Stress, sleep, and the selective consolidation of emotional memories

A visual paired associate learning (vPAL) paradigm to study memory consolidation during sleep

Sleep improves the consolidation and long-term stability of newly formed memories and associations. Most research on human declarative memory and its consolidation during sleep uses word-pair associations requiring exhaustive learning. In the present study, we present the visual paired association learning (vPAL) paradigm, in which participants learn new associations between images of celebrities and animals. The vPAL is based on a one-shot exposure that resembles learning in natural conditions. We tested if vPAL can reveal a role for sleep in memory consolidation by assessing the specificity of memory recognition, and the cued recall performance, before and after sleep. We found that a daytime nap improved the stability of recognition memory and discrimination abilities compared to identical intervals of wakefulness. By contrast, cued recall of associations did not exhibit significant sleep-dependent effects. High-density electroencephalography during naps further revealed an association between sleep spindle density and stability of recognition memory. Thus, the vPAL paradigm opens new avenues for future research on sleep and memory consolidation across ages and heterogeneous populations in health and disease.

The effects of shared, depression-specific, and anxiety-specific internalizing symptoms on negative and neutral episodic memories following post-learning sleep

Emotional memory bias is a common characteristic of internalizing symptomatology and is enhanced during sleep. The current study employs bifactor S-1 modeling to disentangle depression-specific anhedonia, anxiety-specific anxious arousal, and the common internalizing factor, general distress, and test whether these internalizing symptoms interact with sleep to influence memory for emotional and neutral information. Healthy adults (N = 281) encoded scenes featuring either negative objects (e.g., a vicious looking snake) or neutral objects (e.g., a chipmunk) placed on neutral backgrounds (e.g., an outdoor scene). After a 12-hour period of daytime wakefulness (n = 140) or nocturnal sleep (n = 141), participants judged whether objects and backgrounds were the same, similar, or new compared with what they viewed during encoding. Participants also completed the mini version of the Mood and Anxiety Symptom Questionnaire. Higher anxious arousal predicted worse memory across all stimuli features, but only after a day spent being awake-not following a night of sleep. No significant effects were found for general distress and anhedonia in either the sleep or wake condition. In this study, internalizing symptoms were not associated with enhanced emotional memory. Instead, memory performance specifically in individuals with higher anxious arousal was impaired overall, regardless of emotional valence, but this was only the case when the retention interval spanned wakefulness (i.e., not when it spanned sleep). This suggests that sleep may confer a protective effect on general memory impairments associated with anxiety.

The role of objective sleep in implicit and explicit affect regulation: A comprehensive review

Impairments in sleep and affect regulation are evident across a wide range of mental disorders. Understanding the sleep factors that relate to affect regulatory difficulties will inform mechanistic understanding and aid in treatment. Despite rising interest, some research challenges in this area include integrating across different clinical and non-clinical literatures investigating the role of sleep architecture (measured with polysomnography) and experimentally manipulated sleep, as well as integrating more explicit versus implicit affect regulation processes. In this comprehensive review, we use a unifying framework to examine sleep's relationship with implicit-automatic regulation and explicit-controlled regulation, both of which are relevant to mental health (e.g., PTSD and depression). Many studies of implicit-automatic regulation (e.g., fear extinction and safety learning) demonstrate the importance of sleep, and REM sleep specifically. Studies of explicit-controlled regulation (e.g., cognitive reappraisal and expressive suppression) are less consistent in their findings, with results differing depending on the type of affect regulation and/or way that sleep was measured or manipulated. There is a clear relationship between objective sleep and affect regulation processes. However, there is a need for 1) more studies focusing on sleep and explicit-controlled affect regulation; 2) replication with the same types of regulation strategies; 3) more studies experimentally manipulating sleep to examine its impact on affect regulation and vice versa in order to infer cause and effect; and 4) more studies looking at sleep's impact on next-day affect regulation (not just overnight change in affect reactivity).

