Psychosocial Stress Before a Nap Increases Sleep Latency and Decreases Early Slow-Wave Activity

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

No effect of vocabulary reactivation in older adults

Quality of memory and sleep declines with age. However, the mechanistic interactions underlying the memory function of sleep in older adults are still unknown. It is widely assumed that the beneficial effect of sleep on memory relies on reactivation during Non-rapid eye movement (NREM) sleep. Targeting these reactivations by cue re-exposure reliably improves memory in younger participants. Here we tested whether the memory reactivation mechanism during sleep is still functional in old age. For this purpose we applied targeted memory reactivation (TMR) during NREM sleep in healthy adults over 60 years and directly compared the results to a group of younger participants. In contrast to young participants, older adults’ memories did not generally benefit from TMR during NREM sleep. On the oscillatory level, successful reactivation of Dutch words during sleep did not reveal the characteristic increases in early theta activity and frontal spindle activity previously reported in young participants. Only in a later time window, theta oscillations were similarly increased during successful cueing for both young and older participants. Our results suggest that reactivating memories during sleep might be possible also in older adults. However at the same time this reactivation by TMR does not necessarily lead to a strengthening of memories across sleep as in younger participants. Further studies are needed to examine a potential loss of functionality of memory reactivation for consolidation during sleep in older adults

Sleep-Directed Hypnosis Improves Subjective Sleep Quality but not Extinction Memory After Exposure to Analog Trauma

Background Evidence-based treatments of posttraumatic stress disorder (PTSD) aim to promote fear extinction learning. Post-learning sleep, particularly slow wave sleep (SWS), promotes memory consolidation and recall. Thus, boosting SWS might strengthen extinction recall. The current study investigated whether sleep-directed hypnosis designed to increase SWS and sleep quality improves extinction recall and reduces analog PTSD symptoms. Method In two subsamples (remote/laboratory), 211 healthy individuals underwent fear conditioning with a traumatic film clip. On the next evening, they underwent extinction training. Thereafter, the experimental group received sleep-directed hypnosis, whereas the control group listened to a control text. Extinction recall and generalization and film-related intrusions and rumination were assessed on the following morning. Results Subjective sleep quality declined following exposure to an aversive film. No group differences were found in SWS though exploratory analyses indicated less rapid eye movement sleep after hypnosis. After hypnosis, the experimental group reported improved sleep quality, whereas the control group showed a further deterioration. Hypnosis had no effects on extinction retention and generalization nor on analog intrusions and rumination. Conclusion The current results indicate that sleep-directed hypnosis may be beneficial for improving subjective sleep quality after trauma but not for enhancing extinction memory and reducing analog PTSD symptoms

Modulating influences of memory strength and sensitivity of the retrieval test on the detectability of the sleep consolidation effect

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

Lunar cycle effects on sleep and the file drawer problem

Contains fulltext : 135956.pdf (Publisher’s version ) (Open Access)Popular beliefs about the influence of the full moon on humans exist, although no solid evidence has so far confirmed these ideas [1]. Cajochen et al.[2] recently presented fascinating data on lunar cycle effects on human sleep. However, in a re-analysis of sleep electroencephalography (EEG) data in three large samples, we were unable to replicate their findings. In addition, we identified further mostly unpublished null findings, suggesting that the conflicting results might be an example of a publication bias (i.e., the file drawer problem).2 p

