The effects of sleep extension on sleep and cognitive performance in adolescents with chronic sleep reduction: An experimental study

ObjectiveTo investigate the effects of gradual sleep extension in adolescents with chronic sleep reduction. Outcome variables were objectively measured sleep and cognitive performance.MethodsParticipants were randomly assigned to either a sleep extension group (gradual sleep extension by advancing bedtimes in the evening) or to a control group (no instruction). Our sample consisted of 55 adolescents (mean age, 15.44 y; 85.5% girls) with symptoms of chronic sleep reduction (loss of energy, shortness of sleep, sleepiness, and irritation). Sleep was monitored with actigraphy over 3 weeks; the first week was the baseline week and the last two weeks were the experimental weeks. Participants in the experimental group were instructed to extend their sleep during the week by gradually advancing their bedtimes by 5 minutes each night. Additionally participants were asked to prevent bedtime shifts on weekend nights. Cognitive performance was assessed before and after the experimental manipulation.ResultsDuring the last week of the experiment, adolescents in the sleep extension group had earlier bedtimes, earlier sleep onsets, spent more time in bed, and slept longer than adolescents in the control group. These results indicate that the experimental manipulation was successful and that adolescents in the experimental group fell asleep earlier and slept longer than adolescents in the control group. Furthermore some aspects of cognitive performance, especially visuospatial processing, significantly changed in the sleep extension group.ConclusionGradual sleep extension has beneficial effects on adolescents’ sleep and is related to changes in some aspects of cognitive performance.     

Clinical effects of sleep fragmentation versus sleep deprivation

Common symptoms associated with sleep fragmentation and sleep deprivation include increased objective sleepiness (as measured by the Multiple Sleep Latency Test); decreased psychomotor performance on a number of tasks including tasks involving short term memory, reaction time, or vigilance; and degraded mood. Differences in degree of sleepiness are more related to the degree of sleep loss or fragmentation rather than to the type of sleep disturbance. Both sleep fragmentation and sleep deprivation can exacerbate sleep pathology by increasing the length and pathophysiology of sleep apnea. The incidence of both fragmenting sleep disorders and chronic partial sleep deprivation is very high in our society, and clinicians must be able to recognize and treat Insufficient Sleep Syndrome even when present with other sleep disorders.     

Effects of NREM sleep instability on cognitive processing

ObjectiveCyclic alternating pattern (CAP) A1 subtypes, characterized by high-voltage slow waves, are generated by the frontal cortex and are suspected to have a role in cognitive processing during NREM sleep. Conversely, CAP A2 and A3 subtypes are characterized by variable amounts of rapid EEG potentials arising from the parietal–occipital areas and often coincide with arousals. We tested the hypothesis that CAP subtypes differentially correlate with cognitive functions.Subjects and methodsEight healthy participants were recruited. Two nocturnal polysomnography studies and a series of neuropsychological tests were obtained in the subjects during the morning and afternoon of the first day and on the morning of the second day.ResultsIn agreement with our original hypothesis, we found that CAP A1 subtypes were correlated with better neuropsychological functioning the day after, for verbal fluency, working memory, and both delayed recall and recognition of words. These same neuropsychological test results were found to be negatively correlated with CAP A2 subtypes. CAP A3 subtypes were negatively correlated with the Trial Making test Parts A and B.ConclusionsThe results suggest that CAP A1 might be related to better cognitive functioning, whereas CAP A2 and A3 correlated with worse cognitive functioning. Further studies are needed to better understand how CAP influences cognitive performance, especially frontally-dependent functions and memory.     

Increased sleep fragmentation in experimental autoimmune encephalomyelitis

Sleep disturbance in patients with multiple sclerosis is prevalent and has multifactorial causes. In mice with experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, we determined the dynamic changes of sleep architecture and the interactions between sleep changes and EAE symptoms. The changes of sleep patterns were mainly reflected by altered sleep stage distribution and increased sleep fragmentation. Increased waking and decreased non-rapid eye movement sleep occurred after EAE onset and persisted through the symptomatic phase. There also was increased sleep state transition, indicating a reduction of sleep cohesiveness. Furthermore, the extent of sleep fragmentation correlated with the severity of disease. This is the first study of sleep characteristics in EAE mice demarcating specific changes related to the autoimmune disorder without confounding factors such as psychosocial impact and treatment effects. The reduction of sleep efficiency and cohesiveness supports the notion that enhancing sleep might facilitate the recovery of mice from EAE, pertinent to the multimodality treatment of multiple sclerosis.     

The effects of vestibular stimuli on brain cognitive processing: an ERP study

Cognition impairment caused by space motion sickness often is a risk of spaceflight. So the dynamic changes of pattern of brain cognitive processing under varied vestibular stimuli was explored using event-related potentials. Vestibular stimulation was produced by rotary chair and varied linearly, i.e. control, constant 10 degrees/s rotation and constant 0.6 degrees/s, 0.8 degrees/s, 1.0 degrees/s, 1.2 degrees/s acceleration. Thirty-three subjects participated in the study and performed same auditory selective attention task in which the odd numbers in a randomly mixed series of odd and even numbers (go/no-go) presented acoustically in Chinese pronunciation were assigned as target signal during the rotation stimuli. The results showed that the P3 latency induced by target signal and the N1P2, P2N2 and N2P3 peak-to-peak amplitudes decreased significantly during constant 10 degrees/s rotation in contrast to control and constant angular acceleration. The P3 latency induced by target signal was shorter during constant 0.6 degrees/s and 1.2 degrees/s acceleration rotations than that during constant 0.8 degrees/s and 1.0 degrees/s acceleration rotations. It was suggested that constant angular velocity rotation had a promotion effect on brain cognitive processing. The constant angular acceleration inhibited the cognitive processing and its action had at least two different levels.     

The effect of estrogen on cognitive processing

The so-called female sex hormone, estrogen, is best known for its crucial involvement in reproductive cycle. Recent research revealed that estrogen also plays a significant neuromodulatory and neuroprotective role. Evidence from clinical and experimental studies show that estrogen modulates specific cognitive functions such as memory and learning. There are also data suggesting its positive role for the prevention and treatment of dementia and Alzheimer's disease. The present paper presents a review of research in these fields.     

An alternative measure of sleep fragmentation in clinical practice: the sleep fragmentation index

BACKGROUND AND PURPOSE: Micro-arousals (MA) are commonly considered as sleep components reflecting sleep fragmentation. However, their elucidation is time-consuming, with considerable inter-observer variability. The aim of our study was to investigate the usefulness of a sleep fragmentation index (SFI) to detect sleep disruption in a large sample of patients. PATIENTS AND METHODS: Five-hundred ninety-eight polysomnographic studies made in controls and patients were examined. The SFI was calculated as the total number of awakenings and sleep stage shifts divided by total sleep time. RESULTS: In the whole group a significant correlation was found between the SFI and the MA index (MAI) (P<0.001) with good agreement across a wide range of values. When patients were stratified according to final diagnosis a significant relation was noted for patients with insomnia (P<0.001), parasomnia (P<0.001), circadian schedule disorders (P<0.001) and sleep related breathing disorders (P< 0.001). Lower values were found in controls (P<0.01) and in patients with periodic limb movement disorder and/or restless legs syndrome (P<0.05). In 111 patients having two consecutive recording nights, a good reproducibility was present with no differences between nights (P=ns) and with significant correlation (P<0.001). CONCLUSIONS: The SFI seems to be an accurate, reproducible and easy method to detect sleep fragmentation in patients with sleep disorders. Further studies are needed to validate the usefulness of this tool in clinical practice.     

The effects of a poor night sleep on mood, cognitive, autonomic and electrophysiological measures

Sustained sleep problems such as insomnia have been shown to be detrimental to health. This study examines the less understood, finer grained effects of a single bad night's sleep on mood, cognitive, autonomic and electrophysiological functions. We assessed 338 individuals who had no symptoms of a clinical sleep disorder. Of these, 226 individuals had six or more hours sleep and 112 individuals had less than six hours sleep prior to an assessment of mood, cognition, autonomic and electrophysiological functioning. Individuals in the relatively "bad night" sleep group had higher depression, anxiety, and stress scores and reported significantly poorer overall wellbeing. They made more errors on simple cognitive tasks while more complex task components were unaffected. They also had an increase in heart rate and EEG alpha and beta power at rest. Participants in this study had no symptoms of a clinical sleep disorder, however the effects of a poor night sleep on measures of mood, cognition, autonomic and electrophysiological function were similar, but less severe than those reported in insomnia patients. The integrative profile of measures reported here point to an increase in physiological arousal and sub-optimal cognition, following a poor night's sleep.     

EEG spectral activity during paradoxical sleep: further evidence for cognitive processing

Paradoxical sleep (PS), in which periods with (phasic) and without (tonic) rapid eye movements are intermingled, is hypothesized to be related to cognitive processing and dreaming. Based on polysomnographic data from 12 healthy subjects, this study focuses on the spectral differentiation between phasic and tonic periods. Phasic PS periods exhibited decreased theta and alpha power in the posterior brain areas suggesting the interference of visual processing related to dream imagery. Phasic PS periods were also characterized by a shift from beta to gamma activity in frontal, central and occipital areas reflecting specific phasic related activation. Together, these findings bring new evidence for the existence of visual imagery and cognitive processing during phasic PS.     

Daytime vigilance in chronotypes: diurnal variations and effects of behavioral sleep fragmentation

Vigilance levels of 12 morning types (M-types) and 12 evening types (E-types) were investigated after a baseline night, 2 nights of sleep fragmentation (5 min of forced awakening every half-hour) and a recovery night. Sleep timing was adjusted to the preferred sleep schedule of each subject. Daytime vigilance levels were assessed with test series including a scale of subjective alertness, a psychomotor vigilance task (PVT), a waking EEG recording, and a sleep latency test. Test series were administered every 4h, beginning 1.5h after wake time. On the baseline day, significant diurnal variations were found for each vigilance measure, except for the PVT. Diurnal variations were similar in M-types and E-types. Sleep fragmentation decreased vigilance levels on each measure, except the PVT. Effects of sleep fragmentation and recovery were similar in the two chronotypes. These results highlight the similarities in diurnal variations of vigilance in the two chronotypes when studied at their preferred sleep schedule. Results were also compared between chronotypes with extremely early or late circadian phases ("Extreme" subgroup) and between those with similar, intermediate circadian phases ("Intermediate" subgroup). Diurnal variations of subjective alertness and sleep latencies differed between "Extreme" chronotypes but were identical between "Intermediate" chronotypes. There were no major differences in the response to sleep fragmentation in any subgroup. Since phase angles differed by the same amount between chronotypes within each subgroup, the results suggest that a difference in phase angle cannot be the only source of the differences observed in diurnal variations between "Extreme" chronotypes.     

Changes in cognitive processing following short-term cumulative partial sleep deprivation and recovery oversleeping

Abstract

The effects on cognitive processing of 1 and 5 cumulative nights of partial sleep deprivation (PSD) and 1 and 2 nights of subsequent recovery oversleep was studied using an anagrams test and the Wisconsin Card Sorting Test. Seven paid undergraduate volunteers (5 male; 2 female) aged 18–23 who had normative 6.5–8.0 hr sleep patterns participated. They followed an 8-day schedule of morning and afternoon testing sessions consisting of 2 days in each of the experimental conditions: prebase-line, PSD, recovery sleep, and postbaseline. Sleep duration was calculated relative to individual habitual by subtracting 40% per night (PSD) and adding 40% and 20%, respectively (recovery sleep). On the anagrams test, results showed exaggerated time of day differences during both sleep manipulation conditions. Card-sorting performance was characterized by lesser efficiency of cognitive strategies (> non-perseverative errors) during recovery sleep and tendency towards perseveration with sleep loss. Results were discussed with particular reference to hypothesized neural substrates and clinical implications.     

Experimental sleep fragmentation in normal subjects

Recent research has suggested that sleep fragmentation in the absence of sleep loss is an important cause of excessive daytime sleepiness in certain clinical populations (e.g., sleep apnea syndrome or periodic leg movements). This study experimentally varied the number and rate of arousals in sleep to define more clearly the relation of sleep fragmentation and daytime sleepiness. Five male subjects participated in the study. Data from each were recorded for three consecutive nights (one baseline followed by two experimental nights) under three experimental conditions. All nocturnal polysomnograms were followed by a Multiple Sleep Latency Test (MSLT) the next day. The experimental conditions consisted of three different schedules of arousal produced by series of tones presented to subjects over headphones. The MSLT showed statistically significant changes after two nights of fragmented sleep, but the three fragmentation schedules did not differ from each other. Arousal threshold also changed significantly with sleep fragmentation from night one to night two.     

The effects of gamma-hydroxybutyrate on sleep.

Sodium gamma-hydroxybutyrate (GHB) is a remarkably safe and nontoxic hypnotic agent which is reported to be free of addicting properties. It is also a normal metabolite of the mammalian nervous system. We examined its effects on the sleep-EEG of eight patients with histories of impaired sleep, as a prelude to a more detailed study of its clinical potential. Sleep induced with GHB was indistinguishable subjectively from natural sleep as well as by behavioral and electroencephalographic criteria. Unlike most synthetic hypnotics, GHB increased delta sleep and did not suppress REM sleep. It shortened the REM sleep latency and shifted REM sleep into the first third of the night. On one occasion it induced a sleep onset REM period which was experienced as an attack of sleep paralysis. Withdrawal was simple; there was no REM sleep rebound and sleep patterns immediately returned to their pre-drug form. Its major clinical drawback was its short duration of action: its hypnotic effect lasting only 2 to 3 hr. We suggest that GHB may serve as the prototype for a new class of hypnotic compounds derived from natural sources and capable of activating the neurological mechanisms of normal human sleep.     

Recovery after prolonged sleep deprivation: residual effects of slow-release caffeine on recovery sleep, sleepiness and cognitive functions

A long work schedule often results in sleep deprivation, sleepiness, impaired performance and fatigue. We investigated the residual effects of slow-release caffeine (SRC) on sleep, sleepiness and cognitive performance during a 42-hour recovery period following a 64-hour continuous wakefulness period in 16 healthy males, according to a double-blind, randomised, placebo-controlled, crossover study. Three hundred milligrams of SRC or placebo was given twice a day at 21:00 and 9:00 during the first 48 h of wakefulness. Recovery sleep was analysed with electroencephalography (EEG) and wrist actigraphy, daytime sleepiness with continuous EEG, sleep latency tests and actigraphy and cognitive functions with computerized tests from the NATO AGARD STRES battery. Both drug groups exhibited almost the same sleep architecture with a rebound of slow-wave sleep during both recovery nights and of REM sleep during the second night. Wakefulness level and cognitive functions were similarly impaired in both groups on the first day of recovery and partially returned to baseline on the second. To conclude, SRC appears to have no unwanted side-effects on recovery sleep, wakefulness and cognitive performance after a long period of sleep deprivation and might therefore be a useful choice over other psychostimulants for a long work schedule.     

The effects of acute sleep restriction and extension on sleep efficiency

This study employed a repeated measures design to assess the relationship between sleep efficiency and time-in-bed (TIB). Fourteen subjects underwent three TIB conditions: (5 hour, 8 hour, and 11 hour), which were presented in a Latin Square design. Subjects slept a total of six nights (two nights per condition) while being monitored by a wrist actigraph to determine sleep time. Sleep efficiencies (sleep time/TIB) were analyzed with a two-way repeated-measures ANOVA. The main effect of night was not significant. The main effect of TIB and the interaction of nights and TIB were significant. In the 11-hour condition, sleep efficiency fell from night one to night two, and on night two both the 5-hour and the 11-hour conditions were significantly different from the 8-hour condition. Analysis of total sleep time (TST) yielded the same results with the addition of a significant night-to-night difference in the 5-hour condition. It was concluded that sleep efficiency systematically changes with an extension or restriction of TIB from 8 hour.     

Effects of sleep deprivation on cognitive functions

Sleep deprivation （SD） is a common condition that afflicts many people in modem life. Deficits in daytime perfor- mance due to SD are experienced universally. Recent evidence indicates that SD causes impairments in cognitive functions. However, the mechanisms that SD impairs cognitive functions are not clear. This review will focus on the behavioral and neural effects of SD with the aim to elucidate the possible mechanisms of SD-induced deterioration in cognitive functions and to identify directions for future research.     

睡眠剥夺对认知影响的研究进展

现代社会,睡眠剥夺(sleep deprivation,SD)是一种常见现象,困扰着很多人,引起人的日间工作能力降低.近年来的研究结果显示,SD可以使认知功能受损,但是其损害机制尚不清楚.本综述将重点阐述SD对行为和中枢系统的影响,进而阐明SD引起认知功能受损的可能机制,并且展望未来的研究方向.