Sleep as a restorative process and a theory to explain why

Restless nights when sick: ectoparasite infections alter rest-activity cycles of diurnal fish hosts

Circadian rhythms are timekeeping mechanisms responsible for an array of biological processes. Disruption of such cycles can detrimentally affect animal health. Circadian rhythms are critical in the co-evolution of host–parasite systems, as synchronization of parasite rhythms to the host can influence infection dynamics and transmission potential. This study examines the circadian rhythms in behaviour and activity of a model fish species (Poecilia reticulata) in isolation and in shoals, both when uninfected and infected with an ectoparasite (Gyrodactylus turnbulli). Additionally, the rhythmical variance of parasite activity under different light conditions as well as rhythmical variance in parasite transmissibility was explored. Overall, infection alters the circadian rhythm of fish, causing nocturnal restlessness. Increased activity of gyrodactylids on the host's skin at night could potentially contribute to this elevated host activity. Whilst migration of gyrodactylids across the host's skin may have caused irritation to the host resulting in nocturnal restlessness, the disruption in guppy activity rhythm caused by the expression of host innate immunity cannot be excluded. We discuss the wider repercussions such behavioural responses to infection have for host health, the implications for animal behaviour studies of diurnal species as well as the application of chronotherapeutic approaches to aquaculture.

Sleep restores an optimal computational regime in cortical networks

Sleep is assumed to subserve homeostatic processes in the brain; however, the set point around which sleep tunes circuit computations is unknown. Slow-wave activity (SWA) is commonly used to reflect the homeostatic aspect of sleep; although it can indicate sleep pressure, it does not explain why animals need sleep. This study aimed to assess whether criticality may be the computational set point of sleep. By recording cortical neuron activity continuously for 10-14 d in freely behaving rats, we show that normal waking experience progressively disrupts criticality and that sleep functions to restore critical dynamics. Criticality is perturbed in a context-dependent manner, and waking experience is causal in driving these effects. The degree of deviation from criticality predicts future sleep/wake behavior more accurately than SWA, behavioral history or other neural measures. Our results demonstrate that perturbation and recovery of criticality is a network homeostatic mechanism consistent with the core, restorative function of sleep.

Sleep quality, frailty and overall health among community-dwelling older people: A longitudinal study

AIMS

The aims of the study were to describe sleep quality among community-dwelling older people; determine the association between sleep quality (total and multidimensional), frailty and overall health; study frailty as a mediator in the association between sleep quality and overall health.

DESIGN

This longitudinal, correlative study used data from 2020 to 2022.

METHODS

A total of 181 community-dwelling older people in a city in Southeast China were assessed twice. Sleep quality was measured using the Pittsburgh Sleep Quality Index at Time 1 (year 2020); frailty was measured using the FRAIL scale, and overall health was measured using the EuroQol visual analogue scale at Time 1 and 2 (1 year later). Associations and indirect effects were examined using linear regression analyses using the PROCESS Macro (Model 4).

RESULTS

Poor sleep quality (higher scores) was associated with increased frailty over time (total scale), as well as subjective sleep quality, sleep duration, sleep efficiency and daytime dysfunction. Mediation analyses indicated that frailty change had an indirect effect on the association between sleep quality total score Time (T) 1 and overall health T2 and between the dimensions subjective sleep quality, sleep duration, sleep efficiency and daytime dysfunction and overall health. All analyses were adjusted for age, multimorbidity and overall health T1.

CONCLUSIONS

Poor sleep quality is a common problem associated with poor overall health after 1 year, and the progression of frailty mediates this association.

IMPACT

The findings provide a better understanding of the association between sleep quality and overall health and elucidate the mediating effect of frailty. Regular screening and effective treatment by healthcare providers for sleep problems and frailty in older people are necessary to improve their overall health and enhance healthy ageing.

PATIENT OR PUBLIC CONTRIBUTION

Participants in the study provided the data used for all data analysis in the manuscript. Patient or public were not involved in data analysis, interpretation or manuscript preparation. Staff in the community health centre helped with data collection.

Better sleep, better life? testing the role of sleep on quality of life

Previous research has shown that sleep deprivation, low quality sleep or inconvenient sleeping times are associated with lower quality of life. However, research of the longitudinal effects of sleep on quality of life is scarce. Hence, we know very little about the long-term effect of changes in sleep duration, sleep quality and the time when individuals sleep on quality of life. Using longitudinal data from three waves of the Czech Household Panel Study (2018-2020) containing responses from up to 4,523 respondents in up to 2,155 households, the study examines the effect of changes in sleep duration, sleep quality and social jetlag on satisfaction with life, happiness, work stress, subjective health and wellbeing. Although sleep duration and timing are important, panel analyses reveal that sleep quality is the strongest predictor of all sleep variables in explaining both within-person and between-person differences in quality of life indicators.

Sleep Quality: A Narrative Review on Nutrition, Stimulants, and Physical Activity as Important Factors

Sleep is a cyclically occurring, transient, and functional state that is controlled primarily by neurobiological processes. Sleep disorders and insomnia are increasingly being diagnosed at all ages. These are risk factors for depression, mental disorders, coronary heart disease, metabolic syndrome, and/or high blood pressure. A number of factors can negatively affect sleep quality, including the use of stimulants, stress, anxiety, and the use of electronic devices before sleep. A growing body of evidence suggests that nutrition, physical activity, and sleep hygiene can significantly affect the quality of sleep. The aim of this review was to discuss the factors that can affect sleep quality, such as nutrition, stimulants, and physical activity.

