Rapid-Eye-Movement-Sleep (REM) Associated Enhancement of Working Memory Performance after a Daytime Nap

Pharmacokinetics, safety, and efficacy of daridorexant in Japanese subjects: Results from phase 1 and 2 studies

Daridorexant is a dual orexin receptor antagonist for the treatment of insomnia. We report results from the first two randomised, double-blind clinical studies of daridorexant in Japanese subjects. In the Phase 1 study, daridorexant (10, 25, 50 mg) or placebo were administered in the morning for 4 days in 24 young (mean age 26.9 years) and 24 older (mean age 69.7 years) healthy Japanese adults. Daridorexant reached a peak plasma concentration within 1.0 h across every dose and age group. For all doses, the mean plasma concentration of daridorexant showed a similar change between the age groups. Exposure parameters increased dose-dependently with minimal/no accumulation upon repeated dosing. The terminal half-life was ~8 h. In the Phase 2, four-period, four-way crossover study, 47 Japanese subjects (mean age 50.4 years) with insomnia disorder were randomised to receive four treatments (daridorexant 10, 25, 50 mg, placebo) during four treatment periods, each consisting of two treatment nights (5-12 day washout between treatment periods). Subjects continued their fourth treatment for 12 further days. A statistically significant dose-response relationship (multiple-comparison procedure-modelling, p < 0.0001) was found in the reduction of polysomnography-measured wake after sleep onset (WASO; primary endpoint) and latency to persistent sleep (secondary endpoint) from baseline to days 1/2. Statistically significant dose-response relationships were also observed for secondary subjective endpoints from baseline to days 1/2 (sWASO, latency to sleep onset). All daridorexant doses were well tolerated, with no treatment discontinuations and no next-morning residual effects. These results supported further investigation of daridorexant in Japanese patients with insomnia disorder.

Excessive daytime napping independently associated with decreased insulin sensitivity in cross-sectional study - Hyogo Sleep Cardio-Autonomic Atherosclerosis cohort study

Background

Although excessive daytime napping has been shown to be involved in diabetes occurrence, its impact on insulin secretion and sensitivity has not been elucidated. It is speculated that excessive napping disrupts the sleep-wake rhythm and increases sympathetic nerve activity during the day, resulting in decreased insulin sensitivity, which may be a mechanism leading to development of diabetes. We previously conducted a cross-sectional study that showed an association of autonomic dysfunction with decreased insulin sensitivity, though involvement of autonomic function in the association between napping and insulin sensitivity remained unclear. Furthermore, the effects of napping used to supplement to short nighttime sleep on insulin secretion and sensitivity are also unknown. In the present cross-sectional study, we examined the relationships of daytime nap duration and autonomic function with insulin secretion and sensitivity in 436 subjects enrolled in the Hyogo Sleep Cardio-Autonomic Atherosclerosis (HSCAA) Cohort Study who underwent a 75-g oral glucose tolerance test (75-g OGTT), after excluding those already diagnosed with diabetes.

Methods

Daytime nap duration was objectively measured using actigraphy, with the subjects divided into the short (≤1 hour) and long (>1 hour) nap groups. Insulin secretion and sensitivity were determined using 75-g OGTT findings. Standard deviation of normal to normal R-R interval (SDNN), a measure of autonomic function, was also determined based on heart rate variability. Subgroup analysis was performed for the associations of napping with insulin secretion and sensitivity, with the results stratified by nighttime sleep duration of less or greater than six hours.

Results

Subjects in the long nap group exhibited lower insulin sensitivity parameters (QUICKI: β=-0.135, p<0.01; Matsuda index: β=-0.119, p<0.05) independent of other clinical factors. In contrast, no associations with insulin secretion were found in either group. Furthermore, the association of long nap duration with insulin sensitivity was not confounded by SDNN. Specific subgroup analyses revealed more prominent associations of long nap habit with lower insulin sensitivity in subjects with a short nighttime sleep time (β=-0.137, p<0.05).

Conclusion

Long daytime nap duration may be a potential risk factor for decreased insulin sensitivity.

Effect of homeostatic pressure and circadian arousal on the storage and executive components of working memory: Evidence from EEG power spectrum

Diurnal fluctuations in working memory (WM) performance, characterized by task-specific peaks and troughs, are likely attributed to the differential regulation of WM subcomponents by interactions between circadian and homeostatic processes. The current study aimed to investigate the independent effects of circadian and homeostatic processes on the storage and executive subcomponents of WM. We assessed the change in frontal-midline theta (FMT) power supporting WM executive component and posterior alpha/beta power supporting WM storage during N-back tasks in the morning, midafternoon with and without a nap from 31 healthy adults. The results suggested that when the accumulated sleep homeostasis was alleviated in the midafternoon by a daytime nap, higher ACC, less number of omissions, and a stronger increase in FMT power from the no nap to nap conditions. Compared to the morning, a stronger decrease in posterior alpha power, and posterior beta power (only in the 3-back task), was observed in the no-nap condition because of circadian arousal regulation. These findings suggest that the circadian process primarily influences the storage aspect of WM supported by posterior alpha and beta activity, while sleep homeostasis has a greater impact on the execution aspect supported by FMT activity.

