Periodicities in the rate of on-demand electrical stimulation of the mesencephalic reticular formation to maintain wakefulness

Abstract

This study tested the hypothesis that fundamental rhythms such as the circadian and polycyclic sleep-wake cycles and the REM sleep cycle persist in animals maintained in constant wakefulness for up to 7 days. Cats prepared for chronic monitoring of electroencephalographic activity and brain stimulation were placed on an “on demand” schedule of reticular stimulation to maintain continuous wakefulness. Electrical pulses were delivered to the midbrain automatically each time slow-waves developed in the cortical EEG tracing. The rate of this stimulation in successive minute intervals was plotted for periods up to 7 days and submitted to time series analysis. Spectral and complex demodulation analyses revealed periodic activity in the rate of reticular stimulation required to maintain continuous wakefulness. Peaks in spectral estimates of the data corresponded closely to the reported cycle lengths of the circadian and polycyclic sleep-wake cycles and the REM sleep cycle. Complex demodulation analysis indicated that the frequency of these latter two cycles may drift over time. These data offer evidence that the tendency to sleep is modulated in the cat by at least three periodic factors during prolonged wakefulness.