Chronobiology and the case for sleep health interventions in the community

Our sleep-wake cycle is determined by the interaction between our homeostatic sleep drive and circadian rhythm. Each of us has a personalised biological rhythm or chronotype that determines the optimal time to fall asleep and wake up. Chronic sleep deprivation has been linked to the development of several physical and mental health disorders, as well as accidents and occupational errors. Around the world, growing recognition of the importance of sleep has led to the adoption of practices that promote sleep health. Given that Singaporeans were consistently found to be one of the most sleep-deprived populations in the world, we believe that there is an urgent need to pursue the introduction of community-based sleep health interventions here. This includes sleep education and promotion of sleep hygiene, adopting practices to reduce social jetlag and improve sleep health, and enhancing screening and treatment of sleep disorders.

Evidence That Sleep Is an Indicator of Overtraining during the Competition Phase of Adolescent Sprinters

Although sleep disturbance is a common complaint in overtrained athletes, the role of sleep in the overtraining process is not clear. This study aimed (i) to compare sleep efficiency/quantity at the start of a competition phase in elite adolescent sprinters who adapted to prior training with that in those who maladapt and (ii) to examine the influence of prior training, fatigue, and sleep on performance through a moderated mediation model. Fatigue (via Profile of Mood State) and internal training load (via session rating of perceived exertion and duration of training as volume) were measured in 20 sprinters (mean age: 15.9 ± 1.7 years) across 4 mesocycles (baseline (T1); preparatory (T2); precompetitive (T3); and competitive (T4) phases), over 26 weeks. Performances were assessed during the competitive period (T3, T4), while sleep was monitored (via actigraphy) for a week during T4. It was inferred that sprinters who had increasingly greater fatigue and concomitant decrements in performance (35%) were maladapted to training and the remaining sprinters who improved fatigue and performance (65%) were adapted to training. Sleep efficiency (91 ± 3% vs. 82 ± 3%, p < 0.001) and quantity (425 ± 33 min vs. 394 ± 20 min, p < 0.001) at the start of T4 were significantly greater in sprinters who adapted. Moreover, higher prior training volume (mean of T1 to T3 training volume) was associated with lower sleep efficiency at the start of T4 (R² = 0.55, p < 0.001) which was associated with poorer performance (R² = 0.82, p < 0.001). Fatigue moderated the indirect effect of prior training volume on performance through its moderation of the effect of sleep efficiency on performance (R² = 0.89, p < 0.001). Impaired sleep as a result of greater prior training volume may be related to performance decrements through fatigue. Athletes should improve sleep during periods of higher training volume to reduce fatigue for better adaptation to training.

Energy Stores, Oxidative Balance, and Sleep in Migratory Garden Warblers (Sylvia borin) and Whitethroats (Sylvia communis) at a Spring Stopover Site

Little is known about how songbirds modulate sleep during migratory periods. Due to the alternation of nocturnal endurance flights and diurnal refueling stopovers, sleep is likely to be a major constraint for many migratory passerine species. Sleep may help to increase the endogenous antioxidant capacity that counteracts free radicals produced during endurance flight and reduces energy expenditure. Here, we investigated the relationship between sleep behavior, food intake, and two markers of physiological condition-the amount of energy reserves and oxidative status-in two migratory songbird species, the garden warbler (Sylvia borin) and the whitethroat (Sylvia communis). In garden warblers, birds with high energy stores were more prone to sleep during the day, while this condition-dependent sleep pattern was not present in whitethroats. In both species, birds with low energy stores were more likely to sleep with their head tucked in the feathers during nocturnal sleep. Moreover, we found a positive correlation between food intake and the extent of energy reserves in garden warblers, but not in whitethroats. Finally, we did not find significant correlations between oxidative status and sleep, or oxidative status and energy stores. Despite our study was not comparative, it suggests that different species might use different strategies to manage their energy during stopover and, additionally, it raises the possibility that migrants have evolved physiological adaptations to deal with oxidative damage produced during migration.

Better Sleep Experience for the Critically Ill: A Comprehensive Strategy for Designing Hospital Soundscapes

In this paper, the sleep phenomenon is considered in relation to critical care soundscapes with the intention to inform hospital management, medical device producers and policy makers regarding the complexity of the issue and possible modes of design interventions. We propose a comprehensive strategy based on soundscape design approach that facilitates a systematic way of tackling the auditory quality of critical care settings in favor of better patient sleep experience. Future research directions are presented to tackle the knowledge deficits in designing for critical care soundscapes that cater for patient sleep. The need for scientifically-informed design interventions for improving patient sleep experience in critical care is highlighted. The value of the soundscape design approach for resolving other sound-induced problems in critical care and how the approach allows for patient-centred innovation that is beyond the immediate sound issue are further discussed.

Sleep Disturbances and Modulations in Inflammation: Implications for Pregnancy Health

When a woman becomes pregnant, there is a vast series of physiological, vascular, and psychological changes. Among the most commonly reported changes are those involving sleep. Pregnant women report that their ability to maintain sleep and acquire continuous refreshing sleep is impaired during the perinatal period as compared to the non-pregnant period. A growing literature supports the hypothesis that disturbed sleep (which comes in many forms) during the perinatal period is associated with an increased risk of adverse maternal, delivery, and infant outcomes. Among the suggested biological pathways linking sleep and adverse outcomes are disturbances in the immune and hormonal systems. The following paper will discuss (1) the various sleep processes that are commonly disturbed during the perinatal period and the methods used to collect sleep data; (2) the evidence linking sleep to adverse outcomes; and (3) how one specific biological pathway, the immune system, likely mediates these associations. The goal of this paper is to clarify the role that sleep disturbance has during pregnancy.

