The impact of post-learning sleep vs. wakefulness on recognition memory for faces with different facial expressions

A beneficial effect of sleep after learning, compared to wakefulness, on memory formation has been shown in many studies using a variety of tasks. However, none of these studies has specifically addressed recognition memory for faces so far. The recognition of familiar faces, together with the extraction of emotional information from facial expression, is a fundamental cognitive skill in human everyday life, for which specific neural systems and mechanisms of processing have been developed. Here, we investigated the role of post-learning sleep for later recognition memory for neutral, happy, and angry faces. Twelve healthy subjects, after judging the emotional valence of the faces in the evening (learning phase), either slept normally in the subsequent night, with sleep recorded polysomnographically (sleep condition), or remained awake (wake condition) according to a cross-over design. Recognition testing took place in the second evening after learning, i.e. after a further night of regular sleep spent at home. Sleep after learning, compared to wakefulness, enhanced memory accuracy in recognition memory. This effect was independent of the emotional valence of facial expression. The response criterion at recognition testing did not differ between sleep and wake conditions. The amount of non rapid eye movement (NonREM) sleep during post-learning sleep correlated positively with memory accuracy at recognition testing, while time in REM sleep was associated with a speeded responding to the learned faces. Results suggest that face recognition, despite its dependence on specialized brain systems, nevertheless relies on the general neural mechanisms of sleep-associated memory consolidation.     

Sleep in children enhances preferentially emotional declarative but not procedural memories

Although the consolidation of several memory systems is enhanced by sleep in adults, recent studies suggest that sleep supports declarative memory but not procedural memory in children. In the current study, the influence of sleep on emotional declarative memory (recognition task) and procedural memory (mirror tracing task) in 20 healthy children (10-13 years of age) was examined. After sleep, children showed an improvement in declarative memory. Separate analysis with respect to the emotional stimulus content revealed that sleep enhances the recognition of emotional stimuli (p > .001) rather than neutral stimuli (p = .084). In the procedural task, however, no sleep-enhanced memory improvement was observed. The results indicate that sleep in children, comparable to adults, enhances predominantly emotional declarative memory; however, in contrast to adults, it has no effect on the consolidation of procedural memory.     

Does quality of sleep mediate the effect of depression on hopelessness?

The objectives of the study were to evaluate the relationship between sleep quality, depression, and hopelessness in advanced cancer patients and whether sleep quality mediated the effect of depression on hopelessness. The final sample consisted of 102 advanced cancer patients under palliative treatment. Patients completed the Greek Pittsburgh Sleep Quality Index, a sleep quality instrument, the Greek Beck Depression Inventory for measuring depression, and finally the Beck Hopelessness Scale. Patients' performance status was assessed by their overall physical functioning, as defined by the Eastern Cooperative Oncology Group. Depression was highly associated with hopelessness (r = .52, p<.001). Statistically significant associations were found between sleep quality with hopelessness (r = .37, p<.001), as well as with depression (r = .36, p<.001). Mediation analyses indicated that depression influenced hopelessness directly as well as indirectly by its effect on sleep quality. About 14.58% of the variation in hopelessness was explained by depression; 4% of the variance in hopelessness explained by depression was accounted for by the mediation pathway indicating that sleep quality mediated the relationship between depression and hopelessness. Similarly, in the reverse mediation analysis, depression mediated the relationship between sleep quality and hopelessness; 43% of the variation in hopelessness was explained by sleep quality. In conclusion, some of the effect of depression on hopelessness was mediated by sleep quality, but depression had a direct effect on hopelessness as well. Additionally, some of the effect of sleep quality on hopelessness was mediated by depression. The current findings are important because improving sleep quality by treating depression may contribute to decreased hopelessness scores and vice versa: Treating depression by improving sleep quality may also contribute to lower hopelessness scores.     

ERPs studies of cognitive processing during sleep

In the last few decades, several works on cognitive processing during sleep have emerged. The study of cognitive processing with event related potentials (ERPs) during sleep is a topic of great interest, since ERPs allow the study of stimulation with passive paradigms (without conscious response or behavioural response), opening multiple research possibilities during different sleep phases. We review ERPs modulated by cognitive processes during sleep: N1, Mismatch Negativity (MMN), P2, P3, N400-like, N300-N550, among others. The review shows that there are different cognitive discriminations during sleep related to the frequency, intensity, duration, saliency, novelty, proportion of appearance, meaning, and even sentential integration of stimuli. The fascinating results of cognitive processing during sleep imply serious challenges for cognitive models. The studies of ERPs, together with techniques of neuroimaging, have demonstrated the existence of cognitive processing during sleep. A fundamental question to be considered is if these cognitive phenomena are similar to processing that occurs during wakefulness. Based on this question we discussed the existence of possible mechanisms associated with sleep, as well as the specific cognitive and neurophysiologic differences of wakefulness and sleep. Much knowledge is still required to even understand the conjunction of dramatic changes in cerebral dynamics and the occurrence of cognitive processes. We propose some insights based on ERPs research for further construction of theoretical models for integrating both cognitive processing and specific brain sleep dynamics.     

