Baseline Levels of Rapid Eye Movement Sleep May Protect Against Excessive Activity in Fear-Related Neural Circuitry

Sleep deprivation increases the generalization of perceptual and concept-based fear: An fNIRS study

Insufficient sleep can initiate or exacerbate anxiety by triggering excessive fear generalization. In this study, a de novo paradigm was developed and used to examine the neural mechanisms governing the effects of sleep deprivation on processing perceptual and concept-based fear generalizations. A between-subject design was adopted, wherein a control group (who had a typical night's sleep) and a one-night sleep deprivation group completed a fear acquisition task at 9:00 PM on the first day and underwent a generalization test the following morning at 7:00 AM. In the fear acquisition task, navy blue and olive green were used as perceptual cues (P+ and P-, respectively), while animals and furniture items were used as conceptual cues (C+ and C-, respectively). Generalization was tested for four novel generalized categories (C+P+, C+P-, C-P+, and C-P-). Shock expectancy ratings, skin conductance responses, and functional near-infrared spectroscopy were recorded during the fear acquisition and generalization processes. Compared with the group who had a typical night's sleep, the sleep deprived group showed higher shock expectancy ratings (especially for P+ and C-), increased oxygenated hemoglobin in the dorsolateral prefrontal cortex, and increased activation in the triangular inferior frontal gyrus during the generalization test. These findings suggest that sleep deprivation increases the generalization of threat memories, thus providing insights into the overgeneralization characteristics of anxiety and fear-related disorders.

The Impact of Sleep: From Ancient Rituals to Modern Challenges

Although sleep is crucial for mental and physical health, insufficient sleep is a growing problem in our modern society. In general, adults need approximately eight hours of sleep per night, but this is often unfeasible nowadays. This sleep restriction has been observed, and it has worsened, throughout the past two centuries; therefore, it is more attributed to socioeconomic changes than to biological adaptations. The most important factors to contribute to this sleep restriction were the popularization of artificial light and industrialization. The present manuscript briefly overviews, from a socioanthropological perspective, the reasons why sleep has been impacted, disclosing its effects on individuals and on society.

The importance of REM sleep fragmentation in the effects of stress on sleep: Perspectives from preclinical studies

Psychological stress poses a risk for sleep disturbances. Importantly, trauma-exposed individuals who develop posttraumatic stress disorder (PTSD) frequently report insomnia and recurrent nightmares. Clinical studies have provided insight into the mechanisms of these sleep disturbances. We review polysomnographic findings in PTSD and identify analogous measures that have been made in animal models of PTSD. There is a rich empirical and theoretical literature on rapid eye movement sleep (REMS) substrates of insomnia and nightmares, with an emphasis on REMS fragmentation. For future investigations of stress-induced sleep changes, we recommend a focus on tonic, phasic and other microarchitectural REMS measures. Power spectral density analysis of the sleep EEG should also be utilized. Animal models with high construct validity can provide insight into gender and time following stressor exposure as moderating variables. Ultimately, preclinical studies with translational potential will lead to improved treatment for stress-related sleep disturbances.

Sleep deprivation altered encoding of basolateral amygdala on fear acquisition

Sleep deprivation (SD) may lead to the development of fear- and anxiety-related emotional disorders. However, the neural mechanisms underlying the effects of SD on fear acquisition are unclear. Here, we tested whether and how SD influences the behavioral and neural manifestations of fear acquisition. We found that subjective fear ratings and objective fear indices (skin conductance response [SCR]) in the SD group were greater than those in the control group during fear acquisition, suggesting that SD facilitated fear acquisition (nSD = 18 and ncontrol = 23 for self-reported rating analysis; nSD = 10 and ncontrol = 10 for SCR analysis). Neuroimaging data showed that the SD group exhibited stronger activity in the left basolateral amygdala (BLA) and left superficial amygdala (SFA). Moreover, the left BLA activity, which positively correlated with the objective fear indices, significantly mediated the effect of SD on fear acquisition. Together, the present findings indicate that SD facilitates fear acquisition by augmenting threat-specific encoding in the BLA, which may be a potential biomarker of the risk of developing fear-related disorders under traumatic and distressing situations.

