The effect of REM-sleep disruption on affective processing: A systematic review of human and animal experimental studies.

Evidence on the importance of rapid-eye-movement sleep (REMS) in processing emotions is accumulating. The focus of this systematic review is the outcomes of experimental REMS deprivation (REMSD), which is the most common method in animal models and human studies on REMSD. This review revealed that variations in the applied REMSD methods were substantial. Animal models used longer deprivation protocols compared with studies in humans, which mostly reported acute deprivation effects after one night. Studies on animal models showed that REMSD causes aggressive behavior, increased pain sensitivity, reduced sexual behavior, and compromised consolidation of fear memories. Animal models also revealed that REMSD during critical developmental periods elicits lasting consequences on affective-related behavior. The few human studies revealed increases in pain sensitivity and suggest stronger consolidation of emotional memories after REMSD. As pharmacological interventions (such as selective serotonin reuptake inhibitors [SSRIs]) may suppress REMS for long periods, there is a clear gap in knowledge regarding the effects and mechanisms of chronic REMS suppression in humans.

Does sleep promote adaptation to acute stress: An experimental study.

Objectives: Evidence of the impact of chronic stress on sleep is abundant, yet experimental sleep studies with a focus on acute stress are scarce and the results are mixed. Our study aimed to fill this gap by experimentally investigating the effects of pre-sleep social stress on sleep dynamics during the subsequent night, as measured with polysomnography (PSG). Methods: Thirty-four healthy individuals (65% females, Mage = 25.76 years SD = 3.35) underwent a stress-inducing (SC) or neutral control condition (CC) in virtual reality (VR). We used overnight EEG measurements to analyze the basic sleep parameters and power spectral density (PSD) across the sleep cycles, and measured heart rate and its variability (HRV), skin electrodermal activity (EDA), and salivary cortisol to capture physiological arousal during the VR task and the pre-sleep period. Results: Following acute stress (SC), the amount of slow-wave sleep (SWS) was higher and N2 sleep lower relative to CC, specifically in the first sleep cycle. In SC, PSD was elevated in the beta-low (16-24 Hz) and beta-high (25-35 Hz) frequency ranges during both stages N2 and SWS over the entire night. Conclusions: Sleep promoted adaptation to acute social stress by a longer duration of SWS in the subsequent sleep period, especially in early sleep. A similar homeostatic effect towards restorative sleep is well-evidenced in animal model stress studies but has not been previously reported in experimental human studies. Whether the high-frequency PSD activity during stages N2 and SWS also serves in the resolution of transient stress, remains open.

Temporal pathways between circadian rhythm, depression and anxiety in the transition from adolescence to early adulthood.

BACKGROUND: Sleep and circadian rhythm problems intertwine with affective disorders. Adolescents are particularly vulnerable to developing sleep and affective problems. Yet, the temporal pathways between circadian rhythm, depression and anxiety in the transition phase from adolescence to early adulthood are not fully understood. METHODS: 233 adolescents (76 % females) participated at two time points (T1 and T2) at an interval of 19-months (aged 16.8 and 18.4 years). We used The Beck Depression Inventory-II, Generalized Anxiety Disorder Assessment, GENEActiv actigraphy across 8 days (delayed sleep phase (DSP), sleep duration, midpoint, and regularity), and iButton 1922L thermologgers across 3 days (intrinsic circadian period length, amplitude, and mesor). RESULTS: A shorter sleep duration at T1 associated with an increase in affective problems at T2, and affective problems at T1 associated with an increase in sleep irregularity at T2. A longer circadian period at T1 associated with an increase in males' affective problems at T2. Moderate to severe depression and anxiety at T1 associated with a 2.69-fold risk (95 % CI 1.38-5.26, p = 0.004) and 2.11-fold risk (95 % CI 1.04-4.25, p = 0.038) of poor sleep quality at T2. Moderate to severe generalized anxiety associated with a 3.17-fold risk (95 % CI 1.35-7.41, p = 0.008) of DSP at T2. LIMITATIONS: The follow-up period is short. CONCLUSIONS: The results revealed bidirectional temporal links between sleep and affective problems. Novel observations include a heightened risk of future DSP following a current anxiety disorder and a heightened risk of affective problems following a longer circadian period measured from the 24-hour temperature variation in males.

