Rate model - optional threshold setting

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Hi,

This is a very basic question. I just started looking into Brian. I understand it is a spiking neural network simulator. Even the example for a “Rate model”, the threshold condition is set to Poisson, so that Poisson-distributed spikes are generated. But “threshold” is an optional parameter, so what happens if it is not set ? Does the neuron group then just have a voltage, and if another neuron group receives input from this one, it functions as a real “rate model” where there are no spikes - i.e. a dynamic field model, or neural field model etc … (sorry if I mangling the semantics here).

So, after posting, I asked GPT-4 :wink: and it says that if threshold is not set, then no spikes will be fired, and if this neuron group is used as input to another, then there will be no input from this neuron group to the other. Is this correct ? (If yes, perhaps GPT-4 can write Brian documentation ?).

Thanks !

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As usual (for questions around Brian), GPT-4 is not quite correct :wink: Yes, if you do not have a threshold, a neuron does not spike, so the spike-based interaction (on_pre in Synapses) does not work. But you can also directly have the input to a post-synaptic neuron depend on a pre-synaptic variable, i.e. have a continuous interaction that is calculated every time step. This can be used to model all kinds of continuous interactions, e.g. gap junctions (electrical synapses), or complex synapse models. It can also be used to simulate rate models, with the only limitation that you cannot model delayed interactions in this way. We do not have a good example for this, but this discussion explains the general approach: Coupled Van der Pol oscillators

Hope that clears things up!

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