Experimental manipulation of maternal proximity during short sequences of sleep and infant calming response

This study aimed to understand how different mother-infant sleeping arrangements impact infants’ self-regulation, particularly their calming response. Thus this study investigated the effect of three prevalent mother-infant sleeping arrangements, co-sleeping (CS), sleeping beyond arm’s length from their mother (BAL), and solitary sleeping (SS), on infants’ physiological calming through self-regulation during a nap session in 24 infants (50% female, M = 1.85 months SD = 0.93 months), who were identified as either regular co-sleepers with their mothers, infants who slept in the BAL sleeping arrangement from their mother, and infants who are solitary sleepers (SS). The effect of all three sleeping conditions amongst all the three types of infants with different habitual sleeping arrangements was assessed. All infants spent 10 min (2 × 5 min sessions) in each sleeping condition (CS, BAL, SS) during which electrocardiographic recordings were collected to obtain interbeat intervals (IBI) and rMSSD, a measure of heart rate variability (HRV) an index of physiological calming, maintained by the parasympathetic pathway involved in self-regulation. Infants who regularly co-slept with their mothers had the highest IBI, indicating greater physiological calming and self-regulation across all sleeping arrangement conditions (CS, BAL, SS), followed by infants who regularly slept in the BAL sleeping arrangement from their mothers. IBI was lowest amongst regular solitary sleepers, potentially indicating physiological stress due to mother-infant separation. However, HRV indices during the sleeping arrangements (especially across regular solitary sleepers) were inconclusive as to whether the lack of change in HRV across all sleeping conditions was due to physiological stress responses or greater physiological regulation. This study is the first to investigate the effect of manipulated and habitual mother-infant sleeping arrangements on infant physiological calming.     

Fatigue and alertness in the United States railroad industry part I: the nature of the problem

The railroad industry must actively manage employee fatigue and alertness problems to maintain an optimal level of operational safety and productivity. Given the necessity to operate nights and irregular hours, weekends and holidays under a wide range of physical conditions and service demands, we must explore every reasonable avenue to ensure employees are fit, alert, and well-rested. Effective fatigue management programs must address train crews, dispatchers, signalmen, track workers, and others – both operating and non-operating personnel. Work scheduling is a particular problem in on-call operations because of start-time variability, “call” predictability, and the common use of “shorter-than 24-h work/rest schedules”. Extensive night operations are incompatible with normal circadian rhythms. Staffing limitations often require extensive overtime and reduce the effectiveness of any work schedule. These and other institutional factors significantly contribute to employee sleep deficit and overall fatigue. Lack of alertness and reduced vigilance are related not only to sleep disruption and resulting sleep deficits, but also to cognitive workload, workload transition, the physical working environment, and the design of advanced control systems. Ongoing research into fatigue mitigation and alertness enhancement strategies and into advanced technologies such as Positive Train Control (PTC) can lead to improvements. These include better labor–management agreements, more effective fatigue-related educational programs, improved schedule regularity, and more practical and adaptable federal laws and regulations.     

Sleep, watchkeeping and accidents: a content analysis of incident at sea reports

The unique profession of seafaring involves rest and sleep in a 24-h-a-day work environment that usually involves time-zone crossings, noise, heat, cold and motion. Sleep under such conditions is often difficult to obtain, and sleeping and sleep loss are often related to fatigue and contributory to accidents. This study aims to determine how accident investigators report sleep in Incident at Sea Reports and subsequently analyse the relationships between sleep, fatigue and accidents in these reports.The full text of 44 Incident at Sea Reports was coded and analysed using NUDIST software. This sample included collisions and groundings reported since 1991, where significant human factors contributed to the incident. The Incident at Sea Reports were electronically searched for reference to sleep and content was indexed against parameters such as fatigue behaviours, time of day and contributing personnel. Incident at Sea Reports incorporate three levels of reference to sleep, analysis of which may associate sleeping and sleepiness with accident causation. The highest level of reference unequivocally associates either being asleep, or being sleep deprived with accidents, but not always with fatigue. At an intermediate level, reference to the conflicting pressures of work and sleep on board fishing boats and ships suggests a work environment that is not conducive to obtaining sufficient sleep, and accident investigators are usually unable to link the watchkeeping environment with fatigue as a contributing factor. At the lowest level of association, reference is made to the integrated nature of sleeping and work on board.