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Summary: Stimulus control is part of the widely used cognitive behavioural therapy for insomnia. However, there is a lack of knowledge about its mechanisms of action and effectiveness when used alone. This systematic review with network meta‐analysis aimed to evaluate stimulus control efficacy when used alone compared with cognitive behavioural therapy for insomnia or its components. The review also documented stimulus control mechanisms of action proposed by the authors. A search was conducted in several bibliographic databases (MEDLINE, PsycINFO, Embase, CINAHL, Psychology Behavioural Sciences Collection, Web of Science, and Cochrane Library) and in two registers from 1972 to June 2022. Randomised studies with adult participants presenting a diagnosis of insomnia and including at least one stimulus control instruction in a treatment group were included. Risk of bias was assessed with the Quality Assessment of Controlled Intervention Studies. Twenty‐three studies were included and three network meta‐analyses were conducted. The quality of included studies was generally poor. Results indicate that stimulus control is an effective intervention to improve insomnia compared with control conditions. Not all stimulus control instructions seem essential, especially those known to recondition the bedroom for sleep. The review challenges the classical conditioning hypothesis. Results should be interpreted cautiously given the small number of studies included, bias risk, and inconsistencies in the network meta‐analysis. Rigorous research is needed in evaluating stimulus control efficacy and mechanisms. [ABSTRACT FROM AUTHOR]

Nightmares are often associated with psychiatric disorders and acute stress. This study explores how the COVID‐19 pandemic may have influenced the content of nightmares. A sample of N = 419 US adults completed online surveys about sleep and COVID‐19 experiences. Participants were asked about the degree to which they agreed with statements linking greater general stress, worse overall sleep and more middle‐of‐the‐night insomnia with the COVID‐19 pandemic. They were also asked if, during the pandemic, they experienced nightmares related to various themes. Logistic regression analyses examined each nightmare content as outcome and increased stress, worse sleep and more middle‐of‐the‐night insomnia as predictors, adjusted for age, sex and race/ethnicity. Those who reported greater general COVID‐related stress were more likely to have nightmares about confinement, failure, helplessness, anxiety, war, separation, totalitarianism, sickness, death, COVID and an apocalypse. Those who reported worsened sleep were more likely to have nightmares about confinement, oppression, failure, helplessness, disaster, anxiety, evil forces, war, domestic abuse, separation, totalitarianism, sickness, death, COVID and an apocalypse. Those who reported worsened middle‐of‐the‐night insomnia were more likely to have nightmares about confinement, oppression, failure, helplessness, disaster, anxiety, war, domestic abuse, separation, totalitarianism, sickness, death, COVID and an apocalypse. These results suggest that increased pandemic‐related stress may induce negatively‐toned dreams of specific themes. Future investigation might determine whether (and when) this symptom indicates an emotion regulation mechanism at play, or the failure of such a mechanism. [ABSTRACT FROM AUTHOR]

Emotional reactivity in insomnia is affected both subjectively and on a physiological level for negative emotional material, but little is known about reactions to positive stimuli. We here investigated whether in younger adult insomnia patients, presentation of short humorous films would lead to heart rate decreases during and after film viewing, as compared to heart rate changes when falling asleep. Investigating 20 participants with DSM‐5‐diagnosed insomnia and 18 participants without insomnia, we found that heart rate decreased when falling asleep, increased when watching humorous films and returned to normal values afterwards for all participants. Film‐related heart rate increases were strongly related to humour ratings of the films. No differences were found between those with and without insomnia on subjective ratings of the films, film‐related heart rate changes or when falling asleep. We conclude that the experience of positive daily life stimuli in younger adults is not affected by insomnia in our study, despite insomnia having a known more profound effect on negative stimuli. Future studies exploring insomnia‐related autonomous nervous system responses combining different neurophysiological modalities should confirm our findings. [ABSTRACT FROM AUTHOR]

This project assessed the feasibility of in-lab dream collection in insomnia sufferers which have been limited, considering their reported sleep difficulties and heightened arousal. Eleven insomnia sufferers and 10 good sleepers underwent 5 consecutive polysomnography recording nights including 2 in-lab REM sleep full narrative dream collection. Dream recall frequency and sleep onset latency after each dream collection procedure were calculated. Analyses revealed no group effect (p=.14) for in-lab dream recall frequency (.96 for insomnia sufferers vs. .88 for good sleepers). Groups did not differ (p=.33) on sleep onset latency after dream collection. For sleep perception, insomnia individuals significantly underestimated their total sleep time at home (p≤.03) but not in the lab. Good sleepers correctly estimated their total sleep time at home but underestimated it in lab. For wake after sleep onset, insomnia sufferers correctly estimated it at home but underestimated it in the lab, while good sleepers underestimated it both at home and in the lab (p≤.02). These results suggest that in-lab full length dream collection can be successfully conducted with insomnia sufferers. Interestingly, dream collection also appeared to contribute to the underestimation of wake after sleep onset in insomnia individuals and good sleepers. It might be that externally induced awakenings attenuate the distress related to sleep difficulties especially in insomnia sufferers, since awakenings are attributed to dream collection. [ABSTRACT FROM AUTHOR]

Individuals with insomnia present unique patterns of electroencephalographic (EEG) asymmetry between homologous regions of each brain hemisphere, yet few studies have assessed asymmetry within the same hemisphere. Increase in intrahemispheric asymmetry during rapid eye movement (REM) sleep in good sleepers (GS) and disruption of REM sleep in insomnia sufferers (INS) both point out that this activity may be involved in the pathology of insomnia. The objective of the present exploratory study was to evaluate and quantify patterns of fronto-central, fronto-parietal, fronto-occipital, centro-parietal, centro-occipital and parieto-occipital intrahemispheric asymmetry in GS and INS, and to assess their association with sleep-wake misperception, daytime anxiety and depressive symptoms, as well as insomnia severity. This paper provides secondary analysis of standard EEG recorded in 43 INS and 19 GS for three nights in a sleep laboratory. Asymmetry measures were based on EEG power spectral analysis within 0.3–60 Hz computed between pairs of regions at frontal, central, parietal and occipital derivations. Repeated-measures ANOVAs were performed to assess group differences. Exploratory correlations were then performed on asymmetry and sleep-wake misperception, as well as self-reported daytime anxiety and depressive symptoms, and insomnia severity. INS presented increased delta and theta F3/P3 asymmetry during REM sleep compared with GS, positively associated with depressive and insomnia complaints. INS also exhibited decreased centro-occipital (C3/O1, C4/O2) and parieto-occipital (P3–O1, P4/O2) theta asymmetry during REM. These findings suggest that INS present specific patterns of intrahemispheric asymmetry, partially related to their clinical symptoms. Future studies may investigate the extent to which asymmetry is related to sleep-wake misperception or memory impairments. [ABSTRACT FROM AUTHOR]

While there is an extensive literature on predisposing, precipitating, coping, and perpetuating factors in those with chronic insomnia, very little work has been undertaken to evaluate these factors over the early developmental course of insomnia. The present aim was to determine whether several hypothesized factors in each domain (predisposing, precipitating, coping, and perpetuating), assessed during an episode of acute insomnia (AI), are related to its persistence or remission to normal sleep. Participants comprised n = 140 people with AI and n = 737 normal sleepers (NS) recruited from the general public. Participants completed measures assessing predisposing characteristics (personality traits, arousal predisposition, and insomnia vulnerability), precipitating events and outcomes (life events, perceived stress, anxiety, and depression), coping styles (thought control strategies and coping styles), and perpetuating factors (sleep preoccupation, pre-sleep arousal, dysfunctional beliefs, and fatigue). Additionally, insomnia status (from AI at baseline to its persistence or natural remission [NR]) was assessed 1 month later (n = 129). Baseline differences between NS and individuals with AI were observed in each domain with increasing age, lower openness to experience and conscientiousness, higher insomnia severity, levels of anxiety, and affective sleep preoccupation significantly predicting AI status. Further, a previous episode of insomnia, higher depression scores, and affective sleep preoccupation scores significantly predicted its persistence, as opposed to its NR. Results are discussed with reference to the conceptualization of insomnia and how the findings may influence the design of preventative interventions to circumvent the transition from acute to chronic insomnia., (© Sleep Research Society 2021. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.)