Age-related differences in sleep-based memory consolidation: A meta-analysis

Age-Related Changes in Sleep and Its Implications for Cognitive Decline in Aging Persons With Schizophrenia: A Critical Review

BACKGROUND AND HYPOTHESIS

Cognitive impairment is a core feature of schizophrenia that worsens with aging and interferes with quality of life. Recent work identifies sleep as an actionable target to alleviate cognitive deficits. Cardinal non-rapid eye movement (NREM) sleep oscillations such as sleep spindles and slow oscillations are critical for cognition. People living with schizophrenia (PLWS) and their first-degree relatives have a specific reduction in sleep spindles and an abnormality in their temporal coordination with slow oscillations that predict impaired memory consolidation. While NREM oscillatory activity is reduced in typical aging, it is not known how further disruption in these oscillations contributes to cognitive decline in older PLWS. Another understudied risk factor for cognitive deficits among older PLWS is obstructive sleep apnea (OSA) which may contribute to cognitive decline.

STUDY DESIGN

We conducted a narrative review to examine the published literature on aging, OSA, and NREM sleep oscillations in PLWS.

STUDY RESULTS

Spindles are propagated via thalamocortical feedback loops, and this circuitry shows abnormal hyperconnectivity in schizophrenia as revealed by structural and functional MRI studies. While the risk and severity of OSA increase with age, older PLWS are particularly vulnerable to OSA-related cognitive deficits because OSA is often underdiagnosed and undertreated, and OSA adds further damage to the circuitry that generates NREM sleep oscillations.

CONCLUSIONS

We highlight the critical need to study NREM sleep in older PWLS and propose that identifying and treating OSA in older PLWS will provide an avenue to potentially mitigate and prevent cognitive decline.

Age-Related Differences in Motor Skill Transfer with Brief Memory Reactivation

Motor memories can be strengthened through online practice and offline consolidation. Offline consolidation involves the stabilization of memory traces in post-practice periods. Following initial consolidation of a motor memory, subsequent practice of the motor skill can lead to reactivation and reconsolidation of the memory trace. The length of motor memory reactivation may influence motor learning outcomes; for example, brief, as opposed to long, practice of a previously learned motor skill appears to optimize intermanual transfer in healthy young adults. However, the influence of aging on reactivation-based motor learning has been scarcely explored. Here, the effects of brief and long motor memory reactivation schedules on the retention and intermanual transfer of a visuomotor tracing task are explored in healthy older adults. Forty older adults practiced a virtual star-tracing task either three ("brief reactivation") or ten ("long reactivation") times per session over a two-week period. Comparison with a previously reported group of younger adults revealed significant age-related differences in the effect of the motor memory reactivation schedule on the intermanual transfer of the motor task. In older adults, unlike younger adults, no significant between-group differences were found by practice condition in the speed, accuracy, or skill of intermanual task transfer. That is, motor task transfer in healthy younger, but not older, adults appears to benefit from brief memory reactivation. These results support the use of age-specific motor training approaches and may inform motor practice scheduling, with possible implications for physical rehabilitation, sport, and music.

Long-term associations between objective sleep quality and quantity and verbal memory performance in normal cognition and mild cognitive impairment

Introduction

Although the link between sleep and memory function is well established, associations between sleep macrostructure and memory function in normal cognition and Mild Cognitive Impairment remain unclear. We aimed to investigate the longitudinal associations of baseline objectively assessed sleep quality and duration, as well as time in bed, with verbal memory capacity over a 7-9 year period. Participants are a well-characterized subsample of 148 persons (mean age at baseline: 72.8 ± 6.7 years) from the Cretan Aging Cohort. Based on comprehensive neuropsychiatric and neuropsychological evaluation at baseline, participants were diagnosed with Mild Cognitive Impairment (MCI; n = 79) or found to be cognitively unimpaired (CNI; n = 69). Sleep quality/quantity was estimated from a 3-day consecutive actigraphy recording, whereas verbal memory capacity was examined using the Rey Auditory Verbal Learning Test (RAVLT) and the Greek Passage Memory Test at baseline and follow-up. Panel models were applied to the data using AMOS including several sociodemographic and clinical covariates.

Results

Sleep efficiency at baseline directly predicted subsequent memory performance in the total group (immediate passage recall: β = 0.266, p = 0.001; immediate word list recall: β = 0.172, p = 0.01; delayed passage retrieval: β = 0.214, p = 0.002) with the effects in Passage Memory reaching significance in both clinical groups. Wake after sleep onset time directly predicted follow-up immediate passage recall in the total sample (β = -0.211, p = 0.001) and in the MCI group (β = -0.235, p = 0.02). In the total sample, longer 24-h sleep duration was associated with reduced memory performance indirectly through increased sleep duration at follow-up (immediate passage recall: β = -0.045, p = 0.01; passage retention index: β = -0.051, p = 0.01; RAVLT-delayed recall: β = -0.048, p = 0.009; RAVLT-retention index:β = -0.066, p = 0.004). Similar indirect effects were found for baseline 24-h time in bed. Indirect effects of sleep duration/time in bed were found predominantly in the MCI group.

Discussion

Findings corroborate and expand previous work suggesting that poor sleep quality and long sleep duration predict worse memory function in elderly. Timely interventions to improve sleep could help prevent or delay age-related memory decline among non-demented elderly.

The Interactive Role of Sleep and Circadian Rhythms in Episodic Memory in Older Adults

Adequate sleep is essential for healthy physical, emotional, and cognitive functioning, including memory. However, sleep ability worsens with increasing age. Older adults on average have shorter sleep durations and more disrupted sleep compared with younger adults. Age-related sleep changes are thought to contribute to age-related deficits in episodic memory. Nonetheless, the nature of the relationship between sleep and episodic memory deficits in older adults is still unclear. Further complicating this relationship are age-related changes in circadian rhythms such as the shift in chronotype toward morningness and decreased circadian stability, which may influence memory abilities as well. Most sleep and cognitive aging studies do not account for circadian factors, making it unclear whether age-related and sleep-related episodic memory deficits are partly driven by interactions with circadian rhythms. This review will focus on age-related changes in sleep and circadian rhythms and evidence that these factors interact to affect episodic memory, specifically encoding and retrieval. Open questions, methodological considerations, and clinical implications for diagnosis and monitoring of age-related memory impairments are discussed.

Positive impact of sleep on recall of multiplication facts

This study tested the hypothesis that learning complex multiplication problems (e.g. 8 × 23 = 184) prior to sleep would benefit recall in adult participants compared with learning the problems prior to a period of wakefulness. This study used a within-participant design where all participants learnt complex multiplication problems in two conditions separated by one week. In one condition, learning was before bed (sleep learning condition) and in the other condition learning was in the morning (wake learning condition). In each condition, recall was tested approximately 10.5 h later. Data were collected online from 77 participants. In the subset of the sample with greater than or equal to 60% accuracy at the initial learning session (n = 37), the sleep learning condition participants had better recall compared with the wake learning condition. This equated to a moderate effect size, Cohen's d = 0.51. Regardless of initial levels of learning (n = 70) the same beneficial effect of sleep on recall was found with a small effect size, Cohen's d = 0.33. This study has identified a beneficial effect of learning prior to sleep on recall of complex multiplication problems compared with learning these problems during the daytime. Future research should explore whether similar effects are observed with children learning simple multiplication facts.

Behavioural sleep problems in children and adults with intellectual disabilities: An integrative literature review

BACKGROUND

People with intellectual disabilities are more likely to experience sleep problems, which can affect quality of life, physical health, mental health and well-being.

METHODS

An integrative literature review was conducted to investigate what is known about behavioural sleep disturbances in people with an intellectual disability. The search used the following databases: Scopus, PsycInfo and Cinahl, to find papers published since 2015.

RESULTS

Within intellectual disability research, sleep appears as a common issue due to its high prevalence, negative relationships with an individual's physical and mental health, their quality of life, and impact of sleep problems on family or carers. The growing evidence base appears to support the use of behavioural, lifestyle and pharmacological interventions to improve sleep in people with an intellectual disability.

CONCLUSION

A wide array of literature provides evidence that people with intellectual disabilities are affected by and need support with their sleep.

Factors associated with sleep quality in university students

To investigate factors associated with poor sleep quality. A cross-sectional study was conducted in 2019 with random sampling. Information on sleep was obtained using the Mini Sleep Questionnaire (MSQ). Independent variables included sociodemographic, behavioural, academic and psychological health characteristics. Adjusted analyzes were performed using Poisson regression. A total of 996 undergraduate students participated in the study. The poor sleep quality affected 23.1% of the sample (95%CI 20.5-25.9), ranging from 13.4% for those with little concern about violence in the neighbourhood to 36.5% for those with less social support. In the adjusted analysis, female sex [PR] 1.81; (95%CI 1.33-2.45), concern about violence in the neighbourhood [PR] 2.21; (95%CI 1.48-3.28), discrimination at university [PR] 1.42; (95%CI 1.08-1.86) and food insecurity [PR] 1.45; (95%CI 1.11-1.89) were associated with the presence of poor sleep quality, as well as having less social support and income and suffering psychological distress. The results highlight socioeconomic and mental health factors that affect sleep quality and demonstrate the need for reflection and interventions capable of minimizing this problem.

Subjective and objective sleep quality does not predict behavioural episodic foresight in younger or older adults

Episodic foresight refers to one's capacity to use imagined scenarios to guide future-directed behaviors. It is important in facilitating complex activities of daily living, such as managing finances. Broader literature shows that older adults perform more poorly on tests of episodic foresight relative to their younger counterparts. At the same time, age-related changes in sleep often contribute to age-related decline in other cognitive abilities known to support episodic foresight, such as memory. No study to date has tested whether sleep quality is associated with episodic foresight when it is measured behaviorally; or whether this relationship is moderated by age. To address this, in the present study healthy younger (n = 39) and older (n = 41) adults were asked to wear an actigraphy watch and self-report their sleep quality for seven nights. Participants then completed the virtual-week foresight task-a behavioral assessment of episodic foresight. Neither objective or subjective sleep quality predicted episodic foresight outcomes, and this was not moderated by age group. Bayesian analyses provided evidence in favour of the null hypotheses. These results suggest that sleep quality (at least in healthy adult populations) may not be linked to episodic foresight.

Understanding the Need for Sleep to Improve Cognition

The restorative function of sleep is shaped by its duration, timing, continuity, subjective quality, and efficiency. Current sleep recommendations specify only nocturnal duration and have been largely derived from sleep self-reports that can be imprecise and miss relevant details. Sleep duration, preferred timing, and ability to withstand sleep deprivation are heritable traits whose expression may change with age and affect the optimal sleep prescription for an individual. Prevailing societal norms and circumstances related to work and relationships interact to influence sleep opportunity and quality. The value of allocating time for sleep is revealed by the impact of its restriction on behavior, functional brain imaging, sleep macrostructure, and late-life cognition. Augmentation of sleep slow oscillations and spindles have been proposed for enhancing sleep quality, but they inconsistently achieve their goal. Crafting bespoke sleep recommendations could benefit from large-scale, longitudinal collection of objective sleep data integrated with behavioral and self-reported data.

Establishing a community pharmacy-based fall prevention service - An implementation study

BACKGROUND

Community pharmacists are in the position to contribute to fall prevention, but this is not yet common practice.

OBJECTIVE

The aim of this study was to evaluate the implementation of a community pharmacy-based fall prevention service.

METHODS

A fall prevention service, consisting of a fall risk screening and assessment including a medication review, was implemented in pharmacies during three months. A preparative online training was provided to the pharmacy team to enhance adoption of the service. Included patients were aged ≥70 years, using ≥5 drugs of which ≥1 fall risk-increasing drug. The implementation process was quantitively assessed by registering medication adaptations, recommendations, and referrals. Changes in patient scores on the Short Fall Efficacy Scale-International (FES-I) and a fall prevention knowledge test were documented at one month follow-up. Implementation was qualitatively evaluated by conducting semi-structured interviews with pharmacists before and after the project, based on the consolidated framework of implementation research.

RESULTS

The service was implemented in nine pharmacies and 91 consultations were performed. Medication was adapted of 32 patients. Patients' short FES-I scores were significantly higher at follow-up (p = 0.047) and patients' knowledge test scores did not differ (p = 0.86). Pharmacists experienced the following barriers: lack of time, absence of staff, and limited multidisciplinary collaboration. Facilitators were training, motivated staff, patient engagement, and project scheduling.

CONCLUSION

The service resulted in a substantial number of medication adaptations and lifestyle recommendations, but many barriers were identified that hamper the sustained implementation of the service.

Between-person and within-person associations of sleep and working-memory in the everyday lives of old and very old adults: initial level, learning, and variability

STUDY OBJECTIVES

Sleep duration affects various aspects of cognitive performance, such as working-memory and learning, among children and adults. However, it remains open, whether similar or even stronger associations exist in old and very old age when changes in sleep and cognitive decrements are common.

METHODS

Using repeated daily-life assessments from a sample of 121 young-old (66-69 years old) and 39 old-old adults (84-90 years old), we assessed links between sleep duration and different aspects of working-memory (initial level, practice-related learning, and residualized variability) between and within persons. Participants reported their sleep durations every morning and performed a numerical working-memory updating task six times a day for seven consecutive days.

RESULTS

Both people who slept longer and those who slept shorter than the sample average showed lower initial performance levels, but a stronger increase of WM over time (i.e. larger learning effects), relative to people with average sleep. Sleep duration did not predict performance variability. Within-person associations were found for people sleeping relatively little on average: For them, working-memory performance was lower on days with shorter than average sleep, yet higher on days with longer than average sleep. Except for lower initial levels of working-memory in old-old adults, no differences between young-old and old-old adults were observed.

CONCLUSION

We conclude that sufficient sleep remains important for working-memory performance in older adults and that it is relevant to include different aspects of working-memory performance, because effects differed for initial performance and learning.

The effect of sleep on novel word learning in healthy adults: A systematic review and meta-analysis

There is increasing evidence to indicate that sleep plays a role in language acquisition and consolidation; however, there has been substantial variability in methodological approaches used to examine this phenomenon. This systematic review and meta-analysis aimed to investigate the effect of sleep on novel word learning in adults, and explore whether these effects differed by retrieval domain (i.e., recall, recognition, and tests of lexical integration). Twenty-five unique studies met the inclusion criteria for the review, and 42 separate outcome measures were synthesized in the meta-analysis (k = 29 separate between-group comparisons, n = 1,396 participants). The results from the omnibus meta-analysis indicated that sleep was beneficial for novel word learning compared with wakefulness (g = 0.50). Effect sizes differed across the separate domain-specific meta-analyses, with moderate effects for recall (g = 0.57) and recognition memory (g = 0.52), and a small effect for tasks which measured lexical integration (g = 0.39). Overall, the results of this meta-analysis indicate that sleep generally benefits novel word acquisition and consolidation compared with wakefulness across differing retrieval domains. This systematic review highlights the potential for sleep to be used to improve second-language learning in healthy adults, and overall provides further insight into methods to facilitate language development.

Sleep-dependent prospective memory consolidation is impaired with aging

STUDY OBJECTIVES

Existing literature suggests that sleep-dependent memory consolidation is impaired in older adults but may be preserved for personally relevant information. Prospective memory (PM) involves remembering to execute future intentions in a timely manner and has behavioral importance. As previous work suggests that N3 sleep is important for PM in young adults, we investigated if the role of N3 sleep in PM consolidation would be maintained in older adults.

METHODS

Forty-nine young adults (mean age ± SD: 21.8 ± 1.61 years) and 49 healthy older adults (mean age ± SD: 65.7 ± 6.30 years) were randomized into sleep and wake groups. After a semantic categorization task, participants encoded intentions comprising four related and four unrelated cue-action pairs. They were instructed to remember to perform these actions in response to cue words presented during a second semantic categorization task 12 h later that encompassed either daytime wake (09:00 am-21:00 pm) or overnight sleep with polysomnography (21:00 pm-09:00 am).

RESULTS

The significant condition × age group × relatedness interaction suggested that the sleep benefit on PM intentions varied according to age group and relatedness (p = 0.01). For related intentions, sleep relative to wake benefitted young adults' performance (p < 0.001) but not older adults (p = 0.30). For unrelated intentions, sleep did not improve PM for either age group. While post-encoding N3 was significantly associated with related intentions' execution in young adults (r = 0.43, p = 0.02), this relationship was not found for older adults (r = -0.07, p = 0.763).

CONCLUSIONS

The age-related impairment of sleep-dependent memory consolidation extends to PM. Our findings add to an existing body of work suggesting that the link between sleep and memory is functionally weakened in older adulthood.

Are Sleep Complaints Related to Cognitive Functioning in Non-Central Nervous System Cancer? A Systematic Review

Patients with non-central nervous system (CNS) cancer frequently report cognitive complaints, that are recurrent and affect their quality of life. In order to improve supportive care of these cognitive difficulties, it is important to identify associated factors. Sleep disturbance is a good candidate to study, as patients with non-CNS cancer frequently report sleep disorders, and sleep plays a key role in cognitive functioning. The objective of the present systematic review was to summarize the results of studies evaluating the relationship between cognition and sleep in non-CNS cancer, and to highlight the need for further studies. PubMed [Medline] and Scopus databases were screened from April to November 2020 for studies published in English evaluating the association between cognition and sleep in adults with non-CNS cancer. The characteristics and risk of bias for each of the 30 included studies have been reported. Greater cognitive complaints in patients with non-CNS cancer were related to poorer self-reported sleep quality in almost all studies (n = 22/24). By contrast, around half of the studies reported a significant association between poorer neuropsychological performances and sleep complaints (n = 5/11). The studies were found to have several limitations, such as the lack of a control group, which would have shed the light on the period of occurrence of this association (e.g. after cancer diagnosis or after cancer treatments). Our review also identified factors that may influence the relationship between cognition and sleep. Recommendations are given for improving the methodology of future studies and extending the impact of their results.

A systematic review and meta-analysis of individual differences in naturalistic sleep quality and episodic memory performance in young and older adults

Better sleep quality has been associated with better episodic memory performance in young adults. However, the strength of sleep-memory associations in aging has not been well characterized. It is also unknown whether factors such as sleep measurement method (e.g., polysomnography, actigraphy, self-report), sleep parameters (e.g., slow wave sleep, sleep duration), or memory task characteristics (e.g., verbal, pictorial) impact the strength of sleep-memory associations. Here, we assessed if the aforementioned factors modulate sleep-memory relationships. Across age groups, sleep-memory associations were similar for sleep measurement methods, however, associations were stronger for PSG than self-report. Age group moderated sleep-memory associations for certain sleep parameters. Specifically, young adults demonstrated stronger positive sleep-memory associations for slow wave sleep than the old, while older adults demonstrated stronger negative associations between greater wake after sleep onset and poorer memory performance than the young. Collectively, these data show that young and older adults maintain similar strength in sleep-memory relationships, but age impacts the specific sleep correlates that contribute to these relationships.

The impact of nutrition on sleep in people with an intellectual disability: An integrative literature review

BACKGROUND

People with intellectual disabilities are more likely to experience sleep problems. Sleep can impact on health and well-being; therefore, evidence-based interventions are required to improve sleep in this population.

METHOD

An integrative literature review was conducted on the impact of nutrition on sleep in people with intellectual disabilities. Following screening of papers (n = 289), 14 papers met the inclusion criteria.

RESULTS

Themes related to nutrition and improved overall well-being, use of nutritional supplements, specific foods, links to health comorbidities and food fussiness.

CONCLUSION

This is the first comprehensive review completed on nutritional interventions to improve sleep in people with intellectual disabilities. Dietary patterns may be an important factor to improving the quality and quantity of sleep. However, the current literature regarding the benefit of improved nutrition on sleep in people with an intellectual disability needs to be interpreted with caution.

Sleep-Dependent Memory in Older People With and Without MCI: The Relevance of Sleep Microarchitecture, OSA, Hippocampal Subfields, and Episodic Memory

This study aimed to determine if, relative to cognitively healthy controls, sleep-dependent memory consolidation (SDMC) is diminished in mild cognitive impairment (MCI), a group at high risk of conversion to dementia. We also sought to determine whether SDMC is associated with sleep characteristics, daytime episodic memory, and hippocampal integrity. Participants with MCI (n = 43) and controls (n = 20) underwent clinical and neuropsychological profiling. From polysomnography, apnea hypopnea index (AHI) and non-REM sleep spindle characteristics were derived. From magnetic resonance imaging, hippocampal subfield volumes were computed. Participants learned a novel 32-item word-pair prior to sleep; morning retention of the word-pairs was used to determine SDMC. Results showed that SDMC did not differ between MCI and controls, but there was a large effect size decrement in SDMC in those with multiple domain MCI (Hedge's g = 0.85). In MCI, poorer SDMC was correlated with CA1 and CA3 hippocampal atrophy, shorter spindle duration, and worse daytime episodic memory. In controls, poorer SDMC was associated with higher AHI. Impaired daytime memory consolidation, reduced hippocampal volumes, shorter sleep spindles, and greater sleep apnea severity are indicators of diminished SDMC in older adults and should be explored in future studies.

Susceptibility to auditory closed-loop stimulation of sleep slow oscillations changes with age

Study Objectives

Cortical slow oscillations (SOs) and thalamocortical sleep spindles hallmark slow wave sleep and facilitate memory consolidation, both of which are reduced with age. Experiments utilizing auditory closed-loop stimulation to enhance these oscillations showed great potential in young and older subjects. However, the magnitude of responses has yet to be compared between these age groups. We examined the possibility of enhancing SOs and performance on different memory tasks in a healthy middle-aged population using this stimulation and contrast effects to younger adults.

Methods

In a within-subject design, 17 subjects (55.7 ± 1.0 years) received auditory stimulation in synchrony with SO up-states, which was compared to a no-stimulation sham condition. Overnight memory consolidation was assessed for declarative word-pairs and procedural finger-tapping skill. Post-sleep encoding capabilities were tested with a picture recognition task. Electrophysiological effects of stimulation were compared to a previous younger cohort (n = 11, 24.2 ± 0.9 years).

Results

Overnight retention and post-sleep encoding performance of the older cohort revealed no beneficial effect of stimulation, which contrasts with the enhancing effect the same stimulation protocol had in our younger cohort. Auditory stimulation prolonged endogenous SO trains and induced sleep spindles phase-locked to SO up-states in the older population. However, responses were markedly reduced compared to younger subjects. Additionally, the temporal dynamics of stimulation effects on SOs and spindles differed between age groups.

Conclusions

Our findings suggest that the susceptibility to auditory stimulation during sleep drastically changes with age and reveal the difficulties of translating a functional protocol from younger to older populations.

The different roles of sleep on false memory formation between young and older adults

Aging is accompanied by an increase in the probability of false memory. However, what role sleep plays in the age effect in false memory is less understood. Our study utilized a simplified conjoint recognition (SCR)-based Deese-Roediger-McDermott (DRM) paradigm to investigate the role of sleep on false memory in young and older adults. The results showed that sleep effect in false memory was modulated by age, manifested as sleep increased young adults' falsely recognized critical lures, while it reduced older adults'. In addition, in a more fine-grained analysis, the results of multinomial processing tree (MPT) modeling further revealed that young adults were more likely to retrieve memory based on gist traces than older adults, and young adults were more susceptible to guess a probe as "old" than older adults in the sleep condition. Combined findings from the number and ratio of falsely recognized critical lures and the MPT modeling, the current study suggested that sleep might increase young adults' false memory via gist extraction, while it decreased older adults' false memory via verbatim trace consolidation. The study contributes to a comprehensive view on the age-by-sleep effect on false recognition, with the segregation of cognitive components of verbatim memory, gist memory, and response bias.

The age differences of sleep disruption on mood states and memory performance

Objectives: In the present study, we explored the age differences of mood states and memory performance between younger and older adults after one night of sleep disruption.Method: Twenty-nine younger adults and 30 older adults completed mood states assessments and memory tasks before and after sleep disruption. Participants' sleep was disrupted by periodical phone calls once per hour. Sleep parameters of baseline sleep and disrupted sleep were recorded by actigraphy.Results: Regarding the mood states, older adults were less affected than younger adults, more tolerant of sleep disruption. With respect to memory, younger adults showed increased memory performance after nocturnal sleep, even if this sleep was disrupted. In contrast, older adults' sleep-related memory consolidation was impaired.Conclusion: Periodic sleep disruption for one night resulted in impaired function of older adults' sleep-related memory consolidation and younger adults' mood states. These findings shed light on the understanding of sleep function on memory and emotion. Specifically, sleep disruption might be one of the reasons for older adults' memory decline and it might also be one of the causes for younger adults' emotion disorders. Further investigations on the relationship between sleep disruption, cognitive performance and emotional well-being are needed to find potential ways to prevent and treat the sleep-related neuropsychological impairments in both younger and older adults.

Sleep-dependent motor memory consolidation in healthy adults: A meta-analysis

It is widely accepted that sleep better facilitates the consolidation of motor memories than does a corresponding wake interval (King et al., 2017). However, no in-depth analysis of the various motor tasks and their relative sleep gain has been conducted so far. Therefore, the present meta-analysis considered 48 studies with a total of 53 sleep (n = 829) and 53 wake (n = 825) groups. An overall comparison between all sleep and wake groups resulted in a small effect for the relative sleep gain in motor memory consolidation (g = 0.43). While no subgroup differences were identified for differing designs, a small effect for the finger tapping task (g = 0.47) and a medium effect for the mirror tracing task (g = 0.62) were found. In summary, the meta-analysis substantiates that sleep generally benefits the consolidation of motor memories. However, to further our understanding of the mechanisms underlying this effect, examining certain task dimensions and their relative sleep gain would be a promising direction for future research.

How robust are sleep-mediated memory benefits?

Memories benefit from a retention interval filled with sleep. Current theories assume that this beneficial effect relies on consolidation processes occurring during slow-wave sleep (SWS). However, in the last years, several key findings supporting these theories could not be replicated or occurred only under certain conditions, suggesting that effects of sleep on memory are smaller, more task-dependent, less SWS-related, less robust and less long-lasting than previously assumed. In this review, we summarize recent replication failures, null-findings, meta-analyses and studies reporting important boundary conditions for the effect of sleep on declarative memory. We argue that more attempts to replicate and meta-analytic approaches together with higher standards for reproducible science are critical to advance the field of sleep and memory.

High-frequency cardiopulmonary coupling during sleep correlates with memory in depressed patients: A pilot study

BACKGROUND

It has been demonstrated that a reduction in the amount of high-frequency cardiopulmonary coupling (CPC) is indicative of unstable sleep in unmedicated patients with major depressive disorder (MDD). Considering the close relationship between sleep quality and memory consolidation, this study sought to investigate the potential of high-frequency CPC as a novel biomarker for objective evaluation of memory impairment in MDD.

METHODS

A total of 64 depressed patients and 35 healthy controls were included in this cross-sectional study. High-frequency coupling (HFC) was assessed by electrocardiogram-based CPC analysis using a portable sleep-respiration monitor during sleep for one night. The next day, subjects completed the cognition assessment with the Assessment of Neuropsychological Status (RBANS). The 17-Item Hamilton Depression Rating Scale (HAMD₁₇) and the Hamilton Rating Scales for Anxiety (HAMA) were used to evaluate the severity of depression and anxiety in each patient, respectively.

RESULTS

There was no significant difference in the proportion of HFC between depressed patients and healthy controls. In patients with low HFC proportion (<35%), severe anxiety could significantly decrease HFC proportion. The HFC proportion positively correlated with immediate and delayed memory in depressed patients. Further analysis showed that patients with low HFC proportion may have worse delayed memory.

LIMITATIONS

The lack of prior exposure to the monitoring equipment and procedure could have generated artefacts that would have disappeared after habituation.

CONCLUSIONS

These results support a positive correlation between the HFC proportion and memory in depressed patients. Further research is required to explore the clinical implications of these findings.

Boosting Slow Oscillations during Sleep to Improve Memory Function in Elderly People: A Review of the Literature

Sleep represents a crucial time window for the consolidation of memory traces. In this view, some brain rhythms play a pivotal role, first of all the sleep slow waves. In particular, the neocortical slow oscillations (SOs), in coordination with the hippocampal ripples and the thalamocortical spindles, support the long-term storage of the declarative memories. The aging brain is characterized by a disruption of this complex system with outcomes on the related cognitive functions. In recent years, the advancement of the comprehension of the sleep-dependent memory consolidation mechanisms has encouraged the development of techniques of SO enhancement during sleep to induce cognitive benefits. In this review, we focused on the studies reporting on the application of acoustic or electric stimulation procedures in order to improve sleep-dependent memory consolidation in older subjects. Although the current literature is limited and presents inconsistencies, there is promising evidence supporting the perspective to non-invasively manipulate the sleeping brain electrophysiology to improve cognition in the elderly, also shedding light on the mechanisms underlying the sleep-memory relations during healthy and pathological aging.

Evidence against a large effect of sleep in protecting verbal memories from interference

The human brain has evolved to acquire novel information rapidly while serving the need to store long-term memories in a stable and lasting form. Presenting interfering information directly after learning can lead to forgetting of the original material. It has been suggested that sleep aids the stabilization of new memories and protects them from interference. Here, we aim to replicate in two separate experiments the claim that sleep protects memories from retroactive interference (Current Biology, 16, 2006 and 1290; PLoS ONE, 4, 2009 and e4117). We let participants study wordlists before letting them sleep for an afternoon nap or for a full night. In a control condition, subjects stayed awake for the same amount of time. After the consolidation interval, participants learnt an interfering wordlist and were tested on memory of the original wordlist. Sleep did not stabilize memory for the original wordlist in either study. We discuss our findings in the light of recent advances in computational neuroscience, and conclude that the stabilizing effect of sleep against interference has been overestimated.

Memory quality modulates the effect of aging on memory consolidation during sleep: Reduced maintenance but intact gain

Successful consolidation of associative memories relies on the coordinated interplay of slow oscillations and sleep spindles during non-rapid eye movement (NREM) sleep. This enables the transfer of labile information from the hippocampus to permanent memory stores in the neocortex. During senescence, the decline of the structural and functional integrity of the hippocampus and neocortical regions is paralleled by changes of the physiological events that stabilize and enhance associative memories during NREM sleep. However, the currently available evidence is inconclusive as to whether and under which circumstances memory consolidation is impacted during aging. To approach this question, 30 younger adults (19-28 years) and 36 older adults (63-74 years) completed a memory task based on scene-word associations. By tracing the encoding quality of participants' individual memory associations, we demonstrate that previous learning determines the extent of age-related impairments in memory consolidation. Specifically, the detrimental effects of aging on memory maintenance were greatest for mnemonic contents of intermediate encoding quality, whereas memory gain of poorly encoded memories did not differ by age. Ambulatory polysomnography (PSG) and structural magnetic resonance imaging (MRI) data were acquired to extract potential predictors of memory consolidation from each participant's NREM sleep physiology and brain structure. Partial Least Squares Correlation was used to identify profiles of interdependent alterations in sleep physiology and brain structure that are characteristic for increasing age. Across age groups, both the 'aged' sleep profile, defined by decreased slow-wave activity (0.5-4.5 ​Hz), and a reduced presence of slow oscillations (0.5-1 ​Hz), slow, and fast spindles (9-12.5 ​Hz; 12.5-16 ​Hz), as well as the 'aged' brain structure profile, characterized by gray matter reductions in the medial prefrontal cortex, thalamus, entorhinal cortex, and hippocampus, were associated with reduced memory maintenance. However, inter-individual differences in neither sleep nor structural brain integrity alone qualified as the driving force behind age differences in sleep-dependent consolidation in the present study. Our results underscore the need for novel and age-fair analytic tools to provide a mechanistic understanding of age differences in memory consolidation.

