Sleep intensity and the evolution of human cognition

Over the past four decades, scientists have made substantial progress in understanding the evolution of sleep patterns across the Tree of Life. 1 , 2 Remarkably, the specifics of sleep along the human lineage have been slow to emerge. This is surprising, given our unique mental and behavioral capacity and the importance of sleep for individual cognitive performance. 3 - 5 One view is that our species' sleep architecture is in accord with patterns documented in other mammals. 6 We promote an alternative view, that human sleep is highly derived relative to that of other primates. Based on new and existing evidence, we specifically propose that humans are more efficient in their sleep patterns than are other primates, and that human sleep is shorter, deeper, and exhibits a higher proportion of REM than expected. Thus, we propose the sleep intensity hypothesis: Early humans experienced selective pressure to fulfill sleep needs in the shortest time possible. Several factors likely served as selective pressures for more efficient sleep, including increased predation risk in terrestrial environments, threats from intergroup conflict, and benefits arising from increased social interaction. Less sleep would enable longer active periods in which to acquire and transmit new skills and knowledge, while deeper sleep may be critical for the consolidation of those skills, leading to enhanced cognitive abilities in early humans.     

Importance of sleep for avian vocal communication

Sleep is one of the few truly ubiquitous animal behaviours, and though many animals spend enormous periods of time asleep, we have only begun to understand the consequences of sleep disturbances. In humans, sleep is crucial for effective communication. Birds are classic models for understanding the evolution and mechanisms of human language and speech. Bird vocalizations are remarkably diverse, critical, fitness-related behaviours, and the way sleep affects vocalizations is likely similarly varied. However, research on the effects of sleep disturbances on avian vocalizations is shockingly scarce. Consequently, there is a critical gap in our understanding of the extent to which sleep disturbances disrupt communication. Here, we argue that sleep disturbances are likely to affect all birds'' vocal performance by interfering with motivation, memory consolidation and vocal maintenance. Further, we suggest that quality sleep is likely essential when learning new vocalizations and that sleep disturbances will have especially strong effects on learned vocalizations. Finally, we advocate for future research to address gaps in our understanding of how sleep influences vocal learning and performance in birds.     

Effects of short- and long-term pulsed radiofrequency electromagnetic fields on night sleep and cognitive functions in healthy subjects

There has been wide public discussion on whether the electromagnetic fields of mobile telephones and their base stations affect human sleep or cognitive functioning. As there is evidence for learning and memory-consolidating effects of sleep and particularly of REM sleep, disturbance of sleep by radiofrequency electromagnetic fields might also impair cognitive functions. Previously realized sleep studies yielded inconsistent results regarding short-term exposure. Moreover, data are lacking on the effect that short- and long-term exposure might have on sleep as well as on cognitive functions. Therefore, 10 healthy young male subjects were included and nocturnal sleep was recorded during eight consecutive nights. In the second, third, and last night, we investigated polysomnographic night sleep and cognitive functions. After the adaptation and baseline nights, the participants were exposed to a defined radiofrequency electromagnetic field during the following six nights. We analyzed polysomnographic night sleep according to Rechtschaffen and Kales [1968, Manual of Standardized Terminology, Techniques and Scoring System for Sleep of Human Subjects] as well as by power spectra and correlation dimension. Cognitive functions were investigated by an array of neuropsychological tests. Data analysis was done by comparing the baseline night with the first and last exposure night and the first two sleep cycles of the respective nights. We did not find significant effects, either on conventional sleep parameters or on power spectra and correlation dimension, nor were there any significant effects on cognitive functions. With our results, we are unable to reveal either short-term or cumulative long-term effects of radiofrequency electromagnetic fields on night sleep and cognitive functions in healthy young male subjects.     

Scale-Free Fluctuations in Behavioral Performance: Delineating Changes in Spontaneous Behavior of Humans with Induced Sleep Deficiency

The timing and dynamics of many diverse behaviors of mammals, e.g., patterns of animal foraging or human communication in social networks exhibit complex self-similar properties reproducible over multiple time scales. In this paper, we analyze spontaneous locomotor activity of healthy individuals recorded in two different conditions: during a week of regular sleep and a week of chronic partial sleep deprivation. After separating activity from rest with a pre-defined activity threshold, we have detected distinct statistical features of duration times of these two states. The cumulative distributions of activity periods follow a stretched exponential shape, and remain similar for both control and sleep deprived individuals. In contrast, rest periods, which follow power-law statistics over two orders of magnitude, have significantly distinct distributions for these two groups and the difference emerges already after the first night of shortened sleep. We have found steeper distributions for sleep deprived individuals, which indicates fewer long rest periods and more turbulent behavior. This separation of power-law exponents is the main result of our investigations, and might constitute an objective measure demonstrating the severity of sleep deprivation and the effects of sleep disorders.     

Shared and unique features of mammalian sleep spindles – insights from new and old animal models

Sleep spindles are phasic events observed in mammalian non-rapid eye movement sleep. They are relevant today in the study of memory consolidation, sleep quality, mental health and ageing. We argue that our advanced understanding of their mechanisms has not exhausted the utility and need for animal model work. This is both because some topics, like cognitive ageing, have not yet been addressed sufficiently in comparative efforts and because the evolutionary history of this oscillation is still poorly understood. Comparisons across species often are either limited to referencing the classical cat and rodent models, or are over-inclusive, uncritically including reports of sleep spindles in rarely studied animals. In this review, we discuss the emergence of new (dog and sheep) models for sleep spindles and compare the strengths and shortcomings of new and old models based on the three validation criteria for animal models – face, predictive, and construct validity. We conclude that an emphasis on cognitive ageing might dictate the future of comparative sleep spindle studies, a development that is already becoming visible in studies on dogs. Moreover, reconstructing the evolutionary history of sleep spindles will require more stringent criteria for their identification, across more species. In particular, a stronger emphasis on construct and predictive validity can help verify if spindle-like events in other species are actual sleep spindles. Work in accordance with such stricter validation suggests that sleep spindles display more universally shared features, like defining frequency, than previously thought.     

A systematic review of circadian function,chronotype and chronotherapy in attention deficit hyperactivity disorder

Reports of sleep disturbances in attention deficit hyperactivity disorder (ADHD) are common in both children and adults; however, the aetiology of such disturbances is poorly understood. One potentially important mechanism which may be implicated in disrupted sleep in ADHD is the circadian clock, a known key regulator of the sleep/wake cycle. In this systematic review, we analyse the evidence for circadian rhythm changes associated with ADHD, as well as assessing evidence for therapeutic approaches involving the circadian clock in ADHD. We identify 62 relevant studies involving a total of 4462 ADHD patients. We find consistent evidence indicating that ADHD is associated with more eveningness/later chronotype and with phase delay of circadian phase markers such as dim light melatonin onset and delayed sleep onset. We find that there is evidence that melatonin treatment may be efficacious in addressing ADHD-related sleep problems, although there are few studies to date addressing other chronotherapeutic approaches in ADHD. There are only a small number of genetic association studies which report linkages between polymorphisms in circadian clock genes and ADHD symptoms. In conclusion, we find that there is consistent evidence for circadian rhythm disruption in ADHD and that such disruption may present a therapeutic target that future ADHD research might concentrate explicitly on.     

Polygraphic findings in bird-like face syndrome with favorable spontaneous evolution

The syndrome characterized by acquired micrognathia, hypersomnia and periodic apneas during sleep is a rare consequence of mandibular underdevelopment. The pathogenesis is ascribed to incomplete obstruction of the upper airways associated with a hypoexcitability of the respiratory center. Tracheostomy, with the placement of a permanent tracheal cannula, has proved to be the only treatment producing clinical remission of the syndrome. Polygraphic findings were described in a case spontaneously recovered of hypersomnia and periodic apneas with acquired micrognathia due to a bilateral mastoiditis occurring in early childhood. In this patient three polygraphic recordings were carried out during diurnal and nocturnal sleep; another night sleep was recorded after a spontaneous improvement. In the early three recordings there is a prevalence of light sleep over slow-waves sleep and REM sleep is reduced in nocturnal sleep. There is a lot of periodic apneas during sleep stages. During apneas we observe an increase of heart frequency in NonREM sleep and a decrease in REM sleep. In the recording after clinical recovery we observe an improvement of sleep parameters and a disappearing of apneas in NonREM sleep. A temporary hyposensibility of respiratory centers is considered to be a possible interpretation of clinical and polygraphic improvement.     

Sleep characteristics of elite blind soccer players in China

This cross-sectional survey mainly investigated the sleep characteristics and its association with the training volumes of top blind soccer players in China. Additionally, the sleep quality of athletes with and without a visual impairment was compared. Blind soccer players (n = 60) completed the survey form measuring their sleep characteristics and demographic data. A secondary data-set about the sleep quality of athletes without disabilities was used to compare with the current sample. The results showed that 26.7% blind soccer players were classified as poor sleepers. There was a significant difference of sleep quality (poor vs. good sleep quality) by training volume and sleep characteristics (subjective sleep quality, sleep latency, sleep duration, sleep efficiency, and daytime dysfunction). Somewhat unexpectedly, blind soccer players generally showed a better sleep quality than athletes without disabilities. It was concluded that more than one fourth of blind soccer players have poor sleep quality and that training volumes may affect it. There is a need to understand possible reasons and mechanisms of poor sleep quality among this special population in future research.     

Effects of sports training on sleep characteristics of Asian adolescent athletes

Adolescents are predisposed to poorer quality of sleep and experience shortened sleep durations, with these trends being more pronounced amongst Asians. Even though sleep is crucial for athletic recovery, there is a dearth of the literature on the sleep patterns of Asian adolescent athletes. The purpose of this study was to examine the effects of different intensities of sports training on sleep patterns in adolescent athletes, and to describe novel sleep data and daytime sleepiness amongst Asian adolescents who were high-level athletes. Those athletes (age 14.8 ± 0.9 years) in higher-intensity sports showed significantly more deep sleep, less light sleep and waketime after sleep onset. Actigraphically determined bedtimes and waketimes were significantly delayed on weekends, when mean total sleep time was also significantly longer. There was a large effect for an increased daytime sleepiness in high-intensity sport athletes. These findings highlight the phenomenon of social jet lag in Asian adolescent student-athletes.     

Thermal biofeedback and periodic movements in sleep: Patients' subjective reports and a case study

Periodic movements in sleep (PMS) is a sleep disorder characterized by repetitive leg kicks accompanied by arousals. In our clinical experience, many patients with PMS anecdotally report that they suffer from cold feet. This study explored whether there is an increased incidence of cold feet complaints in patients with periodic movements in sleep. Results indicated that, indeed, significantly more patients with leg kicks complain of cold feet as compared to patients without leg kicks. A case study was then conducted to determine whether foot thermal biofeedback training would alleviate symptoms of periodic movements in sleep. The number of leg kicks decreased from a mean of 536 per night before biofeedback training to a mean of 19.5 after training. These data lend support to our hypothesis that poor circulation may be contributing to the severity of periodic movements in sleep and that thermal biofeedback may afford an alternative treatment strategy.     

Thermal biofeedback and periodic movements in sleep: patients' subjective reports and a case study

Periodic movements in sleep (PMS) is a sleep disorder characterized by repetitive leg kicks accompanied by arousals. In our clinical experience, many patients with PMS anecdotally report that they suffer from cold feet. This study explored whether there is an increased incidence of cold feet complaints in patients with periodic movements in sleep. Results indicated that, indeed, significantly more patients with leg kicks complain of cold feet as compared to patients without leg kicks. A case study was then conducted to determine whether foot thermal biofeedback training would alleviate symptoms of periodic movements in sleep. The number of leg kicks decreased from a mean of 536 per night before biofeedback training to a mean of 19.5 after training. These data lend support to our hypothesis that poor circulation may be contributing to the severity of periodic movements in sleep and that thermal biofeedback may afford an alternative treatment strategy.     

Brainstem structures responsible for paradoxical sleep onset and maintenance

This paper is dedicated to our mentor, Michel Jouvet who inspired our career and transmitted to us his passion for the study of the mechanisms responsible for paradoxical sleep genesis and also that of its still mysterious functions. We expose in the following the progresses in the knowledge in this field brought during 40 years by Michel Jouvet and his team and more recently by the members of a new CNRS laboratory in which we aim to pursue in the path opened by Michel Jouvet.     

Pulling the covers in electronic health records for an association study with self-reported sleep behaviors

ABSTRACT

The electronic health record (EHR) contains rich histories of clinical care, but has not traditionally been mined for information related to sleep habits. Here, we performed a retrospective EHR study based on a cohort of 3,652 individuals with self-reported sleep behaviors documented from visits to the sleep clinic. These individuals were obese (mean body mass index 33.6 kg/m²) and had a high prevalence of sleep apnea (60.5%), however we found sleep behaviors largely concordant with prior prospective cohort studies. In our cohort, average wake time was 1 hour later and average sleep duration was 40 minutes longer on weekends than on weekdays (p < 10^?12). Sleep duration varied considerably as a function of age and tended to be longer in females and in whites. Additionally, through phenome-wide association analyses, we found an association of long weekend sleep with depression, and an unexpectedly large number of associations of long weekday sleep with mental health and neurological disorders (q < 0.05). We then sought to replicate previously published genetic associations with morning/evening preference on a subset of our cohort with extant genotyping data (n = 555). While those findings did not replicate in our cohort, a polymorphism (rs3754214) in high linkage disequilibrium with a previously published polymorphism near TARS2 was associated with long sleep duration (p < 0.01). Collectively, our results highlight the potential of the EHR for uncovering the correlates of human sleep in real-world populations.     