Acute Stress Effects on Statistical Learning and Episodic Memory

Stress is widely considered to negatively impact hippocampal function, thus impairing episodic memory. However, the hippocampus is not merely the seat of episodic memory. Rather, it also (via distinct circuitry) supports statistical learning. On the basis of rodent work suggesting that stress may impair the hippocampal pathway involved in episodic memory while sparing or enhancing the pathway involved in statistical learning, we developed a behavioral experiment to investigate the effects of acute stress on both episodic memory and statistical learning in humans. Participants were randomly assigned to one of three conditions: stress (socially evaluated cold pressor) immediately before learning, stress ∼15 min before learning, or no stress. In the learning task, participants viewed a series of trial-unique scenes (allowing for episodic encoding of each image) in which certain scene categories reliably followed one another (allowing for statistical learning of associations between paired categories). Memory was assessed 24 hr later to isolate stress effects on encoding/learning rather than retrieval. We found modest support for our hypothesis that acute stress can amplify statistical learning: Only participants stressed ∼15 min in advance exhibited reliable evidence of learning across multiple measures. Furthermore, stress-induced cortisol levels predicted statistical learning retention 24 hr later. In contrast, episodic memory did not differ by stress condition, although we did find preliminary evidence that acute stress promoted memory for statistically predictable information and attenuated competition between statistical and episodic encoding. Together, these findings provide initial insights into how stress may differentially modulate learning processes within the hippocampus.

Consolidation of emotional memory during waking rest depends on trait anxiety

A short period of eyes-closed waking rest improves long-term memory for recently learned information, including declarative, spatial, and procedural memory. However, the effect of rest on emotional memory consolidation remains unknown. This preregistered study aimed to establish whether post-encoding rest affects emotional memory and how anxiety levels might modulate this effect. Participants completed a modified version of the dot-probe attention task that involved reacting to and encoding word stimuli appearing underneath emotionally negative or neutral photos. We tested the effect of waking rest on memory for these words and pictures by manipulating the state that participants entered just after this task (rest vs. active wake). Trait anxiety levels were measured using the State-Trait Anxiety Inventory and examined as a covariate. Waking rest improved emotional memory consolidation for individuals high in trait anxiety. These results suggest that the beneficial effect of waking rest on memory extends into the emotional memory domain but depends on individual characteristics such as anxiety.

Overnight neuronal plasticity and adaptation to emotional distress

Expressions such as 'sleep on it' refer to the resolution of distressing experiences across a night of sound sleep. Sleep is an active state during which the brain reorganizes the synaptic connections that form memories. This Perspective proposes a model of how sleep modifies emotional memory traces. Sleep-dependent reorganization occurs through neurophysiological events in neurochemical contexts that determine the fates of synapses to grow, to survive or to be pruned. We discuss how low levels of acetylcholine during non-rapid eye movement sleep and low levels of noradrenaline during rapid eye movement sleep provide a unique window of opportunity for plasticity in neuronal representations of emotional memories that resolves the associated distress. We integrate sleep-facilitated adaptation over three levels: experience and behaviour, neuronal circuits, and synaptic events. The model generates testable hypotheses for how failed sleep-dependent adaptation to emotional distress is key to mental disorders, notably disorders of anxiety, depression and post-traumatic stress with the common aetiology of insomnia.

The effect of negative arousal on declarative memory

Arousing events influence retrieval success, with a number of studies supporting a context-dependent effect of arousal on episodic memory retrieval. An improvement in speed and accuracy of episodic memories is observed when negative arousal is attached to them. In contrast, enhancing effects of negative arousal have not been reported to improve semantic memory retrieval. Episodic and semantic memory are highly interactive and yet differ based on their embedded contextual content. Although differences in brain activity exist between episodic and semantic memory, the two types of memory retrieval are part of a common long-term memory system. Considering the shared processes between episodic and semantic memory, the objectives of the current study were twofold: i) to examine, employing a novel paradigm, whether performance on episodic and semantic memory retrieval would be influenced differently by varying levels of arousal, between negative and neutral valence; and ii) to explore the neural patterns underlying these processes. Forty-seven healthy young adults were recruited and completed the experiment in the MRI scanner. The results demonstrated a negative arousal effect on the brain circuitry subserving both memory conditions as well as on behavioural performance, as indicated by better accuracy and faster reaction times. The study provides an insight into the role of negative arousal in memory processes and contributes to our understanding of the interplay between cognitive and emotional factors in memory modulation. Our work also highlights the highly interactive nature of episodic and semantic memory, and emphasises the importance in understanding how negative arousal interacts with the contextual content of a memory, on a behavioural and neurofunctional level.

