Friday, June 28, 2013

Melzack&Katz, Pain. Part 11: Now what? We need a new conceptual brain model!

The paper, Pain

Most recent blogposts: 

(NOTE: please find all the rest of the blogposts linked in at the end, from now on)

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 Part 10eThe neural network that both comprises and moves "Self" is (only) modified by sensory experience

Sorry readers [all three of you..], but I had to make a navigation decision in the course of writing this series. Having all the links to all the other posts in the series at the top was taking up too much room, so from now on you'll find them at the end, just after any references I might want to include. 

Anyway, I planned that we would surface today once the 4 conclusions were drawn, and go back to
Ah, daylight at the end of the tunnel
the 2013 Melzack and Katz paper. I want to stick to that plan, although the Hebb lecture paper remains wonderfully delicious; therefore, I will delve back into it for backup material all the rest of the trip. 

I think we can continue the trip above ground from now on, bearing in mind that our river of discovery is still subject to whatever might happen to it based on the topography of life itself.. 

So, picking up from where we left off, in the last post based on the M&K paper:
"We don't need a body to feel a body."

.... We are now all the way to... Outline of the theory (I wish it had its own link in the paper. But it's a subheading under "Beyond the Gate"). Melzack and Katz deliciously and luxuriously describe each of the aspects of the neuromatrix model, in some detail, with updated references, but not quite as deliciously as does Melzack in the Hebb lecture. This will take a long while to float through. There may even be rapids ahead. I have no idea, really. 

Here we go:

Outline of the theory
"The anatomical substrate of the body-self is a large, widespread network of neurons that consists of loops between the thalamus and cortex as well as between the cortex and limbic system.18,19,21 "

The 1990 paper is the one with all the interesting drawings in it, one of which I inserted in blogpost 9b. 
"The entire network, whose spatial distribution and synaptic links are initially determined genetically and are later sculpted by sensory inputs, is a neuromatrix." 
M&K are talking about the entire brain. Really. Minus the spinal cord maybe. Certainly from the brainstem forward. 
"The loops diverge to permit parallel processing in different components of the neuromatrix and converge repeatedly to permit interactions between the output products of processing."
Loops converging
This is a bit hard to visualize - I can kind of see the verb of it, but an animation would be nice. In
Loops diverging 
my mind I see intersecting, moving, nested spheres. But it's really hard to depict something like that without access to or expertise in CGI

Imagine the jet clouds as spontaneously occurring brain activity, as spoken about by Buzsaki in his book, Rhythms of the Brain

Back to M&K:
"The repeated cyclical processing and synthesis of nerve impulses through the neuromatrix imparts a characteristic pattern: the neurosignature." 
Remember, "signature" is something unique. Unduplicable. Well, except by a clever forger. But given every brain is unique like a fingerprint, each neurosignature will also be unique to each individual. Especially since it derives not only from what's unique to each brain's intrinsic moving patterns, but also each brain's experience in its own lifespan. 
Remember what the Aussies did - they called these things neurotags (which I suspect comes from graffiti-writing culture.. and I think my own brain's "style" is likely close to this one, Flava Wildstyle Grafitti Style.)

"The neurosignature of the neuromatrix is imparted on all nerve impulse patterns that flow through it; the neurosignature is produced by the patterns of synaptic connections in the entire neuromatrix."
Everything that goes through a particular brain is accepted after it receives some sort of stamp of approval by the neurosignature, "tagged" by the intrinsic neurotag. Then it can add to/become part of the overall neuromatrix. Buzsaki: "..brains are foretelling devices and their predictive powers emerge from the various rhythms they perpetually generate. At the same time, brain activity can be tuned to become an ideal observer of the environment, due to an organized system of rhythms." - first sentence of "Prelude" in his book.

"All inputs from the body undergo cyclical processing and synthesis so that characteristic patterns are impressed on them in the neuromatrix."
Neuromatrix = reverse rock tumbler?

Kind of reminds me of a rock tumbler, only in reverse: instead of smoothing off bits, the neuromatrix adds bits.

"Portions of the neuromatrix are specialized to process information related to major sensory events (such as injury, temperature change and stimulation of erogenous tissue) and may be labeled as neuromodules which impress sub signatures on the larger neurosignature."
These sensory experiences aren't continual (tonic) experiences of the body-self - they are cyclic/phasic. They are definitely attention grabbers... evolution must have got rid of any creature that experienced these particular sensory states as a tonic experience.. such creatures would have been so distracted by their own inner sensory experiences that they would have ended up as somebody else's lunch. 

The inclusion of "injury" in the list suggests perhaps "pain" might be going to be discussed at some point. 

The careful reader might have noticed that Melzack's fascination wasn't with pain specifically, it was more with trying to make sense out of sensory experience, e.g., phantom limb sensation etc. It was almost like pain was incidental.. he really was trying to build a new model not of pain, but of something that made sense and could include pain in a better, more logical way. 

"The neurosignature, which is a continuous output from the body-self neuromatrix, is projected to areas in the brain—the sentient neural hub—in which the stream of nerve impulses (the neurosignature modulated by ongoing inputs) is converted into a continually changing stream of awareness."
When I think of the word "hub" I think of something inside, or central. I wonder if this sentence
Brainstem, screenshot from
Damasio's presentation
lines up with what Damasio is talking about when he talks about consciousness originating at the brainstem level. I think it might. Line up I mean. Here is Damasio's TEDtalk, The quest to understand consciousness.

In his presentation Damasio highlights the role of the brainstem in consciousness. If the red (upper) part is damaged by, for example, stroke, the patient will lose their "mind" - will develop coma or vegetative state. There may be "feelings" generated (which would move rostrally I suppose), but no "I"-illusion will be available to "feel" them.

If the green (lower) brainstem is damaged the result is locked-in syndrome, a mind that functions perfectly but has no access anymore to a body. The body is completely paralyzed, except maybe for eye-blink in some. (Can you imagine? Imprisoned by a body? Fully awake but in a body that won't move? Ack. Don't use high velocity manipulations on necks. Just don't.)

I don't know if this is what Melzack was talking about, for certain, but it sure looks like brainstem function is at the heart of the interface of brain "self" and body "self" - therefore, provisionally, I'll put this in the spot marked "body-self neuromatrix." 

"Furthermore, the neurosignature patterns may also activate a second neuromatrix to produce movement, the action-neuromatrix."
Ha! Shades of Wolpert's The Real Reason for Brains.

"That is, the signature patterns bifurcate so that a pattern proceeds to the sentient neural hub (where the pattern is transformed into the experience of movement) and a similar pattern proceeds through a neuromatrix that eventually activates spinal cord neurons to produce muscle patterns for complex actions."
AN ASIDE: Check out this feature article, The electrified brain: the power and promise of neural implants
"It always starts with pain," she says — a hot, radiating pain growing from the base of her skull. Serdans suffers from a neurological disorder called dystonia that, when untreated, leaves her with debilitating muscle pain and movement problems. She keeps it in check with a deep brain stimulation (DBS) device. This pacemaker for the brain works by sending a steady electrical pulse into her globus pallidus. When it's functioning properly, this pulse lets her walk without tripping and move through the world without pain. 
As Spock would say, "Fascinating." 

OK, here's how I see this. The critter brain, aka internal regulation system, does whatever it needs to do. Whatever it's programmed to do. The info flows forward to cognitive-evaluative regions, and motor cortex, and backward to the spinal cord, so all the outflow mechanisms can prepare for the human brain to do whatever it needs to do, in seamless concert with the body, in this case, the puppet. 

The critter brain has to organize everything in advance so that it can manage the all important homeostatic functions, like blood pressure etc. The critter brain is like a combination of Scotty ("I canna giv'er ana'more Captain - she's gonna blow!") in engineering (hindbrain) and Captain Kirk with all his passionate drive and emotional outbursts (limbic system).

I think the rostral centers are Spock. He is mostly just thoughtful and reflective. His biggest outburst is "Interesting." or a bit more charged.. "Fascinating." His job is to inhibit, not inflame further. But also to act, appropriately. 

We have reached the end of that short section titled "Outline of the Theory" - I don't want to leave the topic entirely until I go back to the Hebb paper and fill in more detail for myself, though. So the next few blogposts will still be about the outline. We won't get to the details of each of the neuromatrix domains for a few more days, at this rate. 

Further reading
György Buzsáki, Rhythms of the Brain. Oxford University Press 2006 (full pdf)


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

No comments: