EEG Changes across Multiple Nights of Sleep Restriction and Recovery in Adolescents: The Need for Sleep Study

The impacts of intra-individual daily sleep variability on daytime functioning and sleep architecture in healthy young adults: An experimental study

Sleep variability is commonly seen in the young populations. This study aimed to examine the impacts of experimentally induced sleep variability on sleepiness, mood, cognitive performance and sleep architectures among young adults. Thirty-six healthy individuals (aged 18-22 years) were randomly assigned to either variable sleep schedule (n = 20) or control (n = 16) groups. The protocol involved 1 week of regular sleep (time in bed = 7.5 hr) in the home setting, followed by one adaptation night (time in bed = 7.5 hr), one baseline night (time in bed = 7.5 hr), and 6 nights of sleep manipulation in the laboratory monitored by polysomnography (three cycles of variable sleep schedule by changing daily time in bed alternating between 6 hr and 9 hr for variable sleep schedule group versus fixed sleep schedule with daily time in bed for 7.5 hr for control group). Sleepiness, mood, sustained attention, processing speed, response inhibition and working memory were measured every morning and evening. The variable sleep schedule group reported a higher level of sleepiness, especially in the mornings, and increased negative mood in the evenings. There were no significant differences in positive mood, cognitive performance and sleep macro- and micro-structures. Our results showed the negative effects of sleep variability on daytime functioning especially sleepiness and negative mood, suggesting the need to address variable sleep schedules through sleep intervention.

Sleep Architecture and Sleep EEG Alterations are Associated with Impaired Cognition Under Sleep Restriction

Purpose

Many studies have investigated the cognitive, emotional, and other impairments caused by sleep restriction. However, few studies have explored the relationship between cognitive performance and changes in sleep structure and electroencephalography (EEG) during sleep. The present study aimed to examine whether changes in sleep structure and EEG can account for cognitive impairment caused by sleep restriction.

Patients and Methods

Sixteen young adults spent five consecutive nights (adaptation 9h, baseline 8h, 1st restriction 6h, 2nd restriction 6h, and recovery 10h) in a sleep laboratory, with polysomnography recordings taken during sleep. Throughout waking periods in each condition, participants completed the psychomotor vigilance test (PVT), which measures vigilant attention, and the Go/No-Go task, which measures inhibition control.

Results

The results showed that sleep restriction significantly decreased the proportion of N1 and N2 sleep, increased the proportion of N3 sleep, and reduced the time spent awake after sleep onset (WASO) and sleep onset latency. Poorer performance on the PVT and Go/No Go task was associated with longer WASO, a larger proportion of N3 sleep, and a smaller proportion of N2 sleep. Additionally, the power spectral density of delta waves significantly increased after sleep restriction, and this increase predicted a decrease in vigilance and inhibition control the next day.

Conclusion

These findings suggest that sleep architecture and EEG signatures may partially explain cognitive impairment caused by sleep restriction.

Long-term ear-EEG monitoring of sleep - A case study during shift work

The interest in sleep as a potential clinical biomarker is growing, but the standard method of sleep assessment, polysomnography, is expensive, time consuming, and requires a lot of expert assistance for both set-up and interpretation. To make sleep analysis more available both in research and in the clinic, there is a need for a reliable wearable device for sleep staging. In this case study, we test ear-electroencephalography. A wearable, where electrodes are placed in the outer ear, as a platform for longitudinal at-home recording of sleep. We explore the usability of the ear-electroencephalography in a shift work case with alternating sleep conditions. We find the ear-electroencephalography platform to be reliable both in terms of showing substantial agreement to polysomnography after long-time use (with an overall agreement, using Cohen's kappa, of 0.72) and by being unobtrusive enough to wear during night shift conditions. We find that fractions of non-rapid eye movement sleep and transition probability between sleep stages show great potential as sleep metrics when exploring quantitative differences in sleep architecture between shifting sleep conditions. This study shows that the ear-electroencephalography platform holds great potential as a reliable wearable for quantifying sleep "in the wild", pushing this technology further towards clinical adaptation.

Sleep Architecture and EEG Power Spectrum Following Cumulative Sleep Restriction: A Comparison between Typically Developing Children and Children with ADHD

