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Evidence that dendrites actively process information in the brain

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Re: Evidence that dendrites actively process information in the brain

#21

Post by groovy2shoes »

akavi wrote: post #11

This is the very sort of interaction that leads me to be very, very unoptimistic about ever seeing Moore's Law style runaway advancement in biotechnology. Biology, it seems, is deeply unabstractable . Ie, as one moves up the levels of organization, one rarely (never?) reaches a point where a higher level can be fully modeled without also fully modeling each of the lower levels. This is in sharp contrast to computer e…

The problem is that our knowledge is limited. Once we have a better understanding of certain biological processes, we may be able to find the right abstractions.

Re: Evidence that dendrites actively process information in the brain

#22

Post by invalidOrTaken »

DigitalJack wrote: post #10

It's very interesting research, but I have to say I'd have a hard time being clinically detached with regards to probing a live mouse and working with it, knowing I was going to kill it when my testing was done.

My cousin does biomedical research. She said it gets much, much easier.

Re: Evidence that dendrites actively process information in the brain

#23

Post by bl »

PeterisP wrote: post #13
jasallen wrote: post #9

Earlier quoted context omitted.

Thanks for the answer. So just to close the loop and make sure I got it, a couple follow ups 'processing' in this case would refer to integrating signals/voltages/neurotransmitters from more than one neighboring neuron? How do they show that this was processing/integrating and not just particular sensitivity to one external stimulus? For 'processing' to be meaningful, would it not have to share the result? In other w…

I'm not a biologist and the parent poster seems to know in far more detail, but from a bunch of neuroscience lectures on how the dentritic spikes travel up to the soma, my takeaway (as a computer guy) was 'hmmm, it looks like a system implemented in FPGA layouts - the geometry features can work as logic gates or delays'; and 'hmmmm, it looks I could design a dendritic tree geometry for almost any boolean function of…

"[I]t looks I could design a dendritic tree geometry for almost any boolean function of the inputs".

That's my outlook on the structure-function link between dendritic morphology and dendritic information processing, with the modification that I'd not restrict it to boolean functions. There are very many more types of functions, linear and non-linear, that can conceivably be built out of neuronal dendrites.

And I like the nuance of your second paragraph. There are all sorts of wacky, complex calculations one can image being possible, but any one neuron may implement a subset. Now, across a few hundred billion neurons in a mammalian nervous system...

You're spot on with regard to timing, too. All this "information processing" with branched dendrites + non-linear ion channels are greatly expanded with a timing component.

Re: Evidence that dendrites actively process information in the brain

#24

Post by bl »

jasallen wrote: post #9
bl wrote: post #8

Earlier quoted context omitted.

The voltage change (i.e., depolarization) is not strictly local. In some cases, depending on the actual geometry of the dendrite and the particular complement of voltage-activated ion channels, the voltage change as a result of neurotransmitter release might lead to quite a distributed depolarization even without triggering a dendritic action potential. Conversely, an action potential initiated in the dendrites doesn…

Thanks for the answer. So just to close the loop and make sure I got it, a couple follow ups 'processing' in this case would refer to integrating signals/voltages/neurotransmitters from more than one neighboring neuron? How do they show that this was processing/integrating and not just particular sensitivity to one external stimulus? For 'processing' to be meaningful, would it not have to share the result? In other w…

"Processing" doesn't have a consensus definition in the neuroscience community, but a neuroscientist could, with good justification, use that definition if they had a particular experimental scenario. In this article, Smith, et al., use a more narrow definition based on well-known response in which a neuron is selectively-sensitive to a bar of light at a particular angle. How a neuron becomes selectively-sensitive (i.e., how it fires to that angle and not to all the others) is the "processing".

It is overly simplified to say that for the processing to be useful that it has to share the result. If a particular part of the dendritic sub-tree was stimulated enough, it could bring the neuron into a particular electrophysiological state that succeeding synaptic input would cause a wholly different computation to occur. Thus, you can see the importance of timing discussed by the sister comment.

Re: Evidence that dendrites actively process information in the brain

#25

Post by jostmey »

groovy2shoes wrote: post #21
akavi wrote: post #11

This is the very sort of interaction that leads me to be very, very unoptimistic about ever seeing Moore's Law style runaway advancement in biotechnology. Biology, it seems, is deeply unabstractable . Ie, as one moves up the levels of organization, one rarely (never?) reaches a point where a higher level can be fully modeled without also fully modeling each of the lower levels. This is in sharp contrast to computer e…

The problem is that our knowledge is limited. Once we have a better understanding of certain biological processes, we may be able to find the right abstractions.

