Emotion, emotion regulation and sleep : an intimate relationship

In recent years, research has witnessed an increasing interest in the bidirectional relationship between emotion and sleep. Sleep seems important for restoring daily functioning, whereas deprivation of sleep makes us more emotionally aroused and sensitive to stressful stimuli and events. Sleep appears to be essential to our ability to cope with emotional stress in everyday life. However, when daily stress is insufficiently regulated, it may result in mental health problems and sleep disturbances too. Not only does emotion impact sleep, but there is also evidence that sleep plays a key role in regulating emotion. Emotional events during waking hours affect sleep, and the quality and amount of sleep influences the way we react to these events impacting our general well-being. Although we know that daytime emotional stress affects sleep by influencing sleep physiology, dream patterns, dream content and the emotion within a dream, its exact role is still unclear. Other effects that have been found are the exaggeration of the startle response, decrease in dream recall and elevation of awakening thresholds from rapid eye movement (REM), REM-sleep, increased or decreased latency to REM-sleep, increase in percentage of REM-density, REM-sleep duration, as well as the occurrence of arousals in sleep as a marker of sleep disruption. Equally, the way an individual copes with emotional stress, or the way in which an individual regulates emotion may modulate the effects of emotional stress on sleep. The research presented here supports the idea that adaptive emotion regulation benefits our follow-up sleep. We thus conclude the current review with a call for future research in order to clarify further the precise relationship between sleep, emotion and emotion regulation, as well as to explain further how sleep dissolves our emotional stress

The functional role of dreaming in emotional processes

Dream experience (DE) represents a fascinating condition linked to emotional processes and the human inner world. Although the overlap between REM sleep and dreaming has been overcome, several studies point out that emotional and perceptually vivid contents are more frequent when reported upon awakenings from this sleep stage. Actually, it is well-known that REM sleep plays a pivotal role in the processing of salient and emotional waking-life experiences, strongly contributing to the emotional memory consolidation. In this vein, we highlighted that, to some extent, neuroimaging studies showed that the processes that regulate dreaming and emotional salience in sleep mentation share similar neural substrates of those controlling emotions during wakefulness. Furthermore, the research on EEG correlates of the presence/absence of DE and the results on EEG pattern related to the incorporated memories converged to assign a crucial role of REM theta oscillations in emotional re-processing. In particular, the theta activity is involved in memory processes during REM sleep as well as during the waking state, in line with the continuity hypothesis. Also, the gamma activity seems to be related to emotional processes and dream recall as well as to lucid dreams. Interestingly, similar EEG correlates of DE have been found in clinical samples when nightmares or dreams occur. Research on clinical samples revealed that promoting the rehearsal of frightening contents aimed to change them is a promising method to treat nightmares, and that lucid dreams are associated with an attenuation of nightmares. In this view, DE can defuse emotional traumatic memories when the emotional regulation and the fear extinction mechanisms are compromised by traumatic and frightening events. Finally, dreams could represent a sort of simulation of reality, providing the possibility to create a new scenario with emotional mastery elements to cope with dysphoric items included in nightmares. In addition, it could be hypothesized that the insertion of bizarre items besides traumatic memories might be functional to “impoverish” the negative charge of the experiences

Sleep enhances inhibitory behavioral control in discrimination learning in rats

Sleep supports the consolidation of memory, and it has been proposed that this enhancing effect of sleep pertains in particular to memories which are encoded under control of prefrontal–hippocampal circuitry into an episodic memory system. Furthermore, repeated reactivation and transformation of such memories during sleep are thought to promote the de-contextualization of these memories. Here, we aimed to establish a behavioral model for the study of such sleep-dependent system consolidation in rats, using a go/nogo conditional discrimination learning task known to essentially depend on prefrontal–hippocampal function. Different groups of rats were trained to criterion on this task and, then, subjected to 80-min retention intervals filled with spontaneous morning sleep, sleep deprivation, or spontaneous evening wakefulness. In a subsequent test phase, the speed of relearning of the discrimination task was examined as indicator of memory, whereby rats were either tested in the same context as during training or in a different context. Sleep promoted relearning of the conditional discrimination task, and this effect was similar for testing memory in the same or different context (p < 0.001). Independent of sleep and wakefulness during the retention interval, animals showed faster relearning when tested in the same context as during learning, compared with testing in a different context (p < 0.001). The benefitting effect of sleep on discrimination learning was primarily due to an enhancing effect on response suppression during the nogo stimulus. We infer from these results that sleep enhances memory for inhibitory behavioral control in a generalized context-independent manner and thereby might eventually also contribute to the abstraction of schema-like representations