Sleep and gravity

What is known about sleep results from years of observation at the surface of the Earth. Since a few decade man has been able to reach space, escape from the earth attraction and spend days and nights in a weightless condition. Some major physiological changes have been observed during long stays and in particular the sleep duration in space is shorter than on ground. This paper reviews a novel hypothesis proposing that sleep is partly due to gravity. Gravity is a fundamental part of our environment, but is elusive and difficult to apprehend. At the same time, all creatures on Earth undergo cycles of activity and periods of rest (although not always sleep). Careful analysis of previous research on sleep, on Earth, in space and in water, shows that gravity differs in these three situations, and sleep also varies, at least in its duration. On Earth, Rapid Eye Movement (REM) sleep is conditioned by gravity; in space, astronauts have a shorter sleep duration and this is even more striking when a test subject is immersed in water for a week. In conclusion, sleep is partly due to gravity, which acts on our body and brain during the wake period.

Sleep function: Toward elucidating an enigma

Sleep function remains controversial. Individual perspectives frame the issue of sleep function differently. We briefly illustrate how sleep measurement and the evolution, tissue organization levels, molecular mechanisms, and regulation of sleep could influence one's view of sleep function. Then we discuss six viable theories of sleep function. Sleep serves host-defense mechanisms and conserves caloric expenditures, but these functions likely are opportunistic functions evolving later in evolution. That sleep replenishes brain energy stores and that sleep serves a glymphatic function by removing toxic byproducts of waking activity are attractive ideas, but lack extensive supporting experimental evidence. That sleep restores performance is experimentally demonstrated and has obvious evolutionary value. However, this hypothesis lacks experimentally verified mechanisms although ideas relating to this issue are presented. Finally, the ideas surrounding the broad hypothesis that sleep serves a connectivity/plasticity function are many and attractive. There is experimental evidence that connectivity changes with sleep, sleep loss, and with changing afferent input, and that those changes are linked to sleep regulatory mechanisms. In our view, this is the leading contender for the primordial function of sleep. However, much refinement of ideas and innovative experimental approaches are needed to clarify the sleep-connectivity relationship.

Higher-protein diets improve indexes of sleep in energy-restricted overweight and obese adults: results from 2 randomized controlled trials

BACKGROUND

Limited and inconsistent research findings exist about the effect of dietary protein intake on indexes of sleep.

OBJECTIVE

We assessed the effect of protein intake during dietary energy restriction on indexes of sleep in overweight and obese adults in 2 randomized, controlled feeding studies.

DESIGN

For study 1, 14 participants [3 men and 11 women; mean ± SE age: 56 ± 3 y; body mass index (BMI; in kg/m(2)): 30.9 ± 0.6] consumed energy-restricted diets (a 750-kcal/d deficit) with either beef and pork (BP; n = 5) or soy and legume (SL; n = 9) as the main protein sources for 3 consecutive 4-wk periods with 10% (control), 20%, or 30% of total energy from protein (random order). At baseline and the end of each period, the global sleep score (GSS) was assessed with the use of the Pittsburgh Sleep Quality Index (PSQI) questionnaire. For study 2, 44 participants (12 men and 32 women; age: 52 ± 1 y; BMI: 31.4 ± 0.5) consumed a 3-wk baseline energy-balance diet with 0.8 g protein · kg baseline body mass(-1) · d(-1). Then, study 2 subjects consumed either a normal-protein [NP (control); n = 23] or a high-protein (HP; n = 21) (0.8 compared with 1.5 g · kg(-1) · d(-1), respectively) energy-restricted diet (a 750-kcal/d deficit) for 16 wk. The PSQI was administered during baseline week 3 and intervention weeks 4, 8, 12, and 16. GSSs ranged from 0 to 21 arbitrary units (au), with a higher value representing a worse GSS during the preceding month.

RESULTS

In study 1, we showed that a higher protein quantity improved GSSs independent of the protein source. The GSS was higher (P < 0.05) when 10% (6.0 ± 0.4 au) compared with 20% (5.0 ± 0.4 au) protein was consumed, with 30% protein (5.4 ± 0.6 au) intermediate. In study 2, at baseline, the GSS was not different between NP (5.2 ± 0.5 au) and HP (5.4 ± 0.5 au) groups. Over time, the GSS was unchanged for the NP group and improved for the HP group (P-group-by-time interaction < 0.05). After intervention (week 16), GSSs for NP and HP groups were 5.9 ± 0.5 and 4.0 ± 0.6 au, respectively (P < 0.01).

CONCLUSION

The consumption of a greater proportion of energy from protein while dieting may improve sleep in overweight and obese adults. This trial was registered at clinicaltrials.gov as NCT01005563 (study 1) and NCT01692860 (study 2).

Evidence of disturbed sleep and mood state in well-trained athletes during short-term intensified training with and without a high carbohydrate nutritional intervention

Few studies have investigated the effects of exercise training on sleep physiology in well-trained athletes. We investigated changes in sleep markers, mood state and exercise performance in well-trained cyclists undergoing short-term intensified training and carbohydrate nutritional intervention. Thirteen highly-trained male cyclists (age: 25 ± 6y, [Formula: see text]O_2max: 72 ± 5 ml/kg/min) participated in two 9-day periods of intensified training while undergoing a high (HCHO) or moderate (CON) carbohydrate nutritional intervention before, during and after training sessions. Sleep was measured each night via wristwatch actigraphy. Mood state questionnaires were completed daily. Performance was assessed with maximal oxygen uptake ([Formula: see text]. Percentage sleep time fell during intensified training (87.9 ± 1.5 to 82.5 ± 2.3%; p < 0.05) despite an increase in time in bed (456 ± 50 to 509 ± 48 min; p = 0.02). Sleep efficiency decreased during intensified training (83.1 ± 5.3 to 77.8 ± 8.6%; p < 0.05). Actual sleep time was significantly higher in CON than HCHO throughout intensified training. Mood disturbance increased during intensified training and was higher in CON than HCHO (p < 0.05). Performance in the [Formula: see text] exercise protocol fell significantly with intensified training. The main findings of this study were that 9-days of intensified training in highly-trained cyclists resulted in significant and progressive declines in sleep quality, mood state and maximal exercise performance.