No studies have looked at the effects of cumulative sleep restriction (CSR) on sleep architecture or the power spectrum of sleep EEG (electroencephalogram) in school-age children, as recorded by PSG (polysomnography). This is true for both typically developing (TD) children and children with ADHD (attention deficit/hyperactivity disorder), who are known to have more sleep difficulties. Participants were children (ages 6-12 years), including 18 TD and 18 ADHD, who were age- and sex-matched. The CSR protocol included a two-week baseline and two randomized conditions: Typical (six nights of sleep based on baseline sleep schedules) and Restricted (one-hour reduction of baseline time in bed). This resulted in an average of 28 min per night difference in sleep. Based on ANOVAs (analysis of variance), children with ADHD took longer to reach N3 (non-rapid eye movement), had more WASO (wake after sleep onset) (within the first 5.1 h of the night), and had more REM (rapid eye movement) sleep than TD children regardless of condition. During CSR, ADHD participants had less REM and a trend toward longer durations of N1 and N2 compared to the TD group. No significant differences in the power spectrum were found between groups or conditions. In conclusion, this CSR protocol impacted some physiological aspects of sleep but may not be sufficient to cause changes in the power spectrum of sleep EEG. Although preliminary, group-by-condition interactions suggest that the homeostatic processes in children with ADHD may be impaired during CSR.

Systematic review and meta-analyses on the effects of afternoon napping on cognition

Naps are increasingly considered a means to boost cognitive performance. We quantified the cognitive effects of napping in 60 samples from 54 studies. 52 samples evaluated memory. We first evaluated effect sizes for all tests together, before separately assessing their effects on memory, vigilance, speed of processing and executive function. We next examined whether nap effects were moderated by study features of age, nap length, nap start time, habituality and prior sleep restriction. Naps showed significant benefits for the total aggregate of cognitive tests (Cohen's d = 0.379, CI₉₅ = 0.296-0.462). Significant domain specific effects were present for declarative (Cohen's d = 0.376, CI₉₅ = 0.269-0.482) and procedural memory (Cohen's d = 0.494, CI₉₅ = 0.301-0.686), vigilance (Cohen's d = 0.610, CI₉₅ = 0.291-0.929) and speed of processing (Cohen's d = 0.211, CI₉₅ = 0.052-0.369). There were no significant moderation effects of any of the study features. Nap effects were of comparable magnitude across subgroups of each of the 5 moderators (Q values = 0.009 to 8.572, p values > 0.116). Afternoon naps have a small to medium benefit over multiple cognitive tests. These effects transcend age, nap duration and tentatively, habituality and prior nocturnal sleep.

The Common Effects of Sleep Deprivation on Human Long-Term Memory and Cognitive Control Processes

Sleep deprivation is known to have adverse effects on various cognitive abilities. In particular, a lack of sleep has been reported to disrupt memory consolidation and cognitive control functions. Here, focusing on long-term memory and cognitive control processes, we review the consistency and reliability of the results of previous studies of sleep deprivation effects on behavioral performance with variations in the types of stimuli and tasks. Moreover, we examine neural response changes related to these behavioral changes induced by sleep deprivation based on human fMRI studies to determine the brain regions in which neural responses increase or decrease as a consequence of sleep deprivation. Additionally, we discuss about the possibility that light as an environmentally influential factor affects our sleep cycles and related cognitive processes.

Staying vigilant during recurrent sleep restriction: dose-response effects of time-in-bed and benefits of daytime napping

Study Objectives

We characterized vigilance deterioration with increasing time-on-task (ToT) during recurrent sleep restriction of different extents on simulated weekdays and recovery sleep on weekends, and tested the effectiveness of afternoon napping in ameliorating ToT-related deficits.

Methods

In the Need for Sleep studies, 194 adolescents (age = 15–19 years) underwent two baseline nights of 9-h time-in-bed (TIB), followed by two cycles of weekday manipulation nights and weekend recovery nights (9-h TIB). They were allocated 9 h, 8 h, 6.5 h, or 5 h of TIB for nocturnal sleep on weekdays. Three additional groups with 5 h or 6.5 h TIB were given an afternoon nap opportunity (5 h + 1 h, 5 h + 1.5 h, and 6.5 h + 1.5 h). ToT effects were quantified by performance change from the first 2 min to the last 2 min in a 10-min Psychomotor Vigilance Task administered daily.

Results

The 9 h and the 8 h groups showed comparable ToT effects that remained at baseline levels throughout the protocol. ToT-related deficits were greater among the 5 h and the 6.5 h groups, increased prominently in the second week of sleep restriction despite partial recuperation during the intervening recovery period and diverged between these two groups from the fifth sleep-restricted night. Daytime napping attenuated ToT effects when nocturnal sleep restriction was severe (i.e. 5-h TIB/night), and held steady at baseline levels for a milder dose of nocturnal sleep restriction when total TIB across 24 h was within the age-specific recommended sleep duration (i.e. 6.5 h + 1.5 h).

Conclusions

Reducing TIB beyond the recommended duration significantly increases ToT-associated vigilance impairment, particularly during recurrent periods of sleep restriction. Daytime napping is effective in ameliorating such decrement.

Clinical Trial Registration

NCT02838095, NCT03333512, and NCT04044885.

