Monday, June 24, 2013

Melzack&Katz, Pain. Part 10b: Conclusion 1: The brain generates its own experience of being in a body

The paper, Pain

Previous blogposts:

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! Part 9b: Dawn of the Neuromatrix model Part 9cNeuromatrix: MORE than just spinal projection areas in thalamus and cortex Part 9d: More about phantom body pain in paraplegics

Part 10: "We don't need a body to feel a body."

Going deeper


Imagine our little river completely disappearing from the surface of the landscape for awhile. We are in space; we see it flowing along, then bam, it's gone! Where did it go? If we fly in closer for a look, we see it is pouring into a subterranean sinkhole, and have no idea from where it will emerge. It could be anywhere in a 360° circle, of undetermined radius. 

That's where my meander is at right now; it is as though it is forced to obey gravity and pour straight down into this big sinkhole, into some deep cave, and flow there for awhile, while we examine Melzack's "4 conclusions" - the mysteries about pain and the brain that forced him to think long and hard about the conventional theory of pain-as-input, and consider pain as an output. 

"First, because the phantom limb feels so real, it is reasonable to conclude that the body we normally feel is subserved by the same neural processes in the brain as the phantom; these brain processes are normally activated and modulated by inputs from the body but they can act in the absence of any inputs. 

Get ready for excerpts from Melzack's 1989 paper, Phantom limbs, the self, and the brain (The D.O. Hebb memorial lecture). This is a most delicious paper. 

It's clear (to me at least) that the entire notion of destroying nervous tissue, the gamble, risk, and (often) ultimate futility of doing so, must have weighed a bit on his mind. He had enough discipline to keep his mind steady and on task, and his hand steady typing up that paper we looked at earlier, here, and a consideration of the kinds of surgeries for pain that didn't help, here. But I can imagine his critter brain was reeling a bit from all the exposure to all this.. feeling a bit stressed, churning out dopamine, fuelling his cortex for a ginormous uphill battle - developing a new model. He took great pains to be completely logical about it - after all, he had to chart completely new territory, almost all by himself. He must have gone over every detail a thousand times, looked at the situation from the vantage point of every single detail to make sure the entire picture made sense from each and every angle. 

So, if you will bear with me [both of you], I will pull up bits that I find most fascinating, and feel as though I'm groking for the first time ever. And make notes.
The first section is titled, The Reality of Phantom Limbs.

The Reality of Phantom Limbs

Three types of phantom limb

1. experience of a limb after it has been amputated
2. experience of an arm after sensory roots have been destroyed (brachial plexus avulsion)
3. experience of of legs and body below level of complete break of spinal cord

1. After amputation, the brain invents sensation

"A phantom limb is universally experienced after a limb has been amputated or its sensory roots have been destroyed." 
"The most astonishing feature of the phantom limb is its incredible "reality" to the amputee (Simmel 1956)"
  • vivid sensory qualities
  • precise location in space 
  • more tingly, therefore can feel more "real" than a real limb, makes it more salient (if painful, demand on awareness can become overwhelming)
  • phantom becomes even more "real" when an artificial leg or arm is worn
  • phantom changes shape/lengthens to fully occupy a prosthesis (Riddoch 1941)
  • details of the past can be "felt" (e.g., former bunion, a ring on a former finger)
  • if the patient had Parkinson's, tremor may be experienced in the phantom limb
  • tardive dyskinesia may be induced in phantom limb by drugs (Jankovic & Glass 1985)
  • phantom arm usually hangs by side, moves in coordination with other limbs; in some it is felt to be stuck in an uncontrollable  awkward angle (Poeck 1964, 1969)
Phantoms of other body bits

2. After brachial plexus avulsion
  • all sensory roots are ripped from spinal cord
  • "the phantom "fills" the totally insensate arm and hand, and may feel normal except that movement is not possible" (Wynn-Parry 1980)
  • telescoping does not occur in this situation (possibly because visual reinforcement is readily available)
  • dissociation may occur when patient's eyes are closed and arm is moved to a new location (Melzack & Bromage 1973); when patient can see the new position the phantom moves instantly into it