Associations between non-restorative sleep, short sleep duration and suicidality: findings from a representative sample of Korean adolescents

AIMS

This study clarifies the associations among sleep duration, non-restorative sleep, suicidal ideation and suicide attempts in a representative sample of Korean adolescents.

METHODS

Analyses are based on data from the 2007 Korean Youth Risk Behavior Web-based Survey. The survey used a cross-sectional, national and representative sample consisting of 78 843 students (grades 7-12) who were selected using a stratified, clustered, multistage sampling method. Logistic regression analysis was conducted to test the association between sleep and suicide variables while controlling for demographic characteristics and other potential risk factors of suicide.

RESULTS

Fewer than 4 h of sleep and a lack of feeling refreshed after sleeping increased the likelihood of suicidal ideation but not of suicide attempts.

CONCLUSIONS

Non-restorative sleep as well as short sleep duration are significantly associated with suicidal ideation in adolescents. This finding highlights the need to assess for both non-restorative sleep and short sleep duration when screening suicide risk in adolescents. Future research should examine the moderating or mediating effects of individual and environmental characteristics on the association between sleep and actual suicide attempt.

Schlaf und Sport

Der Schlaf ist eine wichtige Ressource für das psychische und physische Wohlbefinden. Die Erkenntnisse aus der Schlafforschung spielten jedoch in der Sportwissenschaft bislang nur eine untergeordnete Rolle. Nach einer kurzen Einführung zur physiologischen Erfassung von Schlaf werden in diesem Beitrag drei Bereiche aufgeführt, die fruchtbare Verknüpfungen zwischen Schlaf- und Sportwissenschaft aufweisen. Im ersten Bereich wird auf die schlafbegleitende Konsolidierung von motorischen Gedächtnisinhalten eingegangen. Dieser eher grundlagenorientierte Forschungszweig beleuchtet den Zusammenhang zwischen der Aneignung bzw. Optimierung von motorischen Fertigkeiten und verschiedenen Schlafstadien und Schlafparametern (z. B. Schlafspindeln). In dem zweiten Bereich geht es um den Schlaf vor sportlichen Wettkämpfen. Für den Sport liegt eine Vielzahl von anekdotischen Belegen über eine schlecht geschlafene Nacht vor einem sportlichen Wettkampf vor. Systematische Erhebungen existieren jedoch kaum. Anhand verschiedener Studien sollen Aspekte geklärt werden, die die Ursachen und Häufigkeiten von schlechtem Schlaf vor Wettkämpfen und die Auswirkung auf die Wettkampfleistung betreffen. Der dritte Bereich widmet sich dem Einfluss von körperlicher Aktivität auf den Schlaf. Es zeigt sich, dass der Sport einen positiven Effekt auf den Schlaf bei Menschen mit Schlafstörung aufweist. Diese Befunde weisen auf einen therapeutischen Ansatz für Sportwissenschaftler in der Schlafmedizin. Abschließend werden sportpraktische Implikationen erörtert und Perspektiven auf weitere Forschungsfragen eröffnet.

Long-term effect of yogic practices on diurnal metabolic rates of healthy subjects

Background:

The metabolic rate is an indicator of autonomic activity. Reduced sympathetic arousal probably resulting in hypometabolic states has been reported in several yogic studies.

Aim:

The main objective of this study was to assess the effect of yoga training on diurnal metabolic rates in yoga practitioners at two different times of the day (at 6 a.m. and 9 p.m.).

Materials and Methods:

Eighty eight healthy volunteers were selected and their metabolic rates assessed at 6 a.m. and 9 p.m. using an indirect calorimeter at a yoga school in Bangalore, India. Results and conclusions: The results show that the average metabolic rate of the yoga group was 12% lower than that of the non-yoga group (P < 0.001) measured at 9 p.m. and 16% lower at 6 a.m. (P < 0.001). The 9 p.m. metabolic rates of the yoga group were almost equal to their predicted basal metabolic rates (BMRs) whereas the metabolic rate was significantly higher than the predicted BMR for the non-yoga group. The 6 a.m. metabolic rate was comparable to their predicted BMR in the non-yoga group whereas it was much lower in the yoga group (P < 0.001). The lower metabolic rates in the yoga group at 6 a.m. and 9 p.m. may be due to coping strategies for day-to-day stress, decreased sympathetic nervous system activity and probably, a stable autonomic nervous system response (to different stressors) achieved due to training in yoga.

Biological Consequences of Disturbed Sleep: Important Mediators of Health?

There is an extensive literature regarding the immunological and endocrinological consequences of illness, stress, and psychopathology. Yet only a modest literature is available regarding the potential unfavorable effects of chronic sleep loss/disruption on immune and endocrine pathways or on various aspects of health. Given that humans spend approximately 1/3 of their lives asleep, it seems pertinent to evaluate this necessary yet understudied behavior. The evidence overwhelmingly indicates that "excessive" sleep disruption or poor sleep quality/continuity may subsequently increase risk for adverse health outcomes, as well as mortality. This is thought to occur through dysregulation of biological pathways. While our information addressing the immunological or endocrinological consequences of poor sleep is mounting, the majority of evidence stems from epidemiologic and cross-sectional studies. The immune and endocrine systems are dynamic and constantly in flux. Thus, the methodologies and study designs used to understand how sleep affects these systems needs to be as dynamic. Experimental manipulations and longitudinal evaluations are needed to effectively understand sleep as a risk factor for health. Thus, this paper is a primer in which to highlight the immunological and endocrinological consequences of disrupted or disturbed sleep as well as describe how these relationships may impact overall health. It is also meant to spark an interest for future evaluations of how the behavior of sleep is relevant to health.

How disturbed sleep may be a risk factor for adverse pregnancy outcomes

Adverse pregnancy outcomes associated with significant maternal and infant morbidity are on the rise in Western society despite advances of medical technology. Current risk factors are insufficient to identify women at greatest risk of developing an adverse outcome. An attempt to identify novel contributors to increased risk is warranted. Sleep disturbances are frequent during pregnancy, yet are often dismissed as irrelevant. Emerging evidence indicates that sleep disturbances are associated with poor health outcomes, including cardiovascular disease. Disturbed sleep is also linked with an increased inflammatory response. Increased inflammation is proposed as a key biological pathway through which chronic disease and adverse pregnancy outcomes develop. In this paper, we propose a model and a testable hypothesis of how disturbed sleep in the first 20 weeks of pregnancy could contribute to adverse pregnancy outcomes such as preeclampsia, intrauterine growth restriction, and preterm birth via increased inflammation.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians Leaning Objectives: After completion of this article, the reader should be able to outline data linking sleep disturbances with an increased risk of some systemic disorders, recall characteristics of pregnancy complications which support the hypothesis that sleep disturbances may be related to these pregnancy outcomes, and summarize the likelihood and types of sleep disturbances that are common in pregnant women.

Behavioural state linkage in the ovine fetus near term

Nine fetal sheep were surgically prepared with placement of electrocortical and electro-ocular electrodes for monitoring behavioural state activity to determine the relationship of adjacent low-voltage (LV)/rapid eye movement (REM) and high-voltage (HV)/non-(N)REM epoch durations and the inter-epoch transition time. Animals were subsequently studied over an 8-hour period with behavioural state epoch duration and transition time assessed using paired t-test and regression analysis. For all animals, the duration of LV/REM epochs averaged 14.8+/-0.8 (SEM) minutes which was significantly greater than that for HV/NREM epochs at 10.1+/-0.5 min (P<0.01). The mean duration of LV/REM to HV/NREM transition periods at 93+/-3 s was also significantly longer than that for the HV/NREM to LV/REM transition periods at 78+/-6 s (P<0.05). HV/NREM epoch duration was positively correlated with the prior LV/REM epoch duration with a group mean correlation of 0.59 (P<0.01). HV/NREM epoch duration was likewise positively correlated with the subsequent LV/REM epoch duration with a group mean correlation of 0.46 (P<0.01). We conclude that the transition time into HV/NREM is longer than that into LV/REM for the ovine fetus near term which may involve differences in the rate of maturation of cycling control mechanisms for these two behavioural states and earlier development of REM-on versus REM-off pathways. The positive LV/REM-HV/NREM linkage relationships also support a homeostatic model of behavioural state control whereby LV/REM and HV/NREM timings are both controlled by accumulation of propensity for these states during the other state and favours an interactive process between these states in the brain's growth and development.

Induced hyper and hypo amino acidemia in the ovine fetus near term: effects on electrocortical activity

Amino acid infusate (Primene) and insulin euglycemic (insulin + 10% dextrose) clamp techniques were used in the ovine fetus near term and the impact on the incidence of low-voltage and high-voltage electrocortical (ECOG) activities was determined. Fetal sheep were studied over a 2-hour control period and a subsequent 6-hour experimental period.With the Primene infusion, the basic and neutral amino acids were increased by 43% and 25%, respectively, whereas the acidic amino acids showed little change. With the insulin/dextrose infusion, the basic and neutral amino acids decreased by 48% and 30%, respectively, whereas the acidic amino acids were again little changed. A small fall in arterial oxygen saturation and an increase in fetal heart rate for both groups can be attributed to an insulin-mediated increase in fetal metabolic rate. Despite the moderate increases and decreases in circulating amino acid levels, there was no significant change in the mean percent time or duration of fetal ECOG activities for either study group.

Sleep deprivation and energy metabolism: to sleep, perchance to eat?

PURPOSE OF REVIEW

Many people currently sleep only 5-6 h per night. Epidemiological studies have demonstrated that self-reported short sleep is associated with an increased incidence of obesity and diabetes, highlighting the importance of this trend for public health. This finding has triggered renewed research into the mechanisms that link the regulation of mammalian sleep and metabolism.

RECENT FINDINGS

In rodents, periods of starvation are accompanied by increased vigilance and sleep loss, presumably to help maximize food finding and energetic survival, whereas sleep deprivation results in increased energy expenditure and weight loss, consistent with a role of sleep in energy conservation and tissue maintenance. Information about the corresponding processes in humans is limited. Available data indicate that despite the presence of qualitative and quantitative differences, human sleep and metabolism also share reciprocal connections.

SUMMARY

Evolution in an environment with limited resources has established bidirectional links between sleep and energy homeostasis, the molecular mechanisms of which are emerging rapidly. Epidemiological data suggest that the unique ability of humans to restrict their sleep voluntarily in an environment that promotes physical inactivity and overeating may have a negative impact on metabolic health. Randomized intervention trials are needed to confirm the validity of this hypothesis.

Effects of exercise on sleep

Historically, perhaps no daytime behavior has been more closely associated with better sleep than exercise. The assumption that exercise promotes sleep has also been central to various hypotheses about the functions of sleep. Hypotheses that sleep serves an energy conservation function, a body tissue restitution function, or a temperature down-regulation function all have predicted a uniquely potent effect of exercise on sleep because no other stimulus elicits greater depletion of energy stores, tissue breakdown, or elevation of body temperature, respectively. Exercise offers a potentially attractive alternative or adjuvant treatment for insomnia. Sleeping pills have a number of adverse side effects and are not recommended for long-term use, partly on the basis of a significant epidemiologic association of chronic hypnotic use with mortality. Other behavioral/cognitive treatments are more effective for chronic insomnia treatment, but difficult and costly to deliver. By contrast, exercise could be a healthy, safe, inexpensive, and simple means of improving sleep.