Impact of chronic sleep restriction on sleep continuity, sleep structure, and neurobehavioral performance

Chronic sleep restriction (CSR) has been associated with adverse effects including cognitive impairment and increased risk of diabetes and cardiovascular disease. Yet, sleep restriction therapy is an essential component of most behavioral treatments for insomnia. Moreover, little is known about the impact of CSR on sleep continuity and structure in healthy people whose need for sleep is satiated. We investigated the impact of CSR on sleep continuity and structure in nine healthy participants. They had 4 nights of sleep extension, 2 nights of post-extension sleep, 21 nights of CSR (5/5.6-hour time-in-bed), and 9 nights of recovery sleep. Compared to postextension sleep, during CSR sleep duration was reduced by 95.4 ± 21.2 min per night, Slow-Wave Activity was significantly increased, and sleep was more consolidated. During recovery, sleep duration was increased by 103.3 ± 23.8 min compared to CSR, and the CSR-induced increase in Slow-Wave Activity persisted, particularly after the 5-hour exposure. Yet, we found that sustained vigilant attention was not fully recovered even after nine nights of recovery sleep. Our results suggest that CSR improves traditional metrics of sleep quality and may have a persistent impact on sleep depth, which is consistent with the reported benefits on sleep continuity and structure of sleep restriction therapy. However, these improvements in traditional metrics of sleep quality were associated with deterioration rather than improvement in neurobehavioral performance, demonstrating that sleep duration should be included in assessments of sleep quality. These results have implications for the long-term use of sleep restriction in the behavioral treatment of insomnia. Clinical Trial Registration: Impact of Chronic Circadian Disruption vs. Chronic Sleep Restriction on Metabolism (https://clinicaltrials.gov/ct2/show/; #NCT02171273).

Cortical Thinning and Sleep Slow Wave Activity Reductions Mediate Age-Related Improvements in Cognition During Mid-Late Adolescence

Study Objectives

Gains in cognitive test performance that occur during adolescence are associated with brain maturation. Cortical thinning and reduced sleep slow wave activity (SWA) are markers of such developmental changes. Here we investigate whether they mediate age-related improvements in cognition.

Methods

109 adolescents aged 15–19 years (49 males) underwent magnetic resonance imaging, polysomnography (PSG), and a battery of cognitive tasks within a 2-month time window. Cognitive tasks assessed nonverbal intelligence, sustained attention, speed of processing and working memory and executive function. To minimize the effect of sleep history on SWA and cognitive performance, PSG and test batteries were administered only after at least 8 nights of 9-h time-in-bed (TIB) sleep opportunity.

Results

Age-related improvements in speed of processing (r = 0.33, p = 0.001) and nonverbal intelligence (r = 0.24, p = 0.01) domains were observed. These cognitive changes were associated with reduced cortical thickness, particularly in bilateral temporoparietal regions (rs = −0.21 to −0.45, ps < 0.05), as well as SWA (r = −0.35, p < 0.001). Serial mediation models found that ROIs in the middle/superior temporal cortices, together with SWA mediated the age-related improvement observed on cognition.

Conclusions

During adolescence, age-related improvements in cognition are mediated by reductions in cortical thickness and sleep SWA.

Memory performance following napping in habitual and non-habitual nappers

Study Objectives

Afternoon naps benefit memory but this may depend on whether one is a habitual napper (HN; ≥1 nap/week) or non-habitual napper (NN). Here, we investigated whether a nap would benefit HN and NN differently, as well as whether HN would be more adversely affected by nap restriction compared to NN.

Methods

Forty-six participants in the nap condition (HN-nap: n = 25, NN-nap: n = 21) took a 90-min nap (14:00–15:30 pm) on experimental days while 46 participants in the Wake condition (HN-wake: n = 24, NN-wake: n = 22) remained awake in the afternoon. Memory tasks were administered after the nap to assess short-term topographical memory and long-term memory in the form of picture encoding and factual knowledge learning respectively.

Results

An afternoon nap boosted picture encoding and factual knowledge learning irrespective of whether one habitually napped (main effects of condition (nap/wake): ps < 0.037). However, we found a significant interaction for the hippocampal-dependent topographical memory task (p = 0.039) wherein a nap, relative to wake, benefitted habitual nappers (HN-nap vs HN-wake: p = 0.003) compared to non-habitual nappers (NN-nap vs. NN-wake: p = 0.918). Notably for this task, habitual nappers’ performance significantly declined if they were not allowed to nap (HN-wake vs NN-wake: p = 0.037).

Conclusions

Contrary to concerns that napping may be disadvantageous for non-habitual nappers, we found that an afternoon nap was beneficial for long-term memory tasks even if one did not habitually nap. Naps were especially beneficial for habitual nappers performing a short-term topographical memory task, as it restored the decline that would otherwise have been incurred without a nap.

Clinical Trial Information

NCT04044885.

Effects of sleep restriction on the sleep electroencephalogram of adolescents

STUDY OBJECTIVES

This report describes findings from an ongoing longitudinal study of the effects of varied sleep durations on wake and sleep electroencephalogram (EEG) and daytime function in adolescents. Here, we focus on the effects of age and time in bed (TIB) on total sleep time (TST) and nonrapid eye movement (NREM) and rapid eye movement (REM) EEG.

METHODS

We studied 77 participants (41 male) ranging in age from 9.9 to 16.2 years over the 3 years of this study. Each year, participants adhered to each of three different sleep schedules: four consecutive nights of 7, 8.5, or 10 h TIB.

RESULTS

Altering TIB successfully modified TST, which averaged 406, 472 and 530 min on the fourth night of 7, 8.5, and 10 h TIB, respectively. As predicted by homeostatic models, shorter sleep durations produced higher delta power in both NREM and REM although these effects were small. Restricted sleep more substantially reduced alpha power in both NREM and REM sleep. In NREM but not REM sleep, sleep restriction strongly reduced both the all-night accumulation of sigma EEG activity (11-15 Hz energy) and the rate of sigma production (11-15 Hz power).

CONCLUSIONS

The EEG changes in response to TIB reduction are evidence of insufficient sleep recovery. The decrease in sigma activity presumably reflects depressed sleep spindle activity and suggests a manner by which sleep restriction reduces waking cognitive function in adolescents. Our results thus far demonstrate that relatively modest TIB manipulations provide a useful tool for investigating adolescent sleep biology.

Variable objective sleep quality is related to worse spatial learning and memory in young adults

OBJECTIVE

The majority of research on sleep and cognition has focused on mean markers of sleep across multiple nights; however, variable sleep patterns have become increasingly common in the modern era. The purpose of this study was to examine whether objective intraindividual variability in sleep quantity and quality are related to verbal and visuospatial learning and memory functioning in young adults.

METHODS

A total of 218 young adult college students were recruited from a university in the Eastern United States, among which 187 participants (70.6% female; mean age = 20.5, SD = 1.5) had complete actigraphy and cognitive performance data. Objective intraindividual means and variabilities of sleep quantity (total sleep time) and sleep quality (percent wake after sleep onset) were measured over a 1- to 2-week timeframe using wrist actigraphy. Verbal and visuospatial learning and memory were assessed using the International Shopping List and Groton Maze Learning tests of the Cogstate computerized test battery.

RESULTS

Greater intraindividual variability in actigraphy-derived sleep quality was associated with poorer visuospatial learning and memory performance after controlling for mean sleep quality and visuomotor attention and processing speed (ps < 0.05). Actigraphic measures of sleep quantity were not related to any learning and memory measures.

CONCLUSION

In young adults, intraindividual variability in objective sleep quality was significantly related to visuospatial learning and memory, over and above mean sleep quality. Given these associations, future studies should aim to identify modifiable lifestyle and environmental factors contributing to variable sleep quality.

Homeostatic Response to Sleep Restriction in Adolescents

The high prevalence of chronic sleep restriction in adolescents underscores the importance of understanding how adolescent sleep is regulated under such conditions. One component of sleep regulation is a homeostatic process: if sleep is restricted, then sleep intensity increases. Our knowledge of this process is primarily informed by total sleep deprivation studies and has been incorporated in mathematical models of human sleep regulation. Several animal studies, however, suggest that adaptation occurs in chronic sleep restriction conditions, showing an attenuated or even decreased homeostatic response. We investigated the homeostatic response of adolescents to different sleep opportunities. Thirty-four participants were allocated to one of three groups with 5, 7.5 or 10 h of sleep opportunity per night for 5 nights. Each group underwent a protocol of 9 nights designed to mimic a school week between 2 weekends: 2 baseline nights (10 h sleep opportunity), 5 condition nights (5, 7.5 or 10 h), and two recovery nights (10 h). Measures of sleep homeostasis (slow-wave activity and slow-wave energy) were calculated from frontal and central EEG derivations and compared to predictions derived from simulations of the homeostatic process of the two-process model of sleep regulation. Only minor differences were found between empirical data and model predictions, indicating that sleep homeostasis is preserved under chronic sleep restriction in adolescents. These findings improve our understanding of effects of repetitive short sleep in adolescents.

Sleep and human cognitive development

Emerging studies across learning domains have shed light on mechanisms underlying sleep's benefits during numerous developmental periods. In this conceptual review, we survey recent studies of sleep and cognition across infancy, childhood, and adolescence. By summarizing recent findings and integrating across studies with disparate approaches, we provide a novel understanding of sleep's role in human cognitive function. Collectively, these studies point to an interrelation between brain development, sleep, and cognition. Moreover, we point to gaps in our understanding, which inform the agenda for future research in developmental and sleep science.

