Can - on a very coarse level - the functional role of dendritic processing as a whole (at least one of possibly many functional roles it might play) be described as rewarding spatially coherent synaptic inputs when creating action potentials?

This would make sense, when the mapping of neurons to synapses was neighbourhood preserving (in the sense of topology): the efferent synapses of two neurons in close vicinity (in other parts of the brain) sit in close vicinity on the dendritic trees of their common target neurons.

Then it would be desirable, that when a group of $n$ neurons in close vicinity to each other (e.g. a nucleus) projects to a subtree of the dendritic tree (i.e. synapses in close vicinity) and those neurons are firing at the same time, this should evoke an action potential in the target neuron, but not, if $n$ synapses spread randomly over the dendritic tree are active at the same time. To achieve this could be the (or one) function of dendritic processing.

As I said: this is a very coarse level of description, and to be taken with some grains of salt.

(The whole question would break down if there is no such neighbourhood preserving mapping from neurons to synapses.)


I've read the following articles (but maybe not carefully enough to be able to pin them down to the short form above):

  • $\begingroup$ In lieu of a keyword for future google searches, the phenomenon you are describing is referred to as "synaptic clustering". I would rephrase the title of your question to reflect the main text into something like: "Is synaptic clustering reinforced by dendritic spikes?" Dendritic spikes can in principle have other functions as well, so your title suggests a more broad issue than what you are actually asking. $\endgroup$ – vkehayas Sep 21 '17 at 11:59
  • $\begingroup$ As you point out, a separate issue is if there is synaptic clustering, which is one of the 7 questions you asked here. Perhaps you should ask this in a separate question. $\endgroup$ – vkehayas Sep 21 '17 at 11:59
  • $\begingroup$ Is dendritic processing only done by dendritic spikes? In Rall's model there is dendritic processing but no dendritic spikes, isn't it? And I consciously didn't mention dendritic spikes. $\endgroup$ – Hans-Peter Stricker Sep 21 '17 at 12:11
  • $\begingroup$ It depends on your definition: dendritic spikes, NMDA spikes, NMDA plateau potentials. 'Dendritic processing' is better, my point wasn't to remove that part. $\endgroup$ – vkehayas Sep 21 '17 at 12:19

Action potentials are always based on coherent synaptic inputs. So dendritic processing means rewarding specific coherent subsets of synaptic inputs.

So to me it makes more sense to frame dendritic processing as allowing neurons to detect several different patterns (alternatively or at the same time).

In that case each dendritic spike encodes a different pattern. This allows a neuron to play roles (or maybe the same role) in several different contexts (or possibly in different combinations of contexts). If this is the case the neighbourhood mapping you describe doesn't have to exist (though it still might).

  • $\begingroup$ I added "spatially" to make clearer what I mean. BTW: How can a spike encode a pattern? $\endgroup$ – Hans-Peter Stricker Sep 21 '17 at 11:38
  • $\begingroup$ If a neuron always spikes when a certain pattern of other neuron activations occurs, this neuron's spike can be said to encode the pattern. The pattern is not encoded in the specifics of the spike, just in the fact of the spike. $\endgroup$ – BlindKungFuMaster Sep 21 '17 at 11:43
  • $\begingroup$ So do you mean "dendritic spikes" (of which there are many) or "action potentials" (of which there is only one - in response to a certain pattern)? The latter is what I understand when a neuron spikes. $\endgroup$ – Hans-Peter Stricker Sep 21 '17 at 12:01
  • $\begingroup$ I mean that dendritic spikes encode for specific patterns, but these dendritic spikes may lead to the neuron spiking. So the neuron is able to encode many (combinations of) patterns. $\endgroup$ – BlindKungFuMaster Sep 21 '17 at 12:08
  • $\begingroup$ This would be the second step of understanding. My question concerns a first step. $\endgroup$ – Hans-Peter Stricker Sep 21 '17 at 12:12

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