Age-related emotional bias in associative memory consolidation: The role of sleep

Sleep plays a crucial role in memory consolidation. However, the influence of sleep on emotional memory consolidation in older adults, especially in the context of associative memory, which is more cognitively demanding than item memory, remains elusive. For this study we recruited young and older adults, and randomly assigned them into the sleep or wake condition. They were administrated a visual-spatial associative memory task, which required them to remember a picture and its location. We measured memory performance for positive, neutral, and negative stimuli before and after a 12-h interval of being awake or asleep. An accuracy analysis indicated a beneficial effect of sleep on location memory regardless of age and valence. In addition, in a more fine-grained analysis, the drift rate from diffusion modeling showed that sleep facilitated the consolidation of negative stimuli in young adults, while this emotion bias shifted to positive stimuli in older adults. Moreover, negative correlations were observed between the change of memory performance and sleep characteristics in older adults, indicating that more sleep results in fewer negative memories. Our results provide a relatively weak support for an age-related emotional bias in the context of associative memory, manifested in the absence of an age-by-valence interaction in accuracy, whilst a modeling parameter in consideration of both accuracy and response time yielded evidence consistent with the predictions of the socioemotional selectivity theory.

Deciphering Age Differences in Experience-Based Decision-Making: The Role of Sleep

OBJECTIVE

Recent studies have demonstrated that sleep not only facilitates memory consolidation but also benefits more complex cognitive skills such as decision-making in young adults. Older adults use different decision strategies compared with young adults, which leaves the role of sleep in older adults' decision-making unclear. We investigated the age-by-sleep effect on decision-making.

METHODS

We recruited 67 young adults (ages 18 to 29 years) and 66 older adults (ages 60 to 79 years) and randomly assigned them into the "sleep" or "wake" study condition. They were given a modified Iowa gambling task to perform before and after a 12-hour interval with sleep or wakefulness.

RESULTS

Using the typical model-free analysis, we found that young adults' between-session performance improved greater than that of older adults regardless of the sleep/wake condition. Furthermore, older adults with longer total sleep time showed a greater improvement in the selection of one "good" deck. To further examine the sleep effect on age-related differences in cognitive processes underlying decision-making, we conducted computational modelling. This more fine-grained analysis revealed that sleep improved feedback sensitivity for both young and older adults while it increased loss aversion for older adults but not for young adults.

CONCLUSION

These findings indicate that sleep promotes learning-based decision-making performance via facilitating value representation, and such modulation is distinct in young compared to older adults.

Obstructive sleep apnea, cognition and Alzheimer's disease: A systematic review integrating three decades of multidisciplinary research

Increasing evidence links cognitive-decline and Alzheimer's disease (AD) to various sleep disorders, including obstructive sleep apnea (OSA). With increasing age, there are substantial differences in OSA's prevalence, associated comorbidities and phenotypic presentation. An important question for sleep and AD researchers is whether OSA's heterogeneity results in varying cognitive-outcomes in older-adults compared to middle-aged adults. In this review, we systematically integrated research examining OSA and cognition, mild cognitive-impairment (MCI) and AD/AD biomarkers; including the effects of continuous positive airway pressure (CPAP) treatment, particularly focusing on characterizing the heterogeneity of OSA and its cognitive-outcomes. Broadly, in middle-aged adults, OSA is often associated with mild impairment in attention, memory and executive function. In older-adults, OSA is not associated with any particular pattern of cognitive-impairment at cross-section; however, OSA is associated with the development of MCI or AD with symptomatic patients who have a higher likelihood of associated disturbed sleep/cognitive-impairment driving these findings. CPAP treatment may be effective in improving cognition in OSA patients with AD. Recent trends demonstrate links between OSA and AD-biomarkers of neurodegeneration across all age-groups. These distinct patterns provide the foundation for envisioning better characterization of OSA and the need for more sensitive/novel sleep-dependent cognitive assessments to assess OSA-related cognitive-impairment.

The impact of sleep on eyewitness identifications

Sleep aids the consolidation of recently acquired memories. Evidence strongly indicates that sleep yields substantial improvements on recognition memory tasks relative to an equivalent period of wake. Despite the known benefits that sleep has on memory, researchers have not yet investigated the impact of sleep on eyewitness identifications. Eyewitnesses to crimes are often presented with a line-up (which is a type of recognition memory test) that contains the suspect (who is innocent or guilty) and fillers (who are known to be innocent). Sleep may enhance the ability to identify the guilty suspect and not identify the innocent suspect (i.e. discriminability). Sleep may also impact reliability (i.e. the likelihood that the identified suspect is guilty). In the current study, we manipulated the presence or the absence of sleep in a forensically relevant memory task. Participants witnessed a video of a mock crime, made an identification or rejected the line-up, and rated their confidence. Critically, some participants slept between witnessing the crime and making a line-up decision, while others remained awake. The prediction that participants in the sleep condition would have greater discriminability compared to participants in the wake condition was not supported. There were also no differences in reliability.

Rapid eye movement sleep mediates age-related decline in prospective memory consolidation

STUDY OBJECTIVES

Prospective memory, or remembering to execute future intentions, accounts for half of everyday forgetting in older adults. Sleep intervals benefit prospective memory consolidation in young adults, but it is unknown whether age-related changes in slow wave activity, sleep spindles, and/or rapid eye movement (REM) sleep mediate hypothesized effects of aging on prospective memory consolidation.

METHODS

After an adaptation night, 76 adults aged 18-84 completed two experimental nights of in-laboratory polysomnography recording. In the evening, participants encoded and practiced a prospective memory task and were tested the next morning. On a counterbalanced night, they encoded and practiced a control task, and were tested the following morning.

