Adaptation allows more slowly rising current fluctuations to elicit spikes. A, Rasters of spike times evoked during the initial and final segment of a noise stimulus as in Figure 5, but with a different noise stimulus during each sweep. B, Example of spike-triggered average current (STA) for early (black line), old (blue line), and new spikes (red line). C, Change in the STA for early versus old spikes (blue) or early versus new spikes (red). Changes for the maximum slope of the STA (peak value of the first derivative), and amplitude of the negative and positive components of the STA for the new or old spikes relative to the early spikes were calculated by the following formulas: [(X_new − X_early)/X_early]*100% or [(X_old − X_early)/X_early]*100%, respectively (n = 5; *p < 0.01, paired t test).