Fluctuations and synchronizations of neural activities during sleep: Neural basis of possible sleep functions?

Physiological and psychological evidence have been accumulated concerning the function of sleep in development and learning/memory. Many conceptual ideas have been proposed to elucidate the mechanisms underlying them. Sleep consists of a wide variety of physiological processes. It has not yet been clarified which processes are involved in development and learning/memory processes. We have found that single neuronal activity exhibits a slowly fluctuating rate of discharge during rapid eye movement (REM) sleep and a random low discharge rate during non-rapid eye movement (NREM) sleep. It is suggested that a structural change of the neural network attractor underlies this neuronal dynamics-alternation by mathematical modeling. Functional interpretation of the neuronal dynamics-alternation was provided in combination with the phase locking of ponto-geniculo-occipital (PGO)/pontine (P) wave to the hippocampal theta wave, each of which is known to be involved in learning/memory processes. More directly, by the long-term sensory deprivation, the dynamics of neural activity during sleep was found to progressively change in a non-monotonic way. This finding reveals a possible interaction between sleep and reorganization of neural network in the matured brain. Here, in addition to the related findings, we described our idea about how sleep contributes to the learning/memory processes and reorganization of neural network of the matured brain through characteristic neural activities during sleep.

     

Effect of sleep environment of preschool children on children’s sleep problems and mothers’ mental health

Sleep and Biological Rhythms - We evaluated the sleep environment factors that influence children’s sleep, and the relationship between co-sleeping and parenting stress and parents’...     

A HAT for sleep?: Epigenetic regulation of sleep by Tip60 in Drosophila

Sleep disturbances are common in neurodegenerative diseases such as Alzheimer disease (AD). Unfortunately, how AD is mechanistically linked with interference of the body’s natural sleep rhythms remains unclear. Our recent findings provide insight into this question by demonstrating that sleep disruption associated with AD is driven by epigenetic changes mediated by the histone acetyltransferase (HAT) Tip60. In this study, we show that Tip60 functionally interacts with the AD associated amyloid precursor protein (APP) to regulate axonal growth of Drosophila small ventrolateral neuronal (sLNv) pacemaker cells, and their production of neuropeptide pigment dispersing factor (PDF) that stabilizes appropriate sleep-wake patterns in the fly. Loss of Tip60 HAT activity under APP neurodegenerative conditions causes decreased PDF production, retraction of the sLNv synaptic arbor required for PDF release and disruption of sleep-wake cycles in these flies. Remarkably, excess Tip60 in conjunction with APP fully rescues these sleep-wake disturbances by inducing overelaboration of the sLNv synaptic terminals and increasing PDF levels, supporting a neuroprotective role for Tip60 in these processes. Our studies highlight the importance of epigenetic based mechanisms underlying sleep disturbances in neurodegenerative diseases like AD.     

Gifted and non-gifted students’ diurnal preference and the relationship between personality,sleep, and sleep quality

The current study had two main objectives. First, we examined gifted and non-gifted students’ diurnal preferences. Secondly, we examined the relationships among age, gender, personality, sleep quality, and chronotype of gifted students. Data were gathered from 276 gifted students and 1921 non-gifted students whose ages range between 7 and 17 years old, in same three cities in Turkey using the Composite Scale of Morningness (CSM) to assess diurnal preference, the Big Five Inventory (BIG-5) to assess personality and the Pittsburgh Sleep Quality Index (PSQI) to measure sleep quality. The first result indicated that gifted students were more morning-oriented compared to non-gifted students. The other main result was that the conscientiousness was the best predictor of CSM scores in gifted students. Additionally, conscientiousness, age, and global PSQI predicted CSM scores, respectively. Moreover agreeableness, conscientiousness, and emotional stability were positively related to morning orientation, while age, sleep quality, sleep latency, daytime dysfunction, and global PSQI were negatively related with chronotype in gifted students.     

The role of sleep in declarative memory consolidation: passive,permissive, active or none?

Those inclined to relish in scientific controversy will not be disappointed by the literature on the effects of sleep on memory. Opinions abound. Yet refinements in the experimental study of these complex processes of sleep and memory are bringing this fascinating relationship into sharper focus. A longstanding position contends that sleep passively protects memories by temporarily sheltering them from interference, thus providing precious little benefit for memory. But recent evidence is unmasking a more substantial and long-lasting benefit of sleep for declarative memories. Although the precise causal mechanisms within sleep that result in memory consolidation remain elusive, recent evidence leads us to conclude that unique neurobiological processes within sleep actively enhance declarative memories.     

