Wednesday, June 19, 2013

Melzack&Katz, Pain. Part 9b: Dawn of the Neuromatrix model

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 Part 6f: Evaluation of pain theories Part 6g: History of Pain, the cautionary tale. Part 6h: Gate Control Theory.

Part 7: Gate control theory has stood the test of time: Patrick David Wall;  Part 7bGate control: "The theory was a leap of faith but it was right!"
Part 8: Beyond the gate: Self as mayor Part 8b: 3-ring circus of self Part 8c: Getting objective about subjectivity
Part 9: Phantom pain - in the brain!

Dawn of the Neuromatrix model

The authors write,

"It is evident that the gate control theory has taken us a long way. Yet, as historians of science have pointed out, good theories are instrumental in producing facts that eventually require a new theory to incorporate them. And this is what has happened. It is possible to make adjustments to the gate theory so that, for example, it includes long-lasting activity of the sort Wall has described (see Ref 4). But there is a set of observations on pain in paraplegic patients that just does not fit the theory. This does not negate the gate theory, of course. Peripheral and spinal processes are obviously an important part of pain and we need to know more about the mechanisms of peripheral inflammation, spinal modulation, midbrain descending control, and so forth. But the data on painful phantoms below the level of total spinal cord section18,19indicate that we need to go above the spinal cord and into the brain."

Ref. 4 is the book, Challenge of Pain.
References 18 and 19 go to:

Melzack R. Phantom limbs and the concept of neuromatrix. Trend Neurosci 199013:8892.  
Melzack R. Phantom limbs, the self, and the brain (The D.O. Hebb memorial lecture). Canad Psychol 198930:116.

I have that 1990 paper on hand. The font is looks old-fashioned. 

It contains line drawings, fascinating line drawings, of peoples' subjective experiences of their phantom limbs, sensations of them, experiences of them, juxtaposed against their stumps. Some tidbits from that paper:

"Phantom limbs occur in 95-100% of amputees who lose an arm or leg. (Simmel, M. (1956) Arch. Neurol. Psychiatr. 75, 69-78)"

They tingle, these phantom limbs. Their movement can be sensed.

"At first, the phantom limb feels perfectly normal in size and shape, so much so that the amputee may reach out for objects with the phantom hand, or try to step onto the floor with the phantom leg. However, as time passes, the phantom limb begins to change shape. The arm or leg becomes less distinct and may fade away altogether, so that the phantom hand or foot seems to be hanging in midair."
SOURCE: Melzack 1990
"Fig 1: Drawings of phantom arms and legs based on patients' reports. The phantom is indicated by a dotted line, with solid lines to show the most vividly experienced parts. Note that some of the phantoms are telescoped into the stump."
But that's not all. The paper describes phantoms of body parts of all sorts, bladders that feel full, penises that feel erect (with or without pain); phantom rectums that feel as though they are passing gas; phantom breasts after mastectomy, menstrual cramps after hysterectomies, painful bunions that no longer exist because the entire foot isn't there anymore; phantom lower bodies in paraplegics. 
"The phantom appears to inhabit the body when the person's eyes are open and usually moves in a manner that is coordinated with the visually perceived movements of the body."

Right there is a big clue about how much the visual system dominates the sensory system. Context! 
Big clue why seeing both is, and isn't!.. believing. 
Big clue as to why mirror therapy and rubber hand illusion are so powerful. The visual cortex can literally overpower the felt body sense, which (apparently) has no eyes of its own. 

This also might be why I usually keep my eyes closed, most of the time, as I'm treating - I can't trust my own kinaesthesia. I don't really have any to spare. People who do are likely the ones who become effortless athletes or musicians. People [like me..] who don't, probably have just enough to learn how to walk, and then stay mobile! 

Keeping one's eyes closed most of one's working life does seem to save vision... I finally had to go get bifocals, but the eye doctor was amazed at how I had made it to almost my 7th decade before I finally had to get some. 
Keeping eyes closed while doing movement therapy does seem to help to explore new interoceptive territory, or old territory that may have changed over time, build new representations or refresh old ones. When I do short bits of yoga, etc., my eyes are closed so that I can feel into my own breathing, elongation, etc. 
And I lift weights. But my eyes have been open for that. 
I think (just for fun) I'll try lifting with my eyes closed, and see how that goes... run a little interoceptive test for balance, coordination, sense of effort, or ease.. etc.

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