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Neurons unexpectedly encode information in the timing of their firing

quantamagazine.org

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Re: Neurons unexpectedly encode information in the timing of their firing

#91

Post by glopesdev »

vincent-toups wrote: post #25
morpheos137 wrote: post #12

why is this unexpected?

The usual story is that neuron were initially characterized experimentally using current injections to which their firing times are (in a certain sense) maximally disordered and thus the response is characterized only by firing rate. This idea is also born out in most real neural systems, where firing rate is well correlated with various sorts of feature presentation. But at faster timescales other things seem to be…

Interestingly enough, a sequence of maximally disordered bits (poisson distributed) is exactly what you would expect from a highly efficient code.

So either the brain is entirely random, or so exquisitely determined that we can’t possibly figure out its code from statistics on the bits alone. I put my bets on the latter.

Re: Neurons unexpectedly encode information in the timing of their firing

#92

Post by radarsat1 »

londons_explore wrote: post #26
stinos wrote: post #7

Earlier quoted context omitted.

it just feels like often we don’t have a solid (falsifiable, etc) grasp of what’s actually happening, yet… It feels like that, because it is like that: there's probably way more which isn't known about the brain yet, than things known with a decent amount of certainty. Just skimming over recent papers in the fundamental area, a lot of that summarizes as 'So here we found that area A is connected to area B and modulat…

My benchmark of "this thing is well understood" is that it's possible to build that thing, or a replacement for it, again. Kidneys probably meet that criteria - we have dialysis machines which allow someone to survive without kidneys almost perfectly. Yet the idea of replacing someones brain with something artificial and having them function as normal is still a LOOOOOOONG way off.

> Kidneys probably meet that criteria - we have dialysis machines which allow someone to survive without kidneys almost perfectly.

This only means we know what kidneys do, not how they do it.

(But probably we do... I am not a biologist.)

Re: Neurons unexpectedly encode information in the timing of their firing

#93

Post by tsimionescu »

hau wrote: post #89
Robotbeat wrote: post #84

Earlier quoted context omitted.

But there’s no computation a quantum computer can do that a classical computer can’t. In that sense, it’s still a Turing machine. It can do some class of computation faster (in principle).

Richard Feynman describes such computation, that produces incorrect results on classic computer and correct one on quantum in "Simulating Physics with Computers"[0]. He follows one physical experiment detailing every step from start to finish and how it converges to incorrect result on classical computer. [0] - https://doi.org/10.1007/BF02650179

Thank you for the link! I have also found a free version for anyone else interested: http://physics.whu.edu.cn/dfiles/wenjian/1_00_QIC_Feynman.pd...

However, Feynman does not claim what you say he claims. His whole article is about efficiently simulating QM on a classical computer, and he shows that is not possible given what we understand of quantum probability today, at least (he does this by explicitly asking for a computer which does not grow exponentially in size with the size of the physical system it wants to simulate).

In modern CS terms, what he is discussing is whether the complexity classes BPP and BQP are equal or not (as far as we know today, just as he claims, BPP seems to be a smaller subset of BQP, but this is not proven).

This is all perfectly in line with my claim, and is in fact explicitly there in Feynman's paper: a classical computer can perfectly simulate a quantum system/computer, but requires exponential time/space to do so (as far as we know).

Re: Neurons unexpectedly encode information in the timing of their firing

#94

Post by tsimionescu »

throwaway3699 wrote: post #86
Robotbeat wrote: post #84

Earlier quoted context omitted.

But there’s no computation a quantum computer can do that a classical computer can’t. In that sense, it’s still a Turing machine. It can do some class of computation faster (in principle).

If we want to reach AGI within the lifetime of the universe, and quantum effects are required for consciousness [within the lifetime etc...], it stands to reason we'd need quantum computers.

Yes, that is true, at least as far as we know today (it's not yet mathematically proven that quantum computers can't be efficiently simulated by probabilistic classical computers, even though we are almost certain of this).

Re: Neurons unexpectedly encode information in the timing of their firing

#95

Post by tsimionescu »

astrange wrote: post #77
mikewarot wrote: post #64

Earlier quoted context omitted.

Quantum computers are not Turing machines as far a I know. They can encode exponentially many states simultaneously, and are non-deterministic.

They are not computably non-deterministic, so they are still Turing machines with a random number generator attached. Qubits aren't magic either and the amount of data they can store is well known, it's just a complex bit instead of a real one.

> they are still Turing machines with a random number generator attached

It's important to note that probabilistic Turing machines are different from quantum Turing machines in terms of efficiency, as far as it is known today. But still, that doesn't change the fact that they can (inefficiently) simulate each other.

Re: Neurons unexpectedly encode information in the timing of their firing

#96

Post by meroes »

tsimionescu wrote: post #93
hau wrote: post #89

Earlier quoted context omitted.

