Emotional bias of sleep-dependent processing shifts from negative to positive with aging

The emotion paradox in the aging body and brain

With age, parasympathetic activity decreases, while sympathetic activity increases. Thus, the typical older adult has low heart rate variability (HRV) and high noradrenaline levels. Younger adults with this physiological profile tend to be unhappy and stressed. Yet, with age, emotional experience tends to improve. Why does older adults' emotional well-being not suffer as their HRV decreases? To address this apparent paradox, I present the autonomic compensation model. In this model, failing organs, the initial phases of Alzheimer's pathology, and other age-related diseases trigger noradrenergic hyperactivity. To compensate, older brains increase autonomic regulatory activity in the pregenual prefrontal cortex (PFC). Age-related declines in nerve conduction reduce the ability of the pregenual PFC to reduce hyperactive noradrenergic activity and increase peripheral HRV. But these pregenual PFC autonomic compensation efforts have a significant impact in the brain, where they bias processing in favor of stimuli that tend to increase parasympathetic activity (e.g., stimuli that increase feelings of safety) and against stimuli that tend to increase sympathetic activity (e.g., threatening stimuli). In summary, the autonomic compensation model posits that age-related chronic sympathetic/noradrenergic hyperactivity stimulates regulatory attempts that have the side effect of enhancing emotional well-being.

Emotional memory consolidation during sleep is associated with slow oscillation-spindle coupling strength in young and older adults

Emotional memories are processed during sleep; however, the specific mechanisms are unclear. Understanding such mechanisms may provide critical insight into preventing and treating mood disorders. Consolidation of neutral memories is associated with the coupling of NREM sleep slow oscillations (SOs) and sleep spindles (SPs). Whether SO-SP coupling is likewise involved in emotional memory processing is unknown. Furthermore, there is an age-related emotional valence bias such that sleep consolidates and preserves reactivity to negative but not positive emotional memories in young adults and positive but not negative emotional memories in older adults. If SO-SP coupling contributes to the effect of sleep on emotional memory, then it may selectively support negative memory in young adults and positive memory in older adults. To address these questions, we examined whether emotional memory recognition and overnight change in emotional reactivity were associated with the strength of SO-SP coupling in young (n = 22) and older (n = 32) adults. In younger adults, coupling strength predicted negative but not positive emotional memory performance after sleep. In contrast, coupling strength predicted positive but not negative emotional memory performance after sleep in older adults. Coupling strength was not associated with emotional reactivity in either age group. Our findings suggest that SO-SP coupling may play a mechanistic role in sleep-dependent consolidation of emotional memories.

Sleep preferentially consolidates negative aspects of human memory: Well-powered evidence from two large online experiments

Recent research has called into question whether sleep improves memory, especially for emotional information. However, many of these studies used a relatively small number of participants and focused only on college student samples, limiting both the power of these findings and their generalizability to the wider population. Here, using the well-established emotional memory trade-off task, we investigated sleep’s impact on memory for emotional components of scenes in a large online sample of adults ranging in age from 18 to 59 y. Despite the limitations inherent in using online samples, this well-powered study provides strong evidence that sleep selectively consolidates negative emotional aspects of memory and that this effect generalizes to participants across young adulthood and middle age.

Research suggests that sleep benefits memory. Moreover, it is often claimed that sleep selectively benefits memory for emotionally salient information over neutral information. However, not all scientists are convinced by this relationship [e.g., J. M. Siegel. Curr. Sleep Med. Rep., 7, 15–18 (2021)]. One criticism of the overall sleep and memory literature—like other literature—is that many studies are underpowered and lacking in generalizability [M. J. Cordi, B. Rasch. Curr. Opin. Neurobiol., 67, 1–7 (2021)], thus leaving the evidence mixed and confusing to interpret. Because large replication studies are sorely needed, we recruited over 250 participants spanning various age ranges and backgrounds in an effort to confirm sleep’s preferential emotional memory consolidation benefit using a well-established task. We found that sleep selectively benefits memory for negative emotional objects at the expense of their paired neutral backgrounds, confirming our prior work and clearly demonstrating a role for sleep in emotional memory formation. In a second experiment also using a large sample, we examined whether this effect generalized to positive emotional memory. We found that while participants demonstrated better memory for positive objects compared to their neutral backgrounds, sleep did not modulate this effect. This research provides strong support for a sleep-specific benefit on memory consolidation for specifically negative information and more broadly affirms the benefit of sleep for cognition.

Sleep and affect: A conceptual review

Everyday experience suggests that sleep and affect are closely linked, with daytime affect influencing how we sleep, and sleep influencing subsequent affect. Yet empirical evidence for this bidirectional relationship between sleep and affect in non-clinical adult samples remains mixed, which may be due to heterogeneity in both construct definitions and measurement. This conceptual review proposes a granular framework that deconstructs sleep and affect findings according to three subordinate dimensions, namely domains (which are distinct for sleep and affect), methods (i.e., self-report vs. behavioral/physiological measures), and timescale (i.e., shorter vs. longer). We illustrate the value of our granular framework through a systematic review of empirical studies published in PubMed (N = 80 articles). We found that in some cases, particularly for sleep disturbances and sleep duration, our framework identified robust evidence for associations with affect that are separable by domain, method, and timescale. However, in most other cases, evidence was either inconclusive or too sparse, resulting in no clear patterns. Our review did not find support for granular bidirectionality between sleep and affect. We suggest a roadmap for future studies based on gaps identified by our review and discuss advantages and disadvantages of our granular dimensional framework.

Do your troubles today seem further away than yesterday? On sleep's role in mitigating the blushing response to a reactivated embarrassing episode

The "sleep to forget and sleep to remember hypothesis" proposes that sleep weakens the emotional tone of an experience while preserving or even enhancing its content. Prior experimental research however shows contradictory findings on how emotional reactivity changes after a period of sleep, likely explained by methodological variations. By addressing these inconsistencies, we investigated the mitigating effect of overnight sleep on emotional reactivity triggered by memory reactivation. Using a karaoke paradigm, we recorded participants' singing of two songs, followed by exposing them to one of the recordings (rec1) to induce an embarrassing episode. After a 12-hr period of either day-time wakefulness (N = 20) or including nighttime sleep (N = 20), we assessed emotional reactivity to the previously exposed recording (rec1) and the newly exposed recording (rec2). Emotional reactivity was assessed with a physiological measure of facial blushing as the main outcome and subjective ratings of embarrassment and valence. Sleep and wake were monitored with diaries and actigraphy. The embarrassing episode was successfully induced as indicated by objective and subjective measures. After controlling for an order effect in stimulus presentation, we found a reduction in blushing response to the reactivated recording (rec1) from pre- to post-sleep compared to wakefulness. However, emotional reactivity to the reactivated recording (rec1) and the new recording (rec2) did not differ after sleep and wakefulness. This study shows that facial blushing was reduced following overnight sleep, while subjective ratings were unaffected. Whether the beneficial effect of sleep is due to changes in memory representation or rather emotion regulation remains elusive.

The Role of Working Memory in Age-Related Emotional Memory Bias

Aging is accompanied by deterioration in both working memory (WM) and long-term memory (LTM), yet whether these changes are related is not understood. Sleep plays a role in the formation of LTM in young adults, but the findings in older adults are not as clear. The types of memories we store also shift with age as young adults preserve a higher proportion of negative experiences when compared to older adults. The reason for this age-related change in emotional memory bias is also not clear; however, some studies have suggested that WM changes across aging may be an important factor. In the current study, we examined performance in WM and emotional LTM in younger and older adults. We added a daytime nap in half the subjects to examine a possible role of sleep on emotional LTM. In the morning, 93 younger (18–39) and 121 older (60–85) adults completed a WM task. Subjects also encoded neutral or negative word pairs and provided valence and arousal ratings for each pair. After half the subjects took a daytime nap, LTM was examined, and valence and arousal ratings were reassessed. Results indicate that older adults showed worse recognition for negative word pairs compared with neutral, as well as decreased negative valence ratings in the afternoon. This decrease in emotional reactivity was correlated with better LTM performance. In contrast, younger adults performed better on the negative compared to neutral word pairs, with no change in emotional reactivity and no association between emotional reactivity and LTM. In addition, WM was positively related to LTM in younger, but not in older adults. Lastly, no differences were shown across sleep, regardless of age. Our findings suggest that the emotional memory bias may be associated with the emotional saliency of the information in older adults, and with WM capacity in younger adults.

Investigating the effects of sleep and sleep loss on the different stages of episodic emotional memory: A narrative review and guide to the future

For two decades, sleep has been touted as one of the primary drivers for the encoding, consolidation, retention, and retrieval of episodic emotional memory. Recently, however, sleep’s role in emotional memory processing has received renewed scrutiny as meta-analyses and reviews have indicated that sleep may only contribute a small effect that hinges on the content or context of the learning and retrieval episodes. On the one hand, the strong perception of sleep’s importance in maintaining memory for emotional events may have been exacerbated by publication bias phenomena, such as the “winner’s curse” and “file drawer problem.” On the other hand, it is plausible that there are sets of circumstances that lead to consistent and reliable effects of sleep on emotional memory; these circumstances may depend on factors such as the placement and quality of sleep relative to the emotional experience, the content and context of the emotional experience, and the probes and strategies used to assess memory at retrieval. Here, we review the literature on how sleep (and sleep loss) influences each stage of emotional episodic memory. Specifically, we have separated previous work based on the placement of sleep and sleep loss in relation to the different stages of emotional memory processing: (1) prior to encoding, (2) immediately following encoding during early consolidation, (3) during extended consolidation, separated from initial learning, (4) just prior to retrieval, and (5) post-retrieval as memories may be restructured and reconsolidated. The goals of this review are three-fold: (1) examine phases of emotional memory that sleep may influence to a greater or lesser degree, (2) explicitly identify problematic overlaps in traditional sleep–wake study designs that are preventing the ability to better disentangle the potential role of sleep in the different stages of emotional memory processing, and (3) highlight areas for future research by identifying the stages of emotional memory processing in which the effect of sleep and sleep loss remains under-investigated. Here, we begin the task of better understanding the contexts and factors that influence the relationship between sleep and emotional memory processing and aim to be a valuable resource to facilitate hypothesis generation and promote important future research.

Wake after Sleep Onset Time Moderated Age-related Emotional Memory Bias

BACKGROUND

Numerous studies have shown that older adults have positive emotional bias. However, how sleep characteristics such as sleep continuity moderate this emotional bias in older adults is less understood.

OBJECTIVES

The present study aimed to determine whether positive emotional memory bias is associated with sleep continuity in older adults.

METHODS

We recruited 92 community-dwelling older adults for a cross-sectional study. Participants underwent 1 week of objective actigraphic sleep monitoring and completed a visuospatial associative memory task at baseline and 1 week later.

RESULTS

Older adults exhibited better memory performance for positive pictures than for neutral and negative pictures at baseline, and this positive emotional bias was maintained for at least 1 week. Crucially, this effect was moderated by sleep continuity: Older adults with shorter wake after sleep onset times (WASO) exhibited this positive bias, whereas those with longer WASO did not.

DISCUSSION

The present results are the first to demonstrate that positive emotional bias is moderated by sleep continuity in older adults. These findings have implications for emotion regulation in older adults and highlight the need for targeted interventions to increase their sleep continuity, which may help to improve emotional processing in this population.

No evidence for intra-individual correlations between sleep-mediated declarative memory consolidation and slow-wave sleep

STUDY OBJECTIVES

Memory consolidation benefits from a retention period filled with sleep. Several theoretical accounts assume that slow-wave sleep (SWS) contributes functionally to processes underlying the stabilization of declarative memories during sleep. However, reports on correlations between memory retention and the amount of SWS are mixed and typically rely on between-subject correlations and small sample sizes. Here we tested for the first time whether the amount of SWS during sleep predicts the effect of sleep on memory consolidation on an intra-individual level in a large sample.

METHODS

One hundred and fifty-nine healthy participants came to the lab twice and took a 90 min nap in both sessions. Sleep-mediated memory benefits were tested using the paired associates word-learning task in both sessions.

RESULTS

In contrast to the theoretical prediction, intra-individual differences in sleep-mediated memory benefits did not significantly correlate with differences in SWS or SWA between the two naps. Also between subjects, the amount of SWS did not correlate with memory retention across the nap. However, subjective ratings of sleep quality were significantly associated with the amount of SWS.

CONCLUSION

Our results question the notion that the amount of SWS per se is functionally related to processes of memory consolidation during sleep. While our results do not exclude an important role of SWS for memory, they suggest that "more SWS" does not necessarily imply better memory consolidation.

Role of Napping for Learning across the Lifespan

Purpose of review

Napping is a common behavior across age groups. While studies have shown a benefit of overnight sleep on memory consolidation, given differences in nap frequency, composition, and intent, it is important to consider whether naps serve a memory function across development and aging.

Recent findings

We review studies of the role of naps in declarative, emotional, and motor procedural memory consolidation across age groups. Recent findings in both developmental and aging populations find that naps benefit learning of many tasks but may require additional learning or sleep bouts compared to young adult populations. These studies have also identified variations in nap physiology based on the purpose of the nap, timing of the nap, or age.

Summary

These studies lend to our understanding of the function of sleep, and the potential for naps as an intervention for those with reduced nighttime sleep or learning impairments.

Go to Bed and You MIGHT Feel Better in the Morning—the Effect of Sleep on Affective Tone and Intrusiveness of Emotional Memories

Purpose of Review

It is important to examine what effect sleep has after an emotional experience. More knowledge about this topic could help inform us whether there are any potential sleep interventions that could help make sure that memories of negative emotional experiences are processed in the most adaptive manner possible.

Recent Findings

Findings on the role of sleep in altering reactivity to emotional stimuli have been highly varied, with significant findings in opposite directions. A new exciting development in the field is several studies finding that sleep seems to make memories of negative experiences less intrusive.

Summary

This review has mainly aimed to give an overview of the field, and of which issues need to be resolved. We argue for there being a strong need for standardization of how data are analyzed and presented, as well as for better methods for determining to what extent the effects of sleep are specific for a particular memory, or represent general changes in emotional reactivity.

Sleep and human cognitive development

Emerging studies across learning domains have shed light on mechanisms underlying sleep's benefits during numerous developmental periods. In this conceptual review, we survey recent studies of sleep and cognition across infancy, childhood, and adolescence. By summarizing recent findings and integrating across studies with disparate approaches, we provide a novel understanding of sleep's role in human cognitive function. Collectively, these studies point to an interrelation between brain development, sleep, and cognition. Moreover, we point to gaps in our understanding, which inform the agenda for future research in developmental and sleep science.

The role of naps in memory and executive functioning in early childhood

While sleep, including naps, has been shown to benefit many cognitive functions in adults, understanding whether naps are beneficial in early childhood has important translational implications. Here we review recent studies which, collectively, suggest that naps indeed benefit cognition at this age. Specifically, declarative, motor, and emotional memory are better if a nap follows learning. Executive functions such as attention and emotion processing are likewise better following sleep. However, a better understanding of the mechanism supporting these benefits and the generalizability to other forms of learning and executive functions is necessary. It is important for future research to extend such findings, which may promote the use of naps to support early education, particularly for learning-impaired children.

Does Sleep Selectively Strengthen Certain Memories Over Others Based on Emotion and Perceived Future Relevance?

Sleep has been found to have a beneficial effect on memory consolidation. It has furthermore frequently been suggested that sleep does not strengthen all memories equally. The first aim of this review paper was to examine whether sleep selectively strengthens emotional declarative memories more than neutral ones. We examined this first by reviewing the literature focusing on sleep/wake contrasts, and then the literature on whether any specific factors during sleep preferentially benefit emotional memories, with a special focus on the often-suggested claim that rapid eye movement sleep primarily consolidates emotional memories. A second aim was to examine if sleep preferentially benefits memories based on other cues of future relevance such as reward, test-expectancy or different instructions during encoding. Once again, we first focused on studies comparing sleep and wake groups, and then on studies examining the contributions of specific factors during sleep (for each future relevance paradigm, respectively). The review revealed that although some support exists that sleep is more beneficial for certain kinds of memories based on emotion or other cues of future relevance, the majority of studies does not support such an effect. Regarding specific factors during sleep, our review revealed that no sleep variable has reliably been found to be specifically associated with the consolidation of certain kinds of memories over others based on emotion or other cues of future relevance.

The association between sleep-wake ratio and overnight picture recognition is moderated by BDNF genotype

A wealth of studies supports the role of sleep in memory performance. Experimentally controlled studies indicate that prolonged wake after memory encoding is detrimental for memory outcome whereas sleep protects from wake-time interference and promotes memory consolidation. We examined how the natural distribution of wake and sleep between encoding and retrieval associated with overnight picture recognition accuracy among 161 adolescents following their typical sleep schedule with an in-home polysomnography. The memorized pictures varied in their level of arousal (calm to exciting) and valence (negative to positive). Suspecting genotypic influence on the sensitivity for sleep/wake dynamics, we also assessed if these associations were affected by known gene polymorphisms involved in neural plasticity and sleep homeostasis: brain-derived neurotrophic factor (BDNF) Val66Met and Catechol-O-methyltransferase (COMT) Val158Met. In the whole sample, overnight recognition accuracy was associated with the levels of arousal and valence of the pictures, but not with sleep percentage (i.e. the percentage of time spent asleep between memory encoding and retrieval). While the allelic status of BDNF or COMT did not have any main effect on recognition accuracy, a significant moderation by BDNF Val66Met was found (p = .004): the subgroup homozygous for valine allele showed positive association between sleep percentage and recognition accuracy. This was underlain by detrimental influence of wake, rather than by any memory benefit of sleep. Our results complement the mounting evidence that the relation between sleep and memory performance is moderated by BDNF Val66Met. Further studies are needed to clarify the specific mechanisms.

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.

Association of Internet Use with Attitudes Toward Food Safety in China: A Cross-Sectional Study

A growing body of research has shown that people’s attitudes toward food safety is affected by their availability and accessibility to food risk information. In the digital era, the Internet has become the most important channel for information acquisition. However, empirical evidence related to the impact of Internet use on people’s attitudes towards food safety is inadequate. In this study, by employing the Chinese Social Survey for 2013 and 2015, we have investigated the current situation of food safety perceptions and evaluations among Chinese residents and the association between Internet use and individuals’ food safety evaluations. Empirical results indicate that there is a significant negative correlation between Internet use and people’s food safety evaluation in China. Furthermore, heterogeneity analysis shows that Internet use has a stronger negative correlation with food safety evaluation for those lacking rational judgment regarding Internet information. Specifically, the negative correlation between Internet use and food safety evaluations is more obvious among rural residents, young people, and less educated residents. Finally, propensity score matching (PSM) is applied to conduct a robustness check. This paper provides new evidence for studies on the relationship between Internet use and an individuals’ food safety cognition, as well as additional policy enlightenment for food safety risk management in the digital age.

Sleep preserves subjective and sympathetic emotional response of memories

Sleep consolidates episodic content of emotional memories. Whether it likewise preserves or, to the contrary, depotentiates the emotional response associated with memory content is unclear, as there is conflicting evidence. In the current study, we investigated the influence of an afternoon nap (2-hr nap opportunity) on emotional responses of memories using multiple simultaneous measures. Young adults viewed 45 negative and 45 neutral pictures before taking a nap (measured with polysomnography) or remaining awake. Following the nap or wake period, participants viewed the same pictures intermixed with novel ones and indicated whether they remembered each picture. Emotional response to each picture was measured at both time points both subjectively, with valence and arousal ratings, and objectively, with recordings of electrodermal activity, electrocardiography, and corrugator supercilii electromyography. Compared to waking, a nap led to preserved subjective valence for negative pictures and preserved/increased skin conductance response in general. On the other hand, heart rate deceleration response decreased over the nap compared to wake interval, and this result was not influenced by picture type. These data suggest that sleep consolidates aspects of both subjective and physiological emotional response associated with episodic memory content. While sympathetic response appears to be preserved over sleep, parasympathetic response may be diminished.

The Interaction of REM Fragmentation and Night-Time Arousal Modulates Sleep-Dependent Emotional Memory Consolidation