Age-related positivity effect in emotional memory consolidation from middle age to late adulthood

Background

While younger adults are more likely to attend to, process, and remember negative relative to positive information, healthy older adults show the opposite pattern. The current study evaluates when, exactly, this positivity shift begins, and how it influences memory performance for positive, negative, and neutral information.

Methods

A total of 274 healthy early middle-aged (35-47), late middle-aged (48-59), and older adults (>59) viewed scenes consisting of a negative, positive, or a neutral object placed on a plausible neutral background, and rated each scene for its valence and arousal. After 12 h spanning a night of sleep (n = 137) or a day of wakefulness (n = 137), participants completed an unexpected memory test during which they were shown objects and backgrounds separately and indicated whether the scene component was the "same," "similar," or "new" to what they viewed during the study session.

Results and conclusions

We found that both late middle-aged and older adults rated positive and neutral scenes more positively compared to early middle-aged adults. However, only older adults showed better memory for positive objects relative to negative objects, and a greater positive memory trade-off magnitude (i.e., remembering positive objects at the cost of their associated neutral backgrounds) than negative memory trade-off magnitude (i.e., remembering negative objects at the cost of their associated neutral backgrounds). Our findings suggest that while the positivity bias may not emerge in memory until older adulthood, a shift toward positivity in terms of processing may begin in middle age.

Sleep spindles consolidate declarative memory with tags: A meta-analysis of adult data

Tags are attached to salient information during the wake period, which can preferentially determine what information can be consolidated during sleep. Previous studies demonstrated that spindles during non-rapid eye movement (NREM) sleep give priority to strengthening memory representations with tags, indicating a privileged reactivation of tagged information. The current meta-analysis investigated whether and how spindles can capture different tags to consolidate declarative memory. This study searched the Web of Science, Google Scholar, PubMed, PsycINFO, and OATD databases for studies that spindles consolidate declarative memory with tags. A meta-analysis using a random-effects model was performed. Based on 19 datasets from 18 studies (N = 388), spindles had a medium effect on the consolidation of declarative memory with tags ( r = 0.519). In addition, spindles derived from whole-night sleep and nap studies were positively related to the consolidation of memory representations with tags. These findings reveal the shared mechanism that spindles are actively involved in the prefrontal-hippocampus circuits to consolidate memory with tags.

Inducing emotionally negative nonbelieved memories using negative pictures

Memories that can be recalled but are no longer believed are termed nonbelieved memories. The current studies examined the creation of emotionally negative nonbelieved memories after viewing negatively valenced pictures. In both experiments, participants took part in two sessions. In Session 1, after being presented with a set of neutral and negative pictures, participants had to rate their emotional state. One week later, in Session 2, participants had to complete a recognition task to identify pictures that had appeared during the previous session. During this task, participants' memories for some pictures were challenged by telling them that their answers were incorrect in order to evoke nonbelieved memories. The experimental procedure was successful in creating nonbelieved memories in the participants. Specifically, in Experiment 1 (N = 35), we induced nonbelieved true memories for both negative and neutral pictures. We found a significant decrease in both belief and recollection after the challenge, with the change in belief being twice as large as the change in recollection. In Experiment 2 (N = 43), we successfully induced both nonbelieved true and false memories for negative pictures. Again, the reduction of belief was significantly greater than that of recollection. In general, participants evinced better memory for negative pictures, but following challenges people were just as likely to accept false social feedback and change their memories regarding other types of pictures. In both experiments, our challenges did not lead to notable changes in emotional state. In general, our findings show that emotionally negative nonbelieved memories can be successfully evoked in an experimental setting.

