Effects of the SK channel blocker apamin on G(f). A, Typical effect of apamin on the fADP and mAHP, illustrated by the V_m trajectory after a single spike elicited by a 3 ms square current pulse added to I_DC slightly below the rheobase. B, ISI histograms for a typical L2–3 PN stimulated with 5 ms exponential-filtered noise (σ_I = 0.18 nA) before and after wash in of apamin (100 nm). In each case, r₀ was held at ∼10 Hz by adjusting I_DC. C, Average G(f) in L2–3 PNs (n = 7) in control solution and in apamin, with r₀ controlled at 10 Hz. D, Apamin increased the fraction of spikes in bursts. E, Apamin reduced the primary resonance frequency. F, Apamin reduced the strength of the primary resonance. G, Frequency-dependent subthreshold impedance magnitude (n = 4), determined by injection of chirp current (0–30 Hz in 60 s) with V_m set just below spike threshold by addition of I_DC. Values are normalized by the impedance magnitude at 1 Hz. *p < 0.05.