Shift Work and Inter‐Individual Differences in Sleep and Sleepiness

Inter‐individual differences in tolerance for shift work have been studied primarily in terms of external factors affecting alertness on the job or the ability to rest and sleep while at home. However, there is increasing evidence that neurobiological factors play a role as well, particularly the major processes involved in the regulation of sleep and wakefulness. These include a sleep homeostatic process seeking to balance wakefulness and sleep and a circadian process seeking to promote wakefulness during the day and sleep during the night. Shift work is associated with a temporal misalignment of these two endogenous processes. During nightwork, this misalignment makes it difficult to stay awake during the nightshift and sleep during the day. However, inter‐individual variability in the processes involved in sleep/wake regulation is substantial. Recent studies have demonstrated the existence of inter‐individual differences in vulnerability to cognitive deficits from sleep loss. Moreover, these inter‐individual differences were shown to constitute a trait. Interestingly, self‐evaluations of sleepiness did not correspond well with the trait inter‐individual variability in objective levels of performance impairment during sleep deprivation. Perhaps because of this discrepancy, in operational settings, the inter‐individual differences in vulnerability to sleep loss do not appear to be limited due to self‐selection mechanisms. Indeed, even among a highly select group of active‐duty jet fighter pilots flying a series of simulated night missions, systematic inter‐individual differences in performance impairment from sleep loss were still observed. There are significant personal and economic consequences to human error and accidents caused by performance deficits due to sleep loss. It is important, therefore, to study the inter‐individual differences in the regulation of sleep and wakefulness in the work environment so that cognitive impairment during shift work may be better anticipated and prevented.     

The influence of subjective sleep quality on the association between eveningness and depressive symptoms

Increasing evidence suggests that eveningness is associated with increased risk for depression. Eveningness, however, is also associated with poor sleep quality and the unique role of eveningness in depressive symptomatology remains to be elucidated. The goal of the current study, therefore, was to examine the inter-relationships between eveningness, subjective sleep quality and depressive symptoms in healthy participants free of current or previous depression and sleep disorder. Here, 167 healthy participants (mean age 24.16, 129/38 females/males) completed the reduced Morningness–Eveningness Questionnaire (rMEQ), the Pittsburgh Sleep Quality Index (PSQI) and the Centre for Epidemiological Studies Depression Scale (CES-D). Bootstrap mediation analysis for a simple mediation model including rMEQ, PSQI and CES-D was applied. Eveningness was associated with increased depressive symptoms and mediation analysis showed that this relationship was partly mediated by sleep quality. Our results suggest that indicators of depression observed in evening-type individuals cannot be attributed exclusively to disturbed sleep. We suggest that interventions that target both sleep quality and dysfunctional cognitive styles would be optimal to promote well-being in evening-type individuals.     

Nuclear factor-kappaB mediates the cell survival-promoting action of activity-dependent neurotrophic factor peptide-9

Activity-dependent neurotrophic factor (ADNF) is produced by astrocytes in response to neuronal depolarization and, in turn, promotes neuronal survival. A nineamino acid ADNF peptide (ADNF9) exhibits full neurotrophic activity and potently protects cultured embryonic rat hippocampal neurons from oxidative injury and apoptosis. Picomolar concentrations of ADNF9 induced an increase in nuclear factor-kappaB (NF-kappaB) DNA-binding activity within 1 h of exposure, with a maximum increase of approximately 10-fold by 6 h. Activation of NF-kappaB was correlated with increased resistance of neurons to apoptosis induced by exposure to Fe(2+). The antiapoptotic action of ADNF9 was abolished when NF-kappaB activation was specifically blocked with kappaB decoy DNA. Oxidative stress was attenuated in neurons pretreated with ADNF9, and this effect of ADNF9 was blocked by kappaB decoy DNA, suggesting that ADNF9 suppresses apoptosis by reducing oxidative stress. ADNF9 also prevented neuronal apoptosis following trophic factor withdrawal via an NF-kappaB-mediated mechanism. Thus, NF-kappaB mediates the neuron survival-promoting effects of ADNF9 in experimental models relevant to developmental neuronal death and neurodegenerative disorders.     

A brief pre-exercise nap may alleviate physical performance impairments induced by short-term sustained operations with partial sleep deprivation – A field-based study

ABSTRACT

The purpose of the study was to evaluate the recuperative efficacy of pre-exercise napping on physical capacity after military sustained operations (SUSOPS) with partial sleep deprivation. Before and after a 2-day SUSOPS, 61 cadets completed a battery of questionnaires, and performed a 2-min lunges trial and a 3,000-m running time-trial. After the completion of SUSOPS, subjects were randomized to either a control [without pre-exercise nap (CON); n = 32] or a nap [with a 30-min pre-exercise nap (NAP); n = 29] group. SUSOPS enhanced perceived sleepiness and degraded mood in both groups. Following SUSOPS, the repetitions of lunges, in the CON group, were reduced by ~ 2.3%, albeit the difference was not statistically significant (p = 0.62). In the NAP group, however, the repetitions of lunges were increased by ~ 7.1% (p = 0.01). SUSOPS impaired the 3,000-m running performance in the CON group (~ 2.3%; p = 0.02), but not in the NAP group (0.3%; p = 0.71). Present results indicate, therefore, that a relatively brief pre-exercise nap may mitigate physical performance impairments ensued by short-term SUSOPS.     