Continuously changing memories: a framework for proactive and non-linear consolidation

The traditional view of long-term memory is that memory traces mature in a predetermined 'linear' process: their neural substrate shifts from rapidly plastic medial temporal regions towards stable neocortical networks. We propose that memories remain malleable, not by repeated reinstantiations of this linear process but instead via dynamic routes of proactive and non-linear consolidation: memories change, their trajectory is flexible and reversible, and their physical basis develops continuously according to anticipated demands. Studies demonstrating memory updating, increasing hippocampal dependence to support adaptive use, and rapid neocortical plasticity provide evidence for continued non-linear consolidation. Although anticipated demand can affect all stages of memory formation, the extent to which it shapes the physical memory trace repeatedly and proactively will require further dedicated research.

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.

Independent effects of emotional arousal and reward anticipation on episodic memory formation

Events that elicit emotional arousal or are associated with reward are more likely remembered. Emotional arousal activates the amygdala and the central noradrenergic system, whereas reward anticipation results in an activity in the mesocorticolimbic dopaminergic system. The activation of both pathways enhances memory formation in the hippocampus where their effects are based on similar neural substrates, e.g. tagging of active hippocampal synapses. Moreover, emotional arousal and reward anticipation both enhance attention, which can also affect memory formation. In addition, both neuromodulators interact on the cellular level. Therefore, we tested in the current functional magnetic resonance imaging study whether simultaneously occurring emotional arousal and reward anticipation might have interacting effects on memory formation. We did not find evidence for such an interaction, neither on the behavioral nor on the neural level. Our results further suggest that reward anticipation enhances memory formation rather by an increase in anticipation-related arousal-reflected in activity in the dorsal anterior cingulate cortex-and not dopaminergic midbrain activity. Accompanying behavioral experiments indicated that the effect of reward anticipation on memory is (i) caused at least to some extent by anticipating the speeded response to obtain the reward and not by the valance of the outcome and (ii) can be observed already immediately after encoding, i.e. before consolidation.

The power of negative and positive episodic memories

The power of episodic memories is that they bring a past moment into the present, providing opportunities for us to recall details of the experiences, reframe or update the memory, and use the retrieved information to guide our decisions. In these regards, negative and positive memories can be especially powerful: Life’s highs and lows are disproportionately represented in memory, and when they are retrieved, they often impact our current mood and thoughts and influence various forms of behavior. Research rooted in neuroscience and cognitive psychology has historically focused on memory for negative emotional content. Yet the study of autobiographical memories has highlighted the importance of positive emotional memories, and more recently, cognitive neuroscience methods have begun to clarify why positive memories may show powerful relations to mental wellbeing. Here, we review the models that have been proposed to explain why emotional memories are long-lasting (durable) and likely to be retrieved (accessible), describing how in overlapping—but distinctly separable—ways, positive and negative memories can be easier to retrieve, and more likely to influence behavior. We end by identifying potential implications of this literature for broader topics related to mental wellbeing, education, and workplace environments.

Distinct stress-related changes in intrinsic amygdala connectivity predict subsequent positive and negative memory performance

Experiencing stress before an event can influence how that event is later remembered. In the current study, we examine how individual differences in one's physiological response to a stressor are related to changes to underlying brain states and memory performance. Specifically, we examined how changes in intrinsic amygdala connectivity relate to positive and negative memory performance as a function of stress response, defined as a change in cortisol. Twenty-five participants underwent a social stressor before an incidental emotional memory encoding task. Cortisol samples were obtained before and after the stressor to measure individual differences in stress response. Three resting state scans (pre-stressor, post-stressor/pre-encoding and post-encoding) were conducted to evaluate pre- to post-stressor and pre- to post-encoding changes to intrinsic amygdala connectivity. Analyses examined relations between greater cortisol changes and connectivity changes. Greater cortisol increases were associated with a greater decrease in prefrontal-amygdala connectivity following the stressor and a reversal in the relation between prefrontal-amygdala connectivity and negative vs. positive memory performance. Greater cortisol increases were also associated with a greater increase in amygdala connectivity with a number of posterior sensory regions following encoding. Consistent with prior findings in non-stressed individuals, pre- to post-encoding increases in amygdala-posterior connectivity were associated with greater negative relative to positive memory performance, although this was specific to lateral rather than medial posterior regions and to participants with the greatest cortisol changes. These findings suggest that stress response is associated with changes in intrinsic connectivity that have downstream effects on the valence of remembered emotional content.

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.