Right-lateralized sleep spindles are associated with neutral over emotional bias in picture recognition: An overnight study.

Sleep is especially important for emotional memories, although the mechanisms for prioritizing emotional content are insufficiently known. As during waking, emotional processing during sleep may be hemispherically asymmetric; right-lateralized rapid-eye movement (REM) sleep theta (~4-7 Hz) is reportedly associated with emotional memory retention. No research exists on lateralized non-REM sleep oscillations. However, sleep spindles, especially when coupled with slow oscillations (SOs), facilitate off-line memory consolidation.Our primary goal was to examine how the lateralization (right-to-left contrast) of REM theta, sleep spindles, and SO-spindle coupling is associated with overnight recognition memory in a task consisting of neutral and emotionally aversive pictures. Thirty-two healthy adults encoded 150 target pictures before overnight sleep. The recognition of target pictures among foils (discriminability, d') was tested immediately, 12 hours, and 24 hours after encoding.Recognition discriminability between targets and foils was similar for neutral and emotional pictures in immediate and 12-h retrievals. After 24 hours, emotional pictures were less accurately discriminated (p < 0.001). Emotional difference at 24-h retrieval was associated with right-to-left contrast in frontal fast spindle density (p < 0.001). The lateralization of SO-spindle coupling was associated with higher neutral versus emotional difference across all retrievals (p = 0.004).Our findings contribute to a largely unstudied area in sleep-related memory research. Hemispheric asymmetry in non-REM sleep oscillations may contribute to how neutral versus emotional information is processed. This is presumably underlain by both mechanistic offline memory consolidation and a trait-like cognitive/affective bias that influences memory encoding and retrieval. Methodological choices and participants' affective traits are likely involved.

Endogenous circadian temperature rhythms relate to adolescents' daytime physical activity.

Circadian rhythms relate to multiple aspects of health and wellbeing, including physical activity patterns. Susceptible circadian regulation predisposes to circadian misalignment, poor sleep, sleep deprivation, increased sleepiness, and thereby sedentary behavior. Adolescents' circadian regulation is particularly vulnerable, and may lead to sedentary behavior. To investigate which factors associate strongest between physical activity (PA) and circadian behavior, we conducted multimodal circadian rhythm analyses. We investigate how individual characteristics of habitual circadian patterns associate with objectively measured PA. We studied 312 adolescents [70% females) (56% with delayed sleep phase (DSP)], mean age 16.9 years. Circadian period length, temperature mesor (estimated 24 h midline) and amplitude (difference between mesor and peak) were measured using distally attached thermologgers (ibutton 1922L, 3-day-measurement). We additionally utilized algorithm-formed clusters of circadian rhythmicity. Sleep duration, timing, DSP, and PA were measured using actigraphs (GeneActiv Original, 10-day-measurement). We found that continuous circadian period length was not associated with PA, but lower mesor and higher amplitude were consistently associated with higher levels of PA as indicated by mean Metabolic Equivalent (METmean) and moderate-to-vigorous PA (MVPA), even when controlling for sleep duration. Separate circadian clusters formed by an algorithm also reflected distinct patterns of PA accordingly. Late sleepers and those with DSP were less likely to engage in MVPA compared to non-DSP and had more sedentary behavior. Adolescents who engage in higher levels or high-intensity PA have better circadian regulation, as measured by different objective methods including distal temperature measurements as well as actigraphy-measured sleep-wake behavior.

Sleep and physical activity - the dynamics of bi-directional influences over a fortnight.

STUDY OBJECTIVES: The day-to-next day predictions between physical activity (PA) and sleep are not well known, although they are crucial for advancing public health by delivering valid sleep and physical activity recommendations. We used Big Data to examine cross-lagged time-series of sleep and PA over 14 days and nights. METHODS: Bi-directional cross-lagged autoregressive pathways over 153,154 days and nights from 12,638 Polar watch users aged 18-60 years (M = 40.1 SD = 10.1; 44.5% female) were analyzed with cross-lagged panel data modeling (RI-CPL). We tested the effects of moderate-to-vigorous physical activity (MVPA) vs. high intensity PA (vigorous, VPA) on sleep duration and quality, and vice versa. RESULTS: Within-subject results showed that more minutes spent in VPA the previous day was associated with shorter sleep duration the next night, whereas no effect was observed for MVPA. Longer sleep duration the previous night was associated with less MVPA but more VPA the next day. Neither MVPA nor VPA were associated with subsequent night's sleep quality, but better quality of sleep predicted more MVPA and VPA the next day. CONCLUSIONS: Sleep duration and PA are bi-directionally linked, but only for vigorous physical activity. More time spent in VPA shortens sleep the next night, yet longer sleep duration increases VPA the next day. The results imply that a 24-h framing for the interrelations of sleep and physical activity is not sufficient - the dynamics can even extend beyond, and are activated specifically for the links between sleep duration and vigorous activity. The results challenge the view that sleep quality can be improved by increasing the amount of PA. Yet, better sleep quality can result in more PA the next day.

Circadian Type Determines Working Ability: Poorer Working Ability in Evening-Types is Mediated by Insufficient Sleep in a Large Population-Based Sample of Working-Age Adults.

Background: Circadian phenotype has a crucial role in determining wellbeing and health prospective. Evening-types have higher risk for sleep and mental health problems, which is also reflected in work wellbeing. However, there are no population-based studies examining the association of working ability and circadian typology at different working-age-groups. Also, the role of predisposing factors, ie, sleep-related differences between circadian types, has not been studied in relation to working ability among circadian types in a population-based sample. Methods: In this population-based sample of 13,114 working-age Finnish adults from 18 to 64 years of age, we examined the associations between circadian type, exhaustion and working ability and the roles of sleep-wake rhythm misalignment and insufficient sleep on these associations in 10-years-wide age-groups. Circadian type was assessed with the widely-used single item for self-assessed morningness/eveningness from the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ). Results: Evening-types, especially definite evening-types, were more exhausted and had poorer working ability than morning-types. Higher exhaustion among evening-types was apparent in all working ages with a peak at ages 45 to 54 years. Poorer working ability in definite evening-types as compared to definite morning-types was found only at ages 35 to 54 years. Evening-types, especially definite-evening-types, had also more social jet lag and they reported more insufficient sleep than definite morning-types. More frequent insufficient sleep associated with poorer working ability and partly mediated the association between circadian type and working ability. Conclusion: Circadian phenotypes were found to differ in risk for exhaustion and in working ability, and this association was partly mediated by insufficient sleep. Our findings emphasize the importance to improve sleep especially among evening-types to ensure better work wellbeing.

Cross-Sectional and Longitudinal Associations Between Quality of Parent-Child Interaction and Language Ability in Preschool-Age Children With Developmental Language Disorder.

PURPOSE: This study explores whether the quality of parent-child interaction is associated with language abilities cross-sectionally and longitudinally up to preschool-age among children with developmental language disorder (DLD). METHOD: Participants were 97 monolingual children with DLD and their parents from the Helsinki Longitudinal SLI study, HelSLI (baseline, age in years;months, M = 4;3, SD = 0;10), of which 71 pairs were followed longitudinally (age in years;months, M = 6;6, SD = 0;5). Video recordings from three play sessions were scored for child, parent, and dyadic behavior using Erickson's sensitivity scale protocol and mutually responsive orientation at baseline. Children's expressive and receptive language and language reasoning ability were assessed at baseline, and expressive and receptive language were assessed at follow-up. RESULTS: At baseline, engaged child behavior, parent's supportive guidance, and fluent and attuned dyadic behavior were associated with better receptive language ability, and engaged child behavior and dyadic synchrony were positively associated with language reasoning ability in 3- to 6-year-olds. The child's positive engagement and fluent and attuned dyadic behavior at baseline were associated with better expressive and receptive language abilities at follow-up in 6- to 7-year-olds, respectively. CONCLUSIONS: Fluent and attuned dyadic behavior is associated with better receptive language ability in preschool-age children. Parent behavior alone was not associated with language ability. A connected and mutually attuned parent-child relationship could be a protