The emergence of power-law distributions of inter-spike intervals characterizes status epilepticus induced by pilocarpine administration in rats

Objective. To ascertain the existence of power-law distributions of inter-spike intervals (ISI) occurring during the progression of status epilepticus (SE), so that the emergence of critical states could be reasonably hypothesized as being part of the intrinsic nature of the SE. Methods. Status epilepticus was induced by pilocarpine administration in post-natal 21-day rats (n=8). For each animal, 24 hours of EEG from the onset of the SE were analyzed according to the analytical procedure suggested by Clauset et al. (2009) which combines maximum-likelihood fitting methods with goodness-of-fit tests based on the Kolmogorov-Smirnov statistics and likelihood ratios. The analytical procedure was implemented by the freely available R software package 'poweRlaw'. Time of calculations was considerably shorten by the exploitation of High-Throughput Computing technology, a.k.a. Grid Computing technology. Results. The progression of the SE is characterized by the emergence of power-law correlations of ISI whose likelihood of occurrence increases the more the time from the onset of the SE elapses. Log-normal distribution of ISI is however widely represented. Additionally, undetermined distributions of ISI are represented as well, although confined within a restricted temporal window. The final stage of SE appears dominated only by power-law and log-normal distributions of ISI. Significance. The emergence of power-law correlations of ISI concretely supports the concept of the occurrence of critical states during the progression of SE. It is reasonably speculated, as a working hypothesis, that the occurrence of power-law distributions of ISI within the early stages of the SE could be a hallmark of the establishment of the route to epileptogenesis. Highlights • We ascertained the emergence of power-law correlations during the status epilepticus. • Log-normal correlations are however widely represented. • Undetermined correlations also occur, but limited to the first 14-18 hours. • Status epilepticus could evolve through the occurrence of criticalities.