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.     

Alteration in REM sleep and sleep spindles’ characteristics by a model of immobilization stress in rat

Sleep and Biological Rhythms - Investigation of sleep spindles’ oscillations is increasingly considered as a major avenue of inquiry in analyzing the microarchitecture of sleep. Previous...     

Why do birds sleep with one eye open? Light exposure of the chick embryo as a determinant of monocular sleep.

Together with some aquatic mammals, birds exhibit a unique behavioral and electrophysiological state called "unihemispheric sleep," in which one cerebral hemisphere is awake and the other is sleeping. Slow-wave sleep in one hemisphere is associated with closure of the contralateral eye, while the eye contralateral to the awake hemisphere is open; closure of both eyes, in contrast, is associated with bihemispheric slow-wave sleep or with REM sleep. During the last few days of incubation, the chick's embryo is turned in the egg so that it occludes its left eye, whereas light entering through the shell can stimulate the right eye. Here we show that in the first two days after hatching, chicks coming from eggs incubated in the light prevalently slept with their right eye open, whereas those coming from eggs incubated in the dark prevalently slept with their left eye open. Thus, asymmetric light stimulation in the embryo can modulate the left-right direction of eye opening during post-hatching monocular sleep.     

Suppression of electroencephalogram Δ power density during non-rapid eye movement sleep as a result of a prolonged cognitive task prior to sleep onset

The effects of a prolonged cognitive task prior to sleep onset on subsequent sleep patterns were examined in 14 healthy subjects who were randomly assigned to two conditions. Those assigned to a working condition were asked to engage in a prolonged cognitive task until close to bedtime (0200 hours), whereas those assigned to a relaxing condition were instructed to perform the same task during the daytime and then to stay awake in a relaxed state until the same bedtime as the work group. Visual scoring of sleep stages showed no significant differences in the amounts of stage 4 and slow wave sleep (stage 3+4) between the two conditions. Power spectrum analysis of sleep electroencephalogram (EEG) revealed that the EEG (0.5–4.0 Hz) power density in the first non-rapid eye movement (REM)-REM sleep cycle was significantly lower following the prolonged cognitive task prior to sleep onset than following the relaxed wakefulness and that the decreased EEG power density in the first sleep cycle was not compensated for during the later part of the sleep. These findings would indicate that the prolonged cognitive task prior to sleep onset may suppress EEG power density during subsequent sleep, suggesting that such a task may interfere with the development of deep non-REM sleep.     

Why sleep?

All living organisms show a regular, daily period of reduced activity. But to what extent could this be sleep, and what is it for? Whatever the functions of sleep are, they probably shift in emphasis across the animal kingdom. There are fundamental differences between rodents and us. On the other hand, even human sleep has some similarities with that of the bee.     

The effect of chronic exposure to extremely low-frequency electromagnetic fields on sleep quality,stress, depression and anxiety

Exposure to extremely low-frequency electromagnetic fields (ELF-EMF) is inevitable in some industries. There are concerns about the possible effects of this exposure. The present study aimed to investigate the effect of chronic exposure to extremely low-frequency electromagnetic fields on sleep quality, stress, depression and anxiety among power plant workers.

In this cross-sectional study, 132 power plant workers were included as the exposed group and 143 other workers were included as the unexposed group. The intensity of ELF-EMF at work stations was measured by using the IEEE Std C95.3.1 standard and then the time weighted average was calculated. Sleep quality, stress, depression and anxiety were measured by using the Pittsburgh Sleep Quality Index Questionnaire; and the Depression, Anxiety and Stress Scale.

The workers in the exposed group experienced significantly poorer sleep quality than the unexposed group. Depression was also more severe in the exposed group than the unexposed group (P = 0.039). Increased exposure to ELF-EMF had a direct and significant relation with increased stress, depression, and anxiety. Sleep quality in technicians with the highest exposure was significantly lower than the other groups.

This study suggests that long-term occupational exposure to ELF-EMF may lead to depression, stress, anxiety and poor sleep quality.     

Discovery of a potent,selective, and orally bioavailable histamine H3 receptor antagonist SAR110068 for the treatment of sleep–wake disorders

Previous studies have shown that compound 1 displayed high affinity towards histamine H₃ receptor (H₃R), (human (h-H₃R), K_i = 8.6 nM, rhesus monkey (rh-H₃R), K_i = 1.2 nM, and rat (r-H₃R), K_i = 16.5 nM), but exhibited high affinity for hERG channel. Herein, we report the discovery of a novel, potent, and highly selective H₃R antagonist/inverse agonist 5a(SS) (SAR110068) with acceptable hERG channel selectivity and desirable pharmacological and pharmacokinetic properties through lead optimization sequence. The significant awakening effects of 5a(SS) on sleep–wake cycles studied by using EEG recording in rats during their light phase support its potential therapeutic utility in human sleep–wake disorders.     

Are individuals' nighttime sleep characteristics prior to shift-work exposure predictive for parameters of daytime sleep after commencing shift work?

This study aimed to examine prospectively whether individual nighttime sleep characteristics at baseline (prior to shift-work exposure) are related to parameters of daytime sleep after commencing shift work. A longitudinal field study was carried out with novice police officers of the Dutch Police Force. A total of 26 subjects were examined at baseline before they entered shift work and re-examined during follow-up sessions after four and twelve months of shift-work exposure. Wrist actigraphy and sleep diaries were used to study nocturnal sleep at baseline and daytime sleep after night shifts during follow-up sessions. As outcome variables, estimated total sleep time, sleep efficiency, and subjective sleep quality were analyzed. Daytime total sleep time showed a 66 min decline during the first year of shift-work exposure. Systematic inter-individual differences were observed for daytime total sleep time and subjective sleep quality (explaining 53% and 38% of the variance, respectively), suggesting potential predictability of these sleep parameters. Although no predictors were found for daytime total sleep time, the subjective quality of nighttime sleep before the onset of shift work predicted 40% of the variance in the subjective quality of daytime sleep after commencing shift work. Follow-up studies may reveal whether the subjective quality of baseline nighttime sleep also predicts long-term overall tolerance for shift work.     

Evolutionary aspects of sleep–wake cycle development in vertebrates (Modern state of the I.G. Karmanova’s sleep evolution theory)

The genetic basis of rest–activity circadian alternation in animal behavior is considered in the evolutionary range from bacteria to mammals. We scrutinize various concepts of sleep development in the animal world evolution as well as the I.G. Karmanova’s theory of the sleep–wake cycle evolution in vertebrates, beginning from wakefulness–primary sleep (or protosleep) in fish and amphibians through wakefulness–intermediate sleep in reptiles to wakefulness–slow wave sleep (SWS) and paradoxical sleep (PS) in birds and mammals. Primary sleep is represented by the three major sleep-like immobility states: catalepsy, catatonia and cataplexy. The main behavioral, somatovegetative and neurophysiological characteristics of primary sleep and the ancient activation pattern during primary sleep are described. The issues of which of these sleep manifestations are homologous to SWS, PS, hibernation and stress response are discussed. In conclusion, the general diagram of sleep evolution in vertebrates is presented, and the I.G. Karmanova’s contribution to evolutionary somnology is highlighted.     

Sleep disorders in elderly, the sleep apnea syndrome in particular: are they a cause of insomnia? A review of literature

In this publication a review is presented based on the findings resulting from sleep-wake investigations searching for sleep disorders associated with insomnia in relatively healthy elderly. 44 Relevant journal articles published between 1980-1998 were found. The four most important sleep disorders which can be accompanied by sleeplessness in relatively healthy elderly people are periodic leg movements disorder (PLM), restless legs syndrome (RLS), REM sleep behaviour disorder (RBD) and sleep apnea syndrome (SAS). Of these disorders, sleep apnea and periodic leg movements occur most frequently, in a quarter of the elderly. The latter, however, seldom complain about sleeplessness. Within the category of older people disorders characterized by movements during sleep increase significantly with age, nightly respiration disorders do not. SAS, PLM and RBD appear most frequently in men and RLS in women. The disorders characterized by movements during sleep (especially RLS and RBD) are often accompanied by sleeplessness. SAS, however, is more closely associated with day-time sleepiness than with sleeplessness. No combination of demographic variables and symptoms allows a reliable prediction of these sleep disorders. Fortunately, these disorders are not a major threat to the health of older people.     