Modeling integrated stress, sleep, fear and neuroimmune responses: Relevance for understanding trauma and stress-related disorders

Sleep and stress have complex interactions that are implicated in both physical diseases and psychiatric disorders. These interactions can be modulated by learning and memory, and involve additional interactions with the neuroimmune system. In this paper, we propose that stressful challenges induce integrated responses across multiple systems that can vary depending on situational variables in which the initial stress was experienced, and with the ability of the individual to cope with stress- and fear-inducing challenges. Differences in coping may involve differences in resilience and vulnerability and/or whether the stressful context allows adaptive learning and responses. We provide data demonstrating both common (corticosterone, SIH and fear behaviors) and distinguishing (sleep and neuroimmune) responses that are associated with an individual's ability to respond and relative resilience and vulnerability. We discuss neurocircuitry regulating integrated stress, sleep, neuroimmune and fear responses, and show that responses can be modulated at the neural level. Finally, we discuss factors that need to be considered in models of integrated stress responses and their relevance for understanding stress-related disorders in humans.

The Impact of Sleep on Fear Extinction

Sleep plays a crucial role in the consolidation of memories, including those for fear acquisition and extinction training. This chapter reviews findings from studies testing this relationship in laboratory, naturalistic, and clinical settings. While evidence is mixed, several studies in humans have linked fear and extinction recall/retention to both rapid eye-movement and slow wave sleep. Sleep appears to further aid in the processing of both simulated and actual trauma and improves psychotherapeutic treatment outcomes in those with anxiety and trauma- and stressor-related disorders. This chapter concludes with a discussion of the current challenges facing sleep and emotional memory research in addition to suggestions for improving future research.

Sleep Deprivation During Memory Consolidation, but Not Before Memory Retrieval, Widens Threat Generalization to New Stimuli

Past aversive experiences shape our ability to deal with future dangers, through the encoding of implicit and explicit memory traces and through the ability to generalize defensive reactions to new stimuli resembling learned threats. Numerous evidence demonstrate that sleep is important for the consolidation of memories related to threatening events. However, there is a lack of studies examining the effects of sleep deprivation on the retrieval of consolidated threat memories, and previous studies on the role of sleep in threat generalization have produced mixed results. To address these issues, here we adopted a differential threat conditioning and a delayed (second half of the night) sleep deprivation during the first or the seventh night after learning. We found no effects of sleep deprivation on either implicit or explicit threat memories, regardless of its occurrence timing. Conversely, implicit but not explicit responses to novel cues similar to a learned threat displayed a widened generalization pattern, but only if sleep deprivation took place during the first night after conditioning and not if it occurred during the seventh night after conditioning. Therefore, we propose that sleeping after exposure to danger may support optimal implicit discrimination processes to evaluate new signals in the future and that even a brief period of sleeplessness may widen threat generalization to new stimuli, which is a hallmark of several threat-related disorders.

Targeted Memory Reactivation During REM Sleep in Patients With Social Anxiety Disorder

BACKGROUND

Social anxiety disorder (SAD) is characterized by a significant amount of fear when confronted to social situations. Exposure therapy, which is based on fear extinction, does not often lead to full remission. Here, based on evidence showing that rapid eye movement (REM) sleep promotes the consolidation of extinction memory, we used targeted memory reactivation (TMR) during REM sleep to enhance extinction learning in SAD.

METHODS

Forty-eight subjects with SAD were randomly assigned to two groups: control or TMR group. All patients had two successive exposure therapy sessions in a virtual reality (VR) environment, where they were asked to give a public talk in front of a virtual jury. At the end of each session, and only in the TMR group (N = 24), a sound was paired to the positive feedback phase of therapy (i.e., approval of their performance), which represented the memory to be strengthened during REM sleep. All participants slept at home with a wearable headband device which automatically identified sleep stages and administered the sound during REM sleep. Participants' anxiety level was assessed using measures of parasympathetic (root mean square of successive differences between normal heartbeats, RMSSD) and sympathetic (non-specific skin conductance responses, ns-SCRs) activity, and subjective measures (Subjective Units of Distress Scale, SUDS), during the preparation phase of their talks before (T1) and after (T2) one full-night's sleep and after 1 week at home (T3). Participants also filled in a dream diary.

RESULTS

We observed an effect of time on subjective measures of anxiety (SUDS). We did not find any difference in the anxiety levels of the two groups after 1 week of TMR at home. Importantly, the longer the total duration of REM sleep and the more stimulations the TMR group had at home, the less anxious (increased RMSSD) these participants were. Finally, fear in dreams correlated positively with ns-SCRs and SUDS at T3 in the TMR group.

CONCLUSION

TMR during REM sleep did not significantly modulate the beneficial effect of therapy on subjective anxiety. Yet, our results support that REM sleep can contribute to extinction processes and substantiate strong links between emotions in dreams and waking stress levels in these patients.

Sleep and fear conditioning, extinction learning and extinction recall: A systematic review and meta-analysis of polysomnographic findings

Sleep may contribute to the long-lasting consolidation and processing of emotional memories. Experimental fear conditioning and extinction paradigms model the development, maintenance, and treatment of anxiety disorders. The literature provides compelling evidence for the involvement of rapid eye movement (REM) sleep in the consolidation of such memories. This meta-analysis correlated polysomnographic sleep findings with psychophysiological reactivity to the danger (CS+) and safety stimuli (CS-), to clarify the specific role of sleep stages before and after fear conditioning, extinction learning and extinction recall. Overall, there was evidence that more pre-learning sleep stage two and less slow wave sleep was associated with higher psychophysiological reactivity to the safety stimulus during extinction learning. Preliminary evidence found here support the role of REM sleep during the post-extinction consolidation sleep phase in clinical populations with disrupted sleep, but not in healthy controls. Furthermore, the meta-regressions found that sex moderated the associations between sleep and psychophysiological reactivity throughout the paradigm providing evidence for diverging correlations in male and females. Specifically, increased post-extinction REM was associated with poorer extinction and safety recall in females while the opposite was found in males. These results have implications for future research in the role of sleep in emotional memory processing.

Sleep to remember, sleep to forget: Rapid eye movement sleep can have inverse effects on recall and generalization of fear memories

Rapid Eye Movement (REM) sleep has been shown to modulate the consolidation of fear memories, a process that may contribute to the development of Post-Traumatic Stress Disorder (PTSD). However, contradictory findings have been reported regarding the direction of this modulation and its differential effects on recall versus generalization. In two complementary experiments, we addressed this by employing sleep deprivation protocols together with a novel fear-conditioning paradigm that required the discrimination between coexisting threat and safety signals. Using skin conductance responses and functional imaging (fMRI), we found two opposing effects of REM sleep: While REM impaired recall of the original threat memories, it improved the ability to generalize these memories to novel situations that emphasized the discrimination between threat and safety signals. These results, as well as previous findings in healthy participants and patients diagnosed with PTSD, could be explained by the degree to which the balance between threat and safety signals for a given stimulus was predictive of threat. We suggest that this account can be integrated with contemporary theories of sleep and fear learning, such as the REM recalibration hypothesis.

Bed-Sharing in Couples Is Associated With Increased and Stabilized REM Sleep and Sleep-Stage Synchronization

BACKGROUND/OBJECTIVES

Sharing the bed with a partner is common among adults and impacts sleep quality with potential implications for mental health. However, hitherto findings are contradictory and particularly polysomnographic data on co-sleeping couples are extremely rare. The present study aimed to investigate the effects of a bed partner's presence on individual and dyadic sleep neurophysiology.

METHODS

Young healthy heterosexual couples underwent sleep-lab-based polysomnography of two sleeping arrangements: individual sleep and co-sleep. Individual and dyadic sleep parameters (i.e., synchronization of sleep stages) were collected. The latter were assessed using cross-recurrence quantification analysis. Additionally, subjective sleep quality, relationship characteristics, and chronotype were monitored. Data were analyzed comparing co-sleep vs. individual sleep. Interaction effects of the sleeping arrangement with gender, chronotype, or relationship characteristics were moreover tested.

RESULTS

As compared to sleeping individually, co-sleeping was associated with about 10% more REM sleep, less fragmented REM sleep (p = 0.008), longer undisturbed REM fragments (p = 0.0006), and more limb movements (p = 0.007). None of the other sleep stages was significantly altered. Social support interacted with sleeping arrangement in a way that individuals with suboptimal social support showed the biggest impact of the sleeping arrangement on REM sleep. Sleep architectures were more synchronized between partners during co-sleep (p = 0.005) even if wake phases were excluded (p = 0.022). Moreover, sleep architectures are significantly coupled across a lag of ± 5min. Depth of relationship represented an additional significant main effect regarding synchronization, reflecting a positive association between the two. Neither REM sleep nor synchronization was influenced by gender, chronotype, or other relationship characteristics.

CONCLUSION

Depending on the sleeping arrangement, couple's sleep architecture and synchronization show alterations that are modified by relationship characteristics. We discuss that these alterations could be part of a self-enhancing feedback loop of REM sleep and sociality and a mechanism through which sociality prevents mental illness.

The role of sleep in fear learning and memory

During the last 10 years, a large body of studies have used fear conditioning paradigms to study the role of sleep in the consolidation of fear and safety learning. This line of research could allow us to answer if it is adaptive or not to sleep in the aftermath of a negative experience, and if sleep has a role in consolidating extinction learning. This field has so far produced several contrasting findings. Thus, this review will not deliver many clear conclusions, but will instead be an attempt to summarize what we know at the moment, to describe the potential clinical applications of this research, and to discuss where to go from here.

Delayed fear extinction in individuals with insomnia disorder

Study Objectives

Insomnia increases the risk for anxiety disorders that are also associated with fear-extinction deficits. We compared activation of fear and extinction networks between insomnia disorder (ID) without comorbidity and good sleepers (GS).

Methods

Twenty-three ID participants age- and sex-matched to 23 GS participants completed 14 days of actigraphy and diaries, three nights of ambulatory polysomnography and a 2-day fear conditioning and extinction paradigm. Fear conditioning and extinction learning occurred on the first day, followed 24 hours later by extinction recall. Blood-oxygen-level-dependent functional magnetic resonance imaging (fMRI) signal and skin conductance responses (SCR) were recorded. Nineteen participants per group produced usable fMRI data. Beta weights from areas where activation differed between groups were regressed against sleep and psychophysiological measures. SCR was compared between groups at various stages of the paradigm.

Results

During fear conditioning, both ID (N = 19) and GS (N = 19) activated fear-related structures. Across extinction learning, ID (N = 19) demonstrated little change, whereas GS (N = 16) activated both fear and extinction-related areas, including the hippocampus, insula, dorsal anterior cingulate (dACC), and ventromedial prefrontal (vmPFC) cortices. During extinction recall, while GS (N = 17) demonstrated limited activation, ID (N = 16) activated regions similar to those previously activated in GS (vmPFC, dACC, insula). Sleep quality was predictive of activations seen at various stages of the paradigm. SCR data suggested ID were more physiologically reactive than GS.

Conclusions

Across extinction learning, GS but not ID activated both fear and extinction-related networks. At extinction recall, ID engaged similar regions whereas GS no longer did so. Individuals with ID may show a delayed acquisition of fear extinction memories.

Rapid Eye Movement Sleep Percentage and Duration in Posttraumatic Stress Disorder Vary Dynamically and Inversely With Indices of Sympathetic Activation During Sleep and Sleep Fragmentation

