Variations in action potential threshold and temporal coding

Question

I would like to ask a few questions about things I'm not sure I understand in a paper Action potential threshold of hippocampal pyramidal cells (...).

(1) At the start the paper considers the possibility of irregular firing patterns of action potentials may be an argument to hold that the information processed by the CA1 neurons is a temporal code. I think it is hard to see the relation of final results (see the abstract) with these initial considerations. Do the results support the temporal coding hypothesis of CA1 neurons? How?

(2) At the end of the first page it says the following: "significant variations in action potential threshold would have implications for the precise timing of action potentials since the probability of initiating an action potential could not be predicted by only fluctuations in the membrane potential".

Does this mean that they aim to explain the irregular patterns by means of the fluctuations in the threshold?

I also don't see how from "the probability of initiating an action potential could not be predicted by only fluctuations in the membrane potential" follows that "significant variations in action potential threshold would have implications for the precise timing of action potentials".

Answer 1

Hi, For what I read, the objective of the paper is in fact to study the neural code using methods that study the membrane threshold changes (as you said). They mention both rate and temporal code in the introduction and they do give more emphasis to the temporal coding because it explains better the irregularities of the neuronal transmission. They did find some correlations between changes in the threshold, which influences the iniciation of the action potential, and the timing and rate of the firing or the firing pattern. That means that the firing pattern influences the iniciation of the action potential even if in an indirect way (which is by influencing the membrane threshold). Saying that the pattern of firing is important it means that the timing is also important, instead of only the rate the firing. Because this is the major difference between both neural codes theory, it does support more the temporal code.