A network model for activity-dependent sleep regulation

We develop and characterize a dynamical network model for activity-dependent sleep regulation. Specifically, in accordance with the activity-dependent theory for sleep, we view organism sleep as emerging from the local sleep states of functional units known as cortical columns; these local sleep states evolve through integration of local activity inputs, loose couplings with neighboring cortical columns, and global regulation (e.g. by the circadian clock). We model these cortical columns as coupled or networked activity-integrators that transition between sleep and waking states based on thresholds on the total activity. The model dynamics for three canonical experiments (which we have studied both through simulation and system-theoretic analysis) match with experimentally observed characteristics of the cortical-column network. Most notably, assuming connectedness of the network graph, our model predicts the recovery of the columns to a synchronized state upon temporary overstimulation of a single column and/or randomization of the initial sleep and activity-integration states. In analogy with other models for networked oscillators, our model also predicts the possibility for such phenomena as mode-locking.     

Impact of growth hormone on central nervous activity, vigilance, and tiredness after short-term therapy in growth hormone-deficient adults.

Impairment of well-being and cognitive function has been reported in growth hormone-deficient adults, as well as an improvement of these parameters after GH substitution, albeit inconsistently. The effect of growth hormone on central nervous activity, vigilance and sleepiness was studied prospectively in 16 growth hormone-deficient adults (7 females, 9 males, mean age: 36.8 yrs) with multiple pituitary hormone deficiencies before and 3 months after the start of growth hormone substitution using two objective methods of measurement, pupillographic sleepiness test and a choice reaction time test. Significant differences were found for neither pupillary unrest index nor for reaction time, false or missing reactions in 12 evaluable patients (7 females, 5 males, mean age 37.8 years). Because of the known interrelationships between growth hormone, sleep and mood, the visual analogue scale for tiredness and standardized retrospective questionnaires regarding sleep and mood (Pittsburgh sleep quality index, Epworth sleepiness scale, Depression scale) were used as additional methods. After GH substitution, there was no difference in sleep efficiency and daytime sleepiness, but some of the subjective sleep parameters (sleep quality and sleep latency) improved significantly. There was a tendency for mood improvement, too. Although results must be interpreted cautiously due to the small sample size, we conclude that the improved sleep and mood parameters might be caused by other indices of general well-being in our study.     

Local sleep homeostasis in the avian brain: convergence of sleep function in mammals and birds?

The function of the brain activity that defines slow wave sleep (SWS) and rapid eye movement (REM) sleep in mammals is unknown. During SWS, the level of electroencephalogram slow wave activity (SWA or 0.5-4.5 Hz power density) increases and decreases as a function of prior time spent awake and asleep, respectively. Such dynamics occur in response to waking brain use, as SWA increases locally in brain regions used more extensively during prior wakefulness. Thus, SWA is thought to reflect homeostatically regulated processes potentially tied to maintaining optimal brain functioning. Interestingly, birds also engage in SWS and REM sleep, a similarity that arose via convergent evolution, as sleeping reptiles and amphibians do not show similar brain activity. Although birds deprived of sleep show global increases in SWA during subsequent sleep, it is unclear whether avian sleep is likewise regulated locally. Here, we provide, to our knowledge, the first electrophysiological evidence for local sleep homeostasis in the avian brain. After staying awake watching David Attenborough's The Life of Birds with only one eye, SWA and the slope of slow waves (a purported marker of synaptic strength) increased only in the hyperpallium--a primary visual processing region--neurologically connected to the stimulated eye. Asymmetries were specific to the hyperpallium, as the non-visual mesopallium showed a symmetric increase in SWA and wave slope. Thus, hypotheses for the function of mammalian SWS that rely on local sleep homeostasis may apply also to birds.     

A pilot study of the relationship between bowel habits and sleep health by actigraphy measurement and fecal flora analysis

We have previously reported that there may be a relationship between bowel habits including functional constipation (FC) and irritable bowel syndrome and sleep health. However, our previous studies were based on only subjective parameters by self-reported questionnaire. The aim of this study is to investigate the relationship between bowel habits such as FC and sleep health using objective parameters. Sleep health was assessed by actigraphy measurement and bowel habits by fecal flora analysis. The FC and control subjects, whose bowel habits were defined at Rome II, were recruited from evaluated respondents in our previous study directed at middle-aged Japanese women, ten FC and ten control subjects participating in this study. Wake after sleep onset (WASO) and WASO (%) (WASO/total sleep time multiplied by 100) in FC subjects was significantly longer and greater than those in control subjects, respectively. Average activity during sleep in FC subjects was significantly higher than that in control subjects. FC had no effect on total sleep time. Bifidobacterium is broadly accepted to be useful intestinal bacteria for human health and one of the indices showing that the intestinal environment is in a desirable condition. Bifidobacterium counts per gram of wet feces and proportion in total bacterial cell counts in FC subjects were significantly lower than those in control subjects. In conclusion, these results suggest that corresponding to low Bifidobacterium counts and proportion, sleep in FC subjects may be worse than that in control subjects. There may be a relationship between bowel habits and sleep health. Bowel habits such as FC might be a risk factor for sleep disorders.     

A probabilistic model for the ultradian timing of REM sleep in mice

A salient feature of mammalian sleep is the alternation between rapid eye movement (REM) and non-REM (NREM) sleep. However, how these two sleep stages influence each other and thereby regulate the timing of REM sleep episodes is still largely unresolved. Here, we developed a statistical model that specifies the relationship between REM and subsequent NREM sleep to quantify how REM sleep affects the following NREM sleep duration and its electrophysiological features in mice. We show that a lognormal mixture model well describes how the preceding REM sleep duration influences the amount of NREM sleep till the next REM sleep episode. The model supports the existence of two different types of sleep cycles: Short cycles form closely interspaced sequences of REM sleep episodes, whereas during long cycles, REM sleep is first followed by an interval of NREM sleep during which transitions to REM sleep are extremely unlikely. This refractory period is characterized by low power in the theta and sigma range of the electroencephalogram (EEG), low spindle rate and frequent microarousals, and its duration proportionally increases with the preceding REM sleep duration. Using our model, we estimated the propensity for REM sleep at the transition from NREM to REM sleep and found that entering REM sleep with higher propensity resulted in longer REM sleep episodes with reduced EEG power. Compared with the light phase, the buildup of REM sleep propensity was slower during the dark phase. Our data-driven modeling approach uncovered basic principles underlying the timing and duration of REM sleep episodes in mice and provides a flexible framework to describe the ultradian regulation of REM sleep in health and disease.     

Sleep Duration and Obesity in Middle‐aged Australian Adults

The present study examined the association between sleep duration and obesity in 40,834 middle‐aged Australian adults. Multinomial logistic regression was used to test the relationship between sleep duration and obesity while controlling for important demographic and health covariates; separate models were tested for males and females. Short sleep (i.e., <7 h a night) was found to be independently associated with obesity in males and females. To our knowledge, this is the first study to report an association between short sleep and obesity in Australian adults. Although more research is required, interventions targeting short sleep could aid obesity treatment and prevention.     

No association between leptin levels and sleep duration or quality in obese adults

Previous research in lean subjects has found lower leptin levels associated with shorter sleep duration. Since leptin levels are higher and some of the actions of leptin are impaired in obese individuals, one cannot assume that sleep will be similarly associated with leptin in obese individuals. The aim of this paper was to examine the cross-sectional association between habitual sleep duration and quality and plasma leptin levels in a sample of 80 obese men and premenopausal women aged 18-50 years. Leptin levels (ng/ml) were assayed on a fasting blood sample taken in the morning. We calculated a relative leptin level by dividing leptin by body fat percentage. Sleep duration and sleep efficiency were measured by 2 weeks of wrist actigraphy and respiratory disturbance index (RDI), a measure of sleep disordered breathing, was assessed by a portable screening device on a single night. Mean leptin levels and body fat percentage were higher in women than men (P < 0.001), however, mean RDI was higher in men (P = 0.01). There were no significant associations between relative leptin level and any of the sleep measures, including sleep duration, sleep efficiency, and sleep disordered breathing. There was also no difference between men and women in the association between sleep and leptin. In conclusion, contrary to what has been reported in other studies, measures of sleep duration and quality were not associated with leptin levels in our sample of obese adults.