You might be missing the point. Biological systems are the result of Natural selection, and the processes of Natural selection are fundamentally irrational. Any biological system, including our own brain, is essentially the outcome of a random, irrational process. There may be cases where we can arrive at some abstractions, but such cases may be the exception, not the norm.

Re: Evidence that dendrites actively process information in the brain

#26

Post by nooneelse »

DigitalJack wrote: post #10

It's very interesting research, but I have to say I'd have a hard time being clinically detached with regards to probing a live mouse and working with it, knowing I was going to kill it when my testing was done.

In my experience/opinion, the worst part is when you try and try and get no good data at all from one.

Re: Evidence that dendrites actively process information in the brain

#28

Post by PeterisP »

bl wrote: post #23
PeterisP wrote: post #13

Earlier quoted context omitted.

I'm not a biologist and the parent poster seems to know in far more detail, but from a bunch of neuroscience lectures on how the dentritic spikes travel up to the soma, my takeaway (as a computer guy) was 'hmmm, it looks like a system implemented in FPGA layouts - the geometry features can work as logic gates or delays'; and 'hmmmm, it looks I could design a dendritic tree geometry for almost any boolean function of…

"[I]t looks I could design a dendritic tree geometry for almost any boolean function of the inputs". That's my outlook on the structure-function link between dendritic morphology and dendritic information processing, with the modification that I'd not restrict it to boolean functions. There are very many more types of functions, linear and non-linear, that can conceivably be built out of neuronal dendrites. And I lik…

Well, AFAIK you don't need anything more than boolean functions, since if we're talking about single spikes (not spike frequency), then there either is or isn't a spike, you don't get some spikes larger than other.

The linear/nondigital functions IMHO seem to be used as implementation details - for example, a neuron "fire iff 1+ VIP-input fires or 3+ normal inputs fire" can be implemented in wetware by having 'vip-inputs' have thrice as strong synaptic connection, summing all input values in the dendrite, and adjusting so that the firing threshold is appropriate (i.e. a linear function); but in silicon the same thing can (should?) be implemented as a boolean function / logic gates.

Re: Evidence that dendrites actively process information in the brain

#29

Post by PeterisP »

daughart wrote: post #14

I hope people in the connectome camp take this to heart. I strongly doubt that modeling the connections of neurons will reveal the way the brain works. The mouse and rat brains are very similar in connectivity, but the behavior of the mouse and rat are quite different. One explanation is that the individual neurons are actually processing information differently, and so differences arise out of neuron functionality r…

If this is the right way, then exactly the connectome camp will reveal the way the brain works - all their methodologies on how to extract connectomes from brain samples also (by necessity) reconstruct the whole dendritic tree structure through which the synapse is linked; so all parameters for these dentritic computations would also be included in their data.

Re: Evidence that dendrites actively process information in the brain

#30

Post by PeterisP »

daughart wrote: post #17
akavi wrote: post #11

This is the very sort of interaction that leads me to be very, very unoptimistic about ever seeing Moore's Law style runaway advancement in biotechnology. Biology, it seems, is deeply unabstractable . Ie, as one moves up the levels of organization, one rarely (never?) reaches a point where a higher level can be fully modeled without also fully modeling each of the lower levels. This is in sharp contrast to computer e…

Bioengineering and synthetic biology will never be like electrical engineering, but some of the differences can be exploited. For one, you can use directed evolution to optimize a biological system without relying on rational design. For another, biological development is massively flexible. Consider that when you evolve a longer arm, you don't need to mutate genes to ensure you have longer muscles, tendons, nerves,…

As you say, even futuristic bioengineering will never be like electrical engineering, but it does have parallels with software development.

It feels somewhat similar to declarative programming - our genes contain a large bunch of code that, in effect, says 'if you're seeing chemical X (which should mean that you're on the edge of a limb bud, then produce chemical Y/grow differently/become a skin cell'. And a bug in some other, far-away code can make an embryo grow, for example, a sixth toe, by invoking already existing code that will connect it to your foot and add toenails.

And we have some idea on how to work with such code - sure, it's far away from what we'd call well engineered or intelligently designed code, it's a big horrible pile of buggy spaghetti code that mostly works in most conditions if we discount the large portion of cases where the egg doesn't even develop into a valid embryo. And there's 'bug parity' where fixing a single-item bug is likely to create another bug elsewhere because it relied on the first part being always buggy. And, of course, it's undocumented obfuscated 'assembly code'. But the advantage is that it's only a singe codebase (although even larger than healthcare.gov) with no 'completely new and different' releases coming, so all of us together have to learn it once, and it is almost the same codebase that we'd also use to alter our corn, cows, flu and mosquitoes.

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