The sleep-to-forget, sleep-to-remember (SFSR) hypothesis states that the neurobiological environment provided by rapid-eye movement (REM)-rich sleep decouples the content of an emotional memory from its attendant emotional arousal. This decoupling allows divergent attenuation and enhancement effects (i.e., erosion of the memory’s emotional tone and simultaneous strengthening of its content). However, support for this proposal is mixed. An alternative account suggests there might be convergent attenuation and enhancement (i.e., elevated emotional arousal is positively coupled with enhanced emotional memory). We tested predictions emerging from the SFSR hypothesis using (a) individuals diagnosed with post-traumatic stress disorder (PTSD; n = 21), (b) trauma-exposed non-PTSD individuals (n = 19), and (c) healthy controls (n = 20). We included PTSD-diagnosed individuals because they typically experience altered REM sleep, impaired emotional memory, and heightened emotional arousal in response to threatening stimuli. Participants were assessed before and after both an 8-h period of polysomnographically monitored sleep and an 8-h period of waking activity. The assessment included exposure to negatively valenced, positively valenced, and neutral pictures before the 8-h delay, and a recognition task afterward. We measured emotional arousal by recording psychophysiological responses to the pictures, both pre- and post-delay. Results indicated no significant between-group differences in emotional memory accuracy or arousal. However, after a sleep-filled delay, pictures of all categories were recognized with equal accuracy, whereas after a wake-filled delay, negative pictures were recognized preferentially. Furthermore, the findings demonstrated that a sleep-filled delay was associated with attenuated emotional arousal to pictures of all categories, whereas a wake-filled delay was associated with a rise in emotional arousal across the day. Intriguingly, poorer recognition accuracy for valenced (but not neutral) pictures was predicted by an interaction of increased REM fragmentation and increased emotional arousal. In summary, we found some support for the SFSR hypothesis in the way it describes the REM- and arousal-based mechanisms that process emotional material. We also, however, found disconfirming evidence regarding the outcome of that process (i.e., sleep did not favor consolidation of emotional over neutral memory), and we demonstrated a convergence between attenuation of emotional arousal and weakening of emotional content relative to neutral content.

Age differences in the relationship between cortisol and emotional memory

Research has shown that remembering emotional information can occur at the expense of surrounding neutral background information; this emotional memory trade-off occurs similarly in both younger and older adults. We investigated how levels of cortisol, a hormone that acts on the central nervous system, impact emotional memory with age. Younger and older adult participants incidentally encoded emotional (positive, negative, or neutral) items placed on neutral backgrounds and later completed recognition tests for both the items and the backgrounds. Cortisol was measured at multiple time points to assess basal cortisol. Results are reported for prelearning levels, as findings were comparable across time points. Results revealed that higher levels of cortisol predicted a lower memory trade-off effect for older adults compared to younger adults and that this age difference in the role of cortisol tended to be strongest for memory for negative items (rather than for backgrounds or neutral items). No such interaction emerged for the positive trade-off effect. These results suggest that cortisol levels play a different role in supporting emotional memory across the life span, with lower levels of cortisol potentially more adaptive for memory for negative emotional information and higher levels indicating potential impairment with age. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

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.

Sleep Preserves Physiological Arousal in Emotional Memory

Traumatic experiences are associated with increased emotional arousal. Overnight consolidation strengthens the episodic content of emotional memories, but it is still unclear how sleep influences the associated arousal response. To investigate this question, we compared the effects of sleep and wake on psychophysiological and subjective reactivity during emotional memory retrieval. Participants provided affective ratings for negative and neutral images while heart rate deceleration (HRD) and skin conductance responses (SCRs) were monitored. Following a 12-hour delay of sleep or wakefulness, participants completed an image recognition task where HRD, SCRs and affective ratings were recorded again. HRD responses to previously-encoded (“old”) negative images were preserved after sleep but diminished after wakefulness. No between-group difference in HRD was observed for novel negative images at recognition, indicating that the effects of sleep for old images were not driven by a generalised overnight increase in visceral activity, or circadian factors. No significant effects of sleep were observed for SCRs or subjective ratings. Our data suggest that cardiac arousal experienced at the time of encoding is sensitive to plasticity-promoting processes during sleep in a similar manner to episodic aspects of emotional memory.

Emotional Memory Moderates the Relationship Between Sigma Activity and Sleep-Related Improvement in Affect

Sleep is essential for regulating mood and affect, and it also consolidates emotional memories. The mechanisms underlying these effects may overlap. Here, we investigated whether the influence of sleep on affect may be moderated by emotional memory consolidation. Young adults viewed 45 negative and 45 neutral pictures before taking an afternoon nap measured with polysomnography. Following the nap period, participants viewed the same pictures intermixed with novel ones and indicated whether they remembered each picture. Affect was measured with the Positive and Negative Affect Schedule (PANAS) at baseline before the initial picture viewing task, immediately following the initial picture viewing task, and following the nap. The ratio of positive to negative affect declined over the task period and recovered over the nap period. When controlling for pre-nap affect, NREM sigma activity significantly predicted post-nap affect. Memory for negative pictures moderated this relationship such that a positive association between sigma activity and affect occurred when memory was low but not when memory was high. These results indicate that emotional memory consolidation influences the relationship between nap physiology and mood.