Improving sleep and cognition in young adults and the elderly

Sleep, particularly slow-wave sleep (SWS), is a critical factor for health and well-being. Furthermore, SWS provides a brain state supportive for the spontaneous reactivation, stabilization, and long-term storage of declarative memories. Sleep architecture changes across lifespan and the parallel nascent impairments in SWS, cognition, and other health aspects hint at a deteriorating interplay between these three factors. Thus, a profound understanding of the nature of the relationship between sleep and memory in young and old human participants is fundamental in successfully finding new ways of memory- and sleep-related interventions. The first study was designed to clarify the role of induced reactivations for memory consolidation during sleep in different sleep stages. While reactivation during SWS has been reported to improve memory and stabilize it against future interference, the role of reactivations during rapid eye movement (REM) sleep is less clear. On the one hand, spontaneous reactivations, functionally associated with memory performance, exist in REM sleep. On the other hand, declarative memories have proven stable after sleep which is free from REM sleep. As induction of memory reactivations during REM sleep failed to shelter memory from interference, we concluded that spontaneous reactivations which appear during REM sleep do not contribute to the stabilization of declarative memories. The second study tested hypnosis as a tool to objectively improve sleep as its efficacy had previously been proven for subjective sleep measures. Our data was the first to confirm this effectiveness on an objective level by revealing a specific increase in SWS and slow-wave activity (SWA) amounts after hypnotic suggestions to deepen sleep in younger adults. Contrary to expectations, SWS-enriched sleep by hypnosis did not improve memory consolidation. As sleep improvements are particularly critical in advanced age, but generalizations from results of younger adults to older adults are not valid, we replicated the study in the third manuscript with older adults. Hypnotic suggestions again proved effective in increasing the amounts of SWS and SWA. Cognition associated with prefrontal activity benefited from this increase. Results for memory consolidation were less pronounced, but promising. Together, data indicated an age-independent effect of hypnotic suggestions on SWS enrichment. They further supported the assumption that SWS restores prefrontal cortex (PFC) functionality and benefits consolidation. As an outlook, hypnotic suggestions to increase SWS might be combined with induced memory reactivations during this sleep stage to further improve memory consolidation processes in the elderly. Together, the manuscripts in this thesis investigate the relationship between sleep and memory on a theoretical and a practical level. One study clarifies the role of REM sleep reactivations for memory stability and two studies confirm the effectiveness of hypnotic suggestions to objectively increase SWS and SWA independent of age. Owing to these insights, the recommendation of hypnosis as a non-pharmacological technique to improve sleep depth, subjective sleep quality and to positively influence cognitive abilities in older adults can be based on objective and experimentally controlled data. There is great potential inherent in this line of research, which paves the way to positively influence senescence processes in major areas of life and health. Schlaf, vor allem Tiefschlaf (SWS), trägt entscheidend zu Gesundheit und Wohlbefinden bei. Darüber hinaus unterstützt Tiefschlaf spontane Reaktivierungen, sowie die Stabilisierung und Langzeitspeicherung von deklarativen Gedächtnisinhalten. Die Schlafstruktur verändert sich über die Lebensspanne hinweg und die dabei parallel auftretenden Beeinträchtigungen des Tiefschlafs, der Kognition und anderer Gesundheitsaspekte deuten auf ein zerstörerisches Zusammenspiel zwischen diesen drei Faktoren hin. Daher ist ein tiefgreifendes Verständnis des Wesens der Beziehung zwischen Schlaf und Gedächtnis bei jüngeren und älteren Menschen grundlegend, um erfolgreich neue Interventionsmöglichkeiten zu finden. Die erste Studie wurde konzipiert, um die Rolle induzierter Gedächtnisreaktivierungen auf die Konsolidierung im Schlaf während verschiedener Schlafstufen zu klären. Einerseits treten spontane Reaktivierungen, die funktional für die Gedächtnisleistung sind, auch im REM (Rapid Eye Movement) Schlaf auf. Andererseits zeigte sich auch nach einem Schlaf ohne REM Anteil eine Stabilisierung des deklarativen Gedächtnisses. Da die Induktion von Gedächtnisreaktivierungen während des REM Schlafs das Gedächtnis nicht vor Interferenz zu schützen vermochte, schlossen wir auf einen mangelnden Beitrag der Reaktivierungen im REM Schlaf zur Gedächtnisstabilisierung deklarativer Inhalte. Die zweite Studie testete Hypnose als Methode zur Verbesserung des Schlafs, da dessen Wirksamkeit zuvor für subjektive Schlafmaße bestätigt werden konnte. Unsere Daten bestätigten diese Wirksamkeit erstmals an objektiven Maßen, indem sie einen spezifischen Anstieg im Tiefschlafanteil und der Tiefschlafaktivität (SWA) nach einer hypnotischen Suggestion „tiefer zu schlafen“ bei jüngeren Erwachsenen aufwiesen. Entgegen der Erwartung verbesserte der durch Hypnose vertiefte Schlaf die Gedächtniskonsolidierung nicht. Da Verbesserungen des Schlafs besonders im fortgeschrittenen Alter relevant sind, aber Generalisierungen der Ergebnisse von jüngeren auf ältere Erwachsene nicht valide sind, replizierten wir die Studie mit älteren Erwachsenen im dritten Manuskript. Die hypnotischen Suggestionen erwiesen sich abermals als förderlich für SWS und SWA. Des Weiteren war die Leistung bei präfrontal abhängigen Gedächtnisaufgaben verbessert. Die Effekte für die Gedächtniskonsolidierung waren geringer, aber vielversprechend. Insgesamt deuteten die Daten auf einen altersunabhängigen Effekt der hypnotischen Suggestionen auf die Tiefschlaferweiterung hin. Sie unterstützen außerdem die Annahme, dass Tiefschlaf präfrontale Areale funktional restauriert und der Gedächtniskonsolidierung zu Gute kommt. Für künftige Studien wird vorgeschlagen, hypnotische Suggestionen zur Vertiefung des Schlafs mit der Induktion von Gedächtnisreaktivierungen während dieser Schlafstufe zu kombinieren, um die Gedächtniskonsolidierung bei älteren Erwachsenen weiter zu verbessern. Zusammenfassend untersuchen die drei Manuskripte dieser Dissertation die Beziehung zwischen Schlaf und Gedächtnis auf der theoretischen und der praktischen Ebene. Eine Studie klärt die Rolle von Reaktivierungen im REM Schlaf für die Festigung deklarativer Gedächtnisinhalte und zwei Studien bezeugen die altersunabhängige Wirksamkeit hypnotischer Suggestionen zur Erhöhung von SWS und SWA anhand polysomnographischer Daten. Dank dieser Erkenntnisse kann die Empfehlung, Hypnose als nichtmedikamentöse Technik zu nutzen, um den Schlaf zu vertiefen, subjektive Schlafqualität zu erhöhen und kognitive Fähigkeiten bei älteren Erwachsenen positiv zu beeinflussen auf objektiv und experimentell kontrollierte Daten gestützt werden. Dieser Forschungssparte wohnt ein großes Potential inne, Altersprozesse in wesentlichen Bereichen des Lebens und der Gesundheit positiv zu beeinflussen

No evidence for memory decontextualization across one night of sleep

Sleep after learning strengthens memory consolidation. According to the active system consolidation hypothesis, sleep supports the integration of newly acquired memories into cortical knowledge networks, presumably accompanied by a process of decontextualization of the memory trace (i.e., a gradual loss of memory for the learning context). However, the availability of contextual information generally facilitates memory recall and studies on the interaction of sleep and context on memory retrieval have revealed inconsistent results. Here, we do not find any evidence for a role of sleep in the decontextualization of newly learned declarative memories. In two separate studies, 104 healthy young adults incidentally learned words associated with a context. After a 12 h retention interval filled with either sleep or wakefulness, recall (Experiment 1) or recognition (Experiment 2) was tested with the same or different context. Overall, memory retrieval was significantly improved when the learning context was reinstated, as compared to a different context. However, this context effect of memory was not modulated by sleep vs. wakefulness. These findings argue against a decontextualization of memories, at least across a single night of sleep.publishe

No effect of odor-induced memory reactivation during REM sleep on declarative memory stability

Memory reactivations in hippocampal brain areas are critically involved in memory consolidation processes during sleep. In particular, specific firing patterns of hippocampal place cells observed during learning are replayed during subsequent sleep and rest in rodents. In humans, experimentally inducing hippocampal memory reactivations during slow-wave sleep (but not during wakefulness) benefits consolidation and immediately stabilizes declarative memories against future interference. Importantly, spontaneous hippocampal replay activity can also be observed during rapid eye movement (REM) sleep and some authors have suggested that replay during REM sleep is related to processes of memory consolidation. However, the functional role of reactivations during REM sleep for memory stability is still unclear. Here, we reactivated memories during REM sleep and examined its consequences for the stability of declarative memories. After 3 h of early, slow-wave sleep (SWS) rich sleep, 16 healthy young adults learned a 2-D object location task in the presence of a contextual odor. During subsequent REM sleep, participants were either re-exposed to the odor or to an odorless vehicle, in a counterbalanced within subject design. Reactivation was followed by an interference learning task to probe memory stability after awakening. We show that odor-induced memory reactivation during REM sleep does not stabilize memories against future interference. We propose that the beneficial effect of reactivation during sleep on memory stability might be critically linked to processes characterizing SWS including, e.g., slow oscillatory activity, sleep spindles, or low cholinergic tone, which are required for a successful redistribution of memories from medial temporal lobe regions to neocortical long-term stores

Improving sleep and cognition by hypnotic suggestion in the elderly

Sleep quality markedly declines across the human lifespan. Particularly the amount of slow-wave sleep (SWS) decreases with age and this decrease is paralleled by a loss of cognitive functioning in the elderly. Here we show in healthy elderly females that the amount of SWS can be extended by a hypnotic suggestion "to sleep deeper" before sleep. In a placebo-controlled cross-over design, participants listened to hypnotic suggestions or a control tape before a midday nap while high density electroencephalography was recorded. After the hypnotic suggestion, we observed a 57% increase in SWS in females suggestible to hypnosis as compared to the control condition. Furthermore, left frontal slow-wave activity (SWA), characteristic for SWS, was significantly increased, followed by a significant improvement in prefrontal cognitive functioning after sleep. Our results suggest that hypnotic suggestions might be a successful alternative for widely-used sleep-enhancing medication to extend SWS and improve cognition in the elderly

Psychosocial Stress Before a Nap Increases Sleep Latency and Decreases Early Slow-Wave Activity

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