Cognitive consequences of sleep and sleep loss

Assessment of sleep in the National Social Life, Health, and Aging Project

OBJECTIVES

The relationship of sleep to health has been an active area of research in recent years, and the National Social Life, Health, and Aging Project (NSHAP) expanded sleep data collection in Wave 2 with enhanced core questions and a novel sleep module that included an objective measure of sleep duration and quality.

METHOD

A randomly selected one-third of Wave 2 participants and their spouses or coresident partners were invited to participate in the sleep module. Objective sleep data were collected using wrist actigraphy, an accelerometer that records an integrated measure of motion over short epochs (15 s each). This information is stored and subsequently analyzed to determine sleep and wake periods by epoch. Individuals were instructed to wear the actiwatches for 72 hr. Several sleep parameters were derived from the accelerometer. Individuals concurrently kept a sleep diary.

RESULTS

Sleep actigraphy data were successfully collected from 780 individuals. Many of the survey-based and the actigraph-estimated sleep parameters varied by age and gender. However, age and gender patterns often differed for sleep characteristics that were both asked and measured, such as sleep duration.

DISCUSSION

The survey and actigraphy data provide different information about sleep characteristics. The opportunity to examine actigraph-estimated sleep characteristics in a nationally representative sample of older adults allows novel analyses of the associations of sleep parameters with social and health data.

Dementia is Associated with Chronic Rhinosinusitis: A Population-Based Case-Controlled Study

Background

Cardiovascular diseases are reported to be associated with both chronic rhinosinusitis (CRS) and dementia. Nevertheless, whether dementia is associated with CRS is still unknown. In the present study, we explored the association between dementia with prior CRS using a population-based data set.

Methods

This study used the Taiwan Longitudinal Health Insurance Database 2000 as the source of data for a case-control study. We included 8768 subjects with dementia as cases and 8768 age- and sex-matched subjects as controls. We identified cases who had received a diagnosis of CRS before having received a diagnosis of dementia. Conditional logistic regression analyses were performed to examine the association of dementia with previously diagnosed CRS.

Results

Results showed that of all sampled subjects, 875 (5.0%) had been previously diagnosed with CRS. A chi-squared test showed that there was a significant difference in the prevalences of prior CRS between cases and controls (6.0% versus 4.0%; p < 0.001). The adjusted odds ratio (OR) of prior CRS for subjects with dementia was 1.44 (95% CI, 1.25—1.66) compared with controls. Furthermore, compared with controls, the OR of prior CRS was similar for subjects with dementia for both sexes (the OR for male subjects was 1.48 and OR for female subjects was 1.41).

Conclusion

We concluded that subjects with dementia had a higher odds of having had prior CRS than controls. This study implies a potential association between CRS and dementia.

Buying time: a rationale for examining the use of circadian rhythm and sleep interventions to delay progression of mild cognitive impairment to Alzheimer's disease

As of 2010, the worldwide economic impact of dementia was estimated at $604 billion USD; and without discovery of a cure or effective interventions to delay disease progression, dementia's annual global economic impact is expected to surpass $1 trillion USD as early as 2030. Alzheimer's disease (AD) is the leading cause of dementia accounting for over 75% of all cases. Toxic accumulation of amyloid beta (Aβ), either by overproduction or some clearance failure, is thought to be an underlying mechanism of the neuronal cell death characteristic of AD-though this amyloid hypothesis has been increasingly challenged in recent years. A compelling alternative hypothesis points to chronic neuroinflammation as a common root in late-life degenerative diseases including AD. Apolipoprotein-E (APOE) genotype is the strongest genetic risk factor for AD: APOE-ε4 is proinflammatory and individuals with this genotype accumulate more Aβ, are at high risk of developing AD, and almost half of all AD patients have at least one ε4 allele. Recent studies suggest a bidirectional relationship exists between sleep and AD pathology. Sleep may play an important role in Aβ clearance, and getting good quality sleep vs. poor quality sleep might reduce the AD risk associated with neuroinflammation and the ε4 allele. Taken together, these findings are particularly important given the sleep disruptions commonly associated with AD and the increased burden disrupted sleep poses for AD caregivers. The current review aims to: (1) identify individuals at high risk for dementia who may benefit most from sleep interventions; (2) explore the role poor sleep quality plays in exacerbating AD type dementia; (3) examine the science of sleep interventions to date; and (4) provide a road map in pursuit of comprehensive sleep interventions, specifically targeted to promote cognitive function and delay progression of dementia.

Sleep in elite athletes and nutritional interventions to enhance sleep

Sleep has numerous important physiological and cognitive functions that may be particularly important to elite athletes. Recent evidence, as well as anecdotal information, suggests that athletes may experience a reduced quality and/or quantity of sleep. Sleep deprivation can have significant effects on athletic performance, especially submaximal, prolonged exercise. Compromised sleep may also influence learning, memory, cognition, pain perception, immunity and inflammation. Furthermore, changes in glucose metabolism and neuroendocrine function as a result of chronic, partial sleep deprivation may result in alterations in carbohydrate metabolism, appetite, food intake and protein synthesis. These factors can ultimately have a negative influence on an athlete’s nutritional, metabolic and endocrine status and hence potentially reduce athletic performance. Research has identified a number of neurotransmitters associated with the sleep–wake cycle. These include serotonin, gamma-aminobutyric acid, orexin, melanin-concentrating hormone, cholinergic, galanin, noradrenaline, and histamine. Therefore, nutritional interventions that may act on these neurotransmitters in the brain may also influence sleep. Carbohydrate, tryptophan, valerian, melatonin and other nutritional interventions have been investigated as possible sleep inducers and represent promising potential interventions. In this review, the factors influencing sleep quality and quantity in athletic populations are examined and the potential impact of nutritional interventions is considered. While there is some research investigating the effects of nutritional interventions on sleep, future research may highlight the importance of nutritional and dietary interventions to enhance sleep.

Sleep deprivation impairs recall of social transmission of food preference in rats

Evidence indicates that sleep plays an important role in learning and memory, and disruption of sleep especially seems to interfere with hippocampal memory processes. Social transmission of food preference (STFP), a natural test of paired associative learning, has been shown to be dependent on the hippocampus. While social transmission of food preference is not a novel task, it has not been used to examine the role of sleep in memory consolidation. Male Sprague-Dawley rats were randomly divided into three groups: cage control; sleep-deprived; and device control. Demonstrator rats were given powdered food mixed with a target spice. Test rats then interacted with demonstrator rats before being given a two choice test of powered food with the target spice or a novel spice. Sleep-deprived rats were then placed in an automated device that prevented sleep for 24 hours. After sleep deprivation, animals were given a preference test again to determine memory for the target spice at both 24 hours and 72 hours. Polysomnography was used to validate the method of sleep deprivation. During immediate preference testing, rats demonstrated a clear preference for the food containing the target spice. Rats that experienced 24 hours of sleep deprivation following the initial testing indicated a significant reduction in the recall of the target spice at 24 and 72 hours. The cage control and device animals maintained their preference for food containing the target spice. Therefore, the loss of sleep interfered with memory consolidation for food preference learned via social transmission.

TXT me I'm only sleeping: adolescents with mobile phones in their bedroom

The purpose of this study was to determine if mobile phones interfere with adolescent sleep. We conducted a pilot test in a pediatric primary care practice of 454 patients, half female (51.2%), 12 to 20 years old (mean = 15) attending a well-child visit. Adolescents completed paper-and-pencil surveys in the waiting room. More than half took their mobile phone to bed (62.9%) and kept it turned on while sleeping (56.8%). Almost half used their phone as their alarm (45.7%). More than one-third texted after going to bed (36.7%). Two or more times per week, 7.9% were awakened by a text after going to sleep.

Effect of Melatonin on Cognitive Function and Sleep in relation to Breast Cancer Surgery: A Randomized, Double-Blind, Placebo-Controlled Trial

Background. Sleep disturbances and cognitive dysfunction are common in patients with breast cancer. Disturbed sleep leads to poor cognitive performance and exogenous melatonin may improve sleep and attenuate cognitive dysfunction. We hypothesized that melatonin would improve sleep and cognitive function after surgery. Methods. This study reports secondary endpoints from a randomized, double-blind, placebo-controlled trial. Women, 30–75 years, were randomized to 6mg oral melatonin/placebo for 3 months. We assessed postoperative cognitive dysfunction (POCD) with a neuropsychological test battery, sleep with a diary, and sleep quality with VAS. Results. 54 patients were randomized to melatonin (n = 28) or placebo (n = 26); 11 withdrew (10 placebo, 1 melatonin, P = 0.002). The incidence of POCD was 0% (0/20) [95% CI 0.0%; 16.8%] in the placebo group and 0% (0/26) [95% CI 0.0%; 13.2%] in the melatonin group 2 weeks postoperatively (P = 1.00) and 6.3% (1/16) [95% CI 0.0%; 30.2%] in the placebo group and 0% (0/26) [95% CI 0.0%; 13.2%] in the melatonin group 12 weeks postoperatively (P = 0.38). Sleep efficiency was significantly greater in the melatonin group; mean difference was 4.28% [95% CI 0.57; 7.82] (P = 0.02). The total sleep period was significantly longer in the melatonin group; mean difference was 37.0 min [95% CI 3.6; 69.7] (P = 0.03). Conclusion. Melatonin increased sleep efficiency and total sleep time but did not affect cognitive function. The dropout rate was significantly lower in the melatonin group. This trial is registered with Clinicaltrials.gov NCT01355523.

The relation between burnout and sleep disorders in medical students

OBJECTIVE

The aim of this study is to assess the mutual relationships between burnout and sleep disorders in students in the preclinical phase of medical school.

METHODS

This study collected data on 127 medical students who filled in the Maslach Burnout Inventory-Student Survey, Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, Beck Depression Inventory, and Beck Anxiety Inventory. Hierarchical logistic regressions tested the reciprocal influence between sleep disorders and burnout, controlling for depression and anxiety.

RESULTS

Regular occurrence of emotional exhaustion, poor sleep quality, and excessive daytime sleepiness affected 60, 65, and 63% of medical students, respectively. Emotional exhaustion and daytime sleepiness influenced each other. Daytime sleep dysfunctions affected unidirectionally the occurrence of cynicism and academic efficacy. The odds of emotional exhaustion (odds ratio (OR)=1.21, 95% confidence interval (CI)=1.08 to 1.35) and cynicism (OR=2.47, 95% CI=1.25 to 4.90) increased when daytime sleepiness increased. Reciprocally, the odds of excessive daytime sleepiness (OR=2.13, 95% CI=1.22 to 3.73) increased when emotional exhaustion worsened. Finally, the odds of academic efficacy decreased (OR=0.86, 95% CI=0.75 to 0.98) when daytime sleepiness increased.

CONCLUSIONS

Burnout and sleep disorders have relevant bidirectional effects in medical students in the early phase of medical school. Emotional exhaustion and daytime sleepiness showed an important mutual influence. Daytime sleepiness linked unidirectionally with cynicism and academic efficacy.

Transcranial magnetic stimulation in sleep fragmentation: a model to better understand sleep disorders

OBJECTIVE

To investigate practice-dependent plasticity and cortical inhibition/excitability in good sleepers after a night of sleep fragmentation (SF), by means of transcranial magnetic stimulation (TMS).

METHODS

In basal condition (BC), after a full night of spontaneous sleep, and in fragmented condition (FC), after a fragmented night of sleep, motor evoked potential (MEP) amplitude, motor threshold (MT), silent period (SP), and intracortical inhibition were assessed. In both conditions subjects performed, also, a bimanual motor task: MEPs were recorded before and after exercise, and after rest. We evaluated the presence of post-exercise facilitation and delayed facilitation. Subjects reported their alertness level (Stanford Sleepiness Scale-SSS).

RESULTS

MT and SSS were significantly increased in SF. Instead, no significant differences for MEP amplitude or SP or intracortical inhibition were found. In both conditions post-exercise facilitation and delayed facilitation were present.

CONCLUSION

SF produces disruption of nocturnal sleep and increases daytime sleepiness. Confirmatory features of this clinical behaviour could be that in FC we observed a significant increase in SSS and in MT. SF was unable to modify cortical inhibition\excitability and\or to influence plasticity-related parameters. These results seem inconsistent with some of TMS alterations observed in sleep deprivation (SD) and restless legs syndrome (RLS). We suggest that SD and SF represent different phenomena that can depend on various networks acting on motor cortex. We speculate that alterations in cortical excitability found in RLS are intrinsically related to the underlying disease itself and are not instead directly associated with the SF present in RLS.

Sleep disturbance in older ICU patients

Maintaining a stable and adequate sleeping pattern is associated with good health and disease prevention. As a restorative process, sleep is important for supporting immune function and aiding the body in healing and recovery. Aging is associated with characteristic changes to sleep quantity and quality, which make it more difficult to adjust sleep–wake rhythms to changing environmental conditions. Sleep disturbance and abnormal sleep–wake cycles are commonly reported in seriously ill older patients in the intensive care unit (ICU). A combination of intrinsic and extrinsic factors appears to contribute to these disruptions. Little is known regarding the effect that sleep disturbance has on health status in the oldest of old (80+), a group, who with diminishing physiological reserve and increasing prevalence of frailty, is at a greater risk of adverse health outcomes, such as cognitive decline and mortality. Here we review how sleep is altered in the ICU, with particular attention to older patients, especially those aged ≥80 years. Further work is required to understand what impact sleep disturbance has on frailty levels and poor outcomes in older critically ill patients.

Functional connectivity changes between parietal and prefrontal cortices in primary insomnia patients: evidence from resting-state fMRI

Background

Primary insomnia can severely impair daytime function by disrupting attention and working memory and imposes a danger to self and others by increasing the risk of accidents. We speculated that the neurobiological changes impeding working memory in primary insomnia patients would be revealed by resting-state functional MRI (R-fMRI), which estimates the strength of cortical pathways by measuring local and regional correlations in blood oxygen level dependent (BOLD) signs independent of specific task demands.

Methods

We compared the R-fMRI activity patterns of 15 healthy controls to 15 primary insomnia patients (all 30 participants were right-handed) using a 3.0 T MRI scanner. The SPM8 and REST1.7 software packages were used for preprocessing and analysis. Activity was expressed relative to the superior parietal lobe (SPL, the seed region) to reveal differences in functional connectivity to other cortical regions implicated in spatial working memory.

Result

In healthy controls, bilateral SPL activity was associated with activity in the posterior cingulate gyrus, precuneus, ventromedial prefrontal cortex, and superior frontal gyrus, indicating functional connectivity between these regions. Strong functional connectivity between the SPL and bilateral pre-motor cortex, bilateral supplementary motor cortex, and left dorsolateral prefrontal cortex was observed in both the control group and the primary insomnia group. However, the strength of several other functional connectivity pathways to the SPL exhibited significant group differences. Compared to healthy controls, connectivity in the primary insomnia group was stronger between the bilateral SPL and the right ventral anterior cingulate cortex, left ventral posterior cingulate cortex, right splenium of the corpus callosum, right pars triangularis (right inferior frontal gyrus/Broca’s area), and right insular lobe, while connectivity was weaker between the SPL and right superior frontal gyrus (dorsolateral prefrontal cortex).

Conclusion

Primary insomnia appears to alter the functional connectivity between the parietal and frontal lobes, cortical structures critical for spatial and verbal working memory.

The behavioral and health consequences of sleep deprivation among U.S. high school students: relative deprivation matters

OBJECTIVE

To evaluate whether the strength of the association between sleep deprivation and negative behavioral and health outcomes varies according to the relative amount of sleep deprivation experienced by adolescents.

METHODS

2011 Youth Risk Behavior Survey data of high school students (N=15,364) were analyzed. Associations were examined on weighted data using logistic regression. Twelve outcomes were examined, ranging from weapon carrying to obesity. The primary independent variable was a self-reported measure of average number of hours slept on school nights.

RESULTS

Participants who reported deprivations in sleep were at an increased risk of a number of negative outcomes. However, this varied considerably across different degrees of sleep deprivation. For each of the outcomes considered, those who slept less than 5h were more likely to report negative outcomes (adjusted odds ratios ranging from 1.38 to 2.72; p<.05 across all models) relative to sleeping 8 or more hours. However, less extreme forms of sleep deprivation were, in many instances, unrelated to the outcomes considered.

CONCLUSIONS

Among U.S. high school students, deficits in sleep are significantly and substantively associated with a variety of negative outcomes, and this association is particularly pronounced for students achieving fewer than 5h of sleep at night.

Partial sleep in the context of augmentation of brain function

Inability to solve complex problems or errors in decision making is often attributed to poor brain processing, and raises the issue of brain augmentation. Investigation of neuronal activity in the cerebral cortex in the sleep-wake cycle offers insights into the mechanisms underlying the reduction in mental abilities for complex problem solving. Some cortical areas may transit into a sleep state while an organism is still awake. Such local sleep would reduce behavioral ability in the tasks for which the sleeping areas are crucial. The studies of this phenomenon have indicated that local sleep develops in high order cortical areas. This is why complex problem solving is mostly affected by local sleep, and prevention of local sleep might be a potential way of augmentation of brain function. For this approach to brain augmentation not to entail negative consequences for the organism, it is necessary to understand the functional role of sleep. Our studies have given an unexpected answer to this question. It was shown that cortical areas that process signals from extero- and proprioreceptors during wakefulness, switch to the processing of interoceptive information during sleep. It became clear that during sleep all "computational power" of the brain is directed to the restoration of the vital functions of internal organs. These results explain the logic behind the initiation of total and local sleep. Indeed, a mismatch between the current parameters of any visceral system and the genetically determined normal range would provide the feeling of tiredness, or sleep pressure. If an environmental situation allows falling asleep, the organism would transit to a normal total sleep in all cortical areas. However, if it is impossible to go to sleep immediately, partial sleep may develop in some cortical areas in the still behaviorally awake organism. This local sleep may reduce both the "intellectual power" and the restorative function of sleep for visceral organs.

Reduction in ultrasonic vocalizations in pups born to rapid eye movement sleep restricted mothers in rat model

The effects of rapid eye movement sleep restriction (REMSR) in rats during late pregnancy were studied on the ultrasonic vocalizations (USVs) made by the pups. USVs are distress calls inaudible to human ears. Rapid eye movement (REM) sleep was restricted in one group of pregnant rats for 22 hours, starting from gestational day 14 to 20, using standard single platform method. The USVs of male pups were recorded after a brief isolation from their mother for two minutes on alternate post-natal days, from day one till weaning. The USVs were recorded using microphones and were analysed qualitatively and quantitatively using SASPro software. Control pups produced maximum vocalization on post-natal days 9 to 11. In comparison, the pups born to REMSR mothers showed not only a reduction in vocalization but also a delay in peak call making days. The experimental group showed variations in the types and characteristics of call types, and alteration in temporal profile. The blunting of distress call making response in these pups indicates that maternal sleep plays a role in regulating the neural development involved in vocalizations and possibly in shaping the emotional behaviour in neonates. It is suggested that the reduced ultrasonic vocalizations can be utilized as a reliable early marker for affective state in rat pups. Such impaired vocalization responses could provide an important lead in understanding mother-child bonding for an optimal cognitive development during post-partum life. This is the first report showing a potential link between maternal REM sleep deprivation and the vocalization in neonates and infants.

Adenosine, caffeine, and performance: from cognitive neuroscience of sleep to sleep pharmacogenetics

An intricate interplay between circadian and sleep-wake homeostatic processes regulate cognitive performance on specific tasks, and individual differences in circadian preference and sleep pressure may contribute to individual differences in distinct neurocognitive functions. Attentional performance appears to be particularly sensitive to time of day modulations and the effects of sleep deprivation. Consistent with the notion that the neuromodulator, adenosine , plays an important role in regulating sleep pressure, pharmacologic and genetic data in animals and humans demonstrate that differences in adenosinergic tone affect sleepiness, arousal and vigilant attention in rested and sleep-deprived states. Caffeine--the most often consumed stimulant in the world--blocks adenosine receptors and normally attenuates the consequences of sleep deprivation on arousal, vigilance, and attention. Nevertheless, caffeine cannot substitute for sleep, and is virtually ineffective in mitigating the impact of severe sleep loss on higher-order cognitive functions. Thus, the available evidence suggests that adenosinergic mechanisms, in particular adenosine A2A receptor-mediated signal transduction, contribute to waking-induced impairments of attentional processes, whereas additional mechanisms must be involved in higher-order cognitive consequences of sleep deprivation. Future investigations should further clarify the exact types of cognitive processes affected by inappropriate sleep. This research will aid in the quest to better understand the role of different brain systems (e.g., adenosine and adenosine receptors) in regulating sleep, and sleep-related subjective state, and cognitive processes. Furthermore, it will provide more detail on the underlying mechanisms of the detrimental effects of extended wakefulness, as well as lead to the development of effective, evidence-based countermeasures against the health consequences of circadian misalignment and chronic sleep restriction.

The genome-wide landscape of DNA methylation and hydroxymethylation in response to sleep deprivation impacts on synaptic plasticity genes

Sleep is critical for normal brain function and mental health. However, the molecular mechanisms mediating the impact of sleep loss on both cognition and the sleep electroencephalogram remain mostly unknown. Acute sleep loss impacts brain gene expression broadly. These data contributed to current hypotheses regarding the role for sleep in metabolism, synaptic plasticity and neuroprotection. These changes in gene expression likely underlie increased sleep intensity following sleep deprivation (SD). Here we tested the hypothesis that epigenetic mechanisms coordinate the gene expression response driven by SD. We found that SD altered the cortical genome-wide distribution of two major epigenetic marks: DNA methylation and hydroxymethylation. DNA methylation differences were enriched in gene pathways involved in neuritogenesis and synaptic plasticity, whereas large changes (>4000 sites) in hydroxymethylation where observed in genes linked to cytoskeleton, signaling and neurotransmission, which closely matches SD-dependent changes in the transcriptome. Moreover, this epigenetic remodeling applied to elements previously linked to sleep need (for example, Arc and Egr1) and synaptic partners of Neuroligin-1 (Nlgn1; for example, Dlg4, Nrxn1 and Nlgn3), which we recently identified as a regulator of sleep intensity following SD. We show here that Nlgn1 mutant mice display an enhanced slow-wave slope during non-rapid eye movement sleep following SD but this mutation does not affect SD-dependent changes in gene expression, suggesting that the Nlgn pathway acts downstream to mechanisms triggering gene expression changes in SD. These data reveal that acute SD reprograms the epigenetic landscape, providing a unique molecular route by which sleep can impact brain function and health.

Consciousness of seizures and consciousness during seizures: are they related?

Recent advances have been made in the network mechanisms underlying impairment of consciousness during seizures. However, less is known about patient awareness of their own seizures. Studying patient reports or documentation of their seizures is currently the most commonly utilized mechanism to scientifically measure patient awareness of seizures. The purpose of this review is to summarize the available evidence regarding the accuracy of patient seizure counts and identify the variables that may influence unreliable seizure reporting. Several groups looking at patient documentation of seizures during continuous EEG monitoring show that patients do not report as many as 50% of their seizures. These studies also suggest that seizures accompanied by loss of consciousness, arising from the left hemisphere or the temporal lobe, or occurring during sleep are associated with significantly reduced reporting. Baseline memory performance does not appear to have a major influence on the accuracy of seizure report. Further prospective studies using validated ictal behavioral testing as well as using correlation with newer electrophysiological and neuroimaging techniques for seizure localization are needed to more fully understand the mechanisms of underreporting of seizures. Better methods to alert caregivers about unrecognized seizures and to improve seizure documentation are under investigation.

Experimental sleep deprivation as a tool to test memory deficits in rodents

Paradigms of sleep deprivation (SD) and memory testing in rodents (laboratory rats and mice) are here reviewed. The vast majority of these studies have been aimed at understanding the contribution of sleep to cognition, and in particular to memory. Relatively little attention, instead, has been devoted to SD as a challenge to induce a transient memory impairment, and therefore as a tool to test cognitive enhancers in drug discovery. Studies that have accurately described methodological aspects of the SD protocol are first reviewed, followed by procedures to investigate SD-induced impairment of learning and memory consolidation in order to propose SD protocols that could be employed as cognitive challenge. Thus, a platform of knowledge is provided for laboratory protocols that could be used to assess the efficacy of drugs designed to improve memory performance in rodents, including rodent models of neurodegenerative diseases that cause cognitive deficits, and Alzheimer's disease in particular. Issues in the interpretation of such preclinical data and their predictive value for clinical translation are also discussed.

Cell type-specific effects of adenosine on cortical neurons

The neuromodulator adenosine is widely considered to be a key regulator of sleep homeostasis and an indicator of sleep need. Although the effect of adenosine on subcortical areas has been previously described, the effects on cortical neurons have not been addressed systematically to date. To that purpose, we performed in vitro whole-cell patch-clamp recordings and biocytin staining of pyramidal neurons and interneurons throughout all layers of rat prefrontal and somatosensory cortex, followed by morphological analysis. We found that adenosine, via the A1 receptor, exerts differential effects depending on neuronal cell type and laminar location. Interneurons and pyramidal neurons in layer 2 and a subpopulation of layer 3 pyramidal neurons that displayed regular spiking were insensitive to adenosine application, whereas other pyramidal cells in layers 3-6 were hyperpolarized (range 1.2-10.8 mV). Broad tufted pyramidal neurons with little spike adaptation showed a small adenosine response, whereas slender tufted pyramidal neurons with substantial adaptation showed a bigger response. These studies of the action of adenosine at the postsynaptic level may contribute to the understanding of the changes in cortical circuit functioning that take place between sleep and awakening.

Sleep deprivation, low self-control, and delinquency: a test of the strength model of self-control

Recent work provides evidence that sleep deprivation is positively related to delinquency. In this study, we draw on Baumeister and colleagues' strength model of self-control to propose an explanation for this association. Specifically, we argue that low self-control is the construct that bridges the relationship between sleep deprivation and delinquency. To test the proposed model, we examine survey data drawn from a longitudinal multi-city cohort study of adolescents who were followed from birth through age 15 (N = 825; 50% female; 82% non-Hispanic white, 59% two-parent nuclear family). The results from regression models using latent factors indicate: sleep deprivation is positively related to low self-control; low self-control is positively related to delinquency; and the relationship between sleep deprivation and delinquency is indirect and operates through low self-control. Impressively, these relationships emerged when accounting for potential background sources of spuriousness, including neighborhood context, depressive symptoms, parenting practices, unstructured socializing with peers, and prior delinquency. Implications and directions for future research are discussed.

Behavioral parent training to address sleep disturbances in young children with autism spectrum disorder: a pilot trial

OBJECTIVES

A large percentage of children with autism spectrum disorders (ASD) have bedtime and sleep disturbances. However, the treatment of these disturbances has been understudied. The purpose of our study was to develop a manualized behavioral parent training (BPT) program for parents of young children with ASD and sleep disturbances and to test the feasibility, fidelity, and initial efficacy of the treatment in a small randomized controlled trial (RCT).

PARTICIPANTS AND METHODS

Parents of a sample of 40 young children diagnosed with ASD with an average age of 3.5years were enrolled in our study. Participants were randomized to either the BPT program group or a comparison group who were given nonsleep-related parent education. Each participant was individually administered a 5-session program delivered over the 8-week study. Outcome measures of feasibility, fidelity, and efficacy were collected at weeks 4 and 8 after the baseline time point. Children's sleep was assessed by parent report and objectively by actigraphy.

RESULTS

Of the 20 participants in each group, data were available for 15 participants randomized to BPT and 18 participants randomized to the comparison condition. Results supported the feasibility of the manualized parent training program and the comparison program. Treatment fidelity was high for both groups. The BPT program group significantly improved more than the comparison group based on the primary sleep outcome of parent report. There were no objective changes in sleep detected by actigraphy.

CONCLUSIONS

Our study is one of few RCTs of a BPT program to specifically target sleep disturbances in a well-characterized sample of young children with ASD and to demonstrate the feasibility of the approach. Initial efficacy favored the BPT program over the comparison group and suggested that this manualized parent training approach is worthy of further examination of the efficacy within a larger RCT.

Epilepsy, behavior, and art (Epilepsy, Brain, and Mind, part 1)

Epilepsy is both a disease of the brain and the mind. Brain diseases, structural and/or functional, underlie the appearance of epilepsy, but the notion of epilepsy is larger and cannot be reduced exclusively to the brain. We can therefore look at epilepsy from two angles. The first perspective is intrinsic: the etiology and pathophysiology, problems of therapy, impact on the brain networks, and the "mind" aspects of brain functions - cognitive, emotional, and affective. The second perspective is extrinsic: the social interactions of the person with epilepsy, the influence of the surrounding environment, and the influences of epilepsy on society. All these aspects reaching far beyond the pure biological nature of epilepsy have been the topics of two International Congresses of Epilepsy, Brain, and Mind that were held in Prague, Czech Republic, in 2010 and 2012 (the third Congress will be held in Brno, Czech Republic on April 3-5, 2014; www.epilepsy-brain-mind2014.eu). Here, we present the first of two papers with extended summaries of selected presentations of the 2012 Congress that focused on epilepsy, behavior, and art.

Behavioral Sleep Problems and their Potential Impact on Developing Executive Function in Children

Bedtime resistance and night waking are common sleep problems throughout childhood, especially in the early years. These sleep problems may lead to difficulties in neurobehavioral functioning, but most research into childhood sleep problems has not emphasized the importance of the developmental context in which disruptions in neurobehavioral and daytime functioning occur. We review the development of sleep as well as executive functioning (EF) in childhood and suggest that EF may be particularly vulnerable to the effects of these common childhood sleep problems because of its prolonged course of maturation. Behavioral problems associated with common sleep problems suggest poor self-regulation in the context of sleep loss, and developing EF skills play important roles in self-regulation. A research agenda that considers a developmental approach to sleep and sleep problems in the context of childhood EF performance is outlined to promote future research in this area.

CITATION

Turnbull K; Reid GJ; Morton JB. Behavioral sleep problems and their potential impact on developing executive function in children. SLEEP 2013;36(7):1077-1084.

Recovery in soccer : part ii-recovery strategies

In the formerly published part I of this two-part review, we examined fatigue after soccer matchplay and recovery kinetics of physical performance, and cognitive, subjective and biological markers. To reduce the magnitude of fatigue and to accelerate the time to fully recover after completion, several recovery strategies are now used in professional soccer teams. During congested fixture schedules, recovery strategies are highly required to alleviate post-match fatigue, and then to regain performance faster and reduce the risk of injury. Fatigue following competition is multifactorial and mainly related to dehydration, glycogen depletion, muscle damage and mental fatigue. Recovery strategies should consequently be targeted against the major causes of fatigue. Strategies reviewed in part II of this article were nutritional intake, cold water immersion, sleeping, active recovery, stretching, compression garments, massage and electrical stimulation. Some strategies such as hydration, diet and sleep are effective in their ability to counteract the fatigue mechanisms. Providing milk drinks to players at the end of competition and a meal containing high-glycaemic index carbohydrate and protein within the hour following the match are effective in replenishing substrate stores and optimizing muscle-damage repair. Sleep is an essential part of recovery management. Sleep disturbance after a match is common and can negatively impact on the recovery process. Cold water immersion is effective during acute periods of match congestion in order to regain performance levels faster and repress the acute inflammatory process. Scientific evidence for other strategies reviewed in their ability to accelerate the return to the initial level of performance is still lacking. These include active recovery, stretching, compression garments, massage and electrical stimulation. While this does not mean that these strategies do not aid the recovery process, the protocols implemented up until now do not significantly accelerate the return to initial levels of performance in comparison with a control condition. In conclusion, scientific evidence to support the use of strategies commonly used during recovery is lacking. Additional research is required in this area in order to help practitioners establish an efficient recovery protocol immediately after matchplay, but also for the following days. Future studies could focus on the chronic effects of recovery strategies, on combinations of recovery protocols and on the effects of recovery strategies inducing an anti-inflammatory or a pro-inflammatory response.

Is sleep essential for neural plasticity in humans, and how does it affect motor and cognitive recovery?

There is a general consensus that sleep is strictly linked to memory, learning, and, in general, to the mechanisms of neural plasticity, and that this link may directly affect recovery processes. In fact, a coherent pattern of empirical findings points to beneficial effect of sleep on learning and plastic processes, and changes in synaptic plasticity during wakefulness induce coherent modifications in EEG slow wave cortical topography during subsequent sleep. However, the specific nature of the relation between sleep and synaptic plasticity is not clear yet. We reported findings in line with two models conflicting with respect to the underlying mechanisms, that is, the “synaptic homeostasis hypothesis” and the “consolidation” hypothesis, and some recent results that may reconcile them. Independently from the specific mechanisms involved, sleep loss is associated with detrimental effects on plastic processes at a molecular and electrophysiological level. Finally, we reviewed growing evidence supporting the notion that plasticity-dependent recovery could be improved managing sleep quality, while monitoring EEG during sleep may help to explain how specific rehabilitative paradigms work. We conclude that a better understanding of the sleep-plasticity link could be crucial from a rehabilitative point of view.

The beneficial effects of leptin on REM sleep deprivation-induced cognitive deficits in mice

Leptin, a 167 amino acid peptide, is synthesized predominantly in the adipose tissues and plays a key role in the regulation of food intake and body weight. Recent studies indicate that leptin receptor is expressed with high levels in many brain regions that may regulate synaptic plasticity. Here we show that deprivation of rapid eye movement (REMD) sleep resulted in impairment of both cue and contextual fear memory. In parallel, surface expression of GluR1 was reduced in the amygdala. Intraperitoneal injection of leptin to the REMD mice rescued memory impairment and reversed surface GluR1 reduction. Using whole-cell recording to evaluate the synaptic function of the thalamus-lateral amygdala (LA) pathway, we found a decrease in frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) concomitant with reduced AMPA/NMDA ratios in the REMD mice. By contrast, paired-pulse facilitation (PPF) was increased. The effects of REMD on mEPSCs and AMPA/NMDA ratio could be reversed by leptin treatment, whereas on PPR it could not. Phosphatase and tensin homolog (PTEN), a dual protein/lipid phosphatase, down-regulates the effect of the PI-3 kinase pathway. Fear conditioning increased whereas REMD led to a decrease in the phosphorylated states of PTEN, Akt, and glycogen synthase kinase-3β (GSK3β), and the effects of REMD were reversed by leptin. These results suggest that both pre- and postsynaptic functions of the thalamus-LA pathway were altered by fear conditioning and REMD in opposite directions. Leptin treatment reversed REMD-induced memory deficits primarily by a postsynaptic action by restoring surface expression of GluR1 without affecting PPR.

About sleep's role in memory

Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

A dynamical role for acetylcholine in synaptic renormalization

Although sleep is a fundamental behavior observed in virtually all animal species, its functions remain unclear. One leading proposal, known as the synaptic renormalization hypothesis, suggests that sleep is necessary to counteract a global strengthening of synapses that occurs during wakefulness. Evidence for sleep-dependent synaptic downscaling (or synaptic renormalization) has been observed experimentally, but the physiological mechanisms which generate this phenomenon are unknown. In this study, we propose that changes in neuronal membrane excitability induced by acetylcholine may provide a dynamical mechanism for both wake-dependent synaptic upscaling and sleep-dependent downscaling. We show in silico that cholinergically-induced changes in network firing patterns alter overall network synaptic potentiation when synaptic strengths evolve through spike-timing dependent plasticity mechanisms. Specifically, network synaptic potentiation increases dramatically with high cholinergic concentration and decreases dramatically with low levels of acetylcholine. We demonstrate that this phenomenon is robust across variation of many different network parameters.

Sleep loss as risk factor for neurologic disorders: a review

Sleep loss refers to sleep of shorter duration than the average baseline need of seven to eight hours per night. Sleep loss and sleep deprivation have severe effects on human health. In this article, we review the main aspects of sleep loss, taking into account its effects on the central nervous system. The neurocognitive and behavioral effects of sleep loss are well known. However, there is an increasing amount of research pointing to sleep deprivation as a risk factor for neurologic diseases, namely stroke, multiple sclerosis, Alzheimer's disease, headache, epilepsy, pain, and somnambulism. Conversely, sleep loss has been reported to be a potential protective factor against Parkinson's disease. The pathophysiology involved in this relationship is multiple, comprising immune, neuroendocrine, autonomic, and vascular mechanisms. It is extremely important to identify the individuals at risk, since recognition and adequate treatment of their sleep problems may reduce the risk of certain neurologic disorders.

The neuroinflammatory response of postoperative cognitive decline

BACKGROUND

Aseptic surgical trauma provokes a homeostatic neuroinflammatory response to promote healing and protect the organism from further injury. When this response is dysregulated, harmful consequences can follow, including postoperative cognitive decline.

SOURCES OF DATA

We performed a comprehensive search on PubMed related to postoperative cognitive dysfunction (POCD).

AREAS OF AGREEMENT

Although the precise pathogenic mechanisms for POCD remain unclear, certain risk factors are known.

AREAS OF CONTROVERSY

The mechanisms that lead to exaggerated and persistent neuroinflammation and the best way to counteract it are still unknown. AREAS FOR DEVELOPING RESEARCH: It is imperative that we identify the underlying processes that increase the risk of cognitive decline in elderly surgical patients. In this review we explore non-resolution of inflammation as an underlying cause of developing exaggerated and persistent POCD. If interventions can be developed to promote resolution of neuroinflammation, the patient's postoperative recovery will be enhanced and long-term consequences can be prevented.

Triangular relationship between sleep spindle activity, general cognitive ability and the efficiency of declarative learning

EEG sleep spindle activity (SpA) during non-rapid eye movement (NREM) sleep has been reported to be associated with measures of intelligence and overnight performance improvements. The reticular nucleus of the thalamus is generating sleep spindles in interaction with thalamocortical connections. The same system enables efficient encoding and processing during wakefulness. Thus, we examined if the triangular relationship between SpA, measures of intelligence and declarative learning reflect the efficiency of the thalamocortical system. As expected, SpA was associated with general cognitive ability, e.g. information processing speed. SpA was also associated with learning efficiency, however, not with overnight performance improvement in a declarative memory task. SpA might therefore reflect the efficiency of the thalamocortical network and can be seen as a marker for learning during encoding in wakefulness, i.e. learning efficiency.

Effect of chronic sleep restriction and aging on calcium signaling and apoptosis in the hippocampus of young and aged animals

Aging leads to progressive deterioration of physiological function and diminished responses to environmental stress. Organic and functional alterations are frequently observed in elderly subjects. Although chronic sleep loss is observed during senescence, little is known about the impact of insufficient sleep on cellular function in aging neurons. Disruption of neuronal calcium (Ca²⁺) signaling is related to impaired neuronal function and cell death. It has been hypothesized that sleep deprivation may compromise neuronal stability and induce cell death in young neurons; however, it is necessary to evaluate the impact of aging on this process. Therefore, the aim of this study was to evaluate the effects of chronic sleep restriction (CSR) on Ca²⁺ signaling and cell death in the hippocampus of young and aged animals. We found that glutamate and carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) induced a greater elevation in cytosolic Ca²⁺ ([Ca²⁺](c)) in hippocampal slices from aged rats subjected to CSR compared to age-matched controls. Interestingly, aged-matched controls showed a reduced Ca²⁺ response to glutamate and FCCP, relative to both CSR and control young animals. Apoptotic nuclei were observed in aged rats from both treatment groups; however, the profile of apoptotic nuclei in aged CSR rats was highly variable. Bax and Bcl-2 protein expression did not change with aging in the CSR groups. Our study indicates that aging promotes changes in Ca²⁺ signaling, which may also be affected by CSR. These age-dependent changes in Ca²⁺ signaling may increase cellular vulnerability during CSR and contribute to Ca²⁺ signaling dysregulation, which may ultimately induce cell death.

Quantitative proteomic analyses of cerebrospinal fluid using iTRAQ in a primate model of iron deficiency anemia

Iron deficiency affects nearly 2 billion people worldwide, with pregnant women and young children being most severely impacted. Sustained anemia during the first year of life can cause cognitive, attention and motor deficits, which may persist despite iron supplementation. We conducted iTRAQ analyses on cerebrospinal fluid (CSF) from infant monkeys (Macaca mulatta) to identify differential protein expression associated with early iron deficiency. CSF was collected from 5 iron-sufficient and 8 iron-deficient anemic monkeys at weaning age (6-7 months) and again at 12-14 months. Despite consumption of iron-fortified food after weaning, which restored hematological indices into the normal range, expression of 5 proteins in the CSF remained altered. Most of the proteins identified are involved in neurite outgrowth, migration or synapse formation. The results reveal novel ways in which iron deficiency undermines brain growth and results in aberrant neuronal migration and connections. Taken together with gene expression data from rodent models of iron deficiency, we conclude that significant alterations in neuroconnectivity occur in the iron-deficient brain, which may persist even after resolution of the hematological anemia. The compromised brain infrastructure could account for observations of behavioral deficits in children during and after the period of anemia.

Post-transcriptional effects and interactions between chronic mild stress and acute sleep deprivation: regulation of translation factor and cytoplasmic polyadenylation element-binding protein phosphorylation

Stress and restricted or disrupted sleep trigger adaptive responses in the brain at the level of gene transcription. We investigated the possible impact of chronic mild stress (CMS), acute sleep deprivation, and a combination of these in male rats on post-transcriptional mechanisms important for cognitive function and synaptic plasticity. Relationships between sleep architecture and translational regulators were also assessed. After four weeks of CMS, phosphorylation of two key translation factors, eukaryotic initiation factor 4E (eIF4E) and elongation factor 2 (eEF2), was enhanced in the prefrontal cortex, but unchanged in the hippocampus and dentate gyrus. Sleep deprivation decreased phosphorylated eIF4E in the dentate gyrus. In contrast, eEF2 phosphorylation was elevated in all brain regions after sleep deprivation. Thus, CMS and sleep deprivation, when given alone, have distinct region-specific effects. Furthermore, the combined treatment revealed striking interactions with eEF2 phosphorylation in which sleep deprivation counteracts the effect of CMS cortically and CMS modulates the effects of sleep deprivation in the hippocampus proper. Although CMS exposure alone had no effect in the hippocampus, it inhibited the sleep deprivation-induced eIF4E phosphorylation, while inducing phosphorylation of a major regulatory RNA-binding protein, cytoplasmic polyadenylation element-binding protein (CPEB) in the combined treatment. CMS had no effect on plasma corticosterone, but led to disruption of sleep. Sleep quality and sleep quantity in non-stressed animals showed predictive changes in eIF4E and eEF2 phosphorylation cortically. Prior exposure to CMS abolishes this relationship. We conclude that CMS and acute sleep deprivation have interactive and brain region-specific effects on translational regulators of relevance to mechanisms of stress responsiveness and sleep homeostasis.

Sleep deprivation impairs Ca2+ expression in the hippocampus: ionic imaging analysis for cognitive deficiency with TOF-SIMS

Sleep deprivation causes cognitive dysfunction in which impaired neuronal plasticity in hippocampus may underlie the molecular mechanisms of this deficiency. Considering calcium-mediated NMDA receptor subunit 1 (NMDAR1) and neuronal nitric oxide synthase (nNOS) activation plays an important role in the regulation of neuronal plasticity, the present study is aimed to determine whether total sleep deprivation (TSD) would impair calcium expression, together with injury of the neuronal plasticity in hippocampus. Adult rats subjected to TSD were processed for time-of-flight secondary ion mass spectrometry, NMDAR1 immunohistochemistry, nNOS biochemical assay, cytochrome oxidase histochemistry, and the Morris water maze learning test to detect ionic, neurochemical, bioenergetic as well as behavioral changes of neuronal plasticity, respectively. Results indicated that in normal rats, strong calcium signaling along with intense NMDAR1/nNOS expression were observed in hippocampal regions. Enhanced calcium imaging and neurochemical expressions corresponded well with strong bioenergetic activity and good performance of behavioral testing. However, following TSD, both calcium intensity and NMDAR1/nNOS expressions were significantly decreased. Behavioral testing also showed poor responses after TSD. As proper calcium expression is essential for maintaining hippocampal neuronal plasticity, impaired calcium expression would depress downstream NMDAR1-mediated nNOS activation, which might contribute to the initiation or development of TSD-related cognitive deficiency.

A mechanistic appraisal of cognitive dysfunction in epilepsy

A strong relationship between the clinical characteristics of epilepsy and the nature of cognitive impairments associated with the condition has been found, but the nature of this relationship appears to be quite complex and not well understood. This review presents a summary of the research on the interaction between cognition and epilepsy, surveyed from a mechanistic perspective with the aim of clarifying factors that contribute to the co-existence of both disorders. The physiological basis underpinning cognitive processing is first reviewed. The physiology of epilepsy is reviewed, with emphasis placed on interictal discharges and seizures. The nature of the impact of epilepsy on cognition is described, with transient and prolonged effects distinguished. Finally, the complexity of the co-morbidity between cognitive dysfunction and epilepsy is discussed in relation to childhood and adult-onset epilepsy syndromes and severe epileptic encephalopathies. Structural and functional abnormalities exist in patients with epilepsy that may underpin both the cognitive dysfunction and epilepsy, highlighting the complexity of the association. Research, possibly of a longitudinal nature, is needed to elucidate this multifactorial relationship between cognitive dysfunction and epilepsy.

Poor sleep as a potential causal factor in aggression and violence

Clinical observations suggest that sleep problems may be a causal factor in the development of reactive aggression and violence. In this review we give an overview of existing literature on the relation between poor sleep and aggression, irritability, and hostility. Correlational studies are supporting such a relationship. Although limited in number, some studies suggest that treatment of sleep disturbances reduces aggressiveness and problematic behavior. In line with this is the finding that sleep deprivation actually increases aggressive behavior in animals and angriness, short-temperedness, and the outward expression of aggressive impulses in humans. In most people poor sleep will not evoke actual physical aggression, but certain individuals, such as forensic psychiatric patients, may be particularly vulnerable to the emotional dysregulating effects of sleep disturbances. The relation between sleep problems and aggression may be mediated by the negative effect of sleep loss on prefrontal cortical functioning. This most likely contributes to loss of control over emotions, including loss of the regulation of aggressive impulses to context-appropriate behavior. Other potential contributing mechanisms connecting sleep problems to aggression and violence are most likely found within the central serotonergic and the hypothalamic-pituitary-adrenal-axis. Individual variation within these neurobiological systems may be responsible for amplified aggressive responses induced by sleep loss in certain individuals. It is of great importance to identify the individuals at risk, since recognition and adequate treatment of their sleep problems may reduce aggressive and violent incidents.

Comparison of differences and determinants between presence and absence of sleep disturbance in hepatocellular carcinoma patients

BACKGROUND

Hepatocellular carcinoma patients often experience sleep disturbance after undergoing transcatheter arterial chemoembolization (TACE).

OBJECTIVE

The objectives of this study were to (1) examine and compare symptom distress, depression, and sleep quality in hepatocellular carcinoma patients undergoing TACE with sleep disturbance versus without sleep disturbance and (2) examine the determinants of sleep disturbance in these patients.

METHODS

Hepatocellular carcinoma patients undergoing TACE were recruited. The patients were evaluated 1 week (T1) and 1 month (T2) after receiving TACE in terms of performance status, symptom distress, depression (T1), and sleep disturbance (T2). Logistic regression was used to determine the predictive factors of sleep disturbance.

RESULTS

Patients with sleep disturbance reported significantly higher overall symptom distress and depression and lower sleep quality than patients without sleep disturbance. The 5 leading causes of symptom distress in both groups were fatigue, pain, poor appetite, chest tightness, and fever. Older age, greater symptom distress, and higher levels of depression were significantly associated with sleep disturbance.

CONCLUSIONS

The results of this study show significant associations among symptom distress, depression at baseline, and sleep problems 1 month after undergoing TACE. Clinicians should be aware of the possibility of lasting sleep disturbance in hepatocellular carcinoma patients undergoing TACE.

IMPLICATIONS FOR PRACTICE

In clinical care, symptom management, psychological consultation, and relaxation training may promote sleep quality.

The cognitive cost of sleep lost

A substantial body of literature supports the intuitive notion that a good night's sleep can facilitate human cognitive performance the next day. Deficits in attention, learning & memory, emotional reactivity, and higher-order cognitive processes, such as executive function and decision making, have all been documented following sleep disruption in humans. Thus, whilst numerous clinical and experimental studies link human sleep disturbance to cognitive deficits, attempts to develop valid and reliable rodent models of these phenomena are fewer, and relatively more recent. This review focuses primarily on the cognitive impairments produced by sleep disruption in rodent models of several human patterns of sleep loss/sleep disturbance. Though not an exclusive list, this review will focus on four specific types of sleep disturbance: total sleep deprivation, experimental sleep fragmentation, selective REM sleep deprivation, and chronic sleep restriction. The use of rodent models can provide greater opportunities to understand the neurobiological changes underlying sleep loss induced cognitive impairments. Thus, this review concludes with a description of recent neurobiological findings concerning the neuroplastic changes and putative brain mechanisms that may underlie the cognitive deficits produced by sleep disturbances.

Sleep and its regulation in zebrafish

The function of sleep remains a central enigma of modern biology, in spite of the obvious importance of sleep for normal physiology and cognition. The zebrafish has emerged as a promising new model for studying sleep, its changes with age, and the impact of sleep alterations on cognitive function. Recent studies of this diurnal vertebrate have provided new insights into the dual role of the pineal hormone melatonin and its receptors, regulating sleep in diurnal vertebrates through both homeostatic and circadian mechanisms. Research in zebrafish has also revealed interactions between melatonin and the hypocretin/orexin system, another important sleep-wake modulator. Future investigations should benefit from the conservation in zebrafish of mechanisms that regulate normal sleep, our extensive knowledge of their molecular biology, the availability of multiple transgenic and mutant phenotypes, and the feasibility of applying sensitive in vivo imaging techniques to record sleep-related neuronal activity in these optically transparent subjects. The established sensitivity of zebrafish to many pharmacological hypnotics should also contribute to the development of new, safe and effective sleep medications.

REM sleep loss increases brain excitability: role of noradrenaline and its mechanism of action

Ever since the discovery of rapid eye movement sleep (REMS), studies have been undertaken to understand its necessity, function and mechanism of action on normal physiological processes as well as in pathological conditions. In this review, first, we briefly surveyed the literature which led us to hypothesise REMS maintains brain excitability. Thereafter, we present evidence from in vivo and in vitro studies tracing behavioural to cellular to molecular pathways showing REMS deprivation (REMSD) increases noradrenaline level in the brain, which stimulates neuronal Na-K ATPase, the key factor for maintaining neuronal excitability, the fundamental property of a neuron for executing brain functions; we also show for the first time the role of glia in maintaining ionic homeostasis in the brain. As REMSD exerts a global effect on most of the physiological processes regulated by the brain, we propose that REMS possibly serves a housekeeping function in the brain. Finally, subject to confirmation from clinical studies, based on the results reviewed here, it is being proposed that the subjects suffering from REMS loss may be effectively treated by reducing either noradrenaline level or Na-K ATPase activity in the brain.