The interplay between neuroendocrine and sleep alterations following traumatic brain injury

BACKGROUND

Sleep and endocrine disruptions are prevalent after traumatic brain injury (TBI) and are likely to contribute to morbidity.

OBJECTIVE

To describe the interaction between sleep and hormonal regulation following TBI and elucidate the impact that alterations of these systems have on cognitive responses during the posttraumatic chronic period.

METHODS

Review of preclinical and clinical literature describing long-lasting endocrine dysregulation and sleep alterations following TBI. The bidirectional relationship between sleep and hormones is described. Literature describing co-occurrence between sleep-wake disturbances and hormonal dysregulation will be presented. Review of literature describing cognitive effects of seep and hormones. The cognitive and functional impact of sleep disturbances and hormonal dysregulation is discussed within the context of TBI.

RESULTS/CONCLUSIONS

Sleep and hormonal alterations impact cognitive and functional outcome after TBI. Diagnosis and treatment of these disturbances will impact recovery following TBI and should be considered in the post-acute rehabilitative setting.

Sleep extension reduces fatigue in healthy, normally-sleeping young adults

Objective

To assess the effects of one week of sleep extension on mood, fatigue and subjective sleepiness in normal-sleeping young adults.

Methods

Twenty-seven adults (age 24.4±5.4 years, 11 female) participated. At-home baseline sleep/wake patterns were recorded with wrist actigraphy for 14 days. This was followed by two nights of in-lab baseline sleep with 8 hours time in bed (TIB), then 7 nights with TIB extended to 10 hours (2100-0700 hours). Fatigue, mood, and sleepiness were assessed following the 2^nd and 9^th nights of in-laboratory sleep (i.e., 2 nights with 8hTIB and 7 nights with 10 hours TIB, respectively) using the Automated Neuropsychological Assessment Metric and Karolinska Sleepiness Scale. Paired t-tests were used to compare mood, fatigue, and sleepiness ratings between conditions.

Results

At-home wrist actigraphy revealed a mean nightly total sleep time (TST) of 7.53 +/- 0.88 hours of sleep per night. Mean in-lab baseline sleep duration (7.76 +/- 0.59) did not differ from at-home sleep. However, during sleep extension, mean TST was 9.36 +/- 0.37 hours per night, significantly more than during the in-lab baseline (p < .001). Following sleep extension, fatigue ratings were significantly reduced, relative to baseline (p = .03). However, sleep extension had no other significant effects on subjective ratings of mood or sleepiness.

Conclusions

Sleep extension resulted in reduced fatigue in healthy, normal-sleeping young adults, although subjective sleepiness and mood were not improved. Implications include the possibility that (a) the effects of sleep extension on various aspects of mood depend upon the extent to which those aspects of mood are made salient by the study design and methodology; and (b) sleep extension may prove beneficial to fatigue-related conditions such as “burnout.”

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.

Sleep-dependent enhancement of emotional memory in early childhood

Naps in early childhood support declarative memory consolidation. However, emotional memories are unique in the neural basis of encoding as well as the sleep physiology underlying consolidation. Specifically, while consolidation of declarative memories has been associated with slow wave sleep, a prevailing theory suggests that REM sleep is necessary for consolidation of memories with emotional valence. Thus, we presented children (34-64 months) with faces paired with mean or nice descriptions. There were no significant main effects of emotional valence on recognition memory. Change in memory accuracy also did not differ when probed after a nap compared to the change in memory accuracy after an interval awake. However, when memory was probed again following overnight sleep, the change in memory accuracy was greater if the child napped the previous day. Greater nap slow wave activity was associated with greater memory decay during the nap. Yet nap slow wave activity also predicted greater overnight improvement in memory. These results suggest that sleep bouts can interact to benefit memory in early childhood.

The role of sleep in emotional memory processing in middle age

Sleep benefits memory in young adults, and this effect may be particularly strong for representations associated with negative emotion. Many aspects of sleep important for memory consolidation change with aging, particularly by middle age, suggesting that sleep-related consolidation may be reduced. However, the influence of sleep on memory has rarely been investigated in a middle-aged population. In the current study, young and middle-aged adults viewed negative and neutral pictures and underwent a recognition test after sleep or wake. Subjective emotional reactivity was also measured. Compared to waking, sleep benefited memory in young adults. Performance did not differ between sleep and wake groups in middle-aged adults, and it matched the level of young adults who slept. The effect of sleep versus wake was not influenced by memory valence in either age group. These results suggest the relative influence of sleep compared to wake on memory declines with aging, specifically by middle age, and that this decline extends to negative memory.

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

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

Exploring the nap paradox: are mid-day sleep bouts a friend or foe?

The mid-day nap, sometimes called a siesta, is a ubiquitous occurrence across the lifespan. It is well established that in addition to reducing sleepiness, mid-day naps offer a variety of benefits: memory consolidation, preparation for subsequent learning, executive functioning enhancement, and a boost in emotional stability. These benefits are present even if a sufficient amount of sleep is obtained during the night prior. However, we present a paradox: in spite of these reported benefits of naps, frequent napping has also been associated with numerous negative outcomes (eg, cognitive decline, hypertension, diabetes), particularly in older populations. This association exists even when statistically controlling for relevant health- and sleep-affecting determinants. An emerging hypothesis suggests inflammation is a mediator between mid-day naps and poor health outcomes, yet further research is necessary. Given this, it may be premature to 'prescribe' naps as a health enhancer. Herein, we aggregate findings from several branches of sleep research (eg, developmental neuroscience, cognitive neuroscience, sleep medicine) to critically examine the paradoxical role of naps in cognitive and somatic health. This review uncovers gaps in the literature to guide research opportunities in the field.

Mild Traumatic Brain Injury Chronically Impairs Sleep- and Wake-Dependent Emotional Processing

Study Objectives

A single traumatic brain injury (TBI), even when mild (ie, concussion), can cause lasting consequences. Individuals with a history of chronic (>1-year prior) mild TBI have an increased risk of mood disturbances (eg, depression, suicide). This population also has lingering sleep alterations, including poor sleep quality and changes in sleep stage proportions. Given these sleep deficits, we aimed to test whether sleep-dependent emotional memory consolidation is reduced in this population. We utilized a mild TBI group (3.7 ± 2.9 years post injury) and an uninjured (non-TBI) population.

Methods

Participants viewed negative and neutral images both before and after a 12-hour period containing sleep ("Sleep" group) or an equivalent period of time spent awake ("Wake" group). Participants rated images for valence/arousal at both sessions, and memory recognition was tested at session two.

Results

The TBI group had less rapid eye movement (REM), longer REM latency, and more sleep complaints. Sleep-dependent memory consolidation of nonemotional images was present in all participants. However, consolidation of negative images was only present in the non-TBI group. A lack of differentiation between the TBI Sleep and Wake groups was due to poor performance in the sleep group and, unexpectedly, enhanced performance in the wake group. Additionally, although the non-TBI participants habituated to negative images over a waking period, the TBI participants did not.

Conclusions

We propose disrupted sleep- and wake-dependent emotional processing contributes to poor emotional outcomes following chronic, mild TBI. This work has broad implications, as roughly one-third of the US population will sustain a mild TBI during their lifetime.

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

A period of post-learning sleep benefits memory consolidation compared with an equal-length wake interval. However, whether this sleep-based memory consolidation changes as a function of age remains controversial. Here we report a meta-analysis that investigates the age differences in the sleep-based memory consolidation in two types of memory: declarative memory and procedural memory. The meta-analysis included 22 comparisons of the performance between young adults (N =640) and older adults (N =529) on behavioral tasks measuring sleep-based memory consolidation. Our results showed a significant overall sleep-based beneficial effect in young adults but not in older adults. However, further analyses suggested that the age differences were mainly manifested in sleep-based declarative memory consolidation but not in procedural memory consolidation. We discussed the possible underlying mechanisms for the age-related degradation in sleep-based memory consolidation. Further research is needed to determine the crucial components for sleep-related memory consolidation in older adults such as age-related changes in neurobiological and cardiovascular functions, which may play an important role in this context and have the potential to delineate the interrelationships between age-related changes in sleep and memory.