Slow oscillation-spindle coupling is negatively associated with emotional memory formation following stress

Both stress and sleep enhance emotional memory. They also interact, with the largest effect of sleep on emotional memory being seen when stress occurs shortly before or after encoding. Slow wave sleep (SWS) is critical for long-term episodic memory, facilitated by the temporal coupling of slow oscillations and sleep spindles. Prior work in humans has shown these associations for neutral information in non-stressed participants. Whether coupling interacts with stress to facilitate emotional memory formation is unknown. Here, we addressed this question by reanalyzing an existing dataset of 64 individuals. Participants underwent a psychosocial stressor (32) or comparable control (32) prior to the encoding of 150-line drawings of neutral, positive, and negative images. All participants slept overnight with polysomnography, before being given a surprise memory test the following day. In the stress group, time spent in SWS was positively correlated with memory for images of all valences. Results were driven by those who showed a high cortisol response to the stressor, compared to low responders. The amount of slow oscillation-spindle coupling during SWS was negatively associated with neutral and emotional memory in the stress group only. The association with emotional memory was significantly stronger than for neutral memory within the stress group. These results suggest that stress around the time of initial memory formation impacts the relationship between slow wave sleep and memory.

Effects of sleep on positive, negative and neutral valenced story and image memory

During sleep, emotional memories are preferentially strengthened. However, most studies on sleep and emotional memory focus on comparing negative valence with neutral valence stimuli. This study compared the sleep‐dependent memory effects for stories and images, each comprising negative, neutral, and positive stimuli. It was hypothesized that a sleep effect would be seen for negatively and positively valenced stimuli. A novel story memory task (comprising three stories), and photographs from the Nencki Affective Picture database were presented for learning to 61 healthy adults (ages 18–25). They were tested for memory on the two tasks immediately, and then again after either a 2‐hr nap (n = 31; 17 women, 14 men) or 2‐hr wake period (n = 30; 13 women, 17 men). At second testing, the sleep condition had significantly better recall compared to the wake condition on both tasks. There was a relationship with valence only for the story task, with better performance for the sleep condition on the negatively and positively valenced texts, but not on the neutral text. There were no significant relationships between memory measures and sleep‐stage duration and EEG power variables. The story memory findings support the hypothesis that memory consolidation prioritizes emotional memory, whether positively or negatively valenced.

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

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

Optimistic amnesia: how online and offline processing shape belief updating and memory biases in immediate and long-term optimism biases

When people are confronted with feedback that counters their prior beliefs, they preferentially rely on desirable rather than undesirable feedback in belief updating, i.e. an optimism bias. In two pre-registered EEG studies employing an adverse life event probability estimation task, we investigated the neurocognitive processes that support the formation and the change of optimism biases in immediate and 24 h delayed tests. We found that optimistic belief updating biases not only emerged immediately but also became significantly larger after 24 h, suggesting an active role of valence-dependent offline consolidation processes in the change of optimism biases. Participants also showed optimistic memory biases: they were less accurate in remembering undesirable than desirable feedback probabilities, with inferior memories of undesirable feedback associated with lower belief updating in the delayed test. Examining event-related brain potentials (ERPs) revealed that desirability of feedback biased initial encoding: desirable feedback elicited larger P300s than undesirable feedback, with larger P300 amplitudes predicting both higher belief updating and memory accuracies. These results suggest that desirability of feedback could bias both online and offline memory-related processes such as encoding and consolidation, with both processes contributing to the formation and change of optimism biases.

How stress affects sleep and mental health: nocturnal heart rate increases during prolonged stress and interacts with childhood trauma exposure to predict anxiety

STUDY OBJECTIVES

Stress can adversely impact sleep health by eliciting arousal increase and a cascade of endocrine reactions that may impair sleep. To date, little is known regarding continuous effects of real-world stress on physiological sleep characteristics and potential effects on stress-related psychopathology. We examined effects of stress on heart rate (HR) during sleep and total sleep time (TST) during prolonged real-world stress exposure in medical interns. Moreover, we investigated the influence of previous stress and childhood trauma exposure on HR during sleep, TST, and its interaction in predicting anxiety.

