All-or-None Stochastic Fluctuations in the Processing of a Fixed Stimulus

<div><p>(A) Variability in sample spike trains evoked in area A1 by the same 15-ms stimulus, whose duration was close to ignition threshold (with <i>I</i>_neuromodul = −0.9 μA/cm²). Each of the twenty lines represents one trial. Note that the first peak is present on a majority of trials, while most of the variability affects the second peak.</p> <p>(B) Distribution of the mean firing rate in area A1 during the second peak (75–225 ms poststimulus), showing a bimodal distribution.</p> <p>(C) Mean local field potential in area A1, computed separately for trials that lead to ignition (firing peak > 40 spikes/s in the above time window) and for trials that did not (firing peak < 15 spikes/s). Note (1) the essentially identical stimulus-induced waves up to the sharp divergence about 110 ms poststimulus; and (2) the presence of a small but significant difference prior to the stimulus, which indicates that ignition is more likely to occur when stimulus presentation coincides with the depolarized phase of spontaneous ongoing oscillations.</p>