Wednesday, June 05, 2013

Melzack and Katz, Pain. Part 6f: Evaluation of pain theories

The paper, Pain

Part 1 First two sentences Part 2 Pain is personal Also Pain is Personal addendum., Neurotags! Pain is Personal, Always.

Part 3a Pain is more than sensation: Backdrop Part 3b Pain is not receptor stimulation Part 3c: Pain depends on everything ever experienced by an individual

Part 4: Pain is a multidimensional experience across time

Part 5: Pain and purpose

Part 6a: Descartes and his era; Part 6b: History of pain - what’s in “Ref 4”?; Part 6c: History of pain, Ref 4, cont.. : There is no pain matrix, only a neuromatrix; Part 6d: History of Pain: Final takedown Part 6e: Pattern theories in the history of pain

Evaluation of pain theories
p. 162, Challenge of Pain, Ref. 4 of the paper, Pain.

So, back in 1996, Melzack and Wall looked at this history of pain theories, and asked themselves, how can we make sense out of it? What can we retain? How can we move forward?
"When we consider all the theories examined so far, we see that the 'specific-modality' and 'pattern' concepts of pain, although they appear to be mutually exclusive, both contain  valuable concepts that supplement each other.. when all the theories - from specificity theory onward - are examined together, [it] is apparent that each successive theory makes an important contribution. Each provides an additional mechanism to explain some of the complex clinical syndromes or experimental data that were previously inexplicable. Despite the seemingly small differences, each change contains a major conceptual idea that has had a powerful impact on research and therapy." p. 162-64
Click to make big

Receptor specialization could be accepted without having to toss the idea that information reaching the spinal cord might possibly be repackaged into various patterns. The 'law of adequate stimulus' could be kept, and the idea of some sort of narrow/fixed relationship between receptor and perception could be tossed. In fact, in the time that has elapsed since Von Frey, evidence indicates greater receptor specialization that he could have ever imagined in his wildest dreams. There really isn't any doubt that temporal and spatial patterns provide the basis for sensory perception - this is basic to contemporary neurophysiology and psychology. Goldsheider's ideas about central summation mechanisms has been supported for pathological pain syndromes. Livingston (1943) came up with the idea of spinal reverberatory activity persisting in the absence of noxious input, which seems to still hold some water. Noordenbos idea that large fast fibers inhibit small slow fibre activity still makes sense, "is supported by the evidence that pathological pain is often associated with a loss of large myelinated fibres."

"These theories, nevertheless, fail to comprise a satisfactory general theory of pain. They lack unity, and no single theory has yet been proposed that integrates the diverse theoretical mechanisms." p 164
And furthermore... about that problematic word, "specificity"... Melzack and Wall are determined to be crystal clear:
"The concept of 'specificity' lies at the heart of the controversy that surrounds the evolution of pain theories. It is essential, therefore, that we conclude by examining the concept in order to state unequivocally what we mean by it.
"Throughout this chapter, we have distinguished between physiological specialization and psychological specificity 
"The former is an indisputable fact. The latter is a theory for which there is no evidence. 
" Neurons in the nervous system are specialized to conduct patterns of nerve impulses that can be recorded and displayed. But no neurons in the somatic projection system are indisputably linked to a single, specific psychological experience."  p 164
And that's still true. My enlargement. The bolds belong to Melzack and Wall.
"Despite our efforts to establish this distinction, (Melzack and Wall, 1962, 1965), many of our colleagues have failed to understand the distinction or continue to use the word 'specificity' in the sense of specialization but without saying so. 
"If we can all agree that 'specificity' means physiological specialization, without implying that specialized neurons must give rise to the experience of pain and only to pain, or that pain can never occur unless they are activated, then we will have eliminated a major source of unnecessary controversy." p. 164

Another way to say this: nociception does not equal pain, and all the textbook that show "pain" receptors/fibres/pathways labelled in their diagrams or text, need to be redone, or else multiple future generations will continue to confuse nociception and pain.

And there will continue to be needless, useless, undermining conflation and confusion.
C'mon people. Tick tock. The pain epidemic continues to grow. And grow. And grow.



OK, I realize this has been a very long meander. I promise, next time, back to the paper!

No comments: