Monday, April 13, 2009

A Modest Proposal - II

Unreal Nature had some comments on the last post that it seems worthwhile to discuss. Again, some of our differences may well be semantic and thus, once again, I yearn for a lexicon. Statements from the Model are in italics and quotes.

UN: “Memory is a collection of neural structures.” No, it’s not. Dead people have collections of neural structures. Amnesiacs have collections of neural structures.

DrC: Well FX addressed this in the comments but I should have been much more specific and included a definition of "neural structure." What I meant was a collection of neurons, their resting potentials and their internal molecular configuration that would determine a responsive action potential when excited. (does not mean that FX and UN simultaneously jumped on the neuron; that would be a squash)

UN: “There is a one to one correspondence between objects in the “real” world and a neural structure (or collection of structures).” Oh dear (peering down into the philosophical abyss of “one to one”).

DrC: Cannot have ambiguity in the old bean, can we?

UN:pathways” ? Please delineate the extent (start, end) of such. Endocrine and nervous system rolled into one?

DrC: Admittedly vague, but consider a coronal cut of the human brain (image used for demonstration purposes only). All of that white matter represents myelin surrounding axons of nerves going to and fro, i.e. pathways. I doubt if we will ever even begin to untangle them. And, yes, throw in the endocrine system like in the Amydgala which has receptors. Whether these are carried by diffusion or are blood borne is anybody's guess.

UN: “Sensory perception always invokes memory.” No, it doesn’t. Most of the time it doesn’t invoke anything at all.

DrC: What I meant by this is that the act of perceiving is the the sensory impulses interacting with a neural structure (as defined above). For example, nerve impulses along the optic nerve interacting with neural structures in the occipital cortex. I don't think this is controversial.

UN: “Interaction of perceptions with neural structures generates econdary perceptons. They may be a modified version of the original or an entirely novel collection of action potentials.” Exactly. Something we agree on! This is the “butterfly effect” where the tiniest variation in initial input causes exponential, whopping big changes in output — in ways that, by definition, cannot be mapped.

DrC: There is some evidence that things like edges when they are perceived in the visual cortex do so in a collection of neurons that is linear. However, I would agree that very quickly things get out of hand with complexity. That we can't delineate the complexity should not stop us from hypothesizing about what is the mechanism that causes the complexity.

UN: “These potentials are not, for instance, dependent on unknowable spin states and are therefore entirely predictable in theory.” It is my understanding the identical amounts of neurotransmitter sent into the synapse may or may not trigger the action potential. There is not a one-to-one correlation between what is sent from one side of the synapse and the response that it triggers on the other side.

DrC: Maybe this is the crux of the argument. I would say that, if you had a neuron, and you applied a precise amount of neurotransmitter, you would always get the same response, either action potential or not. Actually, there is a break point where one neurotransmitter molecule more or less will make a difference, but I assume in the overwhelming majority of junctions the number of transmitters is either way above or way below the critical point. If this were not true, then the brain would always be in chaos.


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