Our results demonstrate the effectiveness of hypnotic suggestions to specifically increase the amount and duration of slow wave sleep (SWS) in a midday nap using objective measures of sleep in young, healthy, suggestible females. Hypnotic suggestions might be a successful tool with a lower risk of adverse side effects than pharmacological treatments to extend SWS also in clinical and elderly populations.

No abstract

Sleep is vital for human health and wellbeing, and sleep disturbances are comorbid to many mental and physiological disorders. Music consistently improves subjective sleep quality, whereas results for objective sleep parameters diverge. These inconsistencies might be due to inter-individual differences. Here, 27 female subjects listened to either music or a control text before a 90 minutes nap in a within-subjects design. We show that music improved subjective sleep quality as compared to the text condition. In all participants, music resulted in a reduced amount of sleep stage N1 during the nap. In addition, music significantly increased the amount of slow-wave sleep (SWS) and increased the low/high frequency power ratio. However, these effects occurred only in participants with a low suggestibility index. We conclude that listening to music before a nap can improve subjective and objective sleep parameters in some participants.

No abstract

Emotionality can increase recall probability of memories as emotional information is highly relevant for future adaptive behavior. It has been proposed that memory processes acting during sleep selectively promote the consolidation of emotional memories, so that neutral memories no longer profit from sleep consolidation after learning. This appears as a selective effect of sleep for emotional memories. However, other factors contribute to the appearance of a consolidation benefit and influence this interpretation. Here we show that the strength of the memory trace before sleep and the sensitivity of the retrieval test after sleep are critical factors contributing to the detection of the benefit of sleep on memory for emotional and neutral stimuli. 228 subjects learned emotional and neutral pictures and completed a free recall after a 12-h retention interval of either sleep or wakefulness. We manipulated memory strength by including an immediate retrieval test before the retention interval in half of the participants. In addition, we varied the sensitivity of the retrieval test by including an interference learning task before retrieval testing in half of the participants. We show that a "selective" benefit of sleep for emotional memories only occurs in the condition with high memory strength. Furthermore, this "selective" benefit disappeared when we controlled for the memory strength before the retention interval and used a highly sensitive retrieval test. Our results indicate that although sleep benefits are more robust for emotional memories, neutral memories similarly profit from sleep after learning when more sensitive indicators are used. We conclude that whether sleep benefits on memory appear depends on several factors, including emotion, memory strength and sensitivity of the retrieval test.

While slow-wave sleep (SWS) is fundamental for maintaining health and well-being, it is typically reduced with stress or age. The authors have previously reported that hypnotic suggestions before sleep increased SWS duration and slow-wave activity (SWA) during a midday nap in hypnotizable younger and older women. To test generalizability, they investigated this effect across 8 hours nighttime sleep in 43 healthy young French-speaking subjects (19 males) of high and low hypnotizability. In accordance with their previous results, listening to hypnotic suggestions before sleep was followed by higher amounts of SWS in highly hypnotizable subjects and higher SWA power compared to a control condition. The effects were most pronounced at the beginning of the night. Further studies are needed to examine whether hypnotic suggestions can deepen sleep also above non-intervention nights. The findings provide a basis for the examination and potential application of hypnosis to improve sleep in clinical populations.

Magazine R549 470 sleep EEGs from 366 healthy participants in a light-controlled sleep laboratory (see Experimental Procedures in Supplemental Information, published with this article online). Lunar classes were defined as previously [2], with lunar class 1 representing full moon ± 4 nights, lunar class 2 covering the waxing and waning moon periods (full moon ± 5-9 nights) and lunar class 3 representing new moon (full moon ± 10-14 nights). In contrast to the results reported by Cajochen et al.[2], we did not find any evidence for an influence of lunar class on objective sleep parameters (all P >0.1, Table 1).Data set 2 was also recorded in the Max Planck Institute of Psychiatry; however, in contrast to the first sample this data set included 757 sleep EEGs of 29 volunteers each of whom slept for 13-60 consecutive nights in the sleep laboratory, i.e. across all phases of the lunar cycle. Also in this data set we were not able to replicate any of the findings by Cajochen et al.[2] (Table 1).Data set 3 represents a sample recruited at the University of Basel. It includes sleep EEGs of 870 young, healthy volunteers who slept at home. Again, there was no indication of a significant effect of the lunar cycle on sleep variables (Table 1). In addition, oscillatory activity during NREM sleep did not differ between lunar classes in this data set (Figure S1). In particular, no effects were observed in the EEG delta band as reported by Cajochen et al. [2].In sum, we were not able to replicate the large effects of lunar cycle on sleep EEG reported by Cajochen et al. [2] in three large samples consisting of 470, 757 and 870 sleep recordings: none of the variables that were reported to be affected by lunar cycle by Cajochen et al. yielded significant results in any of our samples. This also holds for alternative analyses with outlier exclusion and interaction analyses. Please note that for other sleep variables that were not significant in the data of Cajochen et al., some small and inconsistent effects and interactions with lunar class emerged (for details and discussion, see Supplemental Discussion).Even though exact values of power calculations have to be interpreted with caution due to differences in research designs, in our three samples we can exclude

Sleep disturbances are an important risk factor for stress-related diseases such as burnout or depression. In particular, slow-wave activity (SWA) during sleep might be eminently relevant for optimal maintenance of mental health and cognitive functioning. In spite of the clinical importance and the pertinence of stress-related processes in everyday life, the physiological mechanisms of the association between stress, sleep, and cognition are not well-understood. In the present study, we carefully mapped the time course of the influence of a psychosocial stressor on sleep architecture and sleep-related oscillations during a midday nap. We induced stress using a psychosocial laboratory stressor, the Montreal Imaging Stress Task, vs. a neutral control task. Afterward, participants were allowed to take a 90-min nap (n = 20) or stayed awake (n = 19) and cortisol was measured via saliva samples. We hypothesized that stress would decrease sleep efficiency and SWA in a time-dependent manner, with impairing effects on cognitive functioning. Psychosocial stress resulted in increased cortisol levels, which were elevated throughout the study interval. In the nap group, psychosocial stress increased sleep latency, but had only minor effects on sleep architecture. Still, SWA in the first 30 min of sleep was significantly reduced, whereas alpha activity was enhanced. These effects vanished after approximately 30 min. No impairing effect on cognitive functioning occurred. Our results show that psychosocial stress before sleep has an impact on sleep latency and early SWA during sleep. In contrast to our hypothesis, the effects were rather small and short-lasting. Importantly, cognitive functioning was maintained. We conclude that the effects of psychosocial stress before a nap are possibly better compensated than previously believed.