Low-dimensional dynamic self-organization in δ-sleep: effect of partial sleep deprivation

Studies on extended data including 37 electroencephalographic (EEG) records of -sleep, each 10³ s long (six subjects; up to seven nights per subject, comprising normal sleep, partial deprivation and recovery), confirmed earlier conclusions that rare episodes of low-dimensional dynamic self-organization, with lifetimes between 10 and 20 s, are present in stage 4 sleep. Particular care was taken of the Theiler correction which, in some -sleep signals, required the deletion of trajectory points covering nearly one pseudo-period. The percentage of segments showing an episode, i.e. the attractor probability, decreased with a change in sleep conditions — either deprivation or recovery prior to the next deprivation. Repetition of deprivation over three nights resulted in an adaptation process, manifested by an increase in attractor probability. After the sharp decrease in probability observed when recovery was established prior to the next deprivation, and on return to normal conditions of sleep at 2200 hours, the probability was immediately close to that observed in normal baseline sleep conditions free of any interference. The observation of a definite effect of sleep deprivation and recovery upon the number of stage 4 attractors observed provides a line of approach to the physiological significance of the probability of such attractors.     

Circadian rhythm of activity and sleep‐wakefulness in elderly institutionalized persons

Abstract

The circadian rhythms of blood pressure (BP) and heart rate (HR) were documented in 30 patients for a 24‐hour period before and during the 24 hours that included unilateral surgery for senile cataract or retinal detachment. The patients were premedicated with diazepam. Anaesthesia was induced at a fixed time (09.00) in all patients with thiopentone, and muscle relaxation was with pancuronium. Maintenance was with enflurane in 15 patients and with fentanyl and droperidol in the rest. Though the intraoperative changes in haemodynamic parameters were dissimilar with the two types of maintenance agents, but both types had a similar effect on the circadian rhythms of blood pressure and heart rate. Whereas preoperatively the BP and HR circadian rhythms were nearly in phase, with their peaks in the late morning to early afternoon, the postoperative rhythms underwent a dissociation to a phase shift in the BP 24‐h pattern. The phase effect may be hypothetically attributed to direct pharmacological actions or to masking effects.     

The effect of consecutive transmeridian flights on alertness,sleep–wake cycles and sleepiness: A case study

ABSTRACT

Travel across time zones disrupts circadian rhythms causing increased daytime sleepiness, impaired alertness and sleep disturbance. However, the effect of repeated consecutive transmeridian travel on sleep–wake cycles and circadian dynamics is unknown. The aim of this study was to investigate changes in alertness, sleep–wake schedule and sleepiness and predict circadian and sleep dynamics of an individual undergoing demanding transmeridian travel. A 47-year-old healthy male flew 16 international flights over 12 consecutive days. He maintained a sleep–wake schedule based on Sydney, Australia time (GMT + 10?h). The participant completed a sleep diary and wore an Actiwatch before, during and after the flights. Subjective alertness, fatigue and sleepiness were rated 4 hourly (08:00–00:00), if awake during the flights. A validated physiologically based mathematical model of arousal dynamics was used to further explore the dynamics and compare sleep time predictions with observational data and to estimate circadian phase changes. The participant completed 191?h and 159 736?km of flying and traversed a total of 144 time-zones. Total sleep time during the flights decreased (357.5?min actigraphy; 292.4?min diary) compared to baseline (430.8?min actigraphy; 472.1?min diary), predominately due to restricted sleep opportunities. The daily range of alertness, sleepiness and fatigue increased compared to baseline, with heightened fatigue towards the end of the flight schedule. The arousal dynamics model predicted sleep/wake states during and post travel with 88% and 95% agreement with sleep diary data. The circadian phase predicted a delay of only 34?min over the 16 transmeridian flights. Despite repeated changes in transmeridian travel direction and flight duration, the participant was able to maintain a stable sleep schedule aligned with the Sydney night. Modelling revealed only minor circadian misalignment during the flying period. This was likely due to the transitory time spent in the overseas airports that did not allow for resynchronisation to the new time zone. The robustness of the arousal model in the real-world was demonstrated for the first time using unique transmeridian travel.