Biol. Cybern. 62, 495-502 (1990) Biological Cybernetics Springer-Verlag 1990 Recurring Discharge Patterns in Multiple Spike Trains II. Application in Forebrain Areas Related to Cardiac and Respiratory Control During Different Sleep-Waking States R. D. Frostig, R. C. Frysinger, and R. M. Harper Neuroscience Program, The Brain Research Institute, and Department of Anatomy, University of California at Los Angeles, Los Angeles, CA 90024-1763, USA Abstract. Simultaneously recorded spike trains were obtained using microwire bundles from unrestrained, drug-free cats during different sleep-waking states in forebrain areas associated with cardiac and respiratory activity. Cardiac and respiratory activity was simulta- neously recorded with the spike trains. We applied the recurring discharge patterns detection procedure de- scribed in a companion paper (Frostig et al. 1990) to the spike and cardiorespiratory trains. The pattern detection procedure was applied to detect only precise (in time and structure) recurring patterns. Recurring discharge patterns were detected in all simultaneously recorded groups. Recurring discharge patterns were composed of up to ten spikes per pattern and involved up to four simultaneously recorded spike trains. Fourty-two percent of the recurring patterns con- tained cardiac and/or respiratory events in addition to neuronal spikes. When patterns were compared over different sleep-waking states it was found the the same units produced different patterns in different states, that patterns were significantly more compact in time during quiet sleep, and that changes in the discharge rates accompanying changes in sleep-waking states were not correlated with changes in pattern rate. Introduction Functional interactions between simultaneously re- corded neurons are typically examined by the cross- correlation technique (Perkel et al. 1967), which is applied to pairs of spike trains, or by the "snowflake" technique (Perkel et al. 1975) which is applied on triples of spike trains. These techniques demonstrated that functional interactions between neighboring neurons can be altered by sensory stimulation (Frostig et al. 1983; Blum and Gerstein 1986) or physiological state (Frostig et al. 1984), may involve simultaneously more than one interaction (Frostig et al. 1984) and may be constituted of recurring discharge patterns that exhibit very long interspike delays (Abeles 1982; Abeles et al. 1983). Such recurring patterns recur with very low frequencies. However, such patterns may represent some meaningful repeated wave of activity between neurons and may involve more than pairs or triples of neurons. In order to characterize and quan- tify such recurring patterns we developed a procedure that detects such patterns. In a companion paper (Frostig et al. 1990) we describe such a procedure tuned to detect recurring discharge patterns between simul- taneously recorded spike trains. The procedure, which is based on an association measure rather than averag- ing, can detect repeating discharge patterns starting from recurring patterns in three spike trains and up to all recorded spike trains. By applying the pattern detection method, we aimed to: a) detect and charac- terize recurring discharge patterns b) study their relations to simultaneously recorded event trains and c) study how changes in sleep-waking states affect such patterns. We examined discharge patterns in the sponta- neous discharge of simultaneously recorded groups of neurons from forebrain areas during different sleep- waking states. Changes in sleep-waking state are ac- companied by conspicuous changes in the CNS. Spon- taneous discharge of single neurons of the somato- sensory cortex changes from irregular discharges to burst-pause patterns in quiet sleep (QS) (Evarts 1964). In the waking state (AW), neurons in the visual cortex fire more smoothly and at a lower rates compared with QS (Livingstone and Hubel 1981). During AW and during rapid eye movement sleep (REM), neurons in the gigantocellular field of the reticular system fire rapidly, but they rarely discharge during QS (Siegel et al. 1977). Neurons in the dorsal raphe fire more slowly in REM than in other states (McGinty and Harper 1976). Moreover, direct functional interactions between