“Pain as input” is the natural way to think. When we injure ourselves it seems that the “pain bit” is something organised at the injury site and pain then goes into the nervous system to warn the brain. This is “pain as input thinking”, but the idea is biologically bankrupt and likely to be troublesome for the management of chronic pain. “Pain as output” is a better and more scientific way to think.
There are no pain fibres in the nervous system. When injured, the nerve fibres send “danger signals” not pain signals towards the brain. This is just an increase in amplitude and number of impulses in some fibres (nociception). It is up to the brain to decide if these danger signals are worth listening to. If you have a mild ankle sprain, but you are trying to escape something or score a winning goal, the brain won’t be too bothered listening to the danger signals. However if you have a backache and you have just heard that serious kidney problems can cause back ache and you have a relative with kidney problems, the brain may be particularly attentive to the danger message coming in from the back.
Therefore, while the danger messages from damaged and diseased tissue can contribute to pain, they don’t have to.
We (Butler and Moseley 2003) believe that a good way to help with this reconceptualisation is to consider the notion of threat. While we all know that pain has an emotional influence, “threat” is a wider and more overarching concept. Threats are held in the brain as old memories (“oh no, I have damaged the back again”), made in the brain as the injury occurs (“how will I work next week”), and are in the environment (workmates, insurance). There are a massive number of potential threats. If the brain perceives threats and adds them up, sometimes including the danger impulses, pain may be constructed.
There is research which shows that if a noxious chemical is placed under the skin and you check the brain activation patterns it looks similar to if the noxious chemical was put in muscle (Casey & Bushnell, 2000). This research supports the idea that the tissue injured may not be such a big contributor to pain as most of us thought in the past. Finally, lets never forget phantom limb pain – there are no tissues to create a pain input and what must be the most maddening pain now exists in fresh air.
David Butler, September 24 2007
Butler DS, Moseley GL (2003) Explain Pain. Noigroup Publications, Adelaide
Casey, K. L., & Bushnell, M. C. (2000). Pain imaging. Pain: Clinical Updates, 8, 1-4.
It does’t get any more fundamental than this. Pain as an output; pain as a construction of the human being.
But this vital reconceptualisation can be the most difficult one to make. The allure of pain as an input is hard to shake and seems so intuitive to most people in pain.
Mention the brain to a person in pain and you may quickly find yourself in a hostile environment. In my early fumblings trying to explain pain, I heard on more than one occasion “It’s my (bleeping) back mate, not my (bleeping) brain. GET OUT OF MY (BLEEPING) HEAD AND TREAT MY (BEEPING) BACK“, and on more than one occasion I backed away from the confrontation, not having the skills and knowledge to get in under the radar of a highly sensitive and highly evolved defence system. A defence system that had become so highly protective that even an idea (that pain is an output, a construct of a human) was evaluated as threatening and warranting further protective outputs- recalling these situations I’m pretty sure that there was a sympathetic nervous system mediated fight (or flight) response, along with increased activity in the HPA Axis. This certainly had an impact on the linguistic output, I could definitely see a motor response and more often than not there was even an increase in their pain output.
I like to think now that I have a bit more skill in explaining pain – metaphor and stories can help a lot to slip past initial resistance, and the ever increasing body of knowledge regarding the biology of pain provides powerful credibility and confidence in taking this approach.
It’s not all roses though, and it’s not only people in trouble that can find it hard to make this fundamental reconceptualisation. I noticed just today (not sure if it’s been posted up for a while) a couple of paragraphs on the home page over at Body in Mind. Lorimer Moseley takes a press release from a “rather posh journal” to task for repeating the “unfortunate trivialisation” that Pat Wall pointed out over 30 years ago; that of mislabelling nociceptors as pain fibres with the subsequent “pain stimuli”, “pain receptors” and “pain signals” exemplifying the erroneous “pain as input” model.
I reckon for some people now, those that have ‘got it’, the “pain as an output” message might be sounding a bit like a broken record. But it’s a message that still needs repeating and disseminating, with David’s post about this most vital reconceptualisation being as relevant today as it was seven years ago.
Have you got any stories about colossal successes or resounding “opportunities for learning” from explaining pain to people? Feel free to share them with us in the comments below
Get all the juiciest and most up to date pain science at a noigroup course