Medicinal plants for insomnia: a review of their pharmacology, efficacy and tolerability

A number of medicinal plants are traditionally endowed with anxiolytic or sedative properties and, in the context of this revue, both indications are considered since the former may induce a mood conducive to the latter. For any sleep-inducing drug to be effective, a tranquil ambience needs to be established a priori. Thus, physical ailments (i.e. pain), factors interfering with sleep (i.e. noise), psychological conditions causing stress, psychiatric illnesses (i.e. depression) and other drugs that interfere with sleep (i.e. caffeine) need to be controlled, if possible. Kava-kava is a well-established hypnotic drug, with a rapid onset of effect, adequate duration of action and minimal morning after-effects. However, reports of serious hepatotoxicity with this preparation have led to it being banned in most countries worldwide. On the other hand, side-effects with valerian would appear to be bland indeed. However, it's slow onset of effect (2-3 weeks) renders it unsuitable for short-term use (i.e. 'jet-lag'), but it does have profound beneficial effects on sleep architecture (augments deep sleep) that may make it particularly suitable for long-term use and for the elderly. In a personal trial (not double-blind) in stress-induced insomnia, both kava and valerian improved sleep and the ill-effects of stress, and the combination of the two was even more effective for the control of insomnia. Aromatherapy (lavender, chamomile, Ylang-Ylang) would appear to improve sleep, but how practical a form of treatment this may be remains to be determined. The only other plant drug that may have some effect on sleep is melissa, but reports are too scanty to form any opinion about this. Based on animal experiments, passion flower (passiflora) may have a sedative action, but the sedative action of hops has not been investigated in any detail. In conclusion, there is a need for longer-term controlled studies with some of these compounds (particularly valerian). Aromatherapy constitutes a tantalising possibility. In the interpretation of this review, it should be borne in mind that the evidence on which it is based is often incomplete or missing, but that is all that is available. Consequently some conjecture on the part of the author is inevitable and should be appreciated as such.

Functional imaging of the sleeping brain: review of findings and implications for the study of insomnia

Despite the growing literature indicating that insomnia is prevalent and a substantial risk factor for medical and psychiatric morbidity, the pathophysiology of both Primary and Secondary Insomnia is poorly understood. Multiple trait and state factors are thought to give rise to and/or moderate illness severity in insomnia, but 'hyperarousal' is widely believed to be the final common pathway of the disorder. To date, very little work has been undertaken using functional imaging to explore the CNS correlates, underpinnings, or consequences of hyperarousal as it occurs in Primary Insomnia. In fact, all but one of the extant studies have been of healthy good sleepers or subjects with Secondary Insomnia. In the present article, we: (1) review the studies that have been undertaken in good sleepers and in patients using functional neuroimaging methodologies, and (2) discuss how these data can inform a research agenda aimed at describing the neuropathophysiology of insomnia.

Cerebral leucine uptake and protein synthesis in the near-term ovine fetus: relation to fetal behavioral state

Behavioral/sleep state activity may impact on synthetic processes within the brain, thus accounting for the developmental change in such activity and suggesting a role in the brain's growth and development. We have therefore determined the cerebral uptake of leucine and [(14)C]leucine during continuous tracer infusion as measures of leucine metabolism in relation to behavioral state activity, as well as the regional flux of leucine into brain tissue in the ovine fetus near term. The cerebral fractional protein synthetic rate and the absolute protein synthetic rate averaged approximately 20%/day and approximately 1 g/day, respectively, as measured for the whole brain, which is considerably higher than anticipated protein accretion and indicates a high rate of protein turnover with protein synthesis closely linked to protein degradation. Measures of protein synthesis were significantly higher in the pituitary gland, which may be attributed to the active synthesis and export of peptide hormones from this region. Cerebral leucine and [(14)C]leucine uptakes averaged approximately 630 and approximately 1,000 nmol. 100 g(-1). min(-1), with the latter higher than leucine unidirectional flux and thus supporting a degree of leucine oxidation by the brain. Cerebral leucine metabolism as studied was affected by behavioral state activity, with uptake measurements for both leucine and [(14)C]leucine significantly increased during the high-voltage electrocortical/non-rapid eye movement state by 1.7-fold and 2.8-fold, respectively, indicating that protein synthesis and degradation must also be increased at this time, and supporting a role for behavioral state activity in the brain's growth and development.

Sleep and methods of assessment

Sleep is a complex behavior; adequate sleep is essential for healthy functioning and even for survival. Poor sleep quality and insufficient sleep have been linked to increased risk for various illnesses, as well as with an increased prevalence of excessive daytime sleepiness and reduced quality of life. Daytime sleepiness can lead to dangerous outcomes associated with drowsy driving and has become an important public health issue. Routine health examinations that include questions about sleep habits, daytime sleepiness, and problems with sleep at night can help to educate people about the importance of good sleep habits. They provide a way to identify sleep disorders so that appropriate therapies can be instituted or proper referrals to a sleep specialist can be given.

Sleeping brain, learning brain. The role of sleep for memory systems

The hypothesis that sleep participates in the consolidation of recent memory traces has been investigated using four main paradigms: (1) effects of post-training sleep deprivation on memory consolidation, (2) effects of learning on post-training sleep, (3) effects of within sleep stimulation on the sleep pattern and on overnight memories, and (4) re-expression of behavior-specific neural patterns during post-training sleep. These studies convincingly support the idea that sleep is deeply involved in memory functions in humans and animals. However, the available data still remain too scarce to confirm or reject unequivocally the recently upheld hypothesis that consolidations of non-declarative and declarative memories are respectively dependent upon REM and NREM sleep processes.

