Burst structure of single units and spike avalanches.

<p>(A) The distribution of log-interspike intervals during sleep for a representative example (rat 1, session 1) is bimodal demonstrating a fast spiking regime with long gaps (bursting). The distributions for individual pyramidal cells from the session are shown in gray and the population average is in blue. Interspike intervals < 50ms (red line) indicate that two spikes belong to the same burst event. (B) Single unit bursts are correlated in time to produce ‘spike avalanches’ with many units active in a short period of time. An avalanche is defined as a sequence of time bins with spikes from some cell in the ensemble flanked by empty time bins. An example of parsing the burst activity within an avalanche into a discrete sequence is shown below. The boxed sequence is a ‘large avalanche’ that contains a subsequence that is a length-4 match to the RUN sequence (in red). (C) Rank-frequency plots of spike avalanche sizes (blue, population average over sessions in bold) compared to ISI-randomized data (black, average over sessions in bold) show that large avalanches are more common in the observed data than expected at random (all p < 10⁻¹³, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0147708#pone.0147708.t002" target="_blank">Table 2</a>).