Figure 4. Differential contribution of added and shifted spikes to the histogram peak.

A: Experimental paradigm. A set of 45 different episodes of fluctuating noise with or without immersed aEPSCs were injected in neurons repeatedly (N=110 repetitions).

B: Examples of 4 (out of 45) episodes of the injected currents and firing rate responses. Gray traces of noise without aEPSCs are superimposed on black traces with immersed aEPSCs, vertical dashed lines show aEPSC onset. Horizontal dashed line shows DC current (0.255 nA) used to achieve target firing rate of 4 to 6 imp/sec.

Histograms show firing rate responses to the injected currents with (black) or without (gray) immersed EPSCs, and their difference (colored histograms). Horizontal bars on the bottom show measuring windows corresponding to the duration of aEPSC/histogram peak (dark blue, 0–35 ms), and the period of decreased firing (magenta, 35–100 ms), same as in Fig. 3B. For each of the 45 difference histograms, number of spikes was measured in these windows.

C: Spike count in the peak (0–35 ms) vs. spike count after the peak (35–100 ms) of 45 difference histograms. Red symbols (n=7) show cases when spikes were “shifted” to produce histogram peak: spike number increase in the histogram peak was balanced by the decrease after the peak. Green symbols (n=7) show cases in which the histogram peak was produced by additional, “new” spikes: spike count was increased in the peak but did not change after the peak. Blue symbols (n=4) show cases with both added and shifted spikes. Open symbols show remaining (n=27) cases. Arrows indicate data for 4 episodes from B.