Relationship between self-reported sleep and cognitive function: a specification curve analysis

The relationship between self-reported sleep and cognitive function is complex; it is unclear whether self-reported sleep is a robust correlate of people's cognitive function. We address this gap by using a comprehensive large-scale dataset (N = 1054) coupled with a novel modeling approach, specification curve analysis (SCA), to test the association between self-reported sleep and cognitive function. The results of the SCA showed robust correlations between self-reported sleep and cognitive function, with poorer sleep associated with worse cognitive function. Furthermore, the correlations between sleep components and cognitive function were heterogeneous, with differences emerging across cognitive measures and domains. Specifically, daytime dysfunction was associated with the strongest effect on subjective cognitive function, whereas sleep duration and sleep efficiency had the strongest effect on objective cognitive function. Therefore, the relationship between self-reported sleep and cognition depends largely on what and how cognitive function is measured. Our findings guide measurement and domain selection for future research on the role of sleep in cognitive function.

Decoding information about cognitive health from the brainwaves of sleep

Sleep electroencephalogram (EEG) signals likely encode brain health information that may identify individuals at high risk for age-related brain diseases. Here, we evaluate the correlation of a previously proposed brain age biomarker, the "brain age index" (BAI), with cognitive test scores and use machine learning to develop and validate a series of new sleep EEG-based indices, termed "sleep cognitive indices" (SCIs), that are directly optimized to correlate with specific cognitive scores. Three overarching cognitive processes were examined: total, fluid (a measure of cognitive processes involved in reasoning-based problem solving and susceptible to aging and neuropathology), and crystallized cognition (a measure of cognitive processes involved in applying acquired knowledge toward problem-solving). We show that SCI decoded information about total cognition (Pearson's r = 0.37) and fluid cognition (Pearson's r = 0.56), while BAI correlated only with crystallized cognition (Pearson's r = - 0.25). Overall, these sleep EEG-derived biomarkers may provide accessible and clinically meaningful indicators of neurocognitive health.

A brief nap during an acute stressor improves negative affect

Overnight sleep can reduce perceived stress, and improve associated cognitive disruptions and negative affect after an acute stressor. Whether a brief nap can also bestow these benefits in a non-sleep-restricted population is currently unknown. In this study that used a between-subjects design, stress was triggered by administering a modified Trier Social Stress Test to two groups of participants (nap [n = 29], wake [n = 41]). All participants were instructed they would give a speech during the study but the topic would be withheld until later, and then completed a math task. After a 40-min break in which participants watched a neutral video or took a nap monitored with electroencephalography, stress was reinforced by presenting the speech topics and giving participants a 10-min preparation period. Next, instead of giving a speech, the study ended and participants were debriefed. Negative affect, perceived stress and working memory were measured at multiple time points before and after the break. Both groups showed lower perceived stress and improved working memory after the break than before, but a nap did not confer additional benefits for perceived stress or working memory beyond taking a break. However, the nap group exhibited lower negative affect after the break than the wake group, and only the nap group showed a reduction in negative affect compared with initial negative affect levels. These results indicate a nap can improve negative emotions accompanying a stressor to a greater extent than taking a break, and suggest that brief naps may be a useful way to improve mood while experiencing an acute stressor.

Understanding the roles of central and autonomic activity during sleep in the improvement of working memory and episodic memory

The last decade has seen significant progress in identifying sleep mechanisms that support cognition. Most of these studies focus on the link between electrophysiological events of the central nervous system during sleep and improvements in different cognitive domains, while the dynamic shifts of the autonomic nervous system across sleep have been largely overlooked. Recent studies, however, have identified significant contributions of autonomic inputs during sleep to cognition. Yet, there remain considerable gaps in understanding how central and autonomic systems work together during sleep to facilitate cognitive improvement. In this article we examine the evidence for the independent and interactive roles of central and autonomic activities during sleep and wake in cognitive processing. We specifically focus on the prefrontal-subcortical structures supporting working memory and mechanisms underlying the formation of hippocampal-dependent episodic memory. Our Slow Oscillation Switch Model identifies separate and competing underlying mechanisms supporting the two memory domains at the synaptic, systems, and behavioral levels. We propose that sleep is a competitive arena in which both memory domains vie for limited resources, experimentally demonstrated when boosting one system leads to a functional trade-off in electrophysiological and behavioral outcomes. As these findings inevitably lead to further questions, we suggest areas of future research to better understand how the brain and body interact to support a wide range of cognitive domains during a single sleep episode.

Systematic review and meta-analyses on the effects of afternoon napping on cognition

Naps are increasingly considered a means to boost cognitive performance. We quantified the cognitive effects of napping in 60 samples from 54 studies. 52 samples evaluated memory. We first evaluated effect sizes for all tests together, before separately assessing their effects on memory, vigilance, speed of processing and executive function. We next examined whether nap effects were moderated by study features of age, nap length, nap start time, habituality and prior sleep restriction. Naps showed significant benefits for the total aggregate of cognitive tests (Cohen's d = 0.379, CI₉₅ = 0.296-0.462). Significant domain specific effects were present for declarative (Cohen's d = 0.376, CI₉₅ = 0.269-0.482) and procedural memory (Cohen's d = 0.494, CI₉₅ = 0.301-0.686), vigilance (Cohen's d = 0.610, CI₉₅ = 0.291-0.929) and speed of processing (Cohen's d = 0.211, CI₉₅ = 0.052-0.369). There were no significant moderation effects of any of the study features. Nap effects were of comparable magnitude across subgroups of each of the 5 moderators (Q values = 0.009 to 8.572, p values > 0.116). Afternoon naps have a small to medium benefit over multiple cognitive tests. These effects transcend age, nap duration and tentatively, habituality and prior nocturnal sleep.

Effects of an afternoon nap on sustained attention and working memory: The role of physiological arousal and sleep variables

Taking a short midday nap has been associated with higher alertness and better cognitive task performance. Yet, the mechanisms associated with nap-dependent performance enhancement are unclear. The current study was conducted to explore the impact of physiological arousal during cognitive task and sleep architecture during a pre-task nap on post-nap behavioral outcomes. A within-subjects design (N = 18) was employed, in which participants either took a nap or remained awake for 40 min during the post-lunch period. The psychomotor vigilance test (PVT) and n-back task were administered to assess sustained attention and working memory, respectively, with each task including one block of easy trials and one block of difficult trials. Results showed that a short midday nap improved sustained attention but not working memory. In addition, a midday nap induced lower physiological arousal during the performance on both cognitive tasks, with relatively higher delta and lower beta activity. The relative power of theta and alpha were positively correlated with performance on the easy PVT, whereas the alpha power was negatively correlated with performance on the difficult PVT, and the theta power was negatively correlated with reaction speed in the n-back task regardless of the task difficulty. Meanwhile, the shorter total sleep time and longer time of wake after sleep onset were associated with the faster overall reaction speed in PVT easy trials. These findings suggested that both changes in physiological arousal and sleep variables might account for changes in task performance after a short midday nap.

Effects of Multisession Prefrontal Transcranial Direct Current Stimulation on Long-term Memory and Working Memory in Older Adults

Transcranial direct current stimulation (tDCS) is a noninvasive form of electrical brain stimulation popularly used to augment the effects of working memory (WM) training. Although success has been mixed, some studies report enhancements in WM performance persisting days, weeks, or even months that are actually more reminiscent of consolidation effects typically observed in the long-term memory (LTM) domain, rather than WM improvements per se. Although tDCS has been often reported to enhance both WM and LTM, these effects have never been directly compared within the same study. However, given their considerable neural and behavioral overlap, this is a timely comparison to make. This study reports results from a multisession intervention in older adults comparing active and sham tDCS over the left dorsolateral pFC during training on both an n-back WM task and a word learning LTM task. We found strong and robust effects on LTM, but mixed effects on WM that only emerged for those with lower baseline ability. Importantly, mediation analyses showed an indirect effect of tDCS on WM that was mediated by improvements in consolidation. We conclude that tDCS over the left dorsolateral pFC can be used as an effective intervention to foster long-term learning and memory consolidation in aging, which can manifest in performance improvements across multiple memory domains.

Assessment of the cognitive function in adult Egyptian patients with obstructive sleep apnea using the Montreal Cognitive Assessment: a retrospective large-scale study

STUDY OBJECTIVES

Sleep apnea is a chronic disorder associated with multiple recognized comorbidities. Only a few studies focus on evaluating the cognitive profile in patients diagnosed with sleep apnea. The aim of the study was to assess the cognitive functions in this population using the Montreal Cognitive Assessment.

METHODS

The study cohort was 1,445 adult patients who were referred for overnight polysomnography, 764 cases and 681 healthy controls. All participants' clinical data and comorbidities were taken, and they all performed overnight polysomnography and Montreal Cognitive Assessment.

RESULTS

A significantly higher proportion (57.5%) of sleep apnea groups were males; 15.7% were illiterate compared to the non-sleep apnea group. Hypertension and diabetes mellitus were significantly more prevalent among studied patients with sleep apnea, and the mean total score for the Montreal Cognitive Assessment scale was significantly lower among those with sleep apnea at P < .001. Those with no sleep apnea showed a significantly higher function in all attributes compared to patients with sleep apnea-namely, language, orientation, abstraction, naming, attention, and recall (P < .05).

CONCLUSIONS

Logistic regression analysis was conducted to investigate predictors for occurrence of cognitive impairment (Montreal Cognitive Assessment score < 26) among the studied sample (n = 1,445). The overall model was significant at P < .001. Variables that showed significance in univariate analysis were entered in the model. Significant predictors for cognitive impairment were being male, older age, diabetic, hypertensive, and with a lower level of education and having sleep apnea.

CITATION

Mekky JF, Yousof S, Elsayed I, Elsemelawy R, Mahmoud H, Elweshahi H. Assessment of the cognitive functions in adult Egyptian patients with obstructive sleep apnea using the Montreal Cognitive Assessment: a retrospective large-scale study. J Clin Sleep Med. 2022;18(3):721-729.

Links between the brain and body during sleep: implications for memory processing

Sleep is intimately related to memory processes. The established view is that the transformation of experiences into long-term memories is linked to sleep-related CNS function. However, there is increasing evidence that the autonomic nervous system (ANS), long recognized to modulate cognition during waking, can impact memory processing during sleep. Here, we review human research that examines the role of autonomic activity and sleep in memory formation. We argue that autonomic activity during sleep may set the stage for the CNS dynamics associated with sleep and memory stability and integration. Further, we consider how the link between ANS activity and polysomnographic markers of sleep may help elucidate both healthy and pathological cognitive aging in humans.

Structural Model of Napping Motivation Among Chinese College Students Based on Self-Rating: Evidence from an Exploratory Factor Analysis

PURPOSE

Previous epidemiological and psychological studies have assessed the effects of napping on individual performance and health. However, these studies did not distinguish between spontaneous and passive napping due to sleep disorders. Therefore, this study aimed to explore the potential motivation for napping among Chinese college students and to assess the relationship between different nap motivations and sleep.

PATIENTS AND METHODS

This cross-sectional study was conducted at a university in Shanghai in March 2021 using convenience sampling. A total of 564 Chinese college students with self-reported napping habits participated in this study. Exploratory factor analysis (EFA) was employed to analyze 34 self-rated motivations for napping to derive a potential structural model of napping motivation. Correlation and multiple linear regression analyses were performed to determine the influence of nap motivation on sleep behavior.

RESULTS

Chinese college students mainly take naps to reduce fatigue, usually in the form of frequent and long naps (6.25 ± 1.24 days; 64.62 ± 23.70 min). A structural model of nap motivation named the I-DREAM model was proposed, consisting of six factors: restorative, induced, mindful, appetitive, dysregulative, and exercise naps. There were also sex differences in nap motivation, as women preferred restorative naps and appetitive naps, while men preferred exercise naps (p < 0.01, p < 0.05). Furthermore, there was a significant correlation between nap motivation on nap duration, frequency and nighttime sleep quality (R² = 2.70-18.9%).

CONCLUSION

The proposed I-DREAM model implies that there are population differences in napping motivation. Different motivations also have different relationships with napping patterns and nighttime sleep. In understanding the relationship between naps and health status, nap motivation may be an extremely important influencing factor.

Competitive dynamics underlie cognitive improvements during sleep

Sleep facilitates both long-term episodic memory consolidation and short-term working memory functioning. However, the mechanism by which the sleeping brain performs both complex feats and which sleep features are associated with these processes remain unclear. Using a pharmacological approach, we demonstrate that long-term and working memory are served by distinct offline neural mechanisms and that these mechanisms are mutually antagonistic. We propose a sleep switch model in which the brain toggles between the two memory processes via a complex interaction at the synaptic, systems, and mechanistic level with implications for research on cognitive disturbances observed in neurodegenerative disorders such as Alzheimer’s and Parkinson's disease, both of which involve the decline of sleep.

We provide evidence that human sleep is a competitive arena in which cognitive domains vie for limited resources. Using pharmacology and effective connectivity analysis, we demonstrate that long-term memory and working memory are served by distinct offline neural mechanisms that are mutually antagonistic. Specifically, we administered zolpidem to increase central sigma activity and demonstrated targeted suppression of autonomic vagal activity. With effective connectivity, we determined the central activity has greater causal influence over autonomic activity, and the magnitude of this influence during sleep produced a behavioral trade-off between offline long-term and working memory processing. These findings suggest a sleep switch mechanism that toggles between central sigma-dependent long-term memory and autonomic vagal-dependent working memory processing.

Post-training stimulation of the right dorsolateral prefrontal cortex impairs working memory training performance

Research investigating transcranial direct current stimulation (tDCS) to enhance cognitive training augments both our understanding of its long-term effects on cognitive plasticity as well as potential applications to strengthen cognitive interventions. Previous work has demonstrated enhancement of working memory training while applying concurrent tDCS to the dorsolateral prefrontal cortex (DLPFC). However, the optimal stimulation parameters are still unknown. For example, the timing of tDCS delivery has been shown to be an influential variable that can interact with task learning. In the present study, we used tDCS to target the right DLPFC while participants trained on a visuospatial working memory task. We sought to compare the relative efficacy of online stimulation delivered during training to offline stimulation delivered either immediately before or afterwards. We were unable to replicate previously demonstrated benefits of online stimulation; however, we did find evidence that offline stimulation delivered after training can actually be detrimental to training performance relative to sham. We interpret our results in light of evidence suggesting a role of the right DLPFC in promoting memory interference, and conclude that while tDCS may be a promising tool to influence the results of cognitive training, more research and an abundance of caution are needed before fully endorsing its use for cognitive enhancement. This work suggests that effects can vary substantially in magnitude and direction between studies, and may be heavily dependent on a variety of intervention protocol parameters such as the timing and location of stimulation delivery, about which our understanding is still nascent.

Sleep fragmentation and working memory in healthy adults

Introduction

Sleep is essential for performing cognitive function in humans. We have hypothesized that sleep fragmentation compared to sleep efficiency may have a negative impact on the working memory.

Material and Methods

Twenty-eight healthy adults (18 males and 10 females; mean age 27.8±15.5 years) were enrolled in this study. We measured the total sleep time (TST), sleep efficiency, %stage wakefulness (W), %stage rapid eye movement (REM), %stage N1, %stage N2, %stage N3, wake after sleep onset (WASO), and arousal index using polysomnography. Working memory, executive function, and sustained attention of three domains of cognitive function were evaluated with the number of back task (N-back task), Wisconsin card sorting test (WCST), and continuous performance test-identical pairs (CPT-IP), respectively.

Results

The percentage of correct answers on the 2-back task was significantly correlated with %stage REM, %stage N1, and %stage N2 (%stage REM: r=0.505, p=0.006; %stage N1: r=-0.637, p<0.001; %stage N2: r=0.670, p<0.001), and multiple regression analysis including the stepwise forward selection method revealed that %stage N2 was the most significant factor (%stage N2: β=0.670, p<0.001). The percentage of correct answers on the 2-back task was also significantly correlated with TST, sleep efficiency, WASO, and arousal index (TST: r=0.492, p=0.008; sleep efficiency: r=0.622, p<0.001; WASO: r=-0.721, p<0.001; arousal index: r=-0.656, p<0.001), and WASO was the significant factor (β=-2.086, p=0.007). The WCST category achievement and CPT-IP d-prime score were correlated with none of the sleep variables.

Conclusion

Increased WASO and a decrease in %stage N2 were associated with worse working memory.

The protective effect of daytime sleep on planning and risk-related decision-making in emerging adults

We assessed the effect of a daytime sleep opportunity on planning and risk-related decision-making in emerging adults using multiple neurobehavioral assessments. A total of 136 healthy emerging adults (20.0 ± 1.5 years), 65% female, performed the Risky-Gains Task and the Tower of London test twice. Between these assessments, they were randomized to either have a sleep opportunity monitored by polysomnography (Sleep group, n = 101) or to stay awake (Wake group, n = 35). During Test 2, in comparison to the Sleep group, the Wake group showed increased sleepiness, worse planning ability and more decrease in reaction times when selecting risky choices. Changes in Tower of London test steps used and Risky-Gains Task response time correlated with the number of central and frontal fast sleep spindles, respectively. These results indicate that among emerging adults who commonly have poor sleep patterns, a daytime sleep opportunity was related to better planning ability, better psychomotor vigilance and stable response speeds in risk-related decision-making. Changes in planning and risk-related decision-making correlated with the number of sleep spindles during the nap, supporting a specific role for sleep in modulating planning and potentially other higher-order cognitive functions.

Autonomic Activity during a Daytime Nap Facilitates Working Memory Improvement

Recent investigations have implicated the parasympathetic branch of the autonomic nervous system in higher-order executive functions. These actions are purported to occur through autonomic nervous system's modulation of the pFC, with parasympathetic activity during wake associated with working memory (WM) ability. Compared with wake, sleep is a period with substantially greater parasympathetic tone. Recent work has reported that sleep may also contribute to improvement in WM. Here, we examined the role of cardiac parasympathetic activity during sleep on WM improvement in healthy young adults. Participants were tested in an operation span task in the morning and evening, and during the intertest period, participants experienced either a nap or wake. We measured high-frequency heart rate variability as an index of cardiac, parasympathetic activity during both wake and sleep. Participants showed the expected boost in parasympathetic activity during nap, compared with wake. Furthermore, parasympathetic activity during sleep, but not wake, was significantly correlated with WM improvement. Together, these results indicate that the natural boost in parasympathetic activity during sleep may benefit gains in prefrontal executive function in young adults. We present a conceptual model illustrating the interaction between sleep, autonomic activity, and prefrontal brain function and highlight open research questions that will facilitate understanding of the factors that contribute to executive abilities in young adults as well as in cognitive aging.

Autonomic/central coupling benefits working memory in healthy young adults

Working memory (WM) is an executive function that can improve with training. However, the precise mechanism for this improvement is not known. Studies have shown greater WM gains after a period of sleep than a similar period of wake, and correlations between WM improvement and slow wave activity (SWA; 0.5-1 Hz) during slow wave sleep (SWS). A different body of literature has suggested an important role for autonomic activity during wake for WM. A recent study from our group reported that the temporal coupling of Autonomic/CentralEvents (ACEs) during sleep was associated with memory consolidation. We found that heart rate bursts (HR bursts) during non-rapid eye movement (NREM) sleep are accompanied by increases in SWA and sigma (12-15 Hz) power, as well as increases in the high-frequency (HF) component of the RR interval, reflecting vagal rebound. In addition, ACEs predict long-term, episodic memory improvement. Building on these previous results, we examined whether ACEs also contribute to gains in WM. We tested 104 young adults in an operation span task (OSPAN) in the morning and evening, with either a nap (n = 53; with electroencephalography (EEG) and electrocardiography (ECG)) or wake (n = 51) between testing sessions. We identified HR bursts in the ECG and replicated the increases in SWA and sigma prior to peak of the HR burst, as well as vagal rebound after the peak. Furthermore, we showed sleep-dependent WM improvement, which was predicted by ACE activity. Using regression analyses, we discovered that significantly more variance in WM improvement could be explained with ACE variables than with overall sleep activity not time-locked with ECG. These results provide the first evidence that coordinated autonomic and central events play a significant role in sleep-related WM improvement and implicate the potential of autonomic interventions during sleep for cognitive enhancement.

The fluctuations of metabotropic glutamate receptor subtype 5 (mGluR5) in the amygdala in fear conditioning model of male Wistar rats following sleep deprivation, reverse circadian and napping

Sleep is involved in metabolic system, mental health and cognitive functions. Evidence shows that sleep deprivation (SD) negatively affects mental health and impairs cognitive functions, including learning and memory. Furthermore, the metabotropic glutamate receptor subtype 5 (mGluR5) is a metabolic biomarker, which is affected by various conditions, including stress, sleep deprivation, and cognitive and psychiatric disorders. In this research, we investigated the effect of SD and reverse circadian (RC), and two models of napping (continuous and non-continuous) combined with SD or RC on fear-conditioning memory, anxiety-like behavior and mGluR5 fluctuations in the amygdala. 64 male Wistar rats were used in this study. The water box apparatus was used to induce SD/RC for 48 h, and fear-conditioning memory apparatus was used to assess fear memory. The results showed, fear-conditioning memory was impaired following SD and RC, especially in contextual stage. However, anxiety-like behavior was increased. Furthermore, mGluR5 was increased in the left amygdala more than the right amygdala. Additionally, continuous napping significantly improved fear-conditioning memory, especially freezing behavior. In conclusion, following SD and RC, fear-conditioning memory in contextual stage is more vulnerable than in auditory stage. Furthermore, increase in anxiety-like behavior is related to increase in the activity of left amygdala and mGluR5 receptors.

Effects of REM sleep during a daytime nap on emotional perception in individuals with and without depression

BACKGROUND

It has been theoretically proposed that alteration in sleep physiology may contribute to the development of biased emotional processing featured in depression. The current study investigated the role of sleep and especially REM in modulating perception of emotional faces in depressed versus non-depressed individuals using a napping paradigm.

METHODS

Forty-six individuals with major depressive disorder and 66 age- and education-matched healthy controls completed an emotional face perception task before and after random assignment to one of the three intention-to-treat (ITT) conditions, namely 30-min-nap, 90-min-nap and wake. To delineate the effects of REM, as-treated (30-min-nap, 90-min-REM-nap, 90-min-noREM-nap and wake) analyses were also conducted.

RESULTS

Repeated measures multivariate analysis of covariance (MANCOVA) showed a significant Time *Group *Condition interaction on angry faces for both analyses of ITT (p = .017) and AT (p = .027). Pairwise comparison with Bonferroni corrections revealed a significant increase in the intensity rating of angry faces only after 90-min-REM-nap in the depressed group. Correlational analyses convergingly showed that the increase of intensity rating of angry faces was associated with the proportion of REM sleep in the depressed group, p = .035.

LIMITATIONS

The observed effect of REM sleep during daytime napping may not represent the effect of nighttime REM sleep in depression.

CONCLUSIONS

We provide the first evidence of the association of daytime sleep, particularly REM sleep, with a more negative perception of angry faces exclusively in individuals with depression. The differentiated impact of sleep observed may contribute to the development of altered emotional processing in depression.

The coupling of short sleep duration and high sleep need predicts riskier decision making

Objective: To examine how risk-related decision making might be associated with habitual sleep variables, including sleep variability, sleep duration and perceived sleep need in young adults cross-sectionally and longitudinally. Design: 166 participants completed a 7-day protocol with sleep and risk-related decision-making measures at baseline (T1) and 12 months later (T2). Results: Habitual short sleep duration (averaging < 6 h nightly) was identified in 11.0% in our sample. After controlling for baseline demographic factors and risk-taking measures, self-reported sleep need at T1 interacted with habitual short sleep in predicting risk taking at follow-up (F_8,139=9.575, adjusted R²=.431, p<.001). T1 greater perceived sleep need predicted more risk taking among short sleepers, but decreased risk taking among normal sleepers at T2. Variable sleep timing was cross-sectionally correlated with making more Risky choices at baseline and fewer Safe choices after loss at follow up. Conclusions: Young adults with variable sleep timing and those with short sleep duration coupled with high perceived sleep need were more likely to take risks. The moderating effects of perceived sleep need suggest that individual differences may alter the impact of sleep loss and hence should be measured and accounted for in future studies.

Remembering to Forget: A Dual Role for Sleep Oscillations in Memory Consolidation and Forgetting

It has been known since the time of patient H. M. and Karl Lashley's equipotentiality studies that the hippocampus and cortex serve mnestic functions. Current memory models maintain that these two brain structures accomplish unique, but interactive, memory functions. Specifically, most modeling suggests that memories are rapidly acquired during waking experience by the hippocampus, before being later consolidated into the cortex for long-term storage. Sleep has been shown to be critical for the transfer and consolidation of memories in the cortex. Like memory consolidation, a role for sleep in adaptive forgetting has both historical precedent, as Francis Crick suggested in 1983 that sleep was for "reverse-learning," and recent empirical support. In this article I review the evidence indicating that the same brain activity involved in sleep replay associated memory consolidation is responsible for sleep-dependent forgetting. In reviewing the literature, it became clear that both a cellular mechanism for systems consolidation and an agreed upon general, as well as cellular, mechanism for sleep-dependent forgetting is seldom discussed or is lacking. I advocate here for a candidate cellular systems consolidation mechanism wherein changes in calcium kinetics and the activation of consolidative signaling cascades arise from the triple phase locking of non-rapid eye movement sleep (NREMS) slow oscillation, sleep spindle and sharp-wave ripple rhythms. I go on to speculatively consider several sleep stage specific forgetting mechanisms and conclude by discussing a notional function of NREM-rapid eye movement sleep (REMS) cycling. The discussed model argues that the cyclical organization of sleep functions to first lay down and edit and then stabilize and integrate engrams. All things considered, it is increasingly clear that hallmark sleep stage rhythms, including several NREMS oscillations and the REMS hippocampal theta rhythm, serve the dual function of enabling simultaneous memory consolidation and adaptive forgetting. Specifically, the same sleep rhythms that consolidate new memories, in the cortex and hippocampus, simultaneously organize the adaptive forgetting of older memories in these brain regions.

Does sleep duration, napping, and social jetlag predict hemoglobin A1c among college students with type 1 diabetes mellitus?

AIMS

The first aim examined the relationship between sleep behaviors (duration, napping, and social jetlag) and hemoglobin A1c (HbA1c) among emerging young adults (EYAs) with T1DM between 18 and 25 years old, who are living on a college campus. The second aim characterized the gender differences in glucose management, sleep behaviors, caffeine intake, and nighttime technology.

METHODS

A cross-sectional study of eligible participants used a convenience sample of eligible participants. Using Research Electronic Data Capture (REDCap), participants completed surveys about diabetes management, caffeine intake, nighttime technology use, and sleep-related behaviors. Data were analyzed using correlation and multiple linear regression to predict HbA1c from sleep behaviors, adjusting for covariates.

RESULTS

Participants (N = 76) average years with T1DM was 10.25 ± 5.70. Compared to females, males had a longer sleep duration lower HbA1c levels. HbA1c levels were negatively correlated with weekday sleep (r = -0.24, p = 0.03) and positively correlated with napping (r = 0.34, p = 0.003). After adjusting for covariates, participants who napped had a higher HbA1c level (β = 0.74, p = 0.03) compared with non-nappers.

CONCLUSIONS

Higher HbA1c levels were found among EYAs with T1DM in college who were nappers and had a longer sleep duration. Modifying sleep behaviors may be an appropriate target to improve glycemic control.

The Relationship Between Midday Napping And Neurocognitive Function in Early Adolescents

Objective/Background: The impact of midday napping on neurocognitive function in adolescents has not been well established. This study aimed to investigate the relationship between self-reported midday-napping behaviors and neurocognitive function in early adolescents. Participants: The sample was comprised of 363 early adolescents (12.00 ± 0.38 years old) from Jintan, China. Methods: Midday napping, nighttime sleep duration, and sleep quality were measured by self-reported questionnaires. Neurocognitive function was measured by the Penn Computerized Neurocognitive Battery (accuracy and reaction times). Generalized linear regression was used to analyze the relationships. Results: Sixty-four percent of our sample took more than 3 naps per week, and 70.11% reported nap durations of over 30 min. Participants with higher frequencies or longer durations of midday napping reported significantly better nighttime sleep quality (p < 0.05). Adjusted models showed that frequent nappers (5-7d/week) were significantly associated with heightened accuracy on tasks that measured sustained attention and nonverbal reasoning and faster reaction times on spatial memory compared with other frequency groups (ps < 0.05). For napping duration subgroups, early adolescents who took naps of any length were estimated to have faster reaction speeds on the sustained attention task compared with participants who never napped (ps < 0.05). However, only nappers with a moderate duration (31-60 min) tended to achieve both faster speeds (β = -38.28, p = 0.02) and better accuracy (β = 3.90, p = 0.04) on the sustained attention task. Conclusions: Our findings suggest that there is an association between habitual midday napping and neurocognitive function in early adolescents, especially in China, where midday napping is a cultural practice.

Risk factors for Age-related Macular Degeneration in a Greek population: The Thessaloniki Eye Study

PURPOSE

To assess the association of potential risk factors with early and late age-related macular degeneration (AMD) in the Thessaloniki Eye Study (TES) population Design: Population-based, cross-sectional study of subjects over age of 60 living in Thessaloniki, Greece Methods: Subjects without any AMD features and subjects with early and late AMD (neovascular AMD or geographic atrophy) were identified in the TES cohort using standardized procedures and masked grading of stereo color fundus photos. Demographic, lifestyle, systemic and other ophthalmic covariates were also collected during a detailed examination process. Their association with AMD was investigated using univariate and multivariate adjusted logistic regression models.

