Auditory arousal responses and thresholds during REM and NREM sleep of sleepwalkers and controls

A brainstem-to-mediodorsal thalamic pathway mediates sound-induced arousal from slow-wave sleep

Auditory-induced arousal is a defense mechanism of animals against potential dangers. Although the thalamus is the neural substrate that relays sensory information to the cortex, its function is reduced during slow-wave sleep (SWS), also known as deep sleep. Despite this, animals are capable of waking up in response to external sensory stimuli, suggesting the existence of neural circuits that are involved in this response. Here, we report that kainate-class-type ionotropic glutamate receptor subunit 4 (GRIK4)-positive mediodorsal (MD) thalamic neurons act as a neural substrate for arousals from SWS. These neurons become active during arousal from SWS and their photoactivation can induce arousal from SWS. Moreover, we show that these neurons are influenced by glutamatergic neurons in the brainstem, the activity of which increases during auditory-induced arousals. These results suggest that this brainstem-MD pathway can mediate wakefulness from SWS.

Adaptive Solutions to the Problem of Vulnerability During Sleep

Sleep is a behavioral state whose quantity and quality represent a trade-off between the costs and benefits this state provides versus the costs and benefits of wakefulness. Like many species, we humans are particularly vulnerable during sleep because of our reduced ability to monitor the external environment for nighttime predators and other environmental dangers. A number of variations in sleep characteristics may have evolved over the course of human history to reduce this vulnerability, at both the individual and group level. The goals of this interdisciplinary review paper are (1) to explore a number of biological/instinctual features of sleep that may have adaptive utility in terms of enhancing the detection of external threats, and (2) to consider relatively recent cultural developments that improve vigilance and reduce vulnerability during sleep and the nighttime. This paper will also discuss possible benefits of the proposed adaptations beyond vigilance, as well as the potential costs associated with each of these proposed adaptations. Finally, testable hypotheses will be presented to evaluate the validity of these proposed adaptations.

Autonomic Modulation During Baseline and Recovery Sleep in Adult Sleepwalkers

Sleepwalking has been conceptualized as deregulation between slow-wave sleep and arousal, with its occurrence in predisposed patients increasing following sleep deprivation. Recent evidence showed autonomic changes before arousals and somnambulistic episodes, suggesting that autonomic dysfunctions may contribute to the pathophysiology of sleepwalking. We investigated cardiac autonomic modulation during slow-wave sleep in sleepwalkers and controls during normal and recovery sleep following sleep deprivation. Fourteen adult sleepwalkers (5M; 28.1 ± 5.8 years) and 14 sex- and age-matched normal controls were evaluated by video-polysomnography for one baseline night and during recovery sleep following 25 h of sleep deprivation. Autonomic modulation was investigated with heart rate variability during participants' slow-wave sleep in their first and second sleep cycles. 5-min electrocardiographic segments from slow-wave sleep were analyzed to investigate low-frequency (LF) and high-frequency (HF) components of heart rate spectral decomposition. Group (sleepwalkers, controls) X condition (baseline, recovery) ANOVAs were performed to compare LF and HF in absolute and normalized units (nLF and nHF), and LF/HF ratio. When compared to controls, sleepwalkers' recovery slow-wave sleep showed lower LF/HF ratio and higher nHF during the first sleep cycle. In fact, compared to baseline recordings, sleepwalkers, but not controls, showed a significant decrease in nLF and LF/HF ratio as well as increased nHF during recovery slow-wave sleep during the first cycle. Although non-significant, similar findings with medium effect sizes were observed for absolute values (LF, HF). Patterns of autonomic modulation during sleepwalkers' recovery slow-wave sleep suggest parasympathetic dominance as compared to baseline sleep values and to controls. This parasympathetic predominance may be a marker of abnormal neural mechanisms underlying, or interfere with, the arousal processes and contribute to the pathophysiology of sleepwalking.