METHODS

We examined a sample of 50 medical students prior to and during their first internship, a well described real-world stressor. HR and TST were continuously collected over 12 weeks non-invasively by a wrist-worn activity monitor. Prior to starting the internship, at baseline, participants reported on their sleep, anxiety, and childhood trauma exposure. They also tracked stress exposure during internship and reported on their anxiety symptoms 3 months after this professional stress.

RESULTS

Mean HR during sleep increased over time, while TST remained unchanged. This effect was more pronounced in interns exposed to childhood trauma exposure. In multilevel models, childhood trauma exposure also moderated the relation between individual HR increase and development of anxiety.

CONCLUSIONS

Prolonged stress may lead to increased HR during sleep, whereas individuals with childhood trauma exposure are more vulnerable. Childhood trauma exposure also moderated the relation between individual HR increase and development of anxiety. These findings may inform prevention and intervention measures.

Effects of the antibiotic rifaximin on cortical functional connectivity are mediated through insular cortex

It is well-known that antibiotics affect commensal gut bacteria; however, only recently evidence accumulated that gut microbiota (GM) can influence the central nervous system functions. Preclinical animal studies have repeatedly highlighted the effects of antibiotics on brain activity; however, translational studies in humans are still missing. Here, we present a randomized, double-blind, placebo-controlled study investigating the effects of 7 days intake of Rifaximin (non-absorbable antibiotic) on functional brain connectivity (fc) using magnetoencephalography. Sixteen healthy volunteers were tested before and after the treatment, during resting state (rs), and during a social stressor paradigm (Cyberball game—CBG), designed to elicit feelings of exclusion. Results confirm the hypothesis of an involvement of the insular cortex as a common node of different functional networks, thus suggesting its potential role as a central mediator of cortical fc alterations, following modifications of GM. Also, the Rifaximin group displayed lower connectivity in slow and fast beta bands (15 and 25 Hz) during rest, and higher connectivity in theta (7 Hz) during the inclusion condition of the CBG, compared with controls. Altogether these results indicate a modulation of Rifaximin on frequency-specific functional connectivity that could involve cognitive flexibility and memory processing.

Higher post-encoding cortisol benefits the selective consolidation of emotional aspects of memory

Emotional experiences create durable memory traces in the brain, especially when these memories are consolidated in the presence of stress hormones such as cortisol. Although some research suggests cortisol elevation can increase long-term memory for emotional relative to neutral content, the impact of stress and cortisol on the consolidation of emotional and neutral aspects of memories when they are part of the same experience remains unknown. Here, after encoding complex scenes consisting of negative or neutral objects placed on neutral backgrounds, participants were exposed to a psychosocial stressor (or matched control condition) in order to examine the impact of stress and cortisol on early consolidation processes. The next day, once cortisol levels had returned to baseline, specific and gist recognition memory were tested separately for objects and backgrounds. Results indicate that while there was a numerical increase in memory for negative objects in the stress group, higher endogenous cortisol concentrations were specifically associated with decreased memory for the neutral backgrounds originally paired with negative objects. Moreover, across all participants, cortisol levels were positively correlated with the magnitude of the emotional memory trade-off effect. Specifically, while memory for negative objects was preserved, elevated cortisol during early consolidation was associated with decreased memory for neutral backgrounds that were initially paired with negative objects. These memory effects were observed in both the stricter specific measure of memory and the less conservative measure of gist memory. Together, these findings suggest that rather than influencing all aspects of an experience similarly, elevated cortisol during early consolidation selectively preserves what is most emotionally salient and adaptive to remember while allowing the loss of memory for less important neutral information over time.

Overnight sleep benefits both neutral and negative direct associative and relational memory

Strong evidence suggests that sleep plays a role in memory consolidation, which involves both stabilizing memory into long-term storage as well as integrating new information into existing stores. The current study investigated consolidation, across a day of wakefulness or night of sleep, of emotional and neutral directly learned visual paired associates (A-B/B-C pairs) as well as formation of memory for relational pairs formed via overlapping learned components (A-C pairs). Participants learned 40 negative and 40 neutral face-object pairs followed by a baseline test in session 1 either in the morning or evening. They then spent a 12-hour retention period during which participants either went about their normal day or spent the night in the sleep lab. During session 2, participants completed a surprise test to assess their memory for relational pairs (A-C) as well as memory for direct associates (A-B/B-C). As hypothesized, the results demonstrated that a 12-hour retention period predominantly spent asleep, compared to awake, benefited memory for both relational and direct associative memory. However, contrary to the hypothesis that emotional salience would promote preferential consolidation, sleep appeared to benefit both negative and neutral information similarly for direct associative and relational memories, suggesting that sleep may interact with other factors affecting encoding (e.g., depth of encoding) to benefit direct and relational associative memory. As one of the few studies examining the role of nocturnal sleep and emotion on both direct and relational associative memory, our findings suggest key insights into how overnight sleep consolidates these different forms of memory.

Memory and Sleep: How Sleep Cognition Can Change the Waking Mind for the Better

The memories that we retain can serve many functions. They guide our future actions, form a scaffold for constructing the self, and continue to shape both the self and the way we perceive the world. Although most memories we acquire each day are forgotten, those integrated within the structure of multiple prior memories tend to endure. A rapidly growing body of research is steadily elucidating how the consolidation of memories depends on their reactivation during sleep. Processing memories during sleep not only helps counteract their weakening but also supports problem solving, creativity, and emotional regulation. Yet, sleep-based processing might become maladaptive, such as when worries are excessively revisited. Advances in research on memory and sleep can thus shed light on how this processing influences our waking life, which can further inspire the development of novel strategies for decreasing detrimental rumination-like activity during sleep and for promoting beneficial sleep cognition.

Sharp Wave-Ripples in Human Amygdala and Their Coordination with Hippocampus during NREM Sleep

Cooperative interactions between the amygdala and hippocampus are widely regarded as critical for overnight emotional processing of waking experiences, but direct support from the human brain for such a dialog is absent. Using overnight intracranial recordings in 4 presurgical epilepsy patients (3 female), we discovered ripples within human amygdala during nonrapid eye movement (NREM) sleep, a brain state known to contribute to affective processing. Like hippocampal ripples, amygdala ripples are associated with sharp waves, linked to sleep spindles, and tend to co-occur with their hippocampal counterparts. Moreover, sharp waves and ripples are temporally linked across the 2 brain structures, with amygdala ripples occurring during hippocampal sharp waves and vice versa. Combined with further evidence of interregional sharp-wave and spindle synchronization, these findings offer a potential physiological substrate for the NREM-sleep-dependent consolidation and regulation of emotional experiences.

Brain mechanisms of insomnia: new perspectives on causes and consequences

While insomnia is the second most common mental disorder, progress in our understanding of underlying neurobiological mechanisms has been limited. The present review addresses the definition and prevalence of insomnia and explores its subjective and objective characteristics across the 24-hour day. Subsequently, the review extensively addresses how the vulnerability to develop insomnia is affected by genetic variants, early life stress, major life events, and brain structure and function. Further supported by the clear mental health risks conveyed by insomnia, the integrated findings suggest that the vulnerability to develop insomnia could rather be found in brain circuits regulating emotion and arousal than in circuits involved in circadian and homeostatic sleep regulation. Finally, a testable model is presented. The model proposes that in people with a vulnerability to develop insomnia, the locus coeruleus is more sensitive to-or receives more input from-the salience network and related circuits, even during rapid eye movement sleep, when it should normally be sound asleep. This vulnerability may ignite a downward spiral of insufficient overnight adaptation to distress, resulting in accumulating hyperarousal, which, in turn, impedes restful sleep and moreover increases the risk of other mental health adversity. Sensitized brain circuits are likely to be subjectively experienced as "sleeping with one eye open". The proposed model opens up the possibility for novel intervention studies and animal studies, thus accelerating the ignition of a neuroscience of insomnia, which is direly needed for better treatment.