Basic Scale on Insomnia complaints and Quality of Sleep (BaSIQS): Reliability,initial validity and normative scores in higher education students

Based on successive samples totaling more than 5000 higher education students, we scrutinized the reliability, structure, initial validity and normative scores of a brief self-report seven-item scale to screen for the continuum of nighttime insomnia complaints/perceived sleep quality, used by our team for more than a decade, henceforth labeled the Basic Scale on Insomnia complaints and Quality of Sleep (BaSIQS). In study/sample 1 (n?=?1654), the items were developed based on part of a larger survey on higher education sleep–wake patterns. The test–retest study was conducted in an independent small group (n?=?33) with a 2–8 week gap. In study/sample 2 (n?=?360), focused mainly on validity, the BaSIQS was completed together with the Pittsburgh Sleep Quality Index (PSQI). In study 3, a large recent sample of students from universities all over the country (n?=?2995) answered the BaSIQS items, based on which normative scores were determined, and an additional question on perceived sleep problems in order to further analyze the scale’s validity. Regarding reliability, Cronbach alpha coefficients were systematically higher than 0.7, and the test–retest correlation coefficient was greater than 0.8. Structure analyses revealed consistently satisfactory two-factor and single-factor solutions. Concerning validity analyses, BaSIQS scores were significantly correlated with PSQI component scores and overall score (r?=?0.652 corresponding to a large association); mean scores were significantly higher in those students classifying themselves as having sleep problems (p?<?0.0001, d?=?0.99 corresponding to a large effect size). In conclusion, the BaSIQS is very easy to administer, and appears to be a reliable and valid scale in higher education students. It might be a convenient short tool in research and applied settings to rapidly assess sleep quality or screen for insomnia complaints, and it may be easily used in other populations with minor adaptations.     

The longer the better: Sleep–wake patterns during preparation of the World Rowing Junior Championships

Recovery is essential for high athletic performance, and therefore especially sleep has been identified as a crucial source for physical and psychological well-being. However, due to early-morning trainings, which are general practice in many sports, athletes are likely to experience sleep restrictions. Therefore, this study investigated the sleep–wake patterns of 55 junior national rowers (17.7 ± 0.6 years) via sleep logs and actigraphy during a four-week training camp. Recovery and stress ratings were obtained every morning with the Short Recovery and Stress Scale on a 7-point Likert-type scale ranging from 0 (does not apply at all) to 6 (fully applies). The first training session was scheduled for 6:30 h every day. With two to four training sessions per day, the training load was considerably increased from athletes’ home training. Objective sleep measures (n = 14) revealed less total sleep time (TST) in the first two weeks (409.6 ± 19.1 and 416.0 ± 16.3 min), while training volume and intensity were higher. In the second half of the camp, less training sessions were implemented, more afternoons were training free and TSTs were longer (436.3 ± 15.8 and 456.9 ± 25.7 min). A single occasion of 1.5-h delayed bedtime and usual early morning training (6:30 h) resulted in reduced ratings of Overall Recovery (OR) (M = 3.3 ± 1.3) and greater Negative Emotional State (NES) (M = 1.3 ± 1.2, p < .05), which returned to baseline on the next day. Following an extended night due to the only training-free day, sleep-offset times were shifted from ~5:30 to ~8:00 h, and each recovery and stress score improved (p < .01). Moreover, subjective ratings of the first six days were summarised as a baseline score to generate reference data as well as to explore the association between sleep and recovery. Intercorrelations of these sleep parameters emphasised the relationship between restful sleep and falling asleep quickly (r = .34, p < .05) as well as few awakenings (r = .35, p < .05). Overall, the findings highlight the impact of sleep on subjective recovery measures in the setting of a training camp. Providing the opportunity of extended sleep (and a day off) seems the most simple and effective strategy to enhance recovery and stress-related ratings.     