ABSTRACT

Posttraumatic stress disorder (PTSD) is associated with activation of the brain fear circuitry. Studies of sleep in PTSD provide a unique window into the relation or connection of sleep physiology and autonomic activation. Serial level 3 home sleep apnea tests (HSATs) (10 HSATs over 1 month) in a patient who was medication free, had PTSD, and had refused positive airway pressure therapy, revealed both percentage of rapid eye movement (REM) sleep (mean ± standard deviation [SD]: 19.88% ± 10.11%; range 1.94% to 35.01%) and REM sleep duration (minutes) (mean ± SD: 73.08 ± 48.24; range 3.49- 151.59) varied markedly over the 10 HSATs. Both percentage of REM sleep and REM sleep duration correlated negatively with sleep onset latency (r = -.661, P = .037 and r = -.748, P = .013, respectively) and the mean pulse rate during sleep (r = -.667, P = .035 and r = -.771, P = .009, respectively), and positively with sleep efficiency (r = .824, P = .003 and r = .922, P < .001, respectively) and percentage of stage N3 sleep (r = .784, P = .007 and r = .734, P = .016, respectively), an index of parasympathetic tone during sleep. These empirical findings suggest a previously unreported inverse relation of REM sleep with sleep fragmentation and sympathetic activation.

A Review of the Relationship Between Emotional Learning and Memory, Sleep, and PTSD

PURPOSE OF REVIEW

The emotional memory and learning model of PTSD posits maladaptive fear conditioning, extinction learning, extinction recall, and safety learning as central mechanisms to PTSD. There is increasingly convincing support that sleep disturbance plays a mechanistic role in these processes. The current review consolidates the evidence on the relationships between emotional memory and learning, disturbed sleep, and PTSD acquisition, maintenance, and treatment.

RECENT FINDINGS

While disrupted sleep prior to trauma predicts PTSD onset, maladaptive fear acquisition does not seem to be the mechanism through which PTSD is acquired. Rather, poor extinction learning/recall and safety learning seem to better account for who maintains acute stress responses from trauma versus who naturally recovers; there is convincing evidence that this process is, at least in part, mediated by REM fragmentation. Individuals with PTSD had higher "fear load" during extinction, worse extinction learning, poorer extinction recall, and worse safety learning. Evidence suggests that these processes are also mediated by fragmented REM. Finally, PTSD treatments that require extinction and safety learning may also be affected by REM fragmentation. Addressing fragmented sleep or sleep architecture could be used to increase emotional memory and learning processes and thus ameliorate responses to trauma exposure, reduce PTSD severity, and improve treatment. Future studies should examine relationships between emotional memory and learning and disturbed sleep in clinical PTSD patients.

REM sleep and safety signal learning in posttraumatic stress disorder: A preliminary study in military veterans

Background

Posttraumatic Stress Disorder (PTSD) is associated with a number of negative physical and mental health consequences. Fear conditioning plays an important mechanistic role in PTSD, and PTSD patients also show deficits in safety signal learning. Sleep, particularly REM sleep, is linked to improved safety learning and extinction processes in animal models and healthy humans. No studies have examined the link between REM sleep and safety signal learning or extinction memory in clinical populations.

Methods

This study examined the relationship between REM sleep, safety signal learning, and extinction processes in veterans with PTSD (n = 13). Patients' overnight sleep was characterized in the laboratory via polysomnography (PSG). The next day, participants underwent a fear conditioning paradigm during which they acquired fear toward a visual cue. This testing session also included a visual cue that became a safety signal (CS-). Following conditioning, the veterans' sleep was monitored overnight again, after which they underwent extinction training. Following a third night of sleep, extinction recall and safety recall were tested. Bivariate correlations examined the relationship between the slope of safety signal learning and subsequent REM sleep, as well as the relationship between REM sleep and subsequent extinction recall and safety recall on the last day of testing.

Results

Veterans learned to differentiate the CS+ and the CS- on the first day of testing. Veterans who underwent safety learning more quickly on the first day of testing showed more efficient REM sleep that night (r = .607, p = .028). On the second day of testing, the patients successfully underwent extinction learning. Patients with a higher percentage of REM sleep on the last night of the study showed more safety recall early on the last day of testing (r = .688, p = .009).

Conclusion

To our knowledge, this was the first study to examine the relationship between objective sleep and fear-potentiated startle performance in veterans with PTSD. Study methods were well tolerated by participants, supporting feasibility of the experimental design. Results indicated REM sleep was associated with both initial safety learning and subsequent safety recall. Taken together with previous studies in healthy controls, these preliminary results provide additional evidence suggesting REM sleep could play a mechanistic role in the maintenance of PTSD and thus identify a modifiable biological process to target in treatment of PTSD. These findings should be replicated in larger samples.