Spontaneous Activity of Hippocampal Cells in Various Physiological States

摘要

Time-series of interspike intervals from intracellular recordings in spontaneously firing hippocampal CA1 cells from rabbits are investigated. Slice preparations in three different experimental conditions are tested: immature from young rbbits up to seven postnatal days, mature from adult rabbits, and bicuculline-treated. also from adult rabbits. Bicuculline is a convulsion inducer through inhibition blockade. Preparations from immature rabbits show the dynamical behavior of a Poissonian process, while those from mature animals are periodically firing with additional Gaussian noise. Bicuculline-treated slices from mature animals show again the same dynamics as from immature, namely Poissonian noise. In addition to the Poissonian Processes in some immature and bicuculline preparations large proportions of bursts occur. We correct these bursts away and find better agreement with the null hypothesis of Poissonian processes. In some cases the frequent bursts even lead to signs of short time predictability, which is assumed to characterize deterministic chaos. However, we can also remove this predictability by burst correction. To test for stochasticity we use the Kolomogorov-Smirnov test which is especially well suited for small data sets like in the present experiments. Explicit graphical analysis of the distribution function provides useful qualitative comparison. The predictability tests for nonlinearity are applied to original data and its Gauss-scaled surrogates to test for any linearly correlated process. Conclusions for the dynamical interplay between excitatory and inhibitory networks are drawn.