Neurobehavioural functions during variable and stable short sleep schedules

We investigated whether variable sleep schedules might mitigate the neurobehavioural deficits induced by multiple nights of sleep restriction. In this 4-night experiment, 78 young adults (age: 18-28 years) were randomly assigned to four groups: 8888, 8666, 8846 and 8486, where each digit corresponded to time-in-bed in hours for each study night. After one baseline night of 8-hr time-in-bed, time-in-bed remained unchanged for the 8888 group, while the other groups had short sleep schedules (total time-in-bed = 18 hr) that differed in the number of time-in-bed changes. Sleep was monitored using actigraphy at home. Daytime neurobehavioural functions were assessed in the laboratory at single time points, after the baseline night, and again after 3 nights of the sleep manipulation period. For sustained attention, the 8888 group responded faster in the Psychomotor Vigilance Task after the manipulation period (p = .01), while responses became slower for the less variable sleep schedules (8666 and 8846; p < .01), but not the most variable sleep schedule (8486; p = .14). Processing speed also improved in the 8888 group and the variable 8846 and 8486 groups (p < .01), but not in the stable 8666 group (p = .09). Furthermore, subjective sleepiness was preserved in the 8888 and, importantly, 8486 groups (p > .05), but was elevated in the 8666 and 8846 groups (p < .05). These findings suggest that when sleep opportunities are limited across multiple nights, a variable sleep schedule that allows for prophylactic and/or recovery sleep on some nights may mitigate some daytime neurobehavioural deficits as compared with a schedule with no opportunity for recovery.

Differential effects of split and continuous sleep on neurobehavioral function and glucose tolerance in sleep-restricted adolescents

Study Objectives

Many adolescents are exposed to sleep restriction on school nights. We assessed how different apportionment of restricted sleep (continuous vs. split sleep) influences neurobehavioral function and glucose levels.

Methods

Adolescents, aged 15–19 years, were evaluated in a dormitory setting using a parallel-group design. Following two baseline nights of 9-hour time-in-bed (TIB), participants underwent either 5 nights of continuous 6.5-h TIB (n = 29) or 5-hour nocturnal TIB with a 1.5-hour afternoon nap (n = 29). After two recovery nights of 9-hour TIB, participants were sleep restricted for another three nights. Sleep was assessed using polysomnography (PSG). Cognitive performance and mood were evaluated three times per day. Oral glucose tolerance tests (OGTT) were conducted on mornings after baseline sleep, recovery sleep, and the third day of each sleep restriction cycle.

Results

The split sleep group had fewer vigilance lapses, better working memory and executive function, faster processing speed, lower level of subjective sleepiness, and more positive mood, even though PSG-verified total sleep time was less than the continuous sleep group. However, vigilance in both sleep-restricted groups was inferior to adolescents in a prior sample given 9-hour nocturnal TIB. During both cycles of sleep restriction, blood glucose during the OGTT increased by a greater amount in the split sleep schedule compared with persons receiving 6.5-hour continuous sleep.

Conclusions

In adolescents, modest multinight sleep restriction had divergent negative effects on cognitive performance and glucose levels depending on how the restricted sleep was apportioned. They are best advised to obtain the recommended amount of nocturnal sleep.

Trial registration

https://clinicaltrials.gov/ct2/show/NCT03333512

The effects of recovery sleep on pain perception: A systematic review

Experimental studies highlight profound effects of sleep disruptions on pain, showing that sleep deprivation (SD) leads to hyperalgesic pain changes. On the other hand, given that sleep helps normalizing bodily functions, a crucial role of restorative sleep in the overnight restoration of the pain system seems likely. Thus, a systematic review of experimental studies on effects of recovery sleep (RS; subsequently to SD) on pain was performed with the aim to check whether RS resets hyperalgesic pain changes occurring due to SD. Empirical animal and human studies including SD-paradigms, RS and pain assessments were searched in three databases (PubMed, Web of Science, PsycINFO) using a predefined algorithm. 29 studies were included in this review. Most results indicated a reset of enhanced pain sensitivity and vulnerability following RS, especially when total SD was implemented and pressure pain or painful symptoms (human studies) were assessed. Further research should focus on whether and how recovery is altered in chronic pain patients, as this yields implications for pain treatment by enhancing or stabilizing RS.

Multi-Night Sleep Restriction Impairs Long-Term Retention of Factual Knowledge in Adolescents

PURPOSE

Sleep deprivation is associated with increased forgetting of declarative memories. Sleep restriction across multiple consecutive nights is prevalent in adolescents, but questions remain as to whether this pattern of sleep impairs memory for material typically learned in the classroom and the time course of retention beyond a few days.

