  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.
