Ronald Melzac theory of the body-self neuromatrix is a theory that attempts to explains how the sensation of pain is created. The core of the theory is the matrix whose task is to summarize diverse inputs, decide if homeostasis is lost, and generate a host of outputs. One of the outputs is the sensation of ‘pain’. The theory is revolutionary and a huge step forward in learning how to help those who are suffering. However, as I have stated in previously, it has limits. Although is has great negative predictive power (when homeostasis is preserved there will be no ‘pain’), the theory has poor positive predictive power (when homeostasis is lost there may, or may not be, 'pain').
What are we missing here? Why is the BSN model limited in predicting ‘pain’?
Consider these three independent phenomena:
1. Loss of homeostasis of the BSN.
2. The perception of a bright stimulus attributed to a body part (PBSABP).
3. Tissue damage or inflammation.
Allow me to explain these phenomena:
1. The 'Loss of homeostasis' is what Melzac suggests in the BSN model. I've summarized the preservation of homeostasis of the BSN as "I'm OK". It's loss is "I'm not OK" is a discrete, quantum, binary change.
2. There is not an easy English word for "perception of stimulus attributed to a body part" or “PBSABP”. I fully admit the phrase is very awkward. It is a concept in need of a word. But it is as precise as I can make it. By "perception" I want to include not only what is coming from up from the spinal cord but a higher order creation of the mind that may, or may not, correspond with anything that is going on in the periphery. For example, this will include “phantom pain”. Next, this perception is a "bright stimulus" - something of note. A "bright stimulus" is more than the feeling of normal respiration or the clothing on one's back. Something strong enough to trigger, or stimulate, a habitual response. Next, "attributed to a body part", is a higher order judgement that does not necessarily correspond with any independently verifiable ascending input. The PBSABP is prior to our response, prior to most the judgments or thoughts about it. It might trigger a habitual response, but that has not yet taken place.
3. "Tissue damage or inflammation" is change to the body that threatens our intact, continued survival.
At first glance these phenomena completely overlap. If you are walking barefoot and step on a nail then clearly all three of these phenomena instantly coexisting. However, in closer inspection of these phenomena can exist with or without the other two.
In my last plast post I argued that the loss of homeostasis of the BSN is independent of the other two phenomena. There are many inputs into the BSN that can contribute to "I'm NOT OK!". The loss of homeostasis does not depend on a PBSABP.
This post asks if the PBSABP is always the result of damage or inflammation? Will damage and inflammation always result in PBSABP? If we have the strong sense of something going on in our body, does that mean that there is actually something going on in the body? Is the meaning we ascribe to what we think we are sensing accurate and reliable?
It may be useful to consider the other senses.
Is what we see a reliable indication of what is really out there?
Is the blind spot created by the fovia obvious with monocular vision? Are we susceptible to a wide range of optical illusions? Consider that half of us fail the “gorilla perception test'? If you see a recently deceased family member out of the corner of your eye, will your physician suggest you see an optometrist? Obviously, we do not see what is 'out there'. We see what affords action, what we expect, what makes us feel comfortable, what will help us live long enough to reproduce. Our sense of our vision is not an accurate rendering of what is out there. In short, we see, not with our eyes, but with our visual cortex, and our visual cortex is richly innervated by inputs other than the eyes.
And our sense of hearing? Does a person who suffers from tinnitus need earplugs? Does the stillness of the high desert nights really roar?
Even our sense of smell is vulnerable to corruption.
Given that we have little basis to believe our other senses, why do we always believe our opinions about our what we think we feel? There are endless examples of misperception. The fields of embodied consciousness and the finding related to neuroplasticity provide rich examples demonstrating the unreliability of our interpretations of our somatic sense.
We should be highly skeptical that what we think we feel is a reflection of reality. The entire field of science since Descart is based on skepticism; based on the belief that our impression of our senses are not reliable. Instead, science relies on reproducibility, objective quantification, independent peer review, etc. Even in clinical medicine we rely increasingly on objective data such as radiography and labs and less on history. Even in history taking we are far more interested in chronology and associations than on the pt's interpretations and speculation.
In terms of back pain, why do we abandon skepticism - the foundation of science and medicine - when pt’s ascribe their problem to their back? Why do we believe our patients "back pain" is related to the back when:
- medicine and science are based on doubt?
- when there are no reliable history or physical finding associated with chronic back pain?
- when there are no reliable radiographic finding in chronic back pain?
- when despite hundreds of years we do not have any local interventions that have been found to be effective in the long term?
- when severing ascending nerves and ablating what we think are pain centers have not been shown to provide long term relief
- when all the senses of our patients, especially our interpretation of the somatic sense have been shown to be deeply flawed and unreliable?
- when modern pain theory states that back pain is not created in the back?
In conclusion, PBSABP is not the same as damage or inflammation. They are independent phenomena.
Why is this important? One of the main reasons we have not found local long term therapies for chronic pain is that we have not clearly identified the problem. Is not a clear understanding of the problem the basis of medical research? We are successful in treating and preventing diabetes and vascular disease because we have precisely defined the problem. We have not done this with pain.
What hope do we have for effective treatment and prevention without an understanding of the mechanism behind the problem? Because we a very good understanding about CAD we can talk about primary, secondary and primordial prevention of cardiac events. The field of pain is unique in medicine because we pay so little attention to our words and thinking.
Beyond arm chair speculation, there is important clinical utility in seeing these three phenomena as independent. It is important to understand these phenomena as independent because:
- It explains and gives justification to recommending ‘mindfulness’ meditation
- It explains and gives justification for recommending cognitive based therapies.
- It predicts that ‘back schools’ are at best not helpful.
- It suggests that asking patients about their pain will impede healing.
- It suggest that our medical model is counterproductive.
- It provides a more robust basis for discussing how the Alexander Technique helps, in the long term, with chronic back and neck pain.
I hope to amplify on these clinical points soon. But I do want to be clear that all this does not subtract from the critical need to study and verifying the theory of the BSN.