METHODS

Adolescents aged 15-18 years (n = 29) were given 5 hours sleep opportunity each night for 5 consecutive nights (sleep restricted group; SR), simulating a school week containing insufficient sleep. After the fourth night of restriction, participants learned detailed facts about different species of arthropod across a 6-hour period. Retention was tested 30 minutes and 3 days after learning and contrasted with a control group (n = 30) who had 9 hours sleep opportunity every night of the study. A subset of participants (SR, n = 14; control, n = 22) completed a surprise test 42 days after learning.

RESULTS

Memory was significantly impaired in the SR group relative to controls, with 26% increased forgetting at the 30-minute test (t(57) = 2.54, p = .014, d = .66), 34% at the Day 3 test (t(57) = 2.65, p = .010, d = .69), and 65% at the Day 42 test (t(34) = 3.22, p = .003, d = 1.17). Vigilance was also significantly impaired after 4 nights of restricted sleep (p < .05), but did not correlate significantly with memory (p > .05).

CONCLUSION

Long-term retention of classroom material is significantly compromised when adolescents learn after being sleep restricted, reinforcing the importance of keeping good sleep habits to optimize learning.

The impact of sleep deprivation on declarative memory

Sleep plays a crucial role in memory stabilization and integration, yet many people obtain insufficient sleep. This review assesses what is known about the level of sleep deprivation that leads to impairments during encoding, consolidation and retrieval of declarative memories, and what can be determined about the underlying neurophysiological processes. Neuroimaging studies that deprived sleep after learning have provided some of the most compelling evidence for sleep's role in the long-term reorganization of memories in the brain (systems consolidation). However, the behavioral consequences of losing sleep after learning-shown by increased forgetting-appear to recover over time and are unaffected by more common forms of partial sleep restriction across several nights. The capacity to encode new memories is the most vulnerable to sleep loss, since long-term deficits have been observed after total and partial sleep deprivation, while retrieval mechanisms are relatively unaffected. The negative impact of sleep loss on memory has been explored extensively after a night of total sleep deprivation, but further research is needed on the consequences of partial sleep loss over many days so that impairments may be generalized to more common forms of sleep loss.

Trait-like characteristics of sleep EEG power spectra in adolescents across sleep opportunity manipulations

The electroencephalographic power spectra of non-rapid eye movement sleep in adults demonstrate trait-like consistency within participants across multiple nights, even when prior sleep deprivation is present. Here, we examined the extent to which this finding applies to adolescents who are habitually sleep restricted on school-days and sleep longer on weekends. We evaluated 78 adolescents across three sleep restriction groups who underwent different permutations of adequate sleep (9 hr time-in-bed), sleep restriction (5 hr time-in-bed), afternoon naps (1 hr afternoon) and recovery sleep (9 hr time-in-bed) that simulate behaviour on school-days and weekends. The control group comprised a further 22 adolescents who had 9 hr of sleep opportunity each night. Intra-class correlation coefficients showed moderate to almost perfect within-subject stability in electroencephalographic power spectra across multiple nights in both sleep restriction and control groups, even when changes to sleep macrostructure were observed. While nocturnal intra-class correlation metrics were lower in the low-frequency and spindle frequency bins in the sleep restriction compared with the control group, hierarchical clustering measures could still identify multi-night electroencephalographic spectra as originating from the same individual. The trait-like characteristics of electroencephalographic spectra from an adolescent remain identifiable despite the disruptive effects of multi-night sleep restriction to sleep architecture.

Schizotypal traits are associated with sleep spindles and rapid eye movement in adolescence

Research suggests an association between schizophrenia and a decrease in sleep spindle activity, as well as a change in sleep architecture. It is unknown how the continuum of psychotic symptoms relates to different features in the sleep electroencephalogram. We set out to examine how sleep architecture and stage 2 spindle activity are associated with schizotypy in a healthy adolescent population. The participants in our study (n = 176, 61% girls) came from a community-based cohort. Schizotypal traits were evaluated using the Schizotypal Personality Scale (STA) in early adolescence (mean age 12.3 years, SD = 0.5) and the participants underwent ambulatory overnight polysomnography at mean age 16.9 years (SD = 0.1). Sleep was scored in 30-s epochs into stages 1, 2, 3 and rapid eye movement (REM) sleep. Stage 2 spindles were detected using an automated algorithm. Spindle analyses from central and frontal derivations included spindle duration and density for slow (10-13 Hz) and fast (13-16 Hz) ranges. Covariates included sex and age. Those with the highest STA scores had a higher percentage of REM (B = 2.07 [95% CI, 0.17, 4.0]; p = .03) than those with the lowest scores. Those with the highest scores had shorter spindle duration, as derived from the frontal regions, and a slower oscillation range (B = -0.04 [95% CI, -0.07, -0.01]; p = .023) than those with the lowest scores. We conclude that high levels of schizotypy characteristics measured in early adolescence may be associated with distinguished features of sleep architecture, namely with spindle morphology and a higher proportion of REM sleep.

