyes are watching the back and seeing it move normally without any visible damage. This may cause the brain to conclude that the back is not in as much danger as the nociceptive information might suggest, and that pain is less necessary as a protective mechanism.

Some research supports this theory. For example, looking at your hand when it is being irritated with a laser, or looking at your arm when it is being injected with a needle (but not at the needle!) will reduce pain. If you have CRPS and look at your affected hand with magnifying glasses it will hurt more, and with minimizing glasses it will hurt less. All this goes to show that the brain uses visual data to assess threat, and that when the visual data indicates no threat, there will be less pain.

The authors also discuss the interesting idea that we rarely see our backs, and therefore don't often have the opportunity to get some visual reassurance that everything back there is basically OK. Isn't it interesting that so many parts of the body that tend to be in chronic pain are places we can't see?

Conclusion

Whether the mirror reduced pain by providing nonthreatening visual input, or by correcting mapping errors, I read this paper as saying it can't hurt and might help to give your clients some information about what is going on in their body, provided that the information is basically good news. You certainly don't need a mirror to do this. Manual contacts and novel movements can also give the brain a different perspective on the body.

In Feldenkrais classes I spend a lot of time asking my students to feel the contact their back makes with the floor: which parts touch the floor, which parts don't, how high does the low back arch from the floor, and where does it return to the floor. I wonder if my students might sometimes get a little bored by this. Maybe I can tell them about this paper to convince them that the floor can be a mirror.

Thanks to Chris Johnson for pointing out this paper.