Heuristic Circuits
From Mbscientific_wiki
Comparative Anatomy of Brain Structures
Before pursuing the main track of how our neural networks came to be, lets look at a side track, the neural networks of the arthropods.
The very early development of a central nervous system can be seen in arthropods (insects, crustaceans). In this drawing the nervous system is drawn in blue, the circulatory system in yellow and the digestive system in green (source: http://www.cals.ncsu.edu/course/ent425/tutorial/nerves.html#2).
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This drawing focuses on the central nervous system of the arthropod. In the upper part of the picture you see the formation of a primitive brain in 3 round pairs of ganglia (lobes), the forebrain, midbrain and the hindbrain. The forebrain (Protocerebrum) is largely associated with vision. The mid-brain (Deutocerebrum) processes sensory information collected by the antennae. The hind-brain (Tritocerebrum) and the ganglia below it innervate the mouth parts and integrate sensory inputs from forebrain and mid-brain. It also links the brain with the rest of the ventral nerve cord and the visceral and the peripheral systems, i.e. the wiring of the internal organs and limbs. Even at this early stage neural nets can generate complex behavior. Honey bees, for example, can discern and communicate direction and distance of the food source. |
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In the next slide, I'll show you a developing Zebrafish's (embryonic) nervous system. You essentially see the same fore, mid and hind-brain structures. So, presumably some common ancestor of the early fishes and arthropods developed the fore-mid-hind brain morphology.
Now back to our main track. In the next set of slides we'll look at fish, reptilian, amphibian, and bird brains. As the brains gain complexity, we see increasing heuristic behavior. In the next series of pictures you'll see the evolution of cerebrum and the optic lobes from the elemental forebrain, and the cerebellum and medulla oblongata from the hind-brain. Notice the relative increase in the size of the cerebrum (source: http://k-2.stanford.edu/InfoPackets/2-BioSys.7.0.html).
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Next lets look at the brains of a number of mammals to compare the relative sizes.
 Raccoon |
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 Chimp |
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And finally we'll see a human brain and the functional areas:
So, we clearly see the pictorial (structural) similarities of the brain anatomies of fishes, amphibians, reptiles, birds, and mammals, including man.
Learned functionality of biotic neural networks - heuristics
Now lets talk about functional similarities of these neural networks that manifest themselves in brain structures.
First lets talk about the formation of memories. Stimuli like sound and visual stimuli, are received and encoded by ear and eye neural nets and form patterns that feed into memory neural networks. These memory neural nets can then be Associated with reward (e.g. food) stimuli, forming cues.
Pavlov's dogs put Associative Logic on the map. Say sound by itself is a benign stimulus, but it is consistently present when food is present (sounds like food?), then the control cells would get trained over time and fire if sound is present, even if food isn't. In this example sounds form a pattern. And in normal life Pavlov's dogs would have learned to differentiate arbitrary background chatter from their owner calling them with something like "Spot, Food!".
Neural networks naturally form memory circuits as the following drawings demonstrate:
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The dogs' hearing memory circuits get trained over time to the sound "Spot, Food!" and a pattern corresponding to the sound is established in the network (visualize it as dynamic color patterns, with colors representing strength of connections- above figure). Please note that training of e.g. sound memory clusters requires affirmation by the instinctive stimulus neurons, e.g. taste. This affirmation is the crux of associative logic, the memory of a sound event "Spot Food" is affirmed (committed) when the food stimuli is present.
Lets talk about where these memory circuits are located and cover their functionalities (although this is an over-simplification of the heuristic networks, for the present purposes it shall suffice). To give our narrative context, lets use the learning process of say a baby elephant called Kimba. There are four areas of the brain that we are going to cover within the context of Kimba's learning processes: Cerebellum, Hippocampus and related organs, Cortical Regions and the Frontal Lobe:
(modified image from src: http://www.basalganglia.net/Basal_Ganglia.jpg)
1) Kimba's Motor control/memory circuits are located in the Cerebellum . Now picture Kimba is born, tries to stand up, stumbles, tries again, and eventually after a while he learns to get his feet under him. It takes a good while longer for him to master the art of walking about. What you are picturing is Cerebellar control circuits getting trained. These circuits, when trained, form long term memories, i.e. once Kimba has learned to walk, he is trained for good, unless there is damage to the cerebellum (note: there are other areas of the brain governing functions necessary for walking, e.g. balance control, so it is possible for other functional failures to impede walking) .