Daytime microsleeps during 7 days of sleep restriction followed by 13 days of sleep recovery in healthy young adults

We investigated the consequences of sleep restriction (SR) on maintenance of wakefulness capacities and diurnal sleepiness through microsleeps monitoring. 12 healthy males (20-36 years old) were sleep restricted (4 h per night) during 7 nights followed by 13 nights of recovery sleep. Participants completed Karolinska Sleepiness Scale (KSS) and Maintenance of Wakefulness Test (MWT) at baseline (B), during SR (SR1, SR4 and SR7) and during recovery (R3 and R13), while continuously recorded for EEG analysis. During SR, MWT latencies decreased (SR7: -24.4%), whereas the number, the cumulative duration of microsleeps and KSS scores increased. Recovery nights allowed MWT latencies, KSS scores and all sleep values to return to baseline levels, while a rebound in N3, N3% and REM% sleep stages occurred. During SR, the maintenance of N3 sleep duration seems not sufficient to reduce daytime sleepiness and MWT results did not reflect the sleepiness levels characterized by persistent sleep attacks.

Neurobehavioral Impact of Successive Cycles of Sleep Restriction With and Without Naps in Adolescents

Study Objectives:

To characterize adolescents’ neurobehavioral changes during two cycles of restricted and recovery sleep and to examine the effectiveness of afternoon naps in ameliorating neurobehavioral deficits associated with multiple nights of sleep restriction.

Methods:

Fifty-seven healthy adolescents (aged 15–19 years; 31 males) participated in a parallel group study. They underwent two cycles of sleep restriction (5-hr time in bed [TIB] for five and three nights in the first and the second cycles, respectively; 01:00–06:00) and recovery (9-hr TIB for two nights per cycle; 23:00–08:00) intended to simulate the weekday sleep loss and weekend attempt to “catch up” on sleep. Half of the participants received a 1-hr nap opportunity at 14:00 following each sleep-restricted night, while the other half stayed awake. Sustained attention, sleepiness, speed of processing, executive function, and mood were assessed 3 times each day.

Results:

Participants who were not allowed to nap showed progressive decline in sustained attention that did not return to baseline after two nights of recovery sleep. Exposure to the second period of sleep restriction increased the rate of vigilance deterioration. Similar patterns were found for other neurobehavioral measures. Napping attenuated but did not eliminate performance decline. These findings contrasted with the stable performance of adolescents, given 9-hr TIB each night in our recent study.

Conclusions:

Adolescents’ neurobehavioral functions may not adapt to successive cycles of sleep curtailment and recovery. In sleep-restricted adolescents, weekend “catch-up sleep,” even when combined with napping during weekdays, is inferior to receiving a 9-hr sleep opportunity each night.

Memory encoding is impaired after multiple nights of partial sleep restriction

Sleep is important for normative cognitive functioning. A single night of total sleep deprivation can reduce the capacity to encode new memories. However, it is unclear how sleep restriction during several consecutive nights affects memory encoding. To explore this, we employed a parallel-group design with 59 adolescents randomized into sleep-restricted (SR) and control groups. Both groups were afforded 9 h time in bed (TIB) for 2 baseline nights, followed by 5 consecutive nights of 5 h TIB for the SR group (n = 29) and 9 h TIB for the control group (n = 30). Participants then performed a picture-encoding task. Encoding ability was measured with a recognition test after 3 nights of 9 h TIB recovery sleep for both groups, allowing the assessment of encoding ability without the confounding effects of fatigue at retrieval. Memory was significantly worse in the sleep-restricted group (P = 0.001), and this impairment was not correlated with decline in vigilance. We conclude that memory-encoding deteriorates after several nights of partial sleep restriction, and this typical pattern of sleep negatively affects adolescents' ability to learn declarative information.

Neural Consequences of Chronic Short Sleep: Reversible or Lasting?

Approximately one-third of adolescents and adults in developed countries regularly experience insufficient sleep across the school and/or work week interspersed with weekend catch up sleep. This common practice of weekend recovery sleep reduces subjective sleepiness, yet recent studies demonstrate that one weekend of recovery sleep may not be sufficient in all persons to fully reverse all neurobehavioral impairments observed with chronic sleep loss, particularly vigilance. Moreover, recent studies in animal models demonstrate persistent injury to and loss of specific neuron types in response to chronic short sleep (CSS) with lasting effects on sleep/wake patterns. Here, we provide a comprehensive review of the effects of chronic sleep disruption on neurobehavioral performance and injury to neurons, astrocytes, microglia, and oligodendrocytes and discuss what is known and what is not yet established for reversibility of neural injury. Recent neurobehavioral findings in humans are integrated with animal model research examining long-term consequences of sleep loss on neurobehavioral performance, brain development, neurogenesis, neurodegeneration, and connectivity. While it is now clear that recovery of vigilance following short sleep requires longer than one weekend, less is known of the impact of CSS on cognitive function, mood, and brain health long term. From work performed in animal models, CSS in the young adult and short-term sleep loss in critical developmental windows can have lasting detrimental effects on neurobehavioral performance.