Slow-wave sleep and waking cognitive performance among older adults with and without insomnia complaints

Previous research has shown that healthy young adults with relatively fast reaction times on daytime testing have significantly more nocturnal slow-wave sleep than do age-matched subjects with relatively slow reaction times on such testing. The current study was conducted to examine the relationship between slow-wave sleep and cognitive performance among older adults with and without insomnia complaints. A sample of 32 noncomplaining older (age > or = 60 years) normal sleepers and a like-aged sample of 32 insomniacs, recruited to participate in a larger study, served as subjects. All subjects underwent nocturnal sleep monitoring immediately prior to undergoing a battery of daytime tests that measured simple reaction time, vigilance/signal detection, and complex reaction time. Results from the normal sleepers showed no relationship between daytime cognitive performance measures and a variety of computer-derived nocturnal slow-wave sleep measures. In contrast, insomniac subjects with relatively slow reaction times showed relative deficits in a spectral analytically derived measure of slow-wave power in the 2 to 4 Hz bandwidth. These results suggest that relative performance deficits among some older insomniacs may be related to specific slow-wave sleep deficiencies. However, among older normal sleepers, intersubject differences in performance appear unrelated to slow-wave sleep measures. Additional research is needed to further explore the possible restorative role slow-wave sleep may serve for cognitive functions other than those examined herein.

Alleviating sleep-related discontinuance symptoms associated with benzodiazepine withdrawal: a new approach

There is limited information on the time course of recovery of sleep architecture in patients withdrawn from benzodiazepines (BDZ). This study examined the effects of substituting a new class of hypnotic drugs, namely the cyclopyrrolones, for current BDZs in patients presenting with BDZ dependence. The results indicated a clear improvement in a variety of sleep parameters after commencing with a cyclopyrrolone (zopiclone). These changes remained to some extent after zopiclone was discontinued. Also, the absence of certain withdrawal effects (i.e. rebound insomnia) upon discontinuation of zopiclone allows for patients to be carried through a potentially difficult period after stopping BDZs, while expediting the eventual discontinuation of all hypnotic medication.

24-h variation of vigilance in the cockroach Blaberus giganteus

Our objective was to investigate whether sleep-like states occur in the cockroach, Blaberus giganteus by applying the methods formerly used for another cockroach species, Leucophaea maderae and the scorpions, Heterometrus and Pandinus. The behaviour of isolated animals (n = 10) kept under LD 12:12 h was recorded by time-lapse video for three consecutive 24-h periods. Nine behavioural states were scored for 1-min real-time epochs. Rest was subdivided into 4 sub-states on the basis of body posture and the position of the antennae. The cockroaches showed a nocturnal behaviour exhibiting a bout of locomotion at dark onset which lasted several hours, and a preference for rest in the light period. Immobility with both the body and the antennae touching the substrate (state 1) was the predominating state in the light period. In order to establish whether the sub-states of rest represented different levels of vigilance the arousal threshold was measured by determining the latency of a behavioural response to a vibration stimulus. The levels of arousal differed significantly in four behavioural states in the light period but not in the dark period. In state 1 the animals exhibited the lowest arousal whereas in the activity states arousal was the highest. The state with the highest arousal threshold occurred in the beginning of the light period. Thereafter, arousal progressively increased and remained relatively high during the dark period. The effect of 6-h deprivation of rest by the gentle shaking of the cages whenever the animals were immobile, resulted in a reduced latency to state 1, a small increase of state 1 and a more prominent initial increase of activity during recovery. In conclusion, this study provides evidence for the existence of a 24-h variation of vigilance in the cockroach. It further indicates that a 'rest deficit' gives rise to a compensatory response. The data support the notion that sleep-like states are present in these insects.

Why do we need sleep? Relating theory to nursing practice

By reviewing the literature, this paper explores the nature and function of sleep. Most of the evidence for the functional theories of sleep has been obtained as a result of examining the effects of sleep deprivation, the physiological, emotional and behavioural effects of which are discussed. There is a discussion on how an awareness of the theoretical knowledge may help in the nursing care of patients with advanced cancer and other chronic diseases, as well as their carers. The physiological effects of stress, and the possible relationship to patients and their carers, leads the author to highlight the need for further research, and possible benefit of proactive intervention for the bereaved. The effects of poor nutrition and common symptoms such as pain and dyspnoea on sleep, and the iatrogenic causes of sleep disturbances, are discussed. The importance of individualized patient care is stressed. The conclusion is drawn that although researchers do not seem to have been able to prove conclusively any essential function of sleep, the nurse is in a unique position to facilitate and enable patients and their carers to cope during the waking hours, without the added stress that sleep disruption and deprivation bring.

Sleep EEG and amitryptiline treatment in depressed inpatients

We studied the baseline sleep electroencephalogram (EEG) variables and treatment-related sleep changes after 35-46 days of amitryptiline treatment (AMI) in a group of 18 depressed inpatients, mostly suffering from a major depressive disorder endogenous subtype (according to the Research Diagnostic Criteria, RDC), with a short rapid eye movement (REM) latency. The aim of the study was to identify potential sleep "predictors" of clinical response to AMI as well as short-term sleep changes associated with alleviation of depression. Clinical response to the drug was defined as a reduction of more than 50% of the Hamilton Rating Score for Depression (HRSD). Eleven men and 7 women, 25-68 years old, were included in the study. Their sleep was recorded at baseline and after an average of 39 +/- 4 days of AMI treatment, at a mean daily dose of 165 +/- 35 mg. The comparison of responders (n = 9) and nonresponders (n = 9) with Wilcoxon's test showed that responders (1) were more severely depressed at baseline, and (2) had less stage 4 sleep. A discriminant function using baseline HRSD, stage 4 and the number of stage shifts allowed for discrimination between responders and nonresponders with a 100% hit rate. Antidepressant treatment had, however, no differential effect on sleep parameters in the two response groups.