RESULTS

Increasing age predicted worse prospective memory consolidation (r = -.34), even when controlling for encoding, speed, and control-task performance (all ps < .05). Frontal delta power, slow oscillations, and spindle density were not related to prospective memory consolidation. REM sleep duration, however, explained significant variance in prospective memory consolidation when controlling for age (∆R2 = .10). Bootstrapping mediation showed that less REM sleep significantly mediated the aging effect on prospective memory consolidation [b = -.0016, SE = 0.0009 (95% confidence interval [CI] = -0.0042 to -0.0004)]. REM sleep continued to mediate 24.29% of the total effect of age on prospective memory after controlling for numerous demographic, cognitive, mental health, and sleep variables.

CONCLUSION

Age-related variance in REM sleep is informative to how prospective memory consolidation changes with increasing age. Future work should consider how both REM sleep and slow wave activity contribute, perhaps in a sequential or dynamic manner, to preserving cognitive functioning with increasing age.

Age and Race-Related Differences in Sleep Discontinuity Linked to Associative Memory Performance and Its Neural Underpinnings

There is a strong relationship between sleep and memory for the details of past events. In old age, both episodic memory performance and related neural activity decline. These changes occur in parallel to age-related decreases in sleep quality. Thus, poor sleep quality may be an explanatory factor for poor memory in older adulthood. Furthermore, Black adults tend to sleep more poorly than White adults, and this could be explained by differences in health and psychosocial factors (e.g., socioeconomic status, race-related stress). However, there have been no studies investigating the effect of race on sleep quality, episodic memory, and memory-related neural function. In the current pilot study, we recruited a diverse sample of older and younger adults and measured their habitual sleep using a wrist-worn accelerometer for 1 week. We recorded their electroencephalography (EEG) as they performed an episodic memory task to assess the impact of habitual sleep on memory-related neural oscillations. We found that more variable sleep quality was associated with worse memory performance, particularly for older adults. Additionally, Black participants demonstrated greater intraindividual sleep variance than White participants, and greater sleep variance was strongly linked to reduced memory-related neural activity in Black participants. Taken together, maintaining good sleep quality is especially important for memory performance in older adulthood, and greater sleep variation, that is evident in Black adults, may hamper memory-related neural function.

Preferential Consolidation of Emotional Memory During Sleep: A Meta-Analysis

It is uncertain whether sleep preferentially consolidates emotional over neutral material. Some studies suggest that sleep enhances emotional memory (i.e., that there are large differences in strength of memory for valenced material compared to neutral material after a sleep-filled interval, but that this difference is smaller after a wake-filled interval). Others find no such effect. We attempted to resolve this uncertainty by conducting a meta-analysis that compared valenced to neutral material after both sleep- and wake-filled delays. Standard search strategies identified 31 studies (containing 36 separate datasets) that met our inclusion criteria. Using random effects modeling, we conducted separate analyses for datasets comparing (a) negative vs. neutral material, (b) positive vs. neutral material, or (c) combined negative and positive vs. neutral material. We then specified several subgroup analyses to investigate potential moderators of the relationship between sleep and emotional memory consolidation. Results showed no overall effect for preferential sleep-dependent consolidation of emotional over neutral material. However, moderation analyses provided evidence for stronger effects when (a) studies used free recall rather than recognition outcome measures, or (b) delayed recall or recognition outcomes were controlled for initial learning. Those analyses also suggested that other methodological features (e.g., whether participants experience a full night of sleep and a regular daytime waking control condition rather than a nap and a night-time sleep deprivation control condition) and sample characteristics (e.g. all-male or not, young adult or not) should be carefully addressed in future research in this field. These findings suggest that sleep does enhance emotional memory, but that in the laboratory the effect is only observed under particular methodological conditions. The conditions we identify as being critical to consider are consistent with general theories guiding scientific understanding of memory consolidation during sleep.

Young and Older Adults Benefit From Sleep, but Not From Active Wakefulness for Memory Consolidation of What-Where-When Naturalistic Events

An extensive psychological literature shows that sleep actively promotes human episodic memory (EM) consolidation in younger adults. However, evidence for the benefit of sleep for EM consolidation in aging is still elusive. In addition, most of the previous studies used EM assessments that are very different from everyday life conditions and are far from considering all the hallmarks of this memory system. In this study, the effect of an extended period of sleep was compared to the effect of an extended period of active wakefulness on the EM consolidation of naturalistic events, using a novel (What-Where-When) EM task, rich in perceptual details and spatio-temporal context, presented in a virtual environment. We investigated the long-term What-Where-When and Details binding performances of young and elderly people before and after an interval of sleep or active wakefulness. Although we found a noticeable age-related decline in EM, both age groups benefited from sleep, but not from active wakefulness. In younger adults, only the period of sleep significantly enhanced the capacity to associate different components of EM (binding performance) and more specifically the free recall of what-when information. Interestingly, in the elderly, sleep significantly enhanced not only the recall of factual elements but also associated details and contextual information as well as the amount of high feature binding (i.e., What-Where-When and Details). Thus, this study evidences the benefit of sleep, and the detrimental effect of active wakefulness, on long-term feature binding, which is one of the core characteristics of EM, and its effectiveness in normal aging. However, further research should investigate whether this benefit is specific to sleep or more generally results from the effect of a post-learning period of reduced interference, which could also concern quiet wakefulness.

Can Daytime Napping Assist the Process of Skills Acquisition After Stroke?

Acquisition and reacquisition of skills is a main pillar of functional recovery after stroke. Nighttime sleep has a positive influence on motor learning in healthy individuals, whereas the effect of daytime sleep on neuro-rehabilitative training and relearning of the trained skills is often neglected. The aim of this study was to investigate the relationship between daytime sleep (napping) and the ability to learn a new visuomotor task in chronic stroke patients. The main hypothesis was that sleep enhances motor memory consolidation after training resulting in better motor performance after a period of daytime sleep. Thirty stroke survivors completed the study. They were randomized to one of three different conditions (i) wakeful resting, (ii) short nap (10-20 min), or (iii) long nap (50-80 min). All individuals trained the task with the contralesional, stroke-impaired hand, behavioral evaluation was performed after the break time (wake, nap), and 24 h later. Patients demonstrated a significant task-related behavioral improvement throughout the training. In contrast to the main hypothesis, there was no evidence for sleep-dependent motor consolidation early after the initial, diurnal break, or after an additional full night of sleep. In a secondary analysis, the performance changes of stroke survivors were compared with those of a group of healthy older adults who performed the identical task within the same experimental setup with their non-dominant hand. Performance levels were comparable between both cohorts at all time points. Stroke-related difficulties in motor control did not impact on the degree of performance improvement through training and daytime sleep did not impact on the behavioral gains in the two groups. In summary, the current study indicates that one-time daytime sleep after motor training does not influence behavioral gains.