EEG Changes Accompanying Successive Cycles of Sleep Restriction With and Without Naps in Adolescents

Study objectives

To investigate the temporal evolution of sleep EEG changes in adolescents across two cycles of sleep restriction and recovery simulating an intense school week and to examine the effect of an afternoon nap on nocturnal sleep.

Methods

A parallel-group design, quasi-laboratory study was conducted in a student hostel. Fifty-seven adolescents (31 males, age = 15-19 years) were randomly assigned to nap or no nap groups. Participants underwent a 15-day protocol comprising two sleep restriction (5-hour time-in-bed [TIB]) and recovery (9-hour TIB) cycles. The nap group was also provided with a 1-hour nap opportunity at 14:00 following each sleep restriction night. Polysomnography recordings were obtained on nine nights and five nap episodes.

Results

Naps reduced homeostatic sleep pressure on sleep restriction nights as evidenced by longer N2 latency and reduced total sleep time (TST), sleep efficiency (SE), and slow wave energy. Sleep debt accumulated in both groups, evidenced by increased TST, greater SE, and reduced wake after sleep onset on recovery compared to baseline nights. Changes were greater in the no nap group. Recovery sleep after the first cycle of sleep restriction did not restore sleep architecture to baseline in either group. SE, rapid eye movement (REM), and non-REM sleep increased, and N2 latency was reduced in the second sleep restriction period.

Conclusions

Changes in sleep EEG induced by sleep restriction to 5-hour TIB for five nights were not eliminated after two nights of 9-hour recovery sleep. An afternoon nap helped but residual effects on the sleep EEG suggest that there is no substitute for adequate nocturnal sleep.

Sleep Restriction Impairs Vocabulary Learning when Adolescents Cram for Exams: The Need for Sleep Study

STUDY OBJECTIVES

The ability to recall facts is improved when learning takes place at spaced intervals, or when sleep follows shortly after learning. However, many students cram for exams and trade sleep for other activities. The aim of this study was to examine the interaction of study spacing and time in bed (TIB) for sleep on vocabulary learning in adolescents.

METHODS

In the Need for Sleep Study, which used a parallel-group design, 56 adolescents aged 15-19 years were randomly assigned to a week of either 5 h or 9 h of TIB for sleep each night as part of a 14-day protocol conducted at a boarding school. During the sleep manipulation period, participants studied 40 Graduate Record Examination (GRE)-type English words using digital flashcards. Word pairs were presented over 4 consecutive days (spaced items), or all at once during single study sessions (massed items), with total study time kept constant across conditions. Recall performance was examined 0 h, 24 h, and 120 h after all items were studied.

RESULTS

For all retention intervals examined, recall of massed items was impaired by a greater amount in adolescents exposed to sleep restriction. In contrast, cued recall performance on spaced items was similar between sleep groups.

CONCLUSIONS

Spaced learning conferred strong protection against the effects of sleep restriction on recall performance, whereas students who had insufficient sleep were more likely to forget items studied over short time intervals. These findings in adolescents demonstrate the importance of combining good study habits and good sleep habits to optimize learning outcomes.

Spontaneous eyelid closures link vigilance fluctuation with fMRI dynamic connectivity states

Fluctuations in resting-state functional connectivity occur but their behavioral significance remains unclear, largely because correlating behavioral state with dynamic functional connectivity states (DCS) engages probes that disrupt the very behavioral state we seek to observe. Observing spontaneous eyelid closures following sleep deprivation permits nonintrusive arousal monitoring. During periods of low arousal dominated by eyelid closures, sliding-window correlation analysis uncovered a DCS associated with reduced within-network functional connectivity of default mode and dorsal/ventral attention networks, as well as reduced anticorrelation between these networks. Conversely, during periods when participants' eyelids were wide open, a second DCS was associated with less decoupling between the visual network and higher-order cognitive networks that included dorsal/ventral attention and default mode networks. In subcortical structures, eyelid closures were associated with increased connectivity between the striatum and thalamus with the ventral attention network, and greater anticorrelation with the dorsal attention network. When applied to task-based fMRI data, these two DCS predicted interindividual differences in frequency of behavioral lapsing and intraindividual temporal fluctuations in response speed. These findings with participants who underwent a night of total sleep deprivation were replicated in an independent dataset involving partially sleep-deprived participants. Fluctuations in functional connectivity thus appear to be clearly associated with changes in arousal.