One leaky integrate-and-fire neuron, step by step
Input
Reset
input current I[t]membrane U[t]threshold θoutput spike

Firing rate vs. input: where ReLU comes from

ReLU(I / θ), clipped at 1IF neuron (β = 1)LIF neuron

Each point: a neuron with threshold θ = 1 receives the same input current I on every step for T steps; the rate is spikes ÷ T. Simulated with reset by subtraction.