We calculate the instantaneous firing rate of a stochastic integrate-and-fire neuron driven by an arbitrary time-dependent signal up to second order in the signal amplitude. For cosine signals. this weakly nonlinear theory reveals: (i) a frequency-dependent change of the time-averaged firing rate reminiscent of frequency locking in deterministic oscillators; (ii) higher harmonics in t... https://www.smokeaers.shop/product-category/backpacks/