Interactive effects of stress reactivity and rapid eye movement sleep theta activity on emotional memory formation

Sleep and stress independently enhance emotional memory consolidation. In particular, theta oscillations (4-7 Hz) during rapid eye movement (REM) sleep increase coherence in an emotional memory network (i.e., hippocampus, amygdala, and prefrontal cortex) and enhance emotional memory. However, little is known about how stress during learning might interact with subsequent REM theta activity to affect emotional memory. In the current study, we examined whether the relationship between REM theta activity and emotional memory differs as a function of pre-encoding stress exposure and reactivity. Participants underwent a psychosocial stressor (the Trier Social Stress Task; n = 32) or a comparable control task (n = 32) prior to encoding. Task-evoked cortisol reactivity was assessed by salivary cortisol rise from pre- to post-stressor, and participants in the stress condition were additionally categorized as high or low cortisol responders via a median split. During incidental encoding, participants studied 150 line drawings of negative, neutral, and positive images, followed by the complete color photo. All participants then slept overnight in the lab with polysomnographic recording. The next day, they were given a surprise recognition memory task. Results showed that memory was better for emotional relative to neutral information. Critically, these findings were observed only in the stress condition. No emotional memory benefit was observed in the control condition. In stressed participants, REM theta power significantly predicted memory for emotional information, specifically for positive items. This relationship was observed only in high cortisol responders. For low responders and controls, there was no relationship between REM theta and memory of any valence. These findings provide evidence that elevated stress at encoding, and accompanying changes in neuromodulators such as cortisol, may interact with theta activity during REM sleep to promote selective consolidation of emotional information.

Retrieval of Emotional Events from Memory

The enhancing effects of emotion on memory have been well documented; emotional events are often more frequently and more vividly remembered than their neutral counterparts. Much of the prior research has emphasized the effects of emotion on encoding processes and the downstream effects of these changes at the time of retrieval. In the current review, we focus specifically on how emotional valence influences retrieval processes, examining how emotion influences the experience of remembering an event at the time of retrieval (retrieval as an end point) as well as how emotion alters the way in which remembering the event affects the underlying memory representation and subsequent retrievals (retrieval as a starting point). We suggest ways in which emotion may augment or interfere with the selective enhancement of particular memory details, using both online and offline processes, and discuss how these effects of emotion may contribute to memory distortions in affective disorders.

Acute sleep deprivation and the selective consolidation of emotional memories

Research suggests that sleep preferentially consolidates the negative aspects of memories at the expense of the neutral aspects. However, the mechanisms by which sleep facilitates this emotional memory trade-off remain unknown. Although active processes associated with sleep-dependent memory consolidation have been proposed to underlie this effect, this trade-off may also be modulated by non-sleep-related processes, such as the circadian factors, stress-related factors, and/or mood congruent context effects involved in sleep deprivation. We sought to examine the potential role of these factors by randomizing 39 young adults into either a total sleep deprivation condition (26 consecutive hours awake) or a sleep condition (8 h sleep opportunity). Replicating the emotional memory trade-off effect, negative objects were better remembered than neutral objects or background images. However, in spite of generally worse memory performance (for neutral and background information), sleep-deprived participants showed similar recognition rates for negative emotional memories relative to participants who were given a full night of sleep.

Do different salience cues compete for dominance in memory over a daytime nap?

Information that is the most salient and important for future use is preferentially preserved through active processing during sleep. Emotional salience is a biologically adaptive cue that influences episodic memory processing through interactions between amygdalar and hippocampal activity. However, other cues that influence the importance of information, such as the explicit direction to remember or forget, interact with the inherent salience of information to determine its fate in memory. It is unknown how sleep-based processes selectively consolidate this complex information. The current study examined the development of memory for emotional and neutral information that was either cued to-be-remembered (TBR) or to-be-forgotten (TBF) across a daytime period including either napping or wakefulness. Baseline memory revealed dominance of the TBR cue, regardless of emotional salience. As anticipated, napping was found to preserve memory overall significantly better than remaining awake. Furthermore, we observed a trending interaction indicating that napping specifically enhanced the discrimination between the most salient information (negative TBR items) over other information. We found that memory for negative items was positively associated with the percentage of SWS obtained during a nap. Furthermore, the magnitude of the difference in memory between negative TBR items and negative TBF items increased with greater sleep spindle activity. Taken together, our results suggest that although the cue to actively remember or intentionally forget initially wins out, active processes during sleep facilitate the competition between salience cues to promote the most salient information in memory.