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Comment by lossolo | Hacker News Reader

To simulate something you need to first know how it works and know all the relevant interactions, this is something that we currently do not understand. Neurons are not equivalent of neural networks we use in computers, they are A LOT more complex with whole groups firing the same time and chemicals regulating neurons all the time and whole topology is plastic, it works in a way we can't model or simulate currently. People hugely overestimate our knowledge about brains.

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I'm a biochemist, and I somewhat disagree with this take.

Yes, it's true that modelling just a single cell's interactions with its environments is beyond our capacity.

But here we're talking about simulating how a brain reacts to signals at a higher level of abstraction: we're studying an "emergent" phenomenon. We don't need to model molecular interactions, and we absolutely can model this using artificial neural networks.

This doesn't mean we'll be able to completely accurately model its behaviour, but we should get a lot closer than many HN commenters seem to believe. Biological neurons don't have magical properties, they just have more side-effects.

I specifically used "relevant interactions" to rule out "modelling just a single cell's interactions with its environments" but who knows how deep you need to go to have an accurate model.

> we're studying an "emergent" phenomenon

It's like saying that mapping all cells in human organism to addresses in memory will give us emergent human inside computer.

But still at abstract layer we just do not have a model of a working brain, we only have maps of neurons, not an actual "algorithm" or a model of all relevant environment interactions needed for a working brain or a set of "abstract instructions" needed for it to work. I think you are over optimistic about current state of our knowledge if we can't even model organism with few thousand neurons accurately. Imagine trying to do that for tens of billions of neurons and trillions of synapses, especially that we know brain doesn't work like an ANN at all[1].

1. https://www.nature.com/articles/s41583-020-0277-3/

> It's like saying that mapping all cells in human organism to addresses in memory will give us emergent human inside computer.

Sounds more like they're saying: a knee is a knee, it doesn't have any magical properties. Build something that bends, and it will behave like a knee. I don't know how true that is, obviously.

It's not totally true even for knees. Artificial replacement knees aren't as good as original knees.

I guess the point is that we might be able to simulate an artificial knee equivalent for neurons. It won’t be as good as a real knee, but it might still be useful.

I’d argue they’re better (in some ways), given that they’re “dead” material as opposed to functional tissue. Human knees don’t last nearly as long when the tissue is dead.

Lol. That's an interesting definition of "better".

If you're active, knee implants have to be replaced after 15-20 years, because they detach from the bone. Knee implants can harbor pockets of infections because they don't have an immune system. They are also more prone to dislocations.

They are objectively inferior to a healthy organic knee.

Yes, my comment was made a bit in jest. I think everyone will agree that after an arthroplasty, your quality of life is not as good as it was before.

But most of the reasons why artificial knees are not as good as the real deal have to do with the fact that they're made of inert (albeit fancy) materials. They don't have the ability to continually heal and do tissue remodelling, which is what real tissue does.

I feel very optimistic when I think about this: we're limited, but I think it's absolutely wonderful what we're able to do.

You should be able to relocate the instruction pointers in the stem cell's dna to patch in place the original knee with new living original knee.

Hope that reality isn't 50-years or more into the distant future.

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