A linear summate and fire default model of post-synaptic integration would not require inputting axons to synapse at any particular place within the dendritic tree of the receiving neuron. However, if post-synaptic integration was non-linear and possibly pattern sensitive it might be essential that the site of each synapse bore a relation to the meaning or significance of a specific input signal. Thus for a multimodal high-level sensory neuron signals originating from different primary cortices might arrive at different domains of the dendritic tree.
I would be very interested to know whether there is already useful information on this topic or whether anyone hopes to collect such information.
Dear Jonathan
I wish I can help you but it is not my field
regards
Dear Jonathan:
A very basic circuit is the so-called "canonical" one, as discussed in the paper below.
http://www.mitpressjournals.org/doi/abs/10.1162/neco.2008.02-07-466#.WEqOeyMrLJw
Maybe the linked article might provide useful info.
Hope it does.
Regards,
Karlo
http://journal.frontiersin.org/article/10.3389/fnsys.2016.00088/full
Dear Karlo,
That DOI does not open for me. Can you give me enough to bring it up on PubMed or Google?
The doi seems to match. The Trettenbrein paper is certainly interesting. I see it makes a lot of Randy Gallistel's 2009 book, which I was looking at last week for other reasons. I have sympathy with the idea of information being stored in cell structure independently of synaptic 'weight' but have always thought Gallistel was sticking too closely to a Turing analysis in developing his question.
And I guess my question remains the same: do we know if synaptic site matters for meaning?
Dear dr Edwards,
Yes, it is the T-project (link if still needed http://dx.doi.org/10.3389/fnsys.2016.00088 ).
Further, if interested, I propose to check the prominint sci-blogger's web (Neuroskeptic, http://blogs.discovermagazine.com/neuroskeptic/2016/12/04/do-synapses-store-memories/#.WErCubWkrYW ). His own summary on the aforementioned paper as well as additional comments by mostly scientific community members may offer some resources or ideas that could answer a part of your question.
On the other hand, when thinking comparatively to other principles of neurophysiology, there ought to be spatial and temporal aspect that are salient, but also needed as a robust input - therefore maybe have a wider set of possibilities to yield a particular phenomenon, but it having respective boundaries as well.
Best wishes and follwing this discourse with interest,
Karlo
Good model paper: Regulation of AMPA and NMDA receptor-mediated EPSPs in dendritic trees of thalamocortical cells - J Neurophysiol. 2013 Jan;109(1):13-30. doi: 10.1152/jn.01090.2011. Epub 2012 Oct 24.
[found at the PubMed with the search phrase "dendrite and synapse segregation" - many similar and useful phrases could be coined too]
Thank you, Bratislav, that is a good place to start. Finding the correct PubMed search words was certainly an issue.
I guess the question is why these upstream cells connect to different parts of the tree if the effect on output is the same. My instinct is that the model may not reflect realtime brain context well enough to show departure from summate and fire. I will read more with interest.
Of course, modulation of the output is important - it is obvious. But, these is another question: which group of inputs (out of many group of inputs), and with what probability, and with what significance, and with what meaning will elicit the output or modulate it?
Re: "do we know if synaptic site matters for meaning?"
In my limited knowledge, the jury is still out, at least at the level of cortex. It is clear, that distinct inputs can target different areas of the dendrite, also that location of synapses effects how they interact with each other as well as their ability to trigger somatic (or for that matter) dendritic spikes. However, the causal effect on "meaning" as well as the granularity of the effect, if present, are open and fascinating questions. My 2p.
Hi Ede,
At the same time as putting this question on RG I emailed Marc Tessier Lavigne who kindly suggested the following review: Annu. Rev. Cell Dev. Biol. 2009.25:161-195 by Sanes and Yamagata from 2009 My guess is that there is more known since then but maybe not such a clear review. It seems that the answer to my initial question is clearly yes, but as you say, meaning is a more subtle issue.
I note you work with Michael Hausser, whose work I regard as amongst the best in this sort of area and maybe getting closest to demonstrating some sort of 'pattern based' integration event rather than just linear summation.
People like Gallistel would lie to pin down meaning in specific neural events but it is not clear to me that enough attention is paid to really fundamental issues, like what class of event could meaning be expressed in and what the 'protagonists' in such an event would be. What I find fascinating is that people like Descartes, Hobbes and Leibniz thought very hard about the fundamental questions and I think came up with more plausible suggestions than anything in popular circulation these days.
I suspect a lot of neurobiologists do not think much about the fundamental causal issues because they see no prospect of making any testable predictions. However, the issue of grain the you raise is just the sort of issue that I think might tell us something important. In simple terms, would inputs at every different synapse carry a different meaning or might there be something like tenfold redundancy so that batches of ten synapses would mediate specific meanings.
A related question is whether the elements of meaning are 'data points' as tends to be assumed, or something much more like propositions (there are two similar circles), which would be closer to what a programme like Power Point would use for encoding scenes.
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