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> Even simulating a single synapse in full detail can be challenging I wonder how common it is for serious commentators on NN / brain relationship to hold this

> Even simulating a single synapse in full detail can be challenging I wonder how common it is for serious commentators on NN / brain relationship to hold this supposition that in order for the two to be called... let's say "functionally similar/equivalent", that there would have to be some kind of structural equivalence in their most basic parts. Neurons (and their synaptic connections etc.) developed in a biochemical substrate which is going to bring a certain amount of its own representational baggage with it, i.e. elements which are loosely incidental to "what really matters" in creating the magic of the brain—and we should not expect those features to reappear in artificial NNs (as they are by definition incidental): bringing them up could only establish a trivial non-equivalence imo. I'd like to see more discussions about NN / brain relationship mentioning which level/kind of equivalence they're refuting/confirming when refuting/confirming.

lossolo 4y ago
That has never been thought by anyone but computer scientists who never looked at a biology textbook. To begin approximating what a lone spherical synapse would actually do you'd need to solve 2^n coupled second order differential equations where n is the number of ions used. That is before you throw in things like neuro transmitters and the physical volume of a cell. Simulating a single neuron accurately is beyond any super computer today. The question is how inaccurately can we simulate one and still get meaningful answers. Then how we do it 100e9 more times. source: https://news.ycombinator.com/item?id=32407028 https://news.ycombinator.com/item?id=32407028 There is interesting discussion there.
- RandomBK 4y ago
  While I'm neither a biologist nor a CS PhD, I want to call out the fallacy that simulating a system to a sufficient degree requires simulating each individual molecule in exacting detail. We've gotten quite far with ideal gas laws without needing to simulate every particle, we used kerosene to get us to the moon without needing to simulate all the reaction species of kerosene combustion, etc.
data_maan 4y ago
> there would have to be some kind of structural equivalence in their most basic parts. Of course there doesn't have to be such an equivalence and I didn't whatn to imply one. What I did what to imply though was that unless there is some relationship between NNs and the brain there is no meaningful way to translate results from one to the other. And currently, AFAIK, we do not have a good "dictionary" for that. Something like what RandomBK has mentioned is still missing. That being said I would also like to see more NN/brain relationship discusssions. Currently the discussions are really at a super basic level, there were a number of papers out there whether "the brain" does backpropoagation, which was pretty useless science because, again, the brain was modelled in a pretty crudenway. (The literature is huge and I don't claim being omniscient, so perhaps there is something out already there.)

lossolo 4y ago

That has never been thought by anyone but computer scientists who never looked at a biology textbook. To begin approximating what a lone spherical synapse would actually do you'd need to solve 2^n coupled second order differential equations where n is the number of ions used. That is before you throw in things like neuro transmitters and the physical volume of a cell. Simulating a single neuron accurately is beyond any super computer today. The question is how inaccurately can we simulate one and still get meaningful answers. Then how we do it 100e9 more times. source: https://news.ycombinator.com/item?id=32407028 https://news.ycombinator.com/item?id=32407028 There is interesting discussion there.

RandomBK 4y ago
While I'm neither a biologist nor a CS PhD, I want to call out the fallacy that simulating a system to a sufficient degree requires simulating each individual molecule in exacting detail. We've gotten quite far with ideal gas laws without needing to simulate every particle, we used kerosene to get us to the moon without needing to simulate all the reaction species of kerosene combustion, etc.

data_maan 4y ago

> there would have to be some kind of structural equivalence in their most basic parts. Of course there doesn't have to be such an equivalence and I didn't whatn to imply one. What I did what to imply though was that unless there is some relationship between NNs and the brain there is no meaningful way to translate results from one to the other. And currently, AFAIK, we do not have a good "dictionary" for that. Something like what RandomBK has mentioned is still missing. That being said I would also like to see more NN/brain relationship discusssions. Currently the discussions are really at a super basic level, there were a number of papers out there whether "the brain" does backpropoagation, which was pretty useless science because, again, the brain was modelled in a pretty crudenway. (The literature is huge and I don't claim being omniscient, so perhaps there is something out already there.)