12 ms·
Neurons unexpectedly encode information in the timing of their firing
- jph 5y agoNeurophysiology and phase precession have a storied history, from the 1990's up to the Nobel Prize in 2014. Wikipedia: https://en.wikipedia.org/wiki/Phase_precession https://en.wikipedia.org/wiki/Phase_precession O'Keefe and Reece in 1993: https://onlinelibrary.wiley.com/doi/abs/10.1002/hipo.450030307 https://onlinelibrary.wiley.com/doi/abs/10.1002/hipo.4500303... ... [F]iring consistently began at a particular phase as the rat entered the field but then shifted in a systematic way during traversal of the field, moving progressively forward on each theta cycle... The phase was highly correlated with spatial location... [B]y using the phase relationship as well as the firing rate, place cells can improve the accuracy of place coding.
- johndoe42377 5y agoThat must be wrong. There are no time measuring machinery and no notion of time. Frequency, by the way, is not a synonym for time.
- Robotbeat 5y agoI find a lot of the common explanations of how the brain works in neuroscience to be unsatisfying… compared to molecular biology, it just feels like often we don’t have a solid (falsifiable, etc) grasp of what’s actually happening, yet… too much handwaving (for instance, the lack of any specifics on where precisely some data is located… even “it’s stored in the connections” seems not quite true or falsifiable… although perhaps not exactly false, either). So I find discoveries like this exciting as it’s starting to peel back the curtain on a true understanding of the brain and neurons.
- radicaldreamer 5y agoThere’s a strong bias toward things that are model-able in neuroscience. The role of microtubules, for example, are mostly ignored even though they may explain the complexity of cognition displayed by relatively “simple” brains.
- mikewarot 5y agoFringe Tangent: It's possible those microtubules in our brains are 1 dimensional superconductors, and thus might be capable of holding Qubits. We might have quantum memory. https://arxiv.org/ftp/arxiv/papers/1812/1812.05602.pdf https://arxiv.org/ftp/arxiv/papers/1812/1812.05602.pdf
- airstrike 5y agoThis is why I come to HN daily. Thanks for the very interesting read.
- tsimionescu 5y agoThat's still extremely unlikely given all we know about quantum computers so far, and about biology. It's also important to note that quantum computers are just faster classical computers, they are still Turing machines. Many people who are looking for some non-computable element of consciousness in quantum effects in microtubules seem to forget that.
- mikewarot 5y agoQuantum computers are not Turing machines as far a I know. They can encode exponentially many states simultaneously, and are non-deterministic.
- tsimionescu 5y agoYou can simulate any quantum computer on a Turing machine, though it generally takes exponentially more time than with a real QC. Whether this means they are the same thing or not is a matter of semantics. But what is clear is that there is no computation that can be done on a QC that can't be done on a TM. The role of non-determinism in computation is more debatable. There is even a notable MIT professor (who coined the term Actor model) who claims that real computers, like the Android phone I'm writing this on, are in fact not Turing machines, because of non-determinism / parallelism. He also claims that Godel's incompleteness theorem doesn't apply to actual mathematics, so I would take his words with a huge spoonful of salt.
- stinos 5y agoit 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 modulated when things happen in C, so attributes to function D. But way more research needed, and unsure what this means in relation to E and F'.
- londons_explore 5y agoMy 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.
- munificent 5y ago> My benchmark of "this thing is well understood" is that it's possible to build that thing, or a replacement for it, again. Something I've been thinking a lot about lately: Implicit in statements like this is the idea of a system. That some complex-seeming artifact is actually composed of a relatively smaller number of essential things and all of the observed complexity is just emergent properties of the simpler underlying system. Find the handful of hidden rules and you can build back up to the whole thing from first principles. For example, if you were to learn chess purely by watching people play, it would be a huge struggle at first. Does how they hold the pieces matter? What role does timing play? Why does one player rest their head on their cheek while staring at the board? Eventually you start to figure out which actions are essential and which aren't. It doesn't matter where inside a square a piece is placed. All pawns are behaviorally equivalent, etc. We really really like systems. So much so that we tend to assume everything is one. But I see no evidence to assume that biology and evolution work that. Evolution is a semi-random walk over the phenotype space and fitter organisms are discovered (mutated) entirely randomly. It may be that a kidney mostly filters blood, but also does a little of this other thing, and the fact that it pushes your small intestine out of the way is important, and also and also and also... We can increase our understanding by learning more, but there may simply be no "first principles" for what makes an organism tick and almost all of its complexity may be irreducible. There may be absolutely no separation between "fundamental property" and "implementation detail". It may be that no terms in the grand equation of life cancel out.
- BitwiseFool 5y agoI had a crazy idea about neurons that I'll share here, because why not? What if each time a neuron sends a signal to another neuron the potential required for that connection decreases slightly? So the next time there's an action potential between neurons it's more likely to go where it has already gone. In other words, frequent connections make that same pathway more readily traversed. Could it be that a memory is simply a new signal traveling down a 'worn path'? I realize that there needs to be some way for this resistance change to be reset over time, so is it possible that dreams serve the purpose of writing somewhat random data, like wear leveling or trimming on an SSD? This is just pure speculation and I have "Hello World" levels of knowledge about neuroscience. But hey, it's fun to speculate, right?
- kwertyops 5y agoIt sounds like you are essentially describing long-term potentiation (LTP). See here: https://en.wikipedia.org/wiki/Long-term_potentiation https://en.wikipedia.org/wiki/Long-term_potentiation
- jph 5y agoThe catchphrase is "neurons that fire together wire together".
- mstipetic 5y agoI have a completely layman theory that that’s what dreams are. Worn out pathways that our ego or consciousness is not letting through to us, but are being used in our subconscious, being able to manifest themselves finally. That’s why we can see things that are bothering us or on our mind in the background there
- meowkit 5y agohttps://www.biorxiv.org/content/10.1101/2020.07.24.219089v1 https://www.biorxiv.org/content/10.1101/2020.07.24.219089v1 It’s recently suggested there is nothing special about dreaming - its just a confluence of himan interpretation with a mechanism to stop you from going blind.
- vmception 5y agoFrom my understanding, the current approach is basically the idea that if you put a bunch of neurons in a room, it eventually starts questioning the universe It really lacks nuance
- morpheos137 5y agoWhat if the universe and the room is neurons all the way down?
- bena 5y agoI mean, we can't really completely inspect a working brain to see what's happening. To get that level of inspection, we'd need to dig into the brain while it is functioning. Unfortunately, this kills the patient. And then the brain stops working. It's a black box essentially. We have tools that allow us some degree of insight, but honestly, it is incredibly difficult and progress is slow and staggered.
- nosianu 5y agoYou might want to ask Google about two-photon microscopy links. Example papers: https://pubmed.ncbi.nlm.nih.gov/25391792/ https://pubmed.ncbi.nlm.nih.gov/25391792/ -- "Two-photon excitation microscopy and its applications in neuroscience" https://www.nature.com/articles/s41598-018-26326-3 https://www.nature.com/articles/s41598-018-26326-3 -- "Three dimensional two-photon brain imaging in freely moving mice using a miniature fiber coupled microscope with active axial-scanning" Sure, it's localized and you cannot go deep, but there is so much to learn that that is plenty at this point.
- bena 5y agoSo my point remains. I'm not saying there's nothing to learn. I'm saying that we cannot go deep. That we currently cannot understand the brain to the degree we understand other systems. And that there are fundamental difficulties because we're dealing with living beings.
- stinos 5y agoI mean, we can't really completely inspect a working brain to see what's happening. To get that level of inspection, we'd need to dig into the brain while it is functioning. Unfortunately, this kills the patient Leave out the completely and it's a different story though: it's perfectly possible to 'dig in while functioning' i.e. inspect small parts using electrode arrays and that will not kill the patient and only do minimal damage (the couple of cells killed by that are nothing in comparison with the entirety). Non-invasive fMRI techniques also have come a long way but temporal resolution is low. But as you say: difficult, slow, and by no means a 'complete' view. On the other hand: no idea how one would even begin to handle the insane amount of data which would come from inspecting a complete brain. So what goes on now, tackling smaller areas/connections thereof one by one, is not even that bad of an approach.
- mensetmanusman 5y agoI wish we had a large research effort on just trying to understand a cpu running windows 98. E.g. put all of our best analysis tools to task against an operating pentium chip and see if we can determine from first principals that it is running a W98 screen saver. That would give us a small sense of the challenge we are facing.
- hcineb 5y agoWell, you are not the first one https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1005268 https://journals.plos.org/ploscompbiol/article?id=10.1371/jo...
- jpfed 5y agoMotion-detecting neurons in the visual cortex need to use timing; it would be a little weird for evolution to just use that mechanism once and not try it again.
- morpheos137 5y agowhy is this unexpected?
- vincent-toups 5y agoThe 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 going on.
- glopesdev 5y agoInterestingly 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.
