Effects of a short light-dark cycle on the sleep-wake patterns of the cat

The purpose of this study was to measure the effect of a short, 106 min, light-dark (LD) cycle on the sleep-wake (SW) patterns of the cat. Eight cats prepared for chronic sleep studies were observed with electrographic tracings for 48 hr on a regular 12:12 hr LD schedule and again after 2 weeks of adaptation to a 27 min light and 79 min dark schedule. Each 1 min of data was scored as either alert, drowsy, slow wave sleep (SWS) or REM sleep. The parameters studied were percent electrographic state, state epoch length, polycyclic SW cycle, and mean vigilance. The short LD cycle caused a significant increase in alert state accompanied by reductions in drowsy, SWS, and REM sleep states. Although the effect was more pronounced during lights-on intervals, the trend was also present in dark intervals. Alert episodes of about all lengths increased. There were decreases in longer episodes of the other three states and a tendency for shorter episodes to increase in number. Episodes of the polycyclic SW cycle did not tend to follow the short LD cycle. The mean length of both sleep and wake episodes increased rather than decreased. However, mean vigilance values increased toward wakefulness at or near the light interval. Analyses showed that both the amplitude and phase relationship of this increase was significantly related to the 27 min light interval in comparison to base-line data. It was hypothesized that both light-dark and dark-light transitions represent alerting cues to the cat. Differences between the SW response of the cat and the rat to LD cycles are discussed.