Sleep-Related Hypermotor Epilepsy vs Disorders of Arousal in Adults: A Step-Wise Approach to Diagnosis

Disorders of arousal (DoA) and sleep-related hypermotor epilepsy (SHE) are sleep-related events characterized by complex, often bizarre, and violent behaviors. DoA are involuntary motor manifestations of various complexities occurring during incomplete awakening from non-rapid eye movement sleep. SHE is a focal epilepsy characterized by stereotyped hyperkinetic or/and asymmetric tonic/dystonic seizures usually arising from non-rapid eye movement sleep. Even if many aspects regarding DoA and SHE have been clarified, the differential diagnosis remains challenging, because DoA and SHE share some semiologic features and genetic background. The clinical history, collected from the patient and his/her witness, represents the first and common milestone in the diagnosis. Validated questionnaires constitute suitable screening tools that could guide further analysis. The worldwide availability of homemade video recordings has increased the possibility of adding more objective information to the clinical history alone. The confirmed diagnosis relies on video-polysomnographic recording although it requires time, economic resources, and specific skills for the analysis. In this review we propose a simple diagnostic algorithm for the differential diagnosis between DoA and SHE in adults, based on the most updated knowledge, from the simpler tool to the most specific and tailored one.

The Arousal Disorders Questionnaire: a new and effective screening tool for confusional arousals, Sleepwalking and Sleep Terrors in epilepsy and sleep disorders units

BACKGROUND

Arousal Disorders (DoA) include Confusional Arousals, Sleepwalking and Sleep Terrors. DoA diagnosis is mainly clinical but no validated questionnaires exist for DoA screening according to the criteria of the International Classification of Sleep Disorders, Third Edition. Recently our group proposed the Arousal Disorders Questionnaire (ADQ) as a new diagnostic tool for DoA diagnosis. The objective of this study was to evaluate the diagnostic accuracy of the ADQ in a sleep and epilepsy center.

METHODS

One interviewer blinded to clinical and video-polysomnographic (VPSG) data administered the ADQ to 150 patients consecutively admitted to our Sleep and Epilepsy Centers for a follow-up visit. The final diagnosis, according to VPSG recordings of at least one major episode, classified patients either with DoA (DoA group) or with other sleep-related motor behaviors confounding for DoA (nDoA group).

RESULTS

47 patients (31%) composed the DoA group; 56 patients with REM sleep behavior disorder, 39 with sleep-hypermotor epilepsy, six with night eating syndrome, and two with drug-induced DoA composed the nDoA group. The ADQ had a sensitivity of 72% (95% CI: 60-82) and a specificity of 96% (95% CI: 89-98) for DoA diagnosis; excluding the items regarding consciousness and episode recall, sensitivity was 83% (95% CI: 71-90) and specificity 93% (95% CI: 86-97).

CONCLUSIONS

The ADQ showed good accuracy in screening patients with DoA in a sleep and epilepsy center setting. Diagnostic criteria related to cognition and episode recall reduced ADQ sensitivity, therefore a better definition of these criteria is required, especially in adults.

Spindles insufficiency in sleepwalkers' deep sleep

OBJECTIVES

Sleepwalkers have consistently shown N3 sleep discontinuity, especially after sleep deprivation. In healthy subjects, sleep spindles activity has been positively correlated to sleep stability. We aimed to compare spindles density during N3 sleep between sleepwalkers and healthy controls.

METHODS

Two cohorts of 10 and 21 adult sleepwalkers respectively controlled with 10 and 18 healthy volunteers underwent one baseline and one recovery sleep recording after 38h (cohort 1) and 25h (cohort 2) of sleep deprivation. For the two recordings, we performed an automatic detection of spindles (11-16Hz) from EEG signal during N3 sleep, restricted to the first sleep cycle and repeated for all cycles. For better interpretation of results, we extended the analysis to N2 sleep and we also measured the density of slow waves oscillation (SWO) (0.5-4Hz) during the same periods.

RESULTS

Compared to controls, sleepwalkers showed significantly lower spindle densities during N3 sleep considering the first sleep cycle (both cohorts) or all cycles (cohort 1). SWO densities did not differ (cohort 1) or were lower (cohort 2) for sleepwalkers. The effect of sleep deprivation did not interact with the effect of group on spindles and SWO densities.

CONCLUSION

This work suggests that the instability of N3 sleep inherent to sleepwalkers may be underpinned by a specific alteration of spindles activity.

A Review of Environmental Barriers to Obtaining Adequate Sleep in the Military Operational Context

Introduction

Sleep loss is ubiquitous in military settings, and it can be deleterious to cognitive, physiological, and operational functioning. This is especially true in the military operational context (e.g., training, garrison, combat) where continuous operations prevent adequate time for rest and recuperation. Furthermore, even when servicemembers do have opportunities for sleep, environmental disruptors in the military operational context make it difficult to obtain restorative sleep. Such environmental disruptors are potentially preventable or reversible, yet there is little public awareness of how to minimize or eliminate these sleep disruptors. Therefore, the goal of this review was to outline prominent environmental sleep disruptors, describe how they occur in the military operational context, and also discuss feasible strategies to mitigate these disruptors.

Materials and Methods

We discuss four factors – light, noise, temperature, and air pollution – that have previously been identified as prominent sleep disruptors in non-military settings. Additionally, we extracted publicly-available yearly temperature and pollution data, from the National Oceanic and Atmospheric Association and the Environmental Protection Agency, respectively, for major prominent military installations in the continental US in order to identify the sites at which servicemembers are at the greatest risk for environmental sleep disruptions.

Results

Based on previous literature, we concluded light and noise are the most easily mitigatable sleep-disrupting environmental factors. Air pollution and temperature, on the other hand, are more difficult to mitigate. We also propose that harsh/uncomfortable sleeping surface is a fifth critical, previously unexplored sleep disruptor in the military operational context. Furthermore, we identified several problematic military sites for air pollution for temperature. Specifically, each branch has major installations located in regions with extreme heat (especially the Army), and each branch has at least one major installation in a high air pollution region. These findings show that even when in training or garrison in the US, military servicemembers are at risk for having sleep disruption due to environmental factors.

Conclusions

Environmental disruptors, such as light, noise, temperature, and air pollution, can negatively impact sleep in the military operational context. Simple, feasible steps can be taken to reduce sleep disruptions that are caused by light and noise. Yet there is a need for research and development on tools to mitigate air pollution, extreme temperatures, and inhospitable sleeping surfaces. Leadership at the discussed military bases and training facilities should focus on improving the sleep environment for individuals under their command. Such interventions could ultimately improve warfighter health, wellness, and operational performance, leading to greater warfighter readiness and lethality.

Adult NREM Parasomnias: An Update

Our understanding of non-rapid eye movement (NREM) parasomnias has improved considerably over the last two decades, with research that characterises and explores the causes of these disorders. However, our understanding is far from complete. The aim of this paper is to provide an updated review focusing on adult NREM parasomnias and highlighting new areas in NREM parasomnia research from the recent literature. We outline the prevalence, clinical characteristics, role of onset, pathophysiology, role of predisposing, priming and precipitating factors, diagnostic criteria, treatment options and medico-legal implications of adult NREM parasomnias.

Sleep structure and awakening threshold in delayed sleep-wake phase disorder patients compared to healthy sleepers

STUDY OBJECTIVES

Difficult early morning awakening is a primary symptom of delayed sleep-wake phase disorder (DSWPD), however, it remains poorly investigated. Our main objective was to quantify the awakening threshold in DSWPD-patients and healthy controls as well as investigate a possible relationship with sleep stages. A secondary objective was to compare habitual sleep measured by polysomnography and actigraphy between patients and controls.