- alexmorley 5y ago> For decades, neuroscientists have treated the brain somewhat like a Geiger counter: The rate at which neurons fire is taken as a measure of activity, just as a Geiger counter’s click rate indicates the strength of radiation. This hasn't been true for at least 20 years. There's a classic paper showing evidence of this in 1993 (O'Keefe and Reece) in rats. And has been an active area of discussion both before and since. (Note that it's not to say that rate isn't important, but as a community no one has beleived that all the information would be encoded in rate for many years) There's lots of good explainers here that link to relevant research: http://www.scholarpedia.org/article/Encyclopedia:Computational_neuroscience http://www.scholarpedia.org/article/Encyclopedia:Computation...
- hall0ween 5y agoAgreed, that opening line suits neuroscience poorly. "For decades, meteorologists have treated the environment somewhat like a Geiger counter: the temperature is taken as a measure of energy, just as a...", it's ludicrous!
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- im3w1l 5y agohttps://en.wikipedia.org/wiki/Neural_coding https://en.wikipedia.org/wiki/Neural_coding is pretty good too.
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- nocturnial 5y agoThey mentioned this in the 3rd paragraph: "This temporal firing phenomenon is well documented in certain brain areas of rats, but the new study and others suggest it might be far more widespread in mammalian brains."
- sdenton4 5y ago
- neom 5y agoNeurons might contain something within them - https://news.ycombinator.com/item?id=26838016 https://news.ycombinator.com/item?id=26838016
- imvetri 5y agoDon't get yourself distracted into the light while trying to find how neuron learns. Once get distracted, always be distracted and get into a rabbit hole of plethora of information but loose the initial motive. Shape of the neurons is the memory. A fetus brain doesn't have ups and downs. It is fluidic. As we learn, we get ridges. This is just a fact to prove that neurons/ the neural fluid(neurons together) take shape as it learns. Once we establish a simple, yet truthy foundation, pile up things on this for more missing pieces.
- vincent-toups 5y agoThis is what (mediocre) my PhD thesis was about.
- cosmojg 5y agoThis has been somewhere between highly suspected and well established for a few decades now, certainly not unexpected. These findings simply back up the present consensus.
- mpfundstein 5y agoIsn't that the whole idea of Spiking Neural Networks?
- HarHarVeryFunny 5y agoThe headline seems to be somewhat at odds with explanation of this "phase precession" is the body of the article: "The phenomenon is called phase precession. It’s a relationship between the continuous rhythm of a brain wave — the overall ebb and flow of electrical signaling in an area of the brain — and the specific moments that neurons in that brain area activate. A theta brain wave, for instance, rises and falls in a consistent pattern over time, but neurons fire inconsistently, at different points on the wave’s trajectory. In this way, brain waves act like a clock, said one of the study’s coauthors, Salman Qasim, also of Columbia. They let neurons time their firings precisely so that they’ll land in range of other neurons’ firing — thereby forging connections between neurons." My understanding of what they're saying is that it's related to "neurons that fire together wire together". Given different signal travel distances, it's necessary for neurons to fire at different times if they're to arrive at a given destination at the same time (in order to "wire together"). They achieve this timing by firing in synchrony with the theta brain waves that travel across regions. So, with this understanding, I guess you could say the timing is encoding information, but really in essence it's only the relative spatial position - within the cortex - of the firing neuron that's being "encoded". A more useful way to view it is just that firing times are synchronized to theta waves in order to achieve larger scale coordination that compensates for signal travel distances.
- sdwr 5y agoFire together, wire together refers to the connection between two neurons strengthening. Firing just before the recipient neuron fires strengthens the bond, and firing afterwards/off tempo weakens the bond. It's an elegant concept, because it handles neural weights, a non-linear activation function, and clock speed with a simple, distributed rule.
- HarHarVeryFunny 5y agoRight, but first the "recipient" neuron needs to fire, which requires integrated synaptic inputs to cross some threshold, which requires input spikes to arrive close to the same time. This phase precession mechanism being discussed is what allows inputs arriving from different distances (i.e. with different signal travel times) to arrive close to the same time such that the recipient fires. Once it fires, then "fire together, wire together" can strengthen/weaken the synapses as appropriate.
- akyu 5y agoI'm merely a casual observer of neuroscience, but I feel like I already knew this. This isn't a huge leap if you accept that Spike-timing-dependent plasticity is happening.
- xg15 5y agoSoo... this starts to sound like serial communication. When can we start reverse-engeneering communication protocols? :D
- deleted 5y ago[deleted]
- andyxor 5y agoPreprint of the paper "Phase precession in the human hippocampus and entorhinal cortex": https://www.biorxiv.org/content/10.1101/2020.09.06.285320v1.full.pdf https://www.biorxiv.org/content/10.1101/2020.09.06.285320v1....
