Figure 1.

Action potential and spike trains. The left panel shows the voltage drop recorded across a neuron’s cell membrane. The voltage fluctuates stochastically, but tends to drift upward, and when it rises to a threshold level (dashed line) the neuron fires an action potential, after which it returns to a resting state; the neuron then responds to inputs that will again make its voltage drift upward toward the threshold. This is often modeled as drifting Brownian motion that results from excitatory and inhibitory Poisson process inputs (Tuckwell 1988; Gerstein and Mandelbrot 1964). The right panel shows spike trains recorded from 4 neurons repeatedly across 3 experimental replications, known as trials. The spike times are irregular within trials, and there is substantial variation across trials, and across neurons.