Dynamic Contributions of Slow Wave Sleep and REM Sleep to Cognitive Longevity

Purpose of review

The purpose of this paper was to address how sleep changes with aging, with the broader goal of informing how REM sleep and slow wave activity mechanisms interact to promote cognitive longevity.

Recent findings

We conducted novel analyses based on the National Sleep Research Resource database. Over approximately five years, middle-to-older aged adults, on average, showed dramatically worse sleep fragmentation, a steady decrease in slow wave sleep, and yet a small increase in REM sleep. Averaging across participants, however, masked a major theme: Individuals differ substantially in their longitudinal trajectories for specific components of sleep. We considered this individual variability in light of recent theoretical and empirical work that has shown disrupted sleep and decreased slow wave activity to impair frontal lobe restoration, glymphatic system functioning, and memory consolidation. Based on multiple recent longitudinal studies, we contend that preserved or enhanced REM sleep may compensate for otherwise disrupted sleep in advancing age.

Summary

The scientific community has often debated whether slow wave activity or REM sleep mechanisms are more important to cognitive aging. We propose that a more fruitful approach for future work will be to investigate how REM and slow wave processes dynamically interact to affect cognitive longevity.

Sleep facilitates consolidation of positive emotional memory in healthy older adults

Evidence has demonstrated that sleep-related memory consolidation declines in ageing. However, little is known about age-related changes to sleep-related emotional memory consolidation, especially when considering the positivity effect observed in older adults. In the present study, we sought to explore whether there is a positive emotional bias in sleep-related memory consolidation among healthy older adults. Young and older adults were randomly assigned either into a sleep or wake condition. All participants encoded positive, negative, and neutral stimuli and underwent recognition tests immediately (test 1), after a 12-hour sleep/wake interval (test 2), and 3 days after test 2 (test 3). Results showed that age-related differences of sleep beneficial effect were modulated by emotion valence. In particular, sleep selectively enhanced positive memory in older adults, while in young adults sleep beneficial effect was manifested in neutral memory. Moreover, the sleep beneficial effect can be maintained at least 3 days in both young and older adults. These findings suggest that older adults had preserved but positive bias of sleep-related memory consolidation, which could be one of the underlying mechanisms for their generally better emotional well-being in daily life. These findings highlight the dynamic interplay among sleep and emotional memory in older adults.

The sleep network organization during slow-wave sleep is more stable with age and has small-world characteristics more marked than during REM sleep in healthy men

Sleep plays an important role in cognitive functioning. However, few studies have investigated the sleep network organization. The aim of our study was to empirically investigate the presence and the stability with age of a small-world network organization during REM and slow-wave sleep using the effective connectivity measured by the Granger causality. Polysomnographic data from 30 healthy men recruited prospectively were analysed. To obtain the 19 × 19 connectivity matrix of all possible pairwise combinations of electrodes by the Granger causality method from our EEG data, we used the Toolbox MVGC multivariate Granger causality. The computation of the network measures was realised by importing these connectivity matrices into the EEGNET Toolbox. Even if all small-world coefficients obtained are compatible with a small-world network organization during REM and slow-wave sleep, slow-wave sleep seems to have a small-world network organization more marked than REM sleep. Moreover, the sleep network organization is affected greater by age during REM sleep than during slow-wave sleep. In healthy individuals, the highlighting of a sleep network organization during slow-wave sleep more stable with age and with small-world characteristics more marked than during REM sleep may help to better understand the global and local processing of information during sleep.

Sleep-deprivation and autobiographical memory: evidence from sleep-deprived nurses

Negative effects of sleep deprivation on different types of memory are well documented, but the specific effects on autobiographical memory performance are not well studied. In this study, we investigated performance on the autobiographical memory test in a group of sleep-deprived and well-rested nurses. One-hundred participants divided into sleep-deprived (N = 50, 25 females) and well-rested (N = 50, 25 females) groups took part in the study. The sleep-deprived group included night-shift nurses with 8-12 hr sleep deprivation, while the well-rested group had the usual night sleep before performance assessment. All participants were matched for gender, age, education and employment status. They completed depression and anxiety inventories, and underwent the autobiographical memory test, which included 18 cue words with positive, negative and neutral valence. The sleep-deprived group scored significantly higher in depression scores. Analysis of covariance (ANCOVA) results showed that sleep-deprived participants had a significantly poorer autobiographical memory compared with the well-rested group. Additionally, specific memories were significantly declined in the sleep-deprived group. This group remembered significantly less positive and more negative memories. Findings implicate that sleep deprivation has detrimental effects on autobiographical memory specificity and valence, and is associated with mood dysregulation.

Do Older Adults Need Sleep? A Review of Neuroimaging, Sleep, and Aging Studies

PURPOSE OF REVIEW

Sleep habits, sleep physiology, and sleep disorders change with increasing age. However, there is a longstanding debate regarding whether older adults need sleep to maintain health and daily functioning (reduced-sleep-need view). An alternative possibility is that all older adults need sleep, but that many older adults have lost the ability to obtain restorative sleep (reduced-sleep-ability view). Prior research using behavioral and polysomnography outcomes has not definitively disentangled the reduced-sleep-need and reduced-sleep-ability views. Therefore, this review examines the neuroimaging literature to determine whether age-related changes in sleep cause-or are caused by-age-related changes in brain structure, function, and pathology.

RECENT FINDINGS

In middle-aged and older adults, poorer sleep quality, greater nighttime hypoxia, and shorter sleep duration related to cortical thinning in frontal regions implicated in slow wave generation, in frontoparietal networks implicated in cognitive control, and in hippocampal regions implicated in memory consolidation. Furthermore, poor sleep quality was associated with higher amyloid burden and decreased connectivity in the default mode network, a network that is disrupted in the pathway to Alzheimer's disease.

SUMMARY

All adults need sleep, but cortical thinning and amyloidal deposition with advancing age may weaken the brain's ability to produce restorative sleep. Therefore, sleep in older adults may not always support identical functions for physical, mental, and cognitive health as in young adults.