- tgbugs 5y agoRate coding vs temporal coding is literally a meme in neuroscience because the two camps seem to refuse to compromise. Everyone else has realized that both happen depending on how that particular part of the nervous system works, or even what particular kind of information is flowing through it. This title reads like it was written by a rate coder who woke up one day and was like "Woah, you mean ... there might be more to it than just averaging spike counts per unit time???" edit: Hah, they are literally the first two headings in the wikipedia article on neural coding [0]. 0. https://en.wikipedia.org/wiki/Neural_coding https://en.wikipedia.org/wiki/Neural_coding
- skohan 5y agoI 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 think there almost certainly must be neural behavior which codes fairly simply based on rate, but it's very difficult to believe that there isn't neural computation based on precise timing relationships.
- rewq4321 5y ago> there's evidence that at least some neurons "record" information about their activity in the form of RNA Source? I'm not a neuroscientist, but I'd have thought that I'd have heard of this if there were legit evidence. Are you saying that neurons might use RNA as a sort of "long-term" memory of activation patterns? This seems really unlikely! But again, I'm not a neuroscientist.
- skohan 5y agoHere are a couple articles: https://www.cell.com/neuron/pdf/S0896-6273(18)30901-2.pdf https://www.cell.com/neuron/pdf/S0896-6273(18)30901-2.pdf https://archiv.ub.uni-heidelberg.de/volltextserver/26121/ https://archiv.ub.uni-heidelberg.de/volltextserver/26121/
- theknocker 5y agoHow the fuck is that unexpected?
- stochastimus 5y agoFreeman was right after all.
- LeifCarrotson 5y agoIn my very different field (robotics and industrial automation), temporal coding is one of the most powerful ways to expand your IO. Nearly all PLCs, sensors, and robots make heavy use of digital IO. But this parallel interface is limited, especially with hard-wired signals, and even if you're using serial network protocols the typical fieldbus abstraction represents the network as fixed-size buffers of digital IO that update every few milliseconds. Analog signals are usually an expensive optional extra! However, the controllers all include high-resolution timers. If you need to transmit an analog value, rather than bit-coding it over 12 discrete digital IO, a clever programmer might turn on a digital output for the desired number of milliseconds, or select between 10 or 16 or however many states you want to represent with your one wire using a predefined list of durations. You can convey far richer information this way! Always interesting to see what researchers are discovering in the automated control system that is biology... sometimes we can discover techniques for use in industry with biomimicry, sometimes biology we didn't know about seems to imitate technology we developed independently.
- nielsole 5y agoNot sure I understood you. Did you describe PWM?
- LeifCarrotson 5y agoNo, typical PWM is a repetitive hardware function of an embedded system, and operates at kHz or MHz. Industrial controls usually have a scan time or requested packet interval on the order of 10 ms, much to slow for PWM without dedicated peripherals. And even if you can transmit it, you still need to read it on the other side, again, high-speed IO is a dedicated thing, you won't buy step and direction outputs or encoder inputs for unused spares. A PLC and a robot might interchange digital signals such as "In cycle", "Part present", "Faulted", "Clear of fixture", "Screw present", and "Cycle start". Hopefully the original designers also pulled a couple spare wires in case you need to add another sensor. But the old equipment is being asked to do something new, requirements now say you need to transmit, perhaps, which of dozens of part numbers to select from, or the touch point at which a sensor fired between 10 and 100mm. That's a binary signal with 6 or 7 bits, which means a $200 8-channel output card, multiconductor cable, and a $200 input card. When possible, you'd buy the fieldbus option cards from the factory and pull network cables. But in a pinch, with the more typical two spare inputs and two spare outputs, you can move some data to the time domain and work out "If aux1 is pulsed high for 680ms, the new sensor tripped at 68mm". One wire, one bit of state (0V or 24V), many values transmitted. You could extend this concept with a clock signal, data signal, and transmit arbitrary serial data, but that's going a bit too far for most maintenance techs. A pair of timers is comprehensible.
- davesque 5y agoReminds me a lot of stochastic computing: https://en.m.wikipedia.org/wiki/Stochastic_computing https://en.m.wikipedia.org/wiki/Stochastic_computing
- pontifier 5y agoI totally called this! Watch for firing patterns encoded on MRNA for pattern matching, and to help predict what might come next in a sequence. That was the other part of my theory.
- RocketSyntax 5y agohow is this new? spiking thresholds serve a purpose
- acenes 5y agoAnybody look at the original paper? I'm not convinced at all by their Fig 2 - that's more a blob than a precession.