[General statistical characteristics of the background firing in cat's cortical neurons during slow-wave sleep]

Background activity of 62 neurons in cat cerebral cortex was recorded in the state of slow-wave sleep for evaluation of the firing statistics. In according to their statistical characteristics neurons were subdivided in three groups. In the first group deviation from the Poisson process were comparatively small, and revealed as fragments of increased excitability following immediately after the refractory period. Second group demonstrated positive correlation of the neighbouring interspike intervals what was conditioned by the changes of the mean firing rate. In these neurons the number of spikes included into the bursts reduced after random permutation of the interspike intervals. The third group was characterized by the big number of spikes included into the bursts (> 15%), and number of bursts usually dropped down after random permutation. Some neurons of this group had constant interspike intervals within the bursts while in other units these intervals monotonically increased toward the end of the burst. Only limited number of neurons demonstrated maximums of the autocorrelation function corresponded to the frequency of the EEG delta activity.