Tuesday, January 22, 2008
Readers frequently ask about the definition of neuromatrix in relation to the brain and pain. Wikipedia and Google are not that helpful (yet), though there are some good links on Google to Ronald Melzack’s pioneering work. (Melzack, 1999, 2001).
Cognitive Psychology is merging to some degree with neurobiology. While the term neuromatrix has emerged with the increasing knowledge of brain neuroscience, some of the older cognitive psychology writings provide good definitions and understanding of what we now call the neuromatrix.
I like “a map of event space in the system’s coding space” (Dudai, 1989). So the coding space is all the possible combinations of connections in the brain. Pain or jealousy could be an event which would take up part of this space. The event space has been referred to by Melzack as the neurosignature. So a pain neurosignature exists within the neuromatrix. Moseley and I (Butler & Moseley, 2003), trying to be a bit trendy, refer to the neurosignature as a neurotag.
Of course it is all far more complex than this. A pain neurotag exists in a snapshot of time. It will change over time and context. Everyone’s pain neurotags are different and even our own pain neurotags will be structurally different within the brain over time.
The term “representation” is also used in relation to neurosignature.
– David Butler
Butler, D. S., & Moseley, L. S. (2003). Explain pain. Adelaide: NOI Publications.
Dudai, Y. (1989). The neurobiology of memory. Concepts, findings, trends. Oxford: Oxford University Press.
Melzack, R. (1999). From the gate to the neuromatrix. Pain, Suppl 6, S121-S126.
Melzack, R. (2001). Pain and the neuromatrix in the brain. Journal of Dental Education, 65, 1378-1382.
Searching google for “neuromatrix” now returns 41,500 results with Melzack’s 2001 paper referenced above as the top hit. It’s a seminal paper and freely available.
The neuromatrix model itself has been updated a little (notably more recent depictions has the phrase “trigger points” removed) and somewhere along the way it morphed into the “pain matrix” (Iannetti and Mouraux 2010) which then got reloaded (Legrain et al 2011 – I see what you did there), but 13 years on it still seems to be a useful conceptual model.
Perhaps the most powerful aspect of the neuromatrix model is that Melzack placed pain on the right hand side – as an OUTPUT (along with other protective responses including immune, endocrine and motor) of the Body-Self in response to numerous and contextual inputs – not just nociception.
Where to from here? Is the neuromatrix model too neurocentric? Do we need a biomatrix model? What might we be flashing back to in another 6 years?
Iannetti GD and Mouraux (2010). From the neuromatrix to the pain matrix (and back). Experimental Brain Research, 205(1) 1-12.
Legrain V, Iannetti GD, Plaghki L and Mourax A (2011). The pain matrix reloaded: a salience detection system for the body. Progress in Neurobiology, 93(1) 111-124.
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In the linked Melzack article, he refers to the term “body-self”, which is interesting. It’s the only term he doesn’t flesh out with definitions. But it’s the key to this whole “tragedy of unrelenting suffering” as he puts it. The body is NOT the self. This can be proven using both logic and direct experience.
To realize that the self is not the body is the end of suffering (though not the end of nociception or pain, because they are our biological inheritance). If one pays careful attention to the body’s sensations, one automatically separates the body from the ‘thing doing the attending’. The ‘thing doing the attending’ is the self. Then one can switch one’s attention to this ‘self’ to see what in fact it really is. It is consciousness,…. and when you look at consciousness, thoughts stop. Stopping thoughts puts an end to the body-self identification, even if temporarily. Some say that it can be achieved permanently with enough practice and courage. Courage is required because the self is (for most people) more closely guarded and protected than the life of the body.
I have struggled with concept of the neuromatrix since I first laid eyes on it. While I think it does represent the multifactoral aspects of pain and puts them in relationship with time and input and output. It is tricky to make heads or tails of much of it.
Perhaps it is my experimental mind and my background in physiology but not all inputs are equal in determining outputs. The second is the assumption that the brain is representing the enviroment. While it may be true that the brain has some capacity for manipulation of symbols and thus representing some content in a meaningful way, I am not sure, and have considrable doubt, that the brain reconstructs and represents. This is otherwise known as the homonculus fallacy.
Correlated brain states with pain related behaviors have been dubbed neurotag and neurosignature. However, I struggle to find much meaning in what these concepts actually mean. We can’t really say what is going on with much fidelity when we see FMRI light up either after a experimental stimuli and the pt. reports pain. Is it activation, inhibition, etc? Is this what we are currently labeling as such. Or are we just labeling these a hypothetical pattern of activation that we eventually hope to find and map with greater fidelity?
The current model of the neuromatrix is also not falsifiable and has no predicitave ability since one could put in any input to derrive any output. So as a theoretical construct it provides limited insight for the researcher.
The struggle moving forward with pain researchers is to develop aetiological pathways and determine relationships between the inputs and behavioral output. This is quite a hard problem and I think we are indebeted to Melzack for bracketing (framing) the problem before us.
Thanks for the comments.
As an old clinician, educator and research dabbler only, the neuromatrix as paradigm, despite limitations discussed above, has offered something of a special framework to allow clinicians and their patients to begin to engage the brain. One example would be the presence of a framework to understand the importance of collective brain activity whether inhibitory, excitatory or fluctuating in a construction such as pain or performance. And of course this underpins context variable treatments. But I think and hopefully teach that the neuromatrix paradigm should be seen in a Kuhnian sense, i.e. a framework that changes its importance over time in response to research and need. In reasoning, it would only be one of a number of paradigms which could be called upon. It is surely a step up from gate control which is all we had as a pain associated paradigm in the 70’s 80’s and early 90s. I guess all paradigms are unweildy.
The greatest educational based thrill I get is hearing a young student or new grad who is aware of the neuromatrix paradigm, assessing or discussing a particular patient’s clinical patterns – sometimes widepread, bizarre and numerous symptoms, yet they can follow the story, hold the pattern together, nod at the right time, not lose interactional placebo and still design reasonable strategies. I sometimes think of the complex stories that poured out of my patients’ mouths in the past and how I squirmed and often rejected or avoided some of their symptomatology because I had no framework (neurosignatures) to allow the information to be elaborated in my brain. All I had was a biomechanical paradigm with a touch of gate control. It wasn’t enough.
We look forward to paradigm development, shift or rejection.
Isn’t the term neuromatrix just another way of expressing consciousness ? Are we not talking about the context of embodiment here? And isn’t a neurotag an expression of consciousness, a content? And isn’t the context and content unique and individual to each and everyone of us? Hence the modern practitioner can listen to, historically the most bizarre of case histories and calmly reasure the patient that everything they are expressing makes perfect sense from their perspective, from their world. All we need to do is RESPECT their reality…..