Richard Feynman describes such computation, that produces incorrect results on classic computer and correct one on quantum in "Simulating Physics with Computers"[0]. He follows one physical experiment detailing every step from start to finish and how it converges to incorrect result on classical computer. [0] - https://doi.org/10.1007/BF02650179

Thank you for the link! I have also found a free version for anyone else interested: http://physics.whu.edu.cn/dfiles/wenjian/1_00_QIC_Feynman.pd... However, Feynman does not claim what you say he claims. His whole article is about efficiently simulating QM on a classical computer, and he shows that is not possible given what we understand of quantum probability today, at least (he does this by explicitly asking for…

Perfectly except for random number generation right? The randomness of QM can never be decoded or attacked. If we are talking about fudging/"simulating" randomness with classical pseudorandom number generators and relying on computational complexity prohibiting decoding the patterns, and quantum computers are theoretically able to speed up factorization of large numbers, don't we have a problem?

Isn't there a point where we could say we can't really simulate powerful enough quantum computers because they can "decode" the patterns behind any psuedorandom computation so quickly?

Like no one in the right mind would be using classical computers at that point except for anything except basic computation and word processing. We might as well say humans and pen and papers can simulate quantum computers. Quantum computer capabilities may outstrip classical computers nearly as much as they do humans with pen and paper.

"Simulation" kind of loses it's meaning when taken far enough.

Re: Neurons unexpectedly encode information in the timing of their firing

#97

Post by tsimionescu »

meroes wrote: post #96
tsimionescu wrote: post #93

Earlier quoted context omitted.

Thank you for the link! I have also found a free version for anyone else interested: http://physics.whu.edu.cn/dfiles/wenjian/1_00_QIC_Feynman.pd... However, Feynman does not claim what you say he claims. His whole article is about efficiently simulating QM on a classical computer, and he shows that is not possible given what we understand of quantum probability today, at least (he does this by explicitly asking for…

Perfectly except for random number generation right? The randomness of QM can never be decoded or attacked. If we are talking about fudging/"simulating" randomness with classical pseudorandom number generators and relying on computational complexity prohibiting decoding the patterns, and quantum computers are theoretically able to speed up factorization of large numbers, don't we have a problem? Isn't there a point w…

Random numbers are random numbers. You can calculate the probabilities (the wave function amplitudes, which are deterministic); or you can use any source of random noise to reproduce the data, once you adjust for the difference between quantum and classical probability.

Re: Neurons unexpectedly encode information in the timing of their firing

#98

Post by meroes »

tsimionescu wrote: post #97
meroes wrote: post #96

Earlier quoted context omitted.

Perfectly except for random number generation right? The randomness of QM can never be decoded or attacked. If we are talking about fudging/"simulating" randomness with classical pseudorandom number generators and relying on computational complexity prohibiting decoding the patterns, and quantum computers are theoretically able to speed up factorization of large numbers, don't we have a problem? Isn't there a point w…

Random numbers are random numbers. You can calculate the probabilities (the wave function amplitudes, which are deterministic); or you can use any source of random noise to reproduce the data, once you adjust for the difference between quantum and classical probability.

For an extreme example, there are finite patterns behind the lava lamps at Cloudfare or the chaos of Jupiter's storms. These are sufficiently random for any current need I can currently imagine though.

But then I also see that "classical computers can never be built big enough to explore more than 400, actually more than, probably 100 qubits, 100 qubits doesn’t seem like very much. No classical computer can do the calculation of following what 100 qubits do" https://blog.ycombinator.com/leonard-susskind-on-richard-fey...

Are we really in no danger of quantum computers being able decipher patterns behind these traditional sources of noise? There is no pattern to quantum randomness. Aren't we going to have switch to truly random sources of noise eventually, instead of pseudorandom ones (anything non quantum)?

Re: Neurons unexpectedly encode information in the timing of their firing

#99

Post by skohan »

tsimionescu wrote: post #62
skohan wrote: post #54

Earlier quoted context omitted.

I feel like the more you learn about neuroscience, the more you learn how precise and complex neural information processing is. For instance, there's evidence that at least some neurons "record" information about their activity in the form of RNA. Also the placement of synapses in the dendritic arbour matters, and some synapses can act like logic gates with respect to the synapses farther down the same branches. I th…

I think it's also fascinating to learn about computation, sensing, reaction etc. in other cells, both within multicell organisms and when looking at single cell organisms. There was an article on this that I don't know how to find again - the point being that neurons are not unique in their capacity for computation, they are only the most evolved formed of it.

Yeah I mean if you look at the structure of Neurons it's easy to understand them as an extremely optimized version of "normal" intercellular communication. I mean all a synapse really is is chemical signaling between two adjacent cells.

The structure of neurons allows them to achieve "adjacency" to other cells which would be far from one another in most tissues, and electrical transmission of the action potential just allows neurons to control that chemical signaling in a very precise and directed way.

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