Thursday, June 27, 2013

Melzack&Katz, Pain. Part 10e: Conclusion 4: The neural network that both comprises and moves "Self" is (only!) modified by sensory experience

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." Part 10b: Conclusion1: The brain generates its own experience of being in a body Part 10c:Conclusion 2: Your brain, not your body, tells you what you're feeling Part 10dConclusion 3: The brain's sense of "Self" can INclude missing parts, or EXclude actual parts, of the biological body

[Previously: From the 2013 Melzack and Katz paper:
Fourth, the brain processes that underlie the body-self are ‘built-in’ by genetic specification, although this built-in substrate must, of course, be modified by experience, including social learning and cultural influences. These conclusions provide the basis of the conceptual model18,19,21 depicted in Figure 3. ]
18. Melzack R. Phantom limbs and the concept of neuromatrix. Trend Neurosci 199013:8892.
19. Melzack R. Phantom limbs, the self, and the brain (The D.O. Hebb memorial lecture). Canad Psychol 198930:116.
21. Melzack R. Pain and the neuromatrix in the brain. J Dental Ed 200165:13781382.

Figure 3: 


Well, well, we are nearly there, if by "there" you agree it means, "end of our little detour underground." 
We are going to check out the rationale for Melzack's fourth and final conclusion. Back to the Hebb lecture for just a little bit longer. 

The Innateness of Phantom Limb Experience 
"There is convincing evidence that a substantial number of children who are born without all or part of a limb feel a vivid phantom of the missing part." [Weinstein et al 1964, 1969; Poeck 1964, 1969] "..have made a powerful case that phantoms are experienced by children who are born without a limb (congenital aplasia) or who have lost it before the age of 5."
This section is quite long. Apparently there had been entrenched belief (who knows where these weird ideas come from?) that children who were born without a limb or lost a limb before age 5 wouldn't experience phantoms. Melzack painstakingly gathered evidence to the contrary, all the way back to Valentin 1836. 
An interesting point Melzack notes: estimated percentage of phantoms in congenital aplasia, 18%. In adult amputees, virtually 100%. If the child has worn a prosthesis before age 7, they are more likely (81.2%) to retain a phantom than if they wore one after age 7 (52.6%). 

("Eyew" factor coming up..)

To back up his point, that phantoms are intrinsic to the brain, Melzack discusses some research done on monkeys: Infant monkey upper limbs were "deafferentated" (sounds awful.., but if you think that was awful...), their eyelids were sewn shut so they couldn't learn movement through visual stimuli. 

By age 3 months, the monkeys were using their arms to support walking, and could grasp. Smart little monkeys; smart little monkey brains built to move. Recall Daniel Wolpert

"The only reasonable explanation of such spatially coordinated behaviour in the absence of vision and sensory feedback from limbs after birth is that the monkeys possess built-in brain mechanisms for a phantom body capable of meaningful actions in three-dimensional space."
Capable of meaningful actions in three-dimensional space. That's what brains are for. Manoeuvring huge colonies of cells (in us, one-tenth human, nine-tenths other) through space, as a singular organism, (hopefully) protecting it from harm (unless it has been "deafferentated"..), much of its sense of a "body" already pre-programmed and pre-deployed.

He adds, that, of course, sensory inputs are relevant - people can "feel" the corn or bunion on their phantom toes, etc. 

"Heredity and environment clearly act together to produce the phenomena of phantom limbs."
Conclusion 4: The neural network that underlies the experience of the body-self is genetically determined but can be modified by sensory experience.

There we are, then. All four conclusions, all wrapped. We will conclude the 1989 paper in the next blogpost (I hope) and get back out from underground, into present time, and back into the 2013 paper where we left off. 


Mark Hollis said...

I think the larger implications of this part of the paper are potentially HUGE in terms of understanding whatever the 'self' is, human behaviour in general, and learning (however we manage to do that).

Thanks Diane (as per the u).

Diane Jacobs said...

I think you are entirely correct.