On Sun, Aug 14, 2011 at 1:15 PM, Craig Weinberg <whatsons...@gmail.com> wrote: > On Aug 13, 8:00 pm, Stathis Papaioannou <stath...@gmail.com> wrote: > >> The artificial device must replicate all the I/O behaviour of the >> original neurons at the interface with the rest of the brain. This is >> purely a problem for engineers who neither know nor care about qualia. > > What I and others are pointing out is that how you define 'I/O > behavior' is the determining factor of the thought experiment. For > example (from http://themedicalbiochemistrypage.org/nerves.html): > > "Acetylcholine (ACh) is a simple molecule synthesized from choline and > acetyl-CoA through the action of choline acetyltransferase. Neurons > that synthesize and release ACh are termed cholinergic neurons. When > an action potential reaches the terminal button of a presynaptic > neuron a voltage-gated calcium channel is opened. The influx of > calcium ions, Ca2+, stimulates the exocytosis of presynaptic vesicles > containing ACh, which is thereby released into the synaptic cleft. > Once released, ACh must be removed rapidly in order to allow > repolarization to take place; this step, hydrolysis, is carried out by > the enzyme, acetylcholinesterase. The acetylcholinesterase found at > nerve endings is anchored to the plasma membrane through a > glycolipid." > > So, in order to replicate the I/O behavior of a single axon of a > neuron that traffics in ACh, are you talking about engineering a > nanotech factory which eats the right amount of choline (if not, you'd > have an excess of choline building up in the replaced areas of the > brain), and produces genuine ACh? Are you talking about having an > artificial glycolipid holding a supply of acetylcholinesterase to > accomplish hydrolysis to enable repolarization like the other neurons > of that type? You can't simulate the production of those substances > electronically or produce them inorganically, so any replacement > system would be based on organic chemistry. If you were able to > accomplish the production of those substances as well as conduct > electric signals properly, that still only scratches the surface of > the physiological issues. From > http://www.mind.ilstu.edu/curriculum/neurons_intro/neurons_intro.php
The I/O interface could involve neurotransmitters which are synthesised and released when the artificial neuron sees the appropriate voltage, and an enzyme which mops up the released neurotransmitter. The internals could be completely different: a computer modelling the biochemistry of a neuron and controlling a chemical factory. Another way to handle the interface would be not to use neurotransmitters but to directly connect to the neighboring neurons and control their membrane potentials, mimicking the depolarisation/depolarisation cycle. If done that way there may have to be further signals to the postsynaptic neuron as the neurotransmitter may have an effect on regulating the number of surface receptors and hence to sensitivity to future stimulation. It would be difficult getting it exactly right, but there is no problem *in principle*. > "While we are considering numbers, it is worth noting that there are > as many as 50 times more glia than neurons in our CNS! Glia (or glial > cells) are the cells that provide support to the neurons. In much the > same way that the foundation, framework, walls, and roof of a house > prove the structure through which run various electric, cable, and > telephone lines, along with various pipes for water and waste, not > only do glia provide the structural framework that allows networks of > neurons to remain connected, they also attend to the brain's various > house keeping functions (such as removing debris after neuronal > death). " > > If your replacement neurons don't die, then you're changing the > relationship of them to 98% of the cells in the brain and the I/O is > different to the ecosystem overall. If you could manage to engineer a > replacement component which satisfies all of those electrical, > biological, and chemical roles, but still somehow manages to be, in > some significant way 'not a living cell' then there is still the > matter of whether or not the cell body itself is the thing that > actually experiences the various inputs and determines the outputs > according to uncomputable awareness-based algorithms or whether > experience somehow arises metaphysically through the aggregate of > unexperienced mechanical I/Os which can be replicated > deterministically. If you are proposing that the cell does a computation that a Turing machine cannot do then that would be an argument against computationalism (although not against functionalism). However, there is no evidence that there are non-computable processes in the brain. > If the former case is true, the replacement cell body may not be able > to produce the organic sense required to modulate the functions of the > cell in it's native improvisational mode so that it will neither fool > surrounding tissues nor perform the critical experiential function in > between inputs and outputs which would form the meat of perception and > awareness. If the latter case is true, there is no way to tell whether > the metaphysical requirements form instantiating high level awareness > could be satisfied by the design of the replacement. The exact > mechanism by which dumb I/Os are translated into nonphysical emergent > properties would have to be fully understood in order to accomplish > substitution by engineering. Do you understand this: (a) everything in the universe follows physical laws; (b) these physical laws are computable So you are saying either that cells disobey the laws of physics or that there are certain laws of physics that are non-computable, but that only you know about them. -- Stathis Papaioannou -- You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to firstname.lastname@example.org. To unsubscribe from this group, send email to everything-list+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/everything-list?hl=en.