Cholinergic synaptic inputs to layer 4 reduce neuronal firing in RS cells. A, Top, mIPSC in layer 4 RS cell. Middle, Multiple overlaid trials showing neuronal activity evoked by 2 s depolarizing current step paired with light stimulation applied with a 500 ms delay (indicated by blue bar). Scale bar, 20 mV. Bottom, Raster plot showing timing of action potentials over multiple trials, for the same neuron. B, For the same cell as in A, peristimulus time histogram (PSTH) for paired (blue) and unpaired (gray) current steps. C, Average PSTH (n = 11 RS cells), normalized to the average firing frequency over a 500 ms window before light stimulation. Shaded areas denote SEM.