[HN Gopher] Neurons unexpectedly encode information in the timin...
___________________________________________________________________
Neurons unexpectedly encode information in the timing of their
firing
Author : theafh
Score : 175 points
Date : 2021-07-07 14:47 UTC (8 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| Robotbeat wrote:
| I 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.
| stinos wrote:
| _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
| 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 wrote:
| 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.
| munificent wrote:
| _> 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.
| pengstrom wrote:
| Readers might be interested in the following philosophy
| subjects https://en.m.wikipedia.org/wiki/Property_dualism
| https://en.m.wikipedia.org/wiki/Computational_theory_of_m
| ind https://en.m.wikipedia.org/wiki/Supervenience
| Robotbeat wrote:
| > _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._
|
| But this is NOT true of all biology. I picked molecular
| biology as an example for exactly this reason. It's
| driven by evolution with all its messiness, but yet it
| DOES have some reducible complexity. There really is DNA
| that is transcribed via certain molecules to RNA which is
| transcribed by other molecules into protein via a
| sequence of certain amino acids coded by the DNA base
| pairs. There is reducible complexity in spite of the
| crazy messiness of evolution, and it ends up looking a
| lot like some of our engineered systems in some instances
| (ie we can use the language of information theory and
| bits to describe encoding of genomes). We are able to use
| this to actually develop vaccines specifically using mRNA
| as a delivery mechanism, with specific, engineered
| changes to the transcribed viral protein spike to improve
| the vaccine's effectiveness.
|
| What I see in neuroscience looks a lot like genomics and
| inheritance before the discovery of DNA. And the
| insistence that "biological systems are entirely non
| reducible complexity" feels just a bit too much like a
| cop-out. This is not magic. If you are a neuroscientist
| optimistic about the field, then you must also believe
| there is some reducible complexity in there that will be
| discovered. I do get the feeling, based on research
| progress like in this article, that there really are some
| breakthroughs coming in _really_ understanding what's
| going on.
| munificent wrote:
| _> And the insistence that "biological systems are
| entirely non reducible complexity" feels just a bit too
| much like a cop-out._
|
| What insistence do you refer to?
| HarHarVeryFunny wrote:
| Evolution is an incremental mechanism, which is to say
| that it preserves most of what it has previously done
| (DNA encoded) and just makes small changes on top of
| that. IOW it is essentially structure preserving, and any
| change that undoes anything that still has value is
| likely to be maladaptive and not preserved (as opposed to
| repurposing of gills into ears, etc, where the original
| function is not being used).
|
| Of course evolution is also messy and isn't operating out
| of a playbook of decomposable single-function parts.
| Experiments with evolving electronic hardware have
| resulted in circuits taking advantage of all sorts of
| nasty non-linear analog effects, as you might expect.
|
| Still, given the inherently incremental nature of
| evolution, it is highly likely to result in a system of
| parts operating with some degree of independence to each
| other. While there are still many aspects of the brain's
| functioning we don't understand, it's pretty apparent
| that it is composed of functional parts like this -
| cortex, hippocampus, cerebellum, basal ganglia, etc.
| BitwiseFool wrote:
| I 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?
| xkeysc0re wrote:
| Definitely check out the work of Donald Hebb
| https://en.wikipedia.org/wiki/Hebbian_theory
| kwertyops wrote:
| It sounds like you are essentially describing long-term
| potentiation (LTP).
|
| See here: https://en.wikipedia.org/wiki/Long-
| term_potentiation
| neom wrote:
| This is a good but old article+paper that has some info on
| how neural networks are organized and how neurons work in the
| context of the physiology of the brain (information flow),
| the columns and layers play important but not well known
| functions in this: https://www.frontiersin.org/articles/10.33
| 89/fncir.2017.0008...
|
| Funnily, I think AI is a potentially really good use for
| understanding neurology further. There is so much disparate
| research out there, from the neuron, to the network, to the
| brain itself, it would be interested to feed it all into
| GPT-3, both the research papers and a large compendium of
| imaging and firing maps, and then ask it to look for
| connections. I'd be ridiculously interested in working on
| that (time to get a phd?).
| jph wrote:
| The catchphrase is "neurons that fire together wire
| together".
| mstipetic wrote:
| I 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 wrote:
| 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.
| mstipetic wrote:
| When I went to a therapist and we went to analyze my
| dreams it got weird how many details and meanings one
| could find there
| l33t2328 wrote:
| Is this not the idea of a synapse? A pathway that is easier
| to take because it has been taken before?
|
| I only have an AI understanding here, so this could be too
| simple.
| vmception wrote:
| From 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 wrote:
| What if the universe and the room is neurons all the way
| down?
| radicaldreamer wrote:
| There'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.
| seg_lol wrote:
| Reverse lamp post? We don't routinely take MRIs because of
| false positives, meaning we might have more questions than
| answers so we won't ask.
|
| Seems like neuroscience is still in the phase of reducing
| misunderstanding.
| mikewarot wrote:
| Fringe 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
| airstrike wrote:
| _This_ is why I come to HN daily. Thanks for the very
| interesting read.
