I probed the input to a nengo.Ensemble like:
net.probe = nengo.Probe(net.ens.neurons, 'input')
What do these values represent biologically? Concentrations of neurotransmitter? Post-synaptic voltage? For example, I know the decoded_output is simply spiking information.
Looking at the Nengo code base, it looks like input is the (combined) post-synaptic current J being fed into the neuron non-linearity.
The step function of the LIF provides an example of how this input current is put through the neuron non-linearity to calculate the neuron membrane voltage, which then determines if the neuron has spiked or not.
EDIT: Just a point of clarification, when you probe the .neurons attribute of an ensemble, you are getting at the properties associated with the individual neurons in the ensemble. However, if you are just probing the ensemble (e.g, nengo.Probe(net.ens)), you’ll be probing the properties associated with the ensemble as a whole.