Wednesday, July 03, 2013

Melzack & Katz, Pain. Part 12d... deeper and deeper into basal ganglia

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.


OK, so we're on this detour right now through the motor system, having ended up here by examining Melzack's paper, Pain, and the section inside Beyond the Gate about (scroll down) the Action Neuromatrix.

Over the last few posts we've argued with Wolpert over movement versus mobility, and discussed how the nervous system evolved itself, noted that fish ancestors gave rise to pretty much everything, and left off with basal ganglia, which we'll continue with here, as written up by Peggy Mason, doing a whole pile of research on the raphe nuclei, important parts of the descending modulation system in critter brains/vertebrates. And she just happened to write the fascinating text from which I'm drawing the info on basal ganglia (and so much more). 
[I must thank my sister for turning me on to this text.]

So, here we are.... deep, deep, deep in the "heart" of the critter brain. Maybe the entire neuromatrix!
[I like how the basal ganglia look like a fancy hi-tech headset. Or an intergalactic spaceship from some Start Trek movie.]


Mason says, p.559:
"The striatum and pallidum are the core participants in circuits that adapt behavioral output to conditions with continually changing priorities and dangers. As introduced in Chapter 13, functional and connectional considerations have led to grouping forebrain and midbrain nuclei - the substantia nigra pars compacta, substantia nigra pars reticulata, and the subthalamic nucleus - together with the striatum and globus pallidus as the basal ganglia."

Well, now at least we know who the main players are! 
[The illustration I posted names other nuclei.. maybe not as relevant from Mason's perspective.]
"The GABAergic neurons of the pars reticulata spontaneously fire action potentials." - Wikipedia.
Well well. That does sound very intrinsic, and kind of stimulating. 
But wait!
"The two pallidal nuclei and the two nigral (pars compacta and pars reticulata) parts constitute a high-frequency autonomous pacemaker[6] (see primate basal ganglia system#Pallido-nigral_set_and_pacemaker)" - Wikipedia
Whoa... the little engines that could. 

Mason continues: 
"These regions operate via parallel but interacting loops with the cortex and brainstem to influence motor, oculomotor, motivational, emotional, and cognitive components of behavior."

Melzack talks about "loops" in just about every paper. Just saying. 

"Although they are intimately involved in motor function, the basal ganglia exert their effects indirectly through projections to motor control centers of the brainstem and even more indirectly through projections, via thalamus, to cortex, primarily motor and prefrontal cortices. Targets of basal ganglia output in turn control the motivation, affect, strategy, and initiation of self-generated actions. "

Targets.. hmmmn. 

Mason again: next, a heading..
"The striatum and pallidum are phylogenetically ancient structures, with the former present in the earliest vertebrates - think hagfish - suggesting that the original, and potentially still core, function of the striatopallidal system solves a problem that all animals face. The ubiquitous and fundamental problem resolved by the basal ganglia is that actions that use the same muscles differently simply cannot occur simultaneously. "
My bold: OK, now I'm getting super interested in this motor output system that has so much brain power attached, and always has. 
"A fish cannot swim to the left for food, to the right toward a mate, and forward to get further away from a predator circling behind. The fish has to choose one of these actions."
I.e., it has to "decide" what is going to become its signal out of its "noise"
"Similarly, we cannot turn left to go to a fruit stand, right toward a friend's apartment, and accelerate forward in case the speeding car behind does not slow down. Just as fish do, we must choose one of several, mutually exclusive actions. In fish, reptiles, birds, and mammals, including humans, striatopallidal circuits select and promote one action while suppressing competing actions. The process of choosing one action from many possible ones is termed action selection." 

Apparently, conditions like OCD and ADHD and Turette's indicate problems with this system.

Mason again:
"Although organized similarly in animals throughout the vertebrate tree, neurons and circuits of the basal ganglia achieve far greater complexity and vastly more connections in the cerebral cortex of mammals and especially in humans. The increase in basal ganglia complexity from fish to human reflects:
  • a much more complex body plan - Humans control limb, digit, laryngeal, and facial muscles that fish, sharks, and snakes do not possess (yup, none of those play the piano) 
  • More complex interactions with gravity and the physical environment on land than in sea (more stimulus to develop a humanantigravitysuit) 
  • A larger behavioral repertoire. Fish swim this way and that, whereas humans crawl, swim, walk, hop jump, and skip as well as play guitar, yodel, and so on (some in high heels) 
  • An enormously complex social structure in which individuals tailor their actions to specific persons or people  A child shares her favorite toy with a best friend but not with a stranger (primate troop safety and concept of "other")  
  • The ability to learn from experience and match behavior to particular circumstances  An infant goes to pet the friendly cocker spaniel and unfamiliar pit bull alike whereas after acquiring some experience with dogs, she pets the friendly cocker spaniel and even the familiar pit bull, but walks away, hands in pockets, from the unfamiliar pit bull" (discernment) 

There is much more to come about basal ganglia. Looks like they are the little brains that operate the big 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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