The functions of sleep: further analysis

Most theories addressed to the functions of sleep are proposed primarily according to the results in one area of sleep research and may not be compatible with the results in other areas of sleep research. This paper provides a new theory regarding the functions of sleep by integratively analyzing different areas of sleep research. First, it concludes from the phylogenetic studies and other related sleep research that sleep in mammals has at least one obligatory function which cannot be accomplished during waking. It also shows that the synchronized sleep (SS) period plays a critical role in accomplishing the obligatory functions of sleep and that the obligatory functions of sleep are related to the brain. Then it points out that adjusting and reorganizing emotional behaviors is a very important function of SS. Finally, this theory suggests that the gradual accumulation of various randomly learned memories in the limbic structures would inevitably imbalance and disorganize emotional behaviors so that sleep should be developed in evolution to adjust and reorganize emotions and so that the functions of SS for memory and emotional regulation are the obligatory functions of sleep. Although phylogenetic studies suggest that (PS) may not play obligatory functions across all mammals, there is no doubt that, in tight correlation with SS, PS also plays very important roles in memory and emotion which, however, are different from the corresponding SS roles in those mammals possessing PS.

Hypnotics and sleep physiology: a consensus report. European Sleep Research Society, Committee on Hypnotics and Sleep Physiology

The effects of hypnotics on descriptive and functional aspects of electrophysiological sleep parameters are assessed in this report. Because of the arbitrary definition of some of the criteria underlying the conventional sleep stage scoring procedure, computer-aided methods of EEG analysis have become increasingly important for recording and interpreting pharmacological effects on sleep. Of particular interest are the changes of EEG slow-wave activity, since this parameter varies as a function of prior sleep and waking. Several types of interaction between hypnotics and sleep regulation are discussed, some recent pharmacological developments are highlighted, and some common problems in clinical trials are specified.

Interleukin-1 beta and muramyl dipeptide can prevent decreased antibody response associated with sleep deprivation

A single, brief (8 h) period of sleep deprivation (DEP) was found to suppress secondary antibody response to sheep red blood cells in rats. This decrease could be totally prevented if either interleukin-1 beta (IL-1) or muramyl dipeptide (MDP) was administered at the beginning of the DEP vigil. Twenty-five units of IL-1 or 250 micrograms/kg MDP was found to be immunosuppressive in sleeping rats but, paradoxically, the combination of such doses with DEP alleviated this effect. Increased colonic temperatures associated with antigen and/or adjuvant administration were not related to the differences in antibody levels between sleeping and DEP animals. Activation of hypothalamic dopamine in IL-1-treated rats following DEP suggests that this monoamine transmitter system may participate in the observed protective activity of IL-1. The present findings extend the immune adjuvant effects of both IL-1 and MDP to protection of the host against behaviorally induced immunosuppression.

Regional cerebral glucose metabolic rate in human sleep assessed by positron emission tomography

The cerebral metabolic rate of glucose was measured during nighttime sleep in 36 normal volunteers using positron emission tomography and fluorine-18-labeled 2-deoxyglucose (FDG). In comparison to waking controls, subjects given FDG during non-rapid eye movement (NREM) sleep (primarily stages 2 and 3) showed about a 23% reduction in metabolic rate across the entire brain. This decrease was greater for the frontal than temporal or occipital lobes, and greater for basal ganglia and thalamus than cortex. Subjects in rapid eye movement (REM) sleep tended to have higher cortical metabolic rates than waking subjects. The cingulate gyrus was the only cortical structure to show a significant increase in glucose metabolic rate in REM sleep in comparison to waking. The basal ganglia were relatively more active on the right in REM sleep and symmetrical in NREM sleep.

A life-sustaining function for REM sleep: a theory

A hypothesis has been advanced that the primary function of rapid eye movement (REM) sleep is to provide periodic endogenous stimulation to the brain which serves to maintain minimum requisite levels of CNS activity throughout sleep. REM, in effect, is the mechanism used by the brain to promote and ensure recovery from sleep. Failures of REM may hinder, or in extreme cases, prevent arousal from sleep. The possibility that two fatal sleep-associated syndromes (Sudden Infant Death Syndrome and the Oriental Nocturnal Death Syndrome) may involve deficits of REM was discussed.

Is there a metabolic basis for the fibrositis syndrome?

Patients with the fibrositis syndrome experience moderately severe musculoskeletal discomfort, mood changes associated with nonrestorative sleep, and tenderness to palpation at specific body sites. There is no characteristic abnormal laboratory finding in these patients to help identify the population. A report by Moldofsky and Warsh (Pain 1978; 5: 65-71) of low serum levels of free tryptophan in patients with severe fibrositis syndrome is intriguing but remains unexplained. Those data plus the observation by Hudson et al (Am J Psychiatry 1985; 142: 441-446; Biol Psychiatry 1984; 19: 1489-1493) that patients with fibrositis syndrome exhibit an increased prevalence of anxiety and depression suggest a number of possible avenues for further study. They include potential alterations in the homeostasis of catecholamines, corticosteroids, serotonin, aromatic amino acids, platelet membrane receptor levels, and the activity of platelet membrane monoamine oxidase. Among these possibilities, evidence is now available that suggests an increased production of catecholamines in fibrositis syndrome.