METHODS

Twenty DSWPD patients and 16 controls had two polysomnographic recordings at a sleep laboratory. Participants followed their habitual sleep-wake schedule on the first night and a forced sleep-wake schedule (00:00-07:00 h) on the second night. We used a custom-made alarm clock was for the forced-night awakening, starting at 72 dB sound intensity which increased up to 104 dB.

RESULTS

Mean awakening threshold in dB was higher in patients compared to controls; 75.5 vs. 72.6, p = 0.01, and the difference could not be explained statistically by sleep-time. Patients who were in REM sleep upon attempted awakening had a higher awakening threshold compared to patients who were in NREM sleep; 80.0 vs 74.7, F = 6.4, p = 0.02. Patients had increased sleep onset latency both at home with actigraphy and by PSG during the first laboratory night (20.6 vs 12.1 min, p = 0.004), however no further differences between the groups were observed regarding sleep structure.

CONCLUSIONS

A high early-morning forced awakening threshold in DSWPD was related to REM sleep. Sleep onset problems, even with habitual bedtimes, may also be an integral feature of DSWPD.

Medication induced sleepwalking: A systematic review

Medications that trigger sleepwalking may inadvertently put the patient at risk of injury to themselves and/or others, and contribute to poor treatment adherence. The aim of this study was to systematically review the literature to identify drugs that may increase the risk of sleepwalking. A search of CINAHL, EMBASE, PsycINFO, PubMed, and ScienceDirect was conducted with the keywords 'sleepwalking' OR 'somnambulism'. Of the original 83 sourced papers, 62 met the inclusion criteria and were subsequently included for review. Twenty-nine drugs, primarily in four classes-benzodiazepine receptor agonists and other gamma aminobutyric acid (GABA) modulators, antidepressants and other serotonergic agents, antipsychotics, and β-blockers-were identified as possible triggers for sleepwalking. The strongest evidence for medication-induced sleepwalking was for zolpidem and sodium oxybate. All other associations were based on case reports. This research highlights the importance of considering sleepwalking in risk profiles in clinical trials, particularly for drugs that enhance GABA activity at the GABA_A receptor, enhance serotonergic activity, or block the activity of noradrenaline at β receptors. The results also have implications for prescribers to consider sleepwalking as a potential adverse effect and ensure that: 1) the patient is educated about a safe sleep environment; 2) they are encouraged to report the onset or exacerbation of sleepwalking, and 3) alternative treatments are considered if sleepwalking occurs.

The course and character of sleepwalking in adulthood: a clinical and polysomnographic study

To describe characteristics of adult sleepwalking (potential triggers and correlates with polysomnography), 52 patients were interviewed regarding their sleepwalking episodes and underwent video-polysomnography on two consecutive nights. Sleepwalking history averaged 12 years and frequent episodes (more than once per week) occurred in 62%. Higher frequency was associated with earlier onset of sleepwalking (p < 0.005) and 53.8% reported dangerous sleepwalking behavior. The most common self-reported triggers were sleep deprivation and stressful events, while no specific trigger was reported in 37% of patients. More awakening from slow-wave sleep was associated with a higher frequency of sleepwalking episodes (p < 0.001). A longer history of sleepwalking was associated with more sleepwalking episodes, even without the presence of sleep comorbidities or other known precipitating factors.

Somnambulism: clinical aspects and pathophysiological hypotheses

Somnambulism, or sleepwalking, can give rise to a wide range of adverse consequences and is one of the leading causes of sleep-related injury. Accurate diagnosis is crucial for proper management and imperative in an ever-increasing number of medicolegal cases implicating sleep-related violence. Unfortunately, several widely held views of sleepwalking are characterised by key misconceptions, and some established diagnostic criteria are inconsistent with research findings. The traditional idea of somnambulism as a disorder of arousal might be too restrictive and a comprehensive view should include the idea of simultaneous interplay between states of sleep and wakefulness. Abnormal sleep physiology, state dissociation, and genetic factors might explain the pathophysiology of the disorder.