The Role of REM Sleep in Ocular Dominance Plasticity Consolidation

Despite decades of research, the function of sleep remains controversial. One theory is that sleep plays a role in consolidating plasticity induced during prior waking. Ocular dominance plasticity (ODP) in the cat visual cortex is induced during waking monocular deprivation (MD) and consolidated during subsequent sleep. Extracellular signal-regulated kinase (ERK) signaling is required for ODP and is elevated during post-MD sleep, but its requirement during sleep is unknown. In Chapter 2, we investigated whether ERK activity is required during sleep for ODP consolidation by inhibiting the upstream activator of ERK (MEK) with intracortical infusions of U0126 into V1 during post-MD sleep. ERK inhibition abolished ODP consolidation, as measured by extracellular single unit recording. Furthermore, ERK inhibition reduced phosphorylation of eukaryotic initiation factor 4E (eIF4E) and post-synaptic density protein 95 (PSD-95) levels. MAP kinase-interacting kinase 1 (Mnk1) is activated by ERK and directly phosphorylates eIF4E; inhibition of Mnk1 mimicked the effects of ERK inhibition. These results show that activation of the ERK-Mnk1 pathway during post-MD sleep is required for ODP consolidation, and that this pathway promotes the synthesis of plasticity-related proteins such as PSD-95. However, sleep can be broadly subdivided into rapid eye movement (REM) and non-REM (NREM) sleep, but the relative contributions of these states to ODP and the ERK pathway are unknown. In Chapter 3, we examined whether REM sleep is required for ODP consolidation and ERK activation by depriving animals of REM sleep following six hours of waking MD. REM sleep deprivation (RSD) abolished ODP consolidation, as measured by optical imaging of intrinsic cortical signals, and reduced ERK phosphorylation in V1. These effects were not seen in a group that received NREM-fragmented sleep (as a control for the nonspecific effects of RSD). Furthermore, ODP and ERK phosphorylation correlated with the degree of beta-gamma activity in V1 during REM sleep, suggesting that neuronal activity patterns during REM promote ERK activation and ODP consolidation. Together, the findings in the following chapters suggest that, following the induction of cortical plasticity during waking, the ERK-Mnk1 pathway is activated during REM sleep, promoting the synthesis of plasticity-related proteins to consolidate cortical plasticity

EFFECT OF SLEEP DEPRIVATION ON REMINISCENCE AND APPREHENSION BEHAVIOR IN WISTAR ALBINO RATS

Objective: The aim of the present study is to investigate the effect of paradoxical sleep deprivation (SD) on learning and memory impairment and anxiety-like behavior in female Wistar albino rats. Methods: Eight-arm radial maze, open-field test, and light and dark test were used to assess the animals learning and memory and anxiety-like behavior. Results: SD associated with weaker learning and memory and increased anxiety- and depressive-like behavior in animals. Conclusion: Animals were exposed to SD showed learning and memory impairment and also exhibited increased anxiety- and depressive-like behavior when compared to control animals

Sleep deprivation directly following eyeblink-conditioning impairs memory consolidation

The relation between sleep and different forms of memory formation continues to be a relevant topic in our daily life. Sleep has been found to affect cerebellum-dependent procedural memory formation, but it remains to be elucidated to what extent the level of sleep deprivation directly after motor training also influences our ability to store and retrieve memories. Here, we studied the effect of disturbed sleep in mice during two different time-windows, one covering the first four hours following eyeblink conditioning (EBC) and another window following the next period of four hours. Compared to control mice with sleep ad libitum, the percentage of conditioned responses and their amplitude were impaired when mice were deprived of sleep directly after conditioning

Emotional arousal modulates oscillatory correlates of targeted memory reactivation during NREM, but not REM sleep

Rapid eye movement (REM) sleep is considered to preferentially reprocess emotionally arousing memories. We tested this hypothesis by cueing emotional vs. neutral memories during REM and NREM sleep and wakefulness by presenting associated verbal memory cues after learning. Here we show that cueing during NREM sleep significantly improved memory for emotional pictures, while no cueing benefit was observed during REM sleep. On the oscillatory level, successful memory cueing during NREM sleep resulted in significant increases in theta and spindle oscillations with stronger responses for emotional than neutral memories. In contrast during REM sleep, solely cueing of neutral (but not emotional) memories was associated with increases in theta activity. Our results do not support a preferential role of REM sleep for emotional memories, but rather suggest that emotional arousal modulates memory replay and consolidation processes and their oscillatory correlates during NREM sleep

The Effects of Sleep on the Acquisition of Skill

The current research was designed to evaluate the effect of sleep on memory for the declarative and procedural knowledge components of a cognitive skill. In a training phase, 17 participants in a no-sleep control group practised 120 repetitions of a simple algebra equation at Sam and 22 participants in a sleep group practised the task at 8pm. Novel task inputs were introduced withh1 the same task structure in a transfer phase conducted 12 hours after training for each group. Overnight sleep conferred a 29% performance deficit on the transfer tusk compared to no-sleep controls. The results support the hypothesis that sleep consolidates declarative and procedural knowledge components of an acquired cognitive skill. The prediction that, when consolidated by sleep, knowledge acquired in training creates processing overheads that disrupt post-sleep transfer when task inputs are changed at transfer was upheld. Discussion considered the influence at transfer of three cognitive phenomena: proactive interference, inhibition, and facilitation developed in training. A basis for parsing the relative discrete effects of these phenomena is advanced and a novel framework for predicting skill acquisition and transfer across various training and transfer conditions is outlined. The present study extends support to sleep-consolidation of complex declarative knowledge as well as procedural knowledge, and has implications for theories of memory system dissociation as well as theories of skill acquisition and transfer