3. Paraplegia and quadriplegia
  • patients usually report they can still feel their lower body and legs (Bors 1951, Conomy 1973) and deny phantom
  • dissociation occurs when legs fall out of bed in the dark, or body is moved by someone else, without the person being told about it, or being able to watch
  • dissociation also occurs when activity is felt to occur in genitalia or rectum, but none occurs
  • in quadriplegia associated with complete spinal break patient may experience orgasm (Money 1960)
  • stimulation of nipples or other skin tissue above level of break combined with fantasy or actual activity with a partner may produce experience of orgasm in genital area (Verkuyl 1969) [no link or abstract available]

Melzack's concludes from these data [sentence by sentence]: 
"My conclusion from these data is that the phantom represents our normal experience of the body." 
"It is not a pathological entity due to a psychological aberration, or due to an abnormal functioning of the brain." 
[I.e., there is nothing weird about them (i.e., the people experiencing the phantoms), even though their experience may seem kind of weird - to us. But we can't really know what it's like to be them. Can we? I think not.]

"It is the body we always feel, but without the input that normally modulates the central neural processe that produce the experience."
 [Let's chew on that just for a moment.. it's the body we always feel.. indivisible from our experience of it.. but here, the body they feel now is divisible from their experience of it, because they can't move it anymore. They don't get any sensory or proprioceptive input. NONE. Zip. Nada.
So... where is the "feeling" of having a body coming from? 
Has to be coming from the brain itself, doing the best it can with what it has, some sort of body blueprint up in there.]
"The tingling, strange positions, pain, and other abnormal aspects are due to the absence of input to a neural network which I describe later." 
[Moseley talks about cortical disinhibition, and how that can permit ratcheting up any sort of brain behaviour, like when he found himself playing Orthinology instead of Amazing Grace on the clarinet, as if it were a context-initiated OCD tic. Also, in stroke, one entire hemisphere becomes disinhibited by the other.]

"But that neural system exists within the brain even when the body input is cut off by amputation, nerve avulsion, or spinal break. It is evident that our experience of the body can occur without a body at all. We don't need a body to feel a body."
[This big green sentence impressed me a lot. It's what made me want to delve into and slowly meander through this whole paper. It's an awesome sentence. I think it deserves to become a meme.] 
The experience of the body is produced by networks in the brain, which are normally triggered or modulated by inputs from the body. An analogy is the power of a car which derives from the engine, not the gas pedal." 
[Nice analogy Melzack. Exactly. 
Maybe also like the power of a computer comes from all the hard drive inside it, and the electrical grid into which it is plugged, not from the keyboard or the person posting kitty videos to Facebook with it.] 

The experience of a phantom limb has the quality of reality because it is produced by the same brain processes that underlie the experience of the body when it is intact."


Next we will ponder "Qualities of phantom limb experience" as we continue our meander underground in the cave of this 1989 paper.

Further reading

1. Ronald Melzack, Robyn Israel, Rene´e Lacroix and Geoffrey Schultz; Phantom limbs in people with congenital limb de´Čüciency or amputation in early childhoodBrain (1997), 120, 1603–1620 (Full pdf)
[This paper suggests that 20% of those born without a limb experience a phantom limb, and up to 50% of those with amputations in childhood experience a phantom limb.] 

3. Richard A. ShermanMarshall DevorKim Heermann-Do; Phantom PainSpringer; 1997 edition (Nov 30 1996) (Google eBook)

4. Kyeong-Eon Park, Kwang-Seong Cheon, Seong-Ho Ok, Young Ju Jeong, and Heon Keun LeePhantom bladder painKorean J Anesthesiol. 2012 October; 63(4): 376–377. (Full text)

5. Majid H. Mohajerani, Khatereh Aminoltejari, and Timothy H. Murphy; Targeted mini-strokes produce changes in interhemispheric sensory signal processing that are indicative of disinhibition within minutesPNAS | May 31, 2011 | vol. 108 | no. 22 | E183–E191 (Full pdf)

"An emerging consensus from human imaging studies is that the most successful recovery occurs in individuals that exhibit relatively normal lateralized patterns of sensory activation within the lesioned hemisphere, whereas patients with larger stroke, who often show bilateral cortical activation, typically have less complete recovery"

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