Social and environmental impacts on sleep in captive Asian elephants (Elephas maximus)

Modern zoos strive to improve standards of animal management, husbandry and welfare of their animals as part of a continual evaluation process. Elephants (Elephantidae) have received particular attention in recent years due to the challenge of providing environments which promote natural behavior and opportunities for social interaction. A number of measures have been proposed to measure wellbeing, with sleep quality increasingly being used. Sleep is a vital aspect of life for cell replenishment as well as optimal development of young. Sleep deprivation can lead to immunosuppression and illness; therefore animal managers have a responsibility to ensure they reduce the potential for disturbance through noise, light, or other environmental factors. The social environment also plays an essential role in wellbeing, particularly for species that live in multi-generational family units. In this study the nocturnal behavior of a multi-generational captive herd was observed to determine impacts of husbandry changes on sleep duration and bout length (measured as recumbent rest). As expected, average total duration of sleep was higher in younger elephants and rates were comparable to those reported in other studies of Asian elephants. Overnight access to an outdoor paddock in warmer weather increased overall average bout length of sleep in the herd. Average total duration of sleep also increased for the herd following the movement of an unrelated adult female who had previously shown weak bonds with other herd members. This indicates that social compatibility is a vital component of elephant welfare, impacting not only behavioral interactions but sleep quality and duration.     

One night of sleep deprivation induces release of small extracellular vesicles into circulation and promotes platelet activation by small EVs

Extracellular vesicles (EVs) are emerging as key players in intercellular communication. Few studies have focused on EV levels in subjects with sleep disorders. Here, we aimed to explore the role of acute sleep deprivation on the quantity and functionality of circulating EVs, and their tissue distribution. EVs were isolated by ultracentrifugation from the plasma of volunteers and animals undergoing one night of sleep deprivation. Arterio‐venous shunt, FeCl₃ thrombus test and thrombin‐induced platelet aggregation assay were conducted to evaluate the in vivo and in vitro bioactivity of small EVs. Western blotting was performed to measure the expression of EV proteins. The fate and distribution of circulating small EVs were determined by intravital imaging. We found that one night of sleep deprivation triggers release of small EVs into the circulation in both healthy individuals and animals. Injection of sleep deprivation‐liberated small EVs into animals increased thrombus formation and weight in thrombosis models. Also, sleep deprivation‐liberated small EVs promoted platelet aggregation induced by thrombin. Mechanistically, sleep deprivation increased the levels of HMGB1 protein in small EVs, which play important roles in platelet activation. Furthermore, we found sleep deprivation‐liberated small EVs are more readily localize in the liver. These data suggested that one night of sleep deprivation is a stress for small EV release, and small EVs released here may increase the risk of thrombosis. Further, small EVs may be implicated in long distance signalling during sleep deprivation‐mediated adaptation processes.     

Spectral EEG indicator of pressure to enter into deep sleep: its responsiveness to closing the eyes for just a few minutes exhibits a pure exponential buildup during sleep deprivation

According to the two-process model of sleep–wake regulation, a homeostatic sleep pressure, i.e. a pressure to enter into deep non-rapid eyes movement (NREM) sleep, must exhibit a purely exponential buildup during prolonged wakefulness. However, this pressure is usually measured indirectly, i.e. during the following episode of actual deep NREM sleep. The purpose of this paper was to show that, despite a prominent circadian modulation of time course of any waking EEG index, the model-postulated purely exponential buildup of the homeostatic sleep pressure can be directly confirmed. During two days of sleep deprivation experiments, the EEG of healthy adults (N = 30) was recorded every other hour throughout 5-min eyes closed relaxation. Sixteen ln-transformed single-Hz power densities (from 1 to 16 Hz) were computed for each of 5 one-min intervals. Differences between these densities obtained for the first and the following intervals were calculated and averaged. The obtained 16 values were used as the frequency weighting curve for weighting densities of each set of 16 single-Hz power densities. Summing-up of these weighted densities provided a single measure that was found to co-vary with self-rated sleepiness throughout two-day interval of sleep deprivation, thus reflecting the joint influence of the circadian and homeostatic processes. However, two-day time course of responsiveness of this measure to closing the eyes for just a few minutes exhibited a purely exponential buildup. It was concluded that this result provided a direct experimental confirmation of the model-predicted exponential buildup of the homeostatic sleep pressure across prolonged episode of wakefulness.     

The experience and impact of intrusive thoughts in individuals with late bedtimes

There is increasing awareness of the interplay among sleep, circadian rhythms, and psychopathology. Recent findings show that obsessive–compulsive disorder (OCD) is associated with late bedtimes. Sleep disruption may exacerbate impairments in executive functioning in individuals with OCD, making these individuals vulnerable to experiencing intrusive thoughts that come from “out of the blue” (autogenous obsessions; AO) and to having difficulty dismissing them. The current study investigated types of intrusive thoughts experienced by individuals with (DB) and without (NDB) delayed bedtimes. Bedtime, and AO (uncued, affectively negative) vs. reactive obsessions (RO; triggered by environment, affectively neutral) were examined in 212 adults. As hypothesized, individuals with DB reported more frequent intrusive thoughts, as well as more AO, than NDB individuals. Additionally, DB participants reported a greater urge to neutralize intrusive thoughts than NDB participants. Future work should test the replicability of these findings and explore circadian disruptions in OCD using biological markers.