2) Hippocampus and related organs (e.g. Basal Ganglia, etc., lets call these auto-encoder circuits), this is where new stimuli get encoded. As Kimba goes about his daily life, he runs across rivers, valleys, hills, sees trees and other animals. The new stimuli that have morphologies get encoded in the auto encoder circuits, thus creating Representational Memories , i.e. memories representing the rivers, valley, trees and animals and such.
These representative memories are usually related in the context of tasks of survival. Say Kimba finds Sjambok Tree pods tasty. In time as Kimba's family visits the Sjambok tree locations, Kimba learns to associate the encoded memory representation of the tree with the pod, the river and the valley where the trees are located, the range where the valley is located and the (rainy) season when the tree produces fruit. So he forms associated cues in context of getting to the Sjambok pod: the range, the valley, the river, the tree groves.
But there is more, these cues are acted on. Specifically, in the rainy season, Kibmba's family traverses the trail in the range to get to the valley and the river and the tree groves to get to the pods. So, the reward (the pods) and the cues that get to the reward and the actions that processed the cues, together form the Procedural Memory , i.e. the procedures undertaken following the cues in a specific order to get the reward.
3) Cortical Regions , where representational and procedural memories are stored, forming short term and long term memories. The circuitry of the hippocampus and related organs, where new memories and associated cues are formed are tied in to various cortical regions where they get stored. The memories that are continually reinforced form long term memories.
4) Frontal Lobes , where Selective Attention and Deliberate Action is generated. Say Kimba's matriarch decides that yes it is the rainy season and it its time to take the trail through the field to the valley, to the river where the Sjambok is supposed to be fruiting. That process happens in the matriarch's frontal lobe, further the circuitry of selective attention and the deliberate actions in the duration of the task resides in the frontal lobe as well.
In recent years, particularly since the advent of FMRI (functional magnetic resonance), many of the regions of the brain where specific functional memory/controls are located have been mapped:
If you recall, in the last section we covered the pictorial similarities between brain morphologies from fish to man. Here we covered how the functional circuitry of the brain engenders the behavioral heuristic traits of all of the said animals, man included.
The overriding lesson in this exercise is how the brain, by the virtue of representative and procedural memories, creates in internal image of reality (Perceived Reality ) from the Inherent Reality that it has to deal with. That Perceived Reality in fact becomes its known domain of survival, and everything outside of that domain is the unknown. But that perceived reality is by definition expanding through each new observation, experience, learned behavior.
What we learned, through our virtual Kimba, is that learning is the ongoing stuff of life that builds the hierarchy of complexity that is the known perceived reality.
Next, we'll look at some animal cognitive processes to further examine how that hierarchy of complexity gets coalesced.
Links
Note: For Chapter Key, Courses and further links see Next Section : Animal Cognitive Studies
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookNERV.html - The nervous system - good introductory site
http://www.cals.ncsu.edu/course/ent425/tutorial/nerves.html - Arthropod nervous system
http://www.ucalgary.ca/UofC/eduweb/virtualembryo/why_fish.html - Zebra-fish development, including the nervous system
http://k-2.stanford.edu/InfoPackets/2-BioSys.7.0.html - Comparative brains
http://www.waiting.com/brainanatomy.html - Functional brain anatomy
http://www.gwc.maricopa.edu/class/bio201/cn/cranial.htm - Cranial nerves
http://www.med.harvard.edu/AANLIB/home.html - Harvard medical school Whole Brain Atlas
http://www9.biostr.washington.edu/cgi-bin/DA/PageMaster?atlas:NeuroSyllabus+ffpathIndex:Splash^Page^Syllabus+2 - U. Washington Neuroanatomy Interactive Syllabus
http://www9.biostr.washington.edu/cgi-bin/DA/PageMaster?atlas:Neuroanatomy+ffpathIndex:Splash^Page+2 - U. Washington Interactive Brain Atlas
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