Saturday, July 06, 2013

Melzack&Katz, Pain. Part 12g The Action-Neuromatrix

The paper, Pain

Most recent blogposts:

Part 12: Action! 12b: Examining the motor system, first pass. 12cMotor output and nervous systems - where they EACH came from Part 12d... deeper and deeper into basal ganglia Part 12e: Still awfully deep in basal ganglia Part 12f: Surfacing out of basal ganglia


I wanted to become a bit more familiar with the motor output aspects of brain function, and I think I did - not much - just a bit, but more than I knew before at least. I learned that different bits of brain move physicality according to different inputs, and different requirements of the overall organism. "Movement" doesn't conflate into "action" or into "mobility." If you're a sea squirt, you can still "move"[i.e.,"contract"] with no brain at all. If you aren't attached to a rock, you'll need a brain that can "mobilize" you through space and across terrain, toward mates and food, and away from predators. You'll need an executive brain bit [like basal ganglia] that can cancel "noise," choose the correct "signal," then operate the entire organism by way of the right action. You'll need something that can "learn" from incorrect movement, refine it to perfection [like the cerebellum]. These brain parts will need to interact appropriately/successfully, details of which I know nothing. Somehow all this will be integrated into a long chain of command that flows to motor cortex selection down into actual mesoderm with accurate feedback the entire time. 

Finally! Back to the main river!


So, here we are, back with the paper, Pain, by Melzack and Katz, and back where we left off, on our original meander through it. Thank you for hanging in there with me [all three of you..] We are still in the section, BeyondTheGateScroll down to "Action neuromatrix." I think I'm a bit better prepared to follow this section now. 


The first paragraph:
"The output of the body neuromatrix is directed at two systems: (1) the neuromatrix that produces awareness of the output, and (2) a neuromatrix involved in overt action patterns." 
True, unless we rely on a bunch of "chunked" behavioural output as described by Mason, which can be more cerebellar driven and result in habits we don't need to be aware of, letting us perform more than one task at a time, e.g., driving and tuning the radio. 

"Just as there is a steady stream of awareness, there is also a steady output of behavior (including movements during sleep)."
But of course. Our brain keeps our heart beating and our lungs working all night long. It even rolls us over without waking us up, if it feels the need to decompress its organism on the side it's been sleeping on for awhile. We might even talk in our sleep. Or walk. These are called parasomnias

"It is important to recognize that behavior occurs only after the input has been at least partially synthesized and recognized. For example, when we respond to the experience of pain or itch, it is evident that the experience has been synthesized by the body-self neuromatrix (or relevant neuromodules) sufficiently for the neuromatrix to have imparted the neurosignature patterns that underlie the quality of experience, affect and meaning."

I think this means, basal ganglia (the choosers) might choose to move/protect, or scratch, but only if it registers a pain or itch input (from sensory processing parts of the brain) as the most salient input to respond to.
"Most behavior occurs only after inputs have been analyzed and synthesized sufficiently to produce meaningful experience. When we reach for an apple, the visual input has clearly been synthesized by a neuromatrix so that it has 3-dimensional shape, color and meaning as an edible, desirable object, all of which are produced by the brain and are not in the object ‘out there’."
Yes, forming representations or maps of interoceptive and exteroceptive input is what brains do, every couple nanoseconds [or whatever], then they act on those representations. 

"When we respond to pain (by withdrawal or even by telephoning for an ambulance), we respond to an experience that has sensory qualities, affect and meaning as a dangerous (or potentially dangerous) event to the body."
..And we have our basal ganglia bottleneck to thank for selecting the [hopefully] correct signal against all noise, and letting that "action" make it through the queue. 

Next paragraph: 
"After inputs from the body undergo transformation in the body-neuromatrix, the appropriate action patterns are activated concurrently (or nearly so) with the neuromatrix for experience. Thus, in the action-neuromatrix, cyclical processing and synthesis produces activation of several possible patterns, and their successive elimination, until one particular pattern emerges as the most appropriate for the circumstances at the moment. In this way, input and output are synthesized simultaneously, in parallel, not in series. This permits a smooth, continuous stream of action patterns."
I think "body-neuromatrix" might equate to cerebellum here.. and "action neuromatrix" might equate to basal ganglia.. It's that part, "one particular pattern emerges as the most appropriate" that makes me think so. Also "input and output are synthesized simultaneously...permits smooth continuous stream of action patterns" - makes me think of yesterday's blogpost about the relationship of basal ganglia and cerebellum, both convergent and divergent. [But there is a lot more information about motor formation and execution that has yet to make it into my slow-thinking brain.]  

"The command, which originates in the brain, to perform an action such as running activates the neuromodule which then produces firing in sequences of neurons that send precise messages through ventral horn neuron pools to appropriate sets of muscles. At the same time, the output patterns from the body-neuromatrix that engage the neuromodules for particular actions are also projected to the sentient neural hub and produce experience. In this way, the brain commands may produce the experience of movement of phantom limbs even though there are no limbs to move and no proprioceptive feedback. Indeed, reports by paraplegics of terrible fatigue due to persistent bicycling movements24 and the painful fatigue in a tightly clenched phantom fist in arm-amputees6,25 indicate that feelings of effort and fatigue are produced by the signature of a neuromodule rather than particular input patterns from muscles and joints."
Understanding this paragraph is going to force me back into the 20 pages of Mason that I kind of skipped through, all about the inputs and outputs and portals and projections into basal ganglia, connections rostral and caudal, and neural relationship with cerebellum. But I will do that later, maybe on some future expedition, not right now. 

"The phenomenon of phantom limbs has allowed us to examine some fundamental assumptions in psychology. One assumption is that sensations are produced only by stimuli and that perceptions in the absence of stimuli are psychologically abnormal. Yet phantom limbs, as well as phantom seeing,26 indicate this notion is wrong. The brain does more than detect and analyze inputs; it generates perceptual experience even when no external inputs occur."
This seems pretty straightforward by now. 
Last paragraph in this section:
"Another entrenched assumption is that perception of one's body results from sensory inputs that leave a memory in the brain; the total of these signals becomes the body image. But the existence of phantoms in people born without a limb or who have lost a limb at an early age suggests that the neural networks for perceiving the body and its parts are built into the brain.18,19,27,28 The absence of inputs does not stop the networks from generating messages about missing body parts; they continue to produce such messages throughout life. In short, phantom limbs are a mystery only if we assume the body sends sensory messages to a passively receiving brain. Phantoms become comprehensible once we recognize that the brain generates the experience of the body. Sensory inputs merely modulate that experience; they do not directly cause it."
My take (admittedly lacking much nuance.. )
And so it follows that "noise" emanating from such an inherently organized neural network of Melzack's theoretical "body-self," in the brain, might become the only "signal" available, and thereby, by default, due to lack of competing stimuli via cerebellum, engage the attention of not only the salience network, but also basal ganglia, which would perhaps not be able to turn themselves off. Become disinhibited because of a lack of competing stimuli/noise. Make a paraplegic person experience bicycling movement that leaves them painfully fatigued. If the basal ganglia's job is to choose an action, and there is suddenly no queue at all, then it will still "choose" something, whatever is handy, because that's its job! And it chooses the only thing handy, like maybe a disinhibited movement neurotag. The "output" from this "choice" would go to (1) the neuromatrix that produces awareness of the output, and would try to go to  (2) a neuromatrix involved in overt action patterns, but because there isn't any connection to any actual body part anymore, there won't be any actual feedback (i.e., via cerebellum) available, so there will be this whole positive feedback situation, microphone squeal type of thing, going on inside the brain. 

Eyew, how uncomfortable for the person in that out-of-homeostatic-control brain!

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 Part 10eThe neural network that both comprises and moves "Self" is (only)modified by sensory experience
Part 11We need a new conceptual brain model! Part 11b: Intro to a new conceptual nervous system Part 11c: Older brain models just don't cut it Part 11d: The NEW brain model!

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