Firing variability in cat association cortex during sleep and wakefulness

Abstract

Summary Spontaneous discharges of single neurons in the association (middle suprasylvian) cortex of the cat were studied during natural sleep and wakefulness. Changes in the temporal pattern of neuronal discharges associated with the behavioral shifts were evaluated by the variability in discharge sequences. In individual neurons, changes in discharge rate were always accompanied by an altered temporal pattern characteristic of a particular state. In arousal and REM sleep, these cortical neurons showed considerably higher activity, and the temporal sequences tended to be random but were typically more regular than in other behavioral states. In intermediate sleep with spindle bursts, or in deep sleep with high voltage slow waves in EEG, neuronal activity was reduced and accompanied by irregular discharges. The pattern was then characterized by clustered discharges alternating with long periods of silence. These changes in the degree of variability in the discharge sequences were evaluated numerically in terms of the coefficient of variation, which was smaller in arousal and REM sleep, with means of 1.11 and 1.09 respectively. However, values shifted higher in the progress of behavioral states from wakefulness (¯X = 1.27), to intermediate sleep (¯X = 1.47) and to deep sleep (¯X = 1.56). The temporal arrangement of discharge sequences varied from unit to unit during intermediate and deep sleep. Autocorrelation analysis revealed that during these sleep phases some temporal patterns deviated from randomness and that the discharges then occurred at preferred intervals relative to each other. Occasionally the likelihood of their occurrence varied with time in a periodic and cyclic manner.