| tsimionescu wrote:
| That'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 wrote:
| Quantum computers are not Turing machines as far a I
| know.
|
| They can encode exponentially many states simultaneously,
| and are non-deterministic.
| tsimionescu wrote:
| You 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.
| mensetmanusman wrote:
| I 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.
| bena wrote:
| I 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 wrote:
| You might want to ask Google about two-photon microscopy
| links.
|
| Example papers:
|
| 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 -- "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 wrote:
| So 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.
| andyxor wrote:
| We can though, FMRI and high frequency intracranial EEG come
| to mind, the original paper is based on the latter.
|
| They implanted a small electrode microarray (something like
| 5mm x 5mm size) into brains of live epilepsy patients via
| surgery and asked them to perform certain tasks. I worked on
| this project years go, we had about 30TB of data from two
| weeks of recording.
|
| These days FMRI is all the rage.
| HarHarVeryFunny wrote:
| That's what rats are for. For some experiments the research
| animal will be immediately "sacrificed" then have it's brain
| sliced and diced for inspection. Brings a whole new meaning
| to "thank you for your service".
| stinos wrote:
| _I 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.
| bena wrote:
| That's kind of why I said completely.
|
| Our ability to know how a brain works on the level of how
| well we know, say, the combustion engine works is severely
| limited by the fact that we're dealing with living beings
| and that the state of consciousness of the subject matters.
| stinos wrote:
| _That 's kind of why I said completely._
|
| Sort of, but to people not knowing anything about it it
| might sound as if it's impossible to do anything at all
| in vivo so I added some information about what is
| possible if you do not want a 'complete' recording.
| imvetri wrote:
| Don'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 wrote:
| This is what (mediocre) my PhD thesis was about.
| tgbugs wrote:
| Rate 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
| skohan wrote:
| 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 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 wrote:
| > 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.
| solipsism wrote:
| _I 'd have thought that I'd have heard of this if there
| were legit evidence_
|
| Changes to DNA would be the long term changes, not RNA. But
| yes, look up epigenetics, and especially DNA methylation.
| skohan wrote:
| Here are a couple articles:
|
| https://www.cell.com/neuron/pdf/S0896-6273(18)30901-2.pdf
|
| https://archiv.ub.uni-heidelberg.de/volltextserver/26121/
| tsimionescu wrote:
| 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.
| akyu wrote:
| I'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.
| jph wrote:
| Neurophysiology 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
|
| O'Keefe and Reece in 1993:
| 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.
| xg15 wrote:
| Soo... this starts to sound like serial communication. When can
| we start reverse-engeneering communication protocols? :D
| [deleted]
| cosmojg wrote:
| This 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.
| theknocker wrote:
| How the fuck is that unexpected?
| andyxor wrote:
| Preprint of the paper "Phase precession in the human hippocampus
| and entorhinal cortex":
| https://www.biorxiv.org/content/10.1101/2020.09.06.285320v1....
| mpfundstein wrote:
| Isn't that the whole idea of Spiking Neural Networks?
| morpheos137 wrote:
| why is this unexpected?
| vincent-toups wrote:
| 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 going on.
| alexmorley wrote:
| > 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:Computation...
| hall0ween wrote:
| Agreed, 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!
| [deleted]
| im3w1l wrote:
| https://en.wikipedia.org/wiki/Neural_coding is pretty good too.
| [deleted]
| nocturnial wrote:
| They 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 wrote:
| Hilarious. We shouldn't trust rat/mouse studies, but it's
| typically because the mice are way LESS complicated than
| humans. I would expect complicated behavior in mice to be
| treated as a lower bound for the complexity in humans. (but
| what do i know, i'm just a monkey.)
| eloff wrote:
| There are lots of animals that can beat us at specific
| neural tasks. So I don't think it's helpful to think in
| those terms. For example, our visual short term memory is
| bested by chimpanzees, at least on certain tasks used to
| measure it across both chimps and humans.
|
| Lowly mice likely have better olfactory capabilities than
| us. It wouldn't surprise me if their brains can handle some
| very specific things better than we do.
| [deleted]
| mdp2021 wrote:
| "Scholarpedia [.org] : the peer-reviewed open-access
| encyclopedia (where knowledge is curated by communities of
| experts)."
|
| Thank you, thank you, thank you.
|
| This fills an important gap.
| stochastimus wrote:
| Freeman was right after all.
| johndoe42377 wrote:
| That must be wrong. There are no time measuring machinery and no
| notion of time.
|
| Frequency, by the way, is not a synonym for time.
| HarHarVeryFunny wrote:
| The 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 wrote:
| Fire 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 wrote:
| Right, 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.
| jpfed wrote:
| Motion-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.
| neom wrote:
| Neurons might contain something within them -
| https://news.ycombinator.com/item?id=26838016
| LeifCarrotson wrote:
| In 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 wrote:
| Not sure I understood you.
|
| Did you describe PWM?
___________________________________________________________________
(page generated 2021-07-07 23:00 UTC)