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.     

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.     

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.

     

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...     

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’...     

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.     

Cortical plasticity: learning while you sleep?

Sleep has been suggested to facilitate memory consolidation or learning, but there has been little direct evidence of a link between synaptic plasticity and sleep. A recent study suggests a role for sleep in the plastic changes that the visual cortex undergoes in response to occlusion of one eye early in life.     

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.     

Is sleep per se a zeitgeber in humans?

It is not clear whether shifting of sleep per se, without a concomitant change in the light-dark cycle, can induce a phase shift of the human circadian pacemaker. Two 9-day protocols (crossover, counterbalanced order) were completed by 4 men and 6 women (20-34 years) after adherence to a 2330 to 0800 h sleep episode at home for 2 weeks. Following a modified baseline constant routine (CR) protocol on day 2, they remained under continuous near-darkness (< 0.2 lux, including sleep) for 6 days. Four isocaloric meals were equally distributed during scheduled wakefulness, and their timing was held constant. Subjects remained supine inbed from 2100 to 0800 h on all days; sleep was fixed from 2330 to 0800 h in the control condition and was gradually advanced 20 min per day during the sleep advance condition until a 2-h difference had been attained. On day 9, a 25 to 27 h CR protocol (approximately 0.1 lux) was carried out. Phase markers were the evening decline time of the core body temperature (CBT) rhythm and salivary melatonin onset (3 pg/ml threshhold). In the fixed sleep condition, the phase drift over 7 days ranged from +1.62 to -2.56 h (for both CBT and melatonin rhythms, which drifted in parallel). The drifts were consistently advanced in the sleep advance schedule by +0.66 +/- 0.23 (SEM) h for CBT (p = 0.02) and by 0.27 +/- 0.14 h for melatonin rhythms (p = 0.09). However, this advance was small to medium according to effect size. Sleep per se may feed back onto the circadian pacemaker, but it appears to be a weak zeitgeber in humans.     

Does breaking up prolonged sitting when sleep restricted affect postprandial glucose responses and subsequent sleep architecture? – a pilot study

ABSTRACT

This pilot study investigated the impact of breaking up prolonged sitting with light-intensity walking on postprandial glucose responses and sleep architecture. In a randomized, counterbalanced, crossover design, six healthy males completed a sitting condition and an active condition (sitting interrupted with light-intensity walking) for three consecutive days, following 5-h sleep opportunities at night. Postprandial glucose response and sleep (time spent in all stages) was assessed. Breaking up prolonged sitting with light-intensity walking did not affect postprandial glucose responses in sleep-restricted participants; however a small increase (~9 min) in slow-wave sleep was observed.     

Does sleep really shorten when we get older?

Sleep and Biological Rhythms -     

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.     

Is circadian type associated with sleep duration in twins?

Sleep and Biological Rhythms - We used the community-based University of Washington Twin Registry to investigate the genetic association between circadian type and sleep duration. Habitual sleep...     

Antisense imaging: And miles to go before we sleep?

Labeled oligonucleotide analogues for antisense imaging of messenger RNA (mRNA) have great potential for detection of endogenous gene expression in vivo. Successful antisense imaging may be useful for detecting cellular gene expression patterns and early molecular changes in disease. Conclusive demonstration of this technique has been hindered by formidable challenges in surmounting biological barriers and detecting low concentrations of target mRNA. Recent advances in the development of novel antisense molecules, high specific activity radiolabeling chemistry, sophisticated drug targeting technology, and complementary molecular imaging modalities make it quite possible that true antisense imaging will be realized in the near future.     

Can stress act as a sleep inertia countermeasure when on-call?

The nature of on-call work is such that workers can be called and required to respond immediately after being woken. However, due to sleep inertia, impaired performance immediately upon waking is typical. We investigated the impact of a preceding stressor (an alarm/mobilisation procedure) on sleepiness and performance upon waking. Healthy, adult males (n = 16) attended the sleep laboratory for four consecutive nights which included two, counterbalanced on-call sleeps where participants were woken at 04:00 h by (a) an alarm/mobilisation procedure (Alarm) or (b) gently by a researcher (Control). Following waking was a 2-h testing session comprising the repeated administration of the Karolinska Sleepiness Scale (KSS) and 5-min Psychomotor Vigilance Task (PVT). Results from within-subjects analysis of variance in both the Control and Alarm conditions showed that for subjective sleepiness (KSS) there was a significant fixed effect of time (p = 0.012), with participants becoming less sleepy as time post-wake increased. In terms of PVT performance outcomes, in neither the Alarm or Control conditions were there measurable signs of sleep inertia with performance remaining stable across the 2-h testing period. Based on previous research measuring impact of sleep inertia when woken near the circadian nadir, performance findings in particular were unexpected. We propose that stress caused by study procedures (i.e. finger pricks using lancets) unrelated to the simulated wake-up protocols may have countered any impact of sleep inertia on performance.