This leaky integrate-and-fire (LIF) neuron is a simple, standard model of a spiking single neuron. It resides inside a neural ‘population’, even though there is only one neuron.
This is a single neuron simulation in Nengo. Here we have the input to the neuron. That input is driving the subthreshold voltage of the cell which is plotted here in blue. This plot is quite noisy because the simulation itself includes some Gaussian noise. Each time this subthreshold voltage crosses the threshold at the top of the graph the leaky integrate-and-fire neuron that we are simulating generates a spike. Those spikes are shown up here. These are action potentials generated by the cell. This is another view of those action potentials as well. Each time an potential is generated a yellow square appears, otherwise the subthreshold voltage is shown as grayscale. The final graph we have is the postsynaptic potential that would be induced in a cell that was receiving the spike train from this cell. We can control this simulation by grabbing the input and increasing it. As we increase it, this particular neuron will become more active with an increase in the input. You see that the spike raster has more spikes and the subthreshold voltage graph is crossing that threshold more often. And as we decrease the input we can see that the neuron's activity slows and eventually turns off completely.