A new take on the Gate Control Theory, or, The benefits of rubbing your boo-boos

Two or so posts ago I expounded the potential value of blogging, as an opportunity to 'riff' on things that come to mind without the scrutiny of formal peer review.  Readers will remember, it wasn't about some distaste for the peer-review process, quite the contrary as I am a peer reviewer myself and respect the process deeply.  Rather this blogging thing is an opportunity to allow theories and ideas to form and crystalize out in public, with the added benefit of the internet community to provide input and feedback.

So, with that in mind, why not take on one of the greatest theories that pain science has ever benefited from: Melzack and Wall's Gate Control Theory.  If you're goal is to increase awareness of a new website, might as well go full-out nuttier-than-a-sack-of-squirrels crazy, right?

In truth, this isn't something that I'm devising while I sit here typing.  This is a theory that I've been working on for years, and have recently found empirical evidence to support it.  So I'll say it's time to share and ask the community for feedback.

This is also not meant in any way to be disrespectful of the work of Drs. Melzack or Wall.  In fact, I had the great honour of meeting Dr. Melzack at the IASP conference in Montreal last year, and (albeit quickly) passed the idea by him of updating the GCT.  He himself said (and I admit complete paraphrasing here) that the theory, going on 50 years old now, could probably use some updating.  Interestingly, this isn't the first time he's said that, as a similar quote can be found in Marni Jackson's superb book Pain: The Science and Culture of Why We Hurt.  I also want to be careful here - I'm not quite egomaniacal enough to believe that I'm making even an iota of contribution to understanding pain as compared to the actual GCT.  This is simply an idea, a theory in the works that has yet to be fleshed out and perhaps never will be.  But if nothing else, might be an interesting topic for discussion over the water cooler.

 

Dr. Melzack (left) and me (right) feeling like a 13 year-old girl who had just met Justin Bieber

So I won't say that I've got his blessing, but I don't think I'm stepping too far out of line here.  To start, I'll share a couple of anecdotes:

Near the end of last summer I was driving on warm Canadian afternoon, windows down and hand out the window as I'm apt to do.  The road I was on has become fairly busy in recent years thanks to some big box stores and residential communities recently springing up.  A cement mixer passed me heading the opposite direction, and a small piece of gravel happened to strike me right on the tip of my index finger.  I immediately withdrew my hand (nice flexor withdrawal reflex there) and examined the digit as best I could while driving 80 km/h.  Expecting to see a piece of gravel wedged into my finger, or at least broken skin, I instead saw nothing.  The gravel had clearly bounced off my finger with nary a 'how do you do'.  But I could sense the sting, and I remember thinking to myself 'this can't be right, that had to hit me going at least 160 km/h (combined my speed and the mixer's), there has to be some damage here'.  It was like I didn't believe my own eyes.  What happened next?  I rubbed it.  Incessently.  Rubbed the end of my finger for the rest of the day.  And into the following day.  Until any sensation from the gravel was gone.  Then I continued to rub it a bit more.  It was a fascinating thing for an old reflex and more recent behaviour buff like me - I couldn't stop rubbing it.  My eyes told me nothing was wrong, but it was like I had to convince my neuromatrix that the body part was still in tact.  That the boundaries of my self were still the boundaries.  That all was as it should be, not only optically but also somesthetically and proprioceptively.

On September 11, 2001, I was working as a clinical physiotherapist at an outpatient physio department in the hospital of a small rural town in Southwestern Ontario.  I routinely started work at 7:30am EST.  Sometime around 9:00am EST I catch a few words on a nearby radio about a plane hitting a building in New York City.  I become transfixed.  Over the following days and weeks, I like many others find myself compelled to consume any information on the event that I can.  I need to know the situation.  I need to know the boundaries of it.  I need to know the reality I had constructed for myself remained largely unaltered despite the massive tragedy that sent shockwaves of emotional pain outward in massive ripples.  As per the gravel hitting my finger, I needed as much evidence of personal security as I could find.

The consistency here is that perhaps, through providing as much stimulus/input to those 'sentry' parts of our brain responsible for recognizing and responding to danger, we are able to find some relief.  In the case of personal injury, the neuromatrix needs to know that the boundaries of the 'virtual body' are still in tact.  In the case of massive psychosocial (for lack of a better word) disasters, of which we've had many just recently (my heart goes out to our Japanese friends), those same sentry systems require as much information as is available to provide a sense of personal security and of some kind of rational and understandable reality.  This theory holds for pain, by definition both a sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.

So that's the theory in a nutshell - the rubbing of the injured body part is less about increasing activity in large diameter afferents and closing the 'gate' at the level of the dorsal horn, and more about providing input to the body-self neuromatrix, letting it know things are still in tact and that the heightened arousal that tends to accompany perceived damage is probably no longer necessary.

 

I alluded to this idea in a blog post for the Body in Mind group that I wrote while I visited them in Sydney last summer.  It was in reference to a very nifty rubber arm illusion experiment in which, once the illusino was induced, an immune challenge was introduced to both the quasi-neglected arm and the opposite control arm.  The magnitude of the immune response was significantly different between the two sides.  Lorimer has also shown that people with chronic low back pain have a hard time defining the boundaries of their back when asked to draw an image of themselves.  Whether the loss of an easily recognizable body-self image is a precursor for chronic back pain, or an effect of it can't be stated with any confidence based on our current understanding.  But it is conceivable that the brain's sentry body-self neuromatrix maintains that heightened state of arousal and sensitivity in it's efforts to obtain knowledge about the state of the painful part.  This might also be the mechanism behind Peter O'Sullivan's observations that some people with chronic low back pain exhibit behaviours that result in further pain (ie. it's painful to extend the lumbar spine, but some people habitually adopt this posture despite the pain).  In that case, this theory would suggest that any stimuli coming from the area, even if unpleasant, can offer at least some form of relief to a neuromatrix seeking information, especially in those conditions that you can't see.  Not saying this is good, just saying it makes sense in light of my pseudo-theory.  Note that this theory would also support the notion that manual therapies probably have much of their effect through drawing attention to, and providing neurophysiological stimulus from, painful parts of the body.  The focus on identifying very specific movement impairments (ie. restricted superior glides of the facet) becomes less of a priority than does identifying the amount of stimulus that can be applied to a body in pain that provides adequate stimuli without being perceived as threatening to the sensitized 'pain' system.

This theory also holds in light of findings such as those of Mancini and colleagues, who showed that attending a body part induces analgesia in an acute laboratory pain setting, with the effect enhanced when the body part is magified.  Again, more stimulus, more input for the neuromatrix that is seeking evidence that all is in fact well.  Note that this is in distinct contrast to the findings of Moseley and colleagues, who found that magnifying the hand of a person with complex regional pain syndrome may actually enhance the pain, while reducing it in size (using dollar store binos according to Lorimer) will have the analgesic effect.  I believe this demonstrates that the neuroplastic changes that accompany neuropathic pain conditions, leading to a body-self neuromatrix that's all distorted, renders such conditions beyond the explanatory power of my theory, which was also true for the GCT.

In the interest of time and space I think it's a good time to stop now.  Daylight savings time has allowed me to work later into the evening, but it also means that morning comes an hour earlier than my body thinks it should.  I would love to hear your feedback on this post.  Am I crazy? Maybe.  Am I treading into places I don't belong?  Probably.  Is radical thinking the way that science moves forward?  Almost definitely.  Let me know what you think in the comments section below.