Ever since I read Moseley et al’s (1) paper back in 2009 on visual distortion I was instantly succumbed to the idea of embodiment and wanting to work with people living with Complex Regional Pain Syndrome (CRPS). I admit I didn’t fully understand what embodiment was back then, but there was a small part of me that was intrigued and so I delved further. I have my very cool supervisors at St. Helier’s hospital (they are no longer there, thank goodness) for inspiring me.
CRPS is a strange condition, it’s not fully understood but it appears to be related to maladaptive cortical changes particularly in the sensory-motor cortex of the brain (2-4). Other pain conditions such as phantom limb pain and chronic low back pain have also been associated with these cortical changes (5). We have an area in our brain that represents the entire body. This is called the sensory homunculus. It’s important to note that it can change because the brain is plastic. So, the homunculus is not static it’s dynamic. Studies have found that people with CRPS had a shrinkage or blurring of the hand representation of the homunculus in the brain (6-8). Interestingly the brain changes are correlated with the intensity of persistent pain (9,10).
There is a groovy study out that took 10 CRPS patients to perform a braille-like haptic task to retrain sensory-motor cortical representation. The study showed compelling results, such as pain reduction and that it could be applied clinically was exciting for the practicing clinician. Further study is certainly needed, in particular with a larger sample size (11).
The Rubber Hand Illusion
Considering embodiment (which is determined as having the experience of having sense of ownership of one’s body) I came across the Rubber hand illusion. Straight up, the rubber hand illusion is cool! It’s totally freaky but it’s totally cool! Essentially an individual observes a rubber hand being stroked with a brush while their real hand is stroked in synchrony out of view. What should happen is after a couple of minutes because the individual is feeling the brush on their hand but seeing the brush on the rubber hand, they begin to the experience the sensation of stroking as if it were coming from the rubber hand. Woah!! MIND BLOWN!
So, the loss of the real hand to the rubber hand represents a change in body schema. Changes in the brain, skin temperature, and the awareness of the real hand occur as the brain embody’s the rubber hand. If you think that’s freaky when the rubber hand is made to move in synchrony with real hand movement (out of view) or is threatened the experience is all the more vivid. When a rubber hand is threatened following the experiment, individuals have reported increases in anxiety and even tingling in the rubber hand! See the video.
I have played with the rubber hand illusion and it’s something attendees play with on the Know Pain workshops. Did I say it was cool?
Moseley’s compelling paper studied a small group of individuals that had complex regional pain syndrome of the hand and found that by magnifying their affected arm through binoculars increased movement-induced pain and swelling. Even more fascinating was when the binoculars were flipped the other way (so individuals were looking through the large lens end) thus minifying the hand this reduced movement-induced pain and swelling.
I admit this is one of my favourite papers. It is a paper I frequently return to because I am fascinated by the concept of embodiment and visual distortion.
For those of you that are familiar with visual distortion you may have heard of mirror box therapy. This is now a common tool in most clinical practices. Ramachandran and colleagues (12) found that phantom limb pain (pain in the area of the amputation) could be relieved by creating a visual illusion through reflecting the opposite intact limb in a mirror. Mirror box therapy is used to treat painful conditions such as complex regional pain syndrome, fibromyalgia, and nonspecific low back pain. The problem is the effects of mirror therapy are short lived (13) and this was something I experienced in the NHS. I attempted mirror therapy but to also found the effects short lived. I suspect this was due to not fully understanding the concept and that fact the we were swamped in the NHS. It was difficult to fit people in for intensive mirror therapy without expressed consent from senior clinicians and rightly so.
After I read Moseley’s paper I set out to make myself an minification box that I could use to minify the affected limb. I managed to find a plastic windscreen that van drivers would stick on the rear window to increase their field of vision whilst driving. By placing this piece of plastic on a piece of glass and then mounting into cardboard uprights I could reduce the visual size of the hand by moving the glass higher up the cardboard. Now there were many problems with this. I didn’t know how far away the glass had to be to determine a clinically measurable effect, I had no way of measuring skin conductance for temperature changes and of course the usual constraints of working in the NHS ultimately saw the box sit on the top shelf above my desk in the department for years.
So, what’s the next step?
Well, this is where the shit gets exciting! There are studies being done in body manipulation using live video imaging. One study into people living with OA hand pain. Participants viewed their hand through live video either being lengthened or shortened whilst simultaneously seeing and feeling the experimenter gently pulling or pushing on the participants hand. Thus the participants feels and sees what is being done via the live video feed (14). The study results are intriguing, showing that perceived hand size was smaller in OA hand participants compared to healthy controls. Interestingly this too is something I have experimented with in clinic in my own way. The idea of combining mirror therapy with the rubber hand illusion technique. I use it for pattern recognition in CRPS patients in hands and feet. I use the standard mirror therapy approach but add in brush stroking to identify if clients can match sensory and visual stimuli. Essentially attempting to identify what they see matches what they feel.
There is also the exciting prospect of Virtual Reality (VR). Up until now VR has required the use of powerful computers. Of course, now we have google cardboard and Samsung gear for use on mobile phones. It would seem obvious that with the flexibility of apps and cameras visual distortion is something that can be explored on these platforms, and with any luck be used clinically for complex pain presentations such as CRPS.
Thank for having a read
- Moseley GL, Parsons TJ, Spence C. Visual distortion of a limb modulates the pain and swelling evoked by movement. Curr. Biol. 18(22), R1047–R1048 (2008).
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