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The human sleep-wake cycle is regulated by two processes which act primarily in opposition to consolidate sleep and wake (Borbély, 1982). Process S reflects the homeostatic accumulation and dissipation of sleep drive across wake and sleep, respectively, while Process C reflects the endogenous circadian modulation of alertness, promoting wake during the biological day and sleep during the biological night (Borbély, 1982). During the waking day, the circadian signal for alertness peaks during a 2-3 hr window of minimal sleep propensity prior to the evening onset of melatonin secretion, described as the wake maintenance zone (WMZ; Dijk et al., 1992;

Introduction Many sleep and circadian studies require participants to adhere to structured sleep-wake schedules designed to stabilize sleep outcomes and circadian phase prior to in-laboratory testing. The effectiveness of this approach has not been rigorously evaluated, however. We therefore investigated the differences between participants' unstructured and structured sleep over a three-week interval. Methods Twenty-three healthy young adults completed three weeks of sleep monitoring, including one week of unstructured sleep and two weeks of structured sleep with consistent bed and wake times. Circadian phase was assessed via salivary dim light melatonin onset (DLMO) during both the unstructured and structured sleep episodes. Results Compared to their unstructured sleep schedule, participants' bed-and wake times were significantly earlier in their structured sleep, by 34 ± 44 mins (M ± SD) and 44 ± 41 mins, respectively. During structured sleep, circadian phase was earlier in 65% of participants (40 ± 32 mins) and was later in 35% (41 ± 25 mins) compared to unstructured sleep but did not change at the group level. While structured sleep reduced night-tonight variability in sleep timing and sleep duration, and improved the alignment (phase angle) between sleep onset and circadian phase in the most poorly aligned individuals (DLMO < 1h or > 3h before sleep onset time; 25% of our sample), sleep duration and quality were unchanged. Conclusion Our results show adherence to a structured sleep schedule results in more regular sleep timing, and improved alignment between sleep and circadian timing for those individuals

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A. Basic Sleep Science VI. Learning, Memory, Cognition is attributable to sleep or the intervening nocturnal period (i.e., a circadian effect). Methods: Participants included 39 young adults between the ages of 18 -29. The protocol included spending two nights in the laboratory. After an adaptation night, participants were randomized into either a sleep deprivation condition (29 consecutive hours awake; n = 20) or a sleep condition (8-hour sleep opportunity; n = 19). The encoding portion of the memory scenes task occurred prior to the experimental manipulation, whereas, the recognition portion occurred during the subsequent morning. We conducted a 2 (condition: sleep, deprivation) x 2 (valence: negative, neutral) x 2 (scene component: object, background) mixed ANOVA on overall recognition.Results: There was a main effect of condition and scene component, and a significant two-way interaction between valence and scene component. The three-way interaction was not significant. Results revealed that negative objects were better remembered compared to both neutral objects and background images, but that this was true across both experimental conditions. Conclusion: The current study replicated the emotional memory trade-off observed in previous studies. Specifically, participants who experienced an intervening period of sleep between encoding and recognition trials were better able to remember negative components of scenes, relative to neutral components. The emotional memory tradeoff, however, was not specific to participants in the sleep condition. Similar recognition rates for negative components were observed among acutely sleep-deprived participants. While specific explanations for these results are unknown, these findings may be related to circadian effects and/or the impact of acute stress (i.e., sleep deprivation) on selective memory consolidation.