On modelling the variability of interspike intervals during epileptic unit activity

In spite of the fact that the participation of well defined ionic particles in generating convulsive unit discharges is established, there is a gap between the data on ionic movements and on first-order statistics of firing patterns. Our aim was to tight this gap by studying the effectiveness of functionally separated electrical conductances of membrane during the generation of consecutive interspike interval histograms (IIHs) of unitary discharges. On account of the non-stationarity of the process curve fitting analysis which based on the simple modifications of the integrate-and-fire model has been implemented in the sequential interspike interval histogram procedure (SIIH). The experimental data were recorded from cat cortex treated with 3-Aminopyridine (3-Ap) by glass microelectrodes during nembutal anesthesia. Assuming the normal distribution of input parameters it is concluded, that the efficiency of the fluctuations of the active spike-generating conductance gg and the passive diffusional conductance gl may increase during the generation of the unimodal IIHs and the first mode of the bimodal IIHs. The simple conductance coupling gl=gg + b may participate in gg activation, moreover, the reciprocally coupled mechanism gg=c/gl may be driven by gl activation (a, b, c are the coupling constants). A temporal separation of processes governed by gg or gl respectively was observed. The time-independent occurrences of the reciprocally coupled conductance processes may be involved in the unit activities represented by the prolonged IIHs and second modes of the bimodal IIHs.