Figure 3.

Exogenous melatonin has both direct and indirect effects on sleep. 1.5 mg surge sustained release at 1600 h daily for 8 days, recumbent, < 5 lux, 1600–0800 h, evaluated in constant routine. Mean sleep efficiency levels (% per hour: n = 8). The direct, sleep-facilitating effect of melatonin (left) is illustrated by a comparison between sleep efficiency profiles on the last day of melatonin treatment and sleep efficiency on the following washout day. Increased sleep efficiency (direct effect) is observed for the first 2–3 h during melatonin treatment. The circadian effect of melatonin on sleep (right) is shown by comparing the sleep efficiency on the washout day (the day after melatonin or placebo). On the washout day, placebo was administered to all participants. A shift in the distribution of sleep can be observed after melatonin treatment, with the major bout of sleep occurring earlier in the sleep opportunity. On the corresponding day after placebo, the major bout of sleep occurred later in the sleep opportunity, although an initial rise in sleep efficiency is noted at around the commencement of the sleep opportunity. With Permission from Rajaratnam et al. (70). *Significant difference between CR1 and CR2.