RESULTS

Among the 2108 participants with gradable photos, the grading process identified 1204 subjects with no AMD, 848 subjects with early AMD, and 56 subjects with late AMD (24 with geographic atrophy and 32 with neovascular AMD). In multivariate analysis, compared to no AMD, late AMD was positively associated with older age (OR:1.16; 95%CI:1.10-1.22 per year of age), current smoking (smoking vs. never smoking, OR:2.34; 95%CI:1.12-4.90), prior cataract surgery (cataract surgery vs. no cataract surgery OR:2.06; 95%CI:0.96-4.40), marital status (divorced/separated vs. married, OR:3.10; 95%CI:1.08-8.93) and with 60% lower odds when sleeping in the afternoon (yes vs. no, OR:0.40; 95%CI:0.22-0.72). Early AMD was positively associated with older age (OR: 1.03; 95%CI:1.01-1.05 per year of age) and negatively with higher pulse pressure (OR:0.99; 95%CI:0.98-0.99 per mmHg).

CONCLUSIONS

In TES, apart for well-known risk factors for AMD like age, smoking, and cataract surgery, two novel behavioral risk factors for prevalent late AMD were suggested. Sleeping in the afternoon was associated with 60% decreased odds for late AMD and 67% decreased odds for neovascular AMD. Being divorced/separated compared to married was associated with 3-fold higher odds for late AMD. Large longitudinal population-based studies will be necessary to further establish the potential late AMD risk effects of these two novel factors, to demonstrate potential implications of underlying pathogenetic mechanisms, and to explore preventive measures and therapeutic targets.

Beneficial effects of a daytime nap on verbal memory in adolescents

This study aimed to examine the sleep-dependent memory consolidation of verbal declarative memory in Chinese adolescents in a naturalistic experimental setting. Thirty-nine healthy boarding school students (ages 15-18, 70% female) were randomized to either a one-hour afternoon nap or wake group between the baseline and the retest sessions of three verbal declarative memory tasks: a Prose Stories Recall task, a Word Pair Associates task, and Rey Auditory Verbal Learning Test. Results showed that the nap group performed better than the no-nap group on both the Prose Stories Recall task and the Word Pair Associates task, but not on list learning. Our findings suggest that napping is beneficial to verbal declarative memory in adolescents, providing ecologically-valid empirical support for the sleep-dependent memory consolidation hypothesis using a napping paradigm in participants' naturalistic habitat. Our results demonstrate the potential importance of napping as a practical mnemonic intervention/compensatory strategy for student populations.

Effects of Afternoon Nap Deprivation on Adult Habitual Nappers' Inhibition Functions

Multiple studies have established the effects of afternoon naps on cognition. However, relatively few studies have investigated the domain of executive functions. Moreover, the effects of napping on inhibition are far from conclusive. The present study employed adult habitual nappers to investigate the effects of afternoon nap deprivation on response-based inhibition assessed by a Go/No-go task and stimulus-based inhibition assessed by a Flanker task and on alertness assessed by a psychomotor vigilance test (PVT) and the Karolinska Sleepiness Scale (KSS). The results showed that afternoon nap deprivation significantly decreased participants' accuracy and reaction speed for the Go/No-go task but not for the Flanker task. In addition, participants' alertness was significantly impaired after nap deprivation in terms of increased subjective sleepiness and worse PVT performance. Task-specific effects of napping on inhibition were demonstrated. The implications of the results are discussed.

Sex-Related Differences in the Effects of Sleep Habits on Verbal and Visuospatial Working Memory

Poor sleep quality negatively affects memory performance, and working memory in particular. We investigated sleep habits related to sleep quality including sleep duration, daytime nap duration, nap frequency, and dream content recall frequency (DCRF). Declarative working memory can be subdivided into verbal working memory (VWM) and visuospatial working memory (VSWM). We hypothesized that sleep habits would have different effects on VWM and VSWM. To our knowledge, our study is the first to investigate differences between VWM and VSWM related to daytime nap duration, nap frequency, and DCRF. Furthermore, we tested the hypothesis that the effects of duration and frequency of daytime naps and DCRF on VWM and VSWM differed according to sex. We assessed 779 healthy right-handed individuals (434 males and 345 females; mean age: 20.7 ± 1.8 years) using a digit span forward and backward VWM task, a forward and backward VSWM task, and sleep habits scales. A correlation analysis was used to test the relationships between VWM capacity (VWMC) and VSWM capacity (VSWMC) scores and sleep duration, nap duration, nap frequency, and DCRF. Furthermore, multiple regression analyses were conducted to identify factors associated with VWMC and VSWMC scores and to identify sex-related differences. We found significant positive correlations between VSWMC and nap duration and DCRF, and between VWMC and sleep duration in all subjects. Furthermore, we found that working memory capacity (WMC) was positively correlated with nap duration in males and with sleep duration in females, and DCRF was positively correlated with VSWMC in females. Our finding of sex-related differences in the effects of sleep habits on WMC has not been reported previously. The associations between WMC and sleep habits differed according to sex because of differences in the underlying neural correlates of VWM and VSWM, and effectiveness of the sleep habits in males and females.