Pacing of behavioral and electroencephalographic events.

Time characteristics of lateral-hypothalamic self-stimulation were analyzed in rats using point process statistics. Inter-barpressing interval distributions were usually unimodal and asymmetrical and resembled shifted exponential distribution, i.e. bar-pressings seem to be performed more or less randomly over time. When self-stimulation was made ineffective for several seconds after stimulation, the probability of bar-pressing increased gradually, i.e. the brain seems to posses a system generating time intervals, which tend to reach certain predetermined values. When fixed rations (1:2–1:5) between rewarded and unrewarded bar-pressing were introduced, the animals followed certain patterns of alternation of inter-bar-pressing intervals of different duration. The mean inter-bar-pressing intervals remained at ratio 1:2 similar to those, when all reactions were rewarded, they decreased gradually at rations 1:3 to 1:5, i.e. the decrease of rewarding rate under one third to one half of the initial value is compensated by an increase of bar-pressing rate. Alternation of EEG alpha and non-alpha periods in human subjects with closed eyes was analyzed as a realization of an alternating random point process without and with feedback. The distribution of alpha periods was in the majority of cases of shifted exponential type and their incidence increased when feedback was used. The results are explained by means of a hypothesis about two alternating discrete states of the brain that correspond to particular levels of consciousness.