Evidence that dendrites actively process information in the brain
1–10 of 33 posts
Re: Evidence that dendrites actively process information in the brain
#2Amazing to have some evidence of the processing capabilities dendrites could possess. Though this only makes our understanding of the brain that much slimmer.
With billions of neurons and dendrites interacting all the time, if each are compartmentalized we're going to have a difficult time coming up with a model to replicate the effects. Which, as I understand it, is our goal in an effort to better understand how the brain works overall.
Still, with this insight it's clear we've got some immensely powerful hardware bouncing around between our ears. What a truly brilliant machine.
Re: Evidence that dendrites actively process information in the brain
#3If you are interested in making a very stretched analogy, demonstrating dendritic information processing is like realizing that a CPU's transistor is actually itself a little CPU that is itself capable of quite sophisticated computation. In fact, most of a neuron's computation my be carried out by the dendrites. Don't get tied up in the over-simplified model of dendrite=antenna, soma=computer, axon=wires.
Active dendritic information processing has, for several decades, been theorized and modeled. The combination of two-photon microscopy and more "classical" electrophysiology techniques (like patch clamping used in this article) is finally opening the theories to experimentation.
[Not to be too critical, but this paper is far from the first to experimentally investigate dendritic information processing. I, personally, am glad some segment of HN is interested in neural computation.]
Re: Evidence that dendrites actively process information in the brain
#4I like this connection between memristors and nuerons: "From an information processing perspective, this tutorial shows that synapses are locally-passive memristors, and that neurons are made of locally-active memristors."[1]
Re: Evidence that dendrites actively process information in the brain
#5Reminds me of Roger Penrose's assertion in Shadows of the Mind that the microtubules within the neurons might be doing the work - making each Neuron into a metaphorical computer with millions of transistors. This is a different idea but the same conclusion - Neurons aren't the lowest level of computational structure in the brain, which means we have been underestimating the complexity and power of the brain by many orders of magnitude.
Re: Evidence that dendrites actively process information in the brain
#6Reminds me of Roger Penrose's assertion in Shadows of the Mind that the microtubules within the neurons might be doing the work - making each Neuron into a metaphorical computer with millions of transistors. This is a different idea but the same conclusion - Neurons aren't the lowest level of computational structure in the brain, which means we have been underestimating the complexity and power of the brain by many o…
And this is, somewhat ironically, very bad news for Mr. Kurzweil.
Re: Evidence that dendrites actively process information in the brain
#7Novice question:
A given dendrite has a voltage raise, presumable because of transmitter from a neighboring neuron. That voltage increase will always be local unless it is adequate (as it spread and dissipates on its way to the cell body) for an action potential.
If they showed an action potential starting at the dendrite, then I would expect it to eventually move to the rest of the cell body and then I wouldn't expect the language about 'not seeing the rest of the cell light up'. So, how did they measure/show actual processing? I'm missing that part.
Re: Evidence that dendrites actively process information in the brain
#8Novice question: A given dendrite has a voltage raise, presumable because of transmitter from a neighboring neuron. That voltage increase will always be local unless it is adequate (as it spread and dissipates on its way to the cell body) for an action potential. If they showed an action potential starting at the dendrite, then I would expect it to eventually move to the rest of the cell body and then I wouldn't expe…
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't necessarily faithfully propagate to the cell body (soma). This is also dependent on the local geometry and ion channel distribution. Dendritic action potentials are not all-or-nothing events like those of the axon.
To answer your question: Smith, et al., did observe dendritic action potentials (spikes) by measuring a proxy: calcium influx indicated by a fluorescent dye that changes efficiency when bound to calcium. This calcium influx, and by extension, the dendritic spike, is what was spatially-restricted. The authors are extrapolating information processing from the spatially-restricted dendritic spike.
Re: Evidence that dendrites actively process information in the brain
#9Novice question: A given dendrite has a voltage raise, presumable because of transmitter from a neighboring neuron. That voltage increase will always be local unless it is adequate (as it spread and dissipates on its way to the cell body) for an action potential. If they showed an action potential starting at the dendrite, then I would expect it to eventually move to the rest of the cell body and then I wouldn't expe…
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 words propagate the action potential or release neurotransmitter?
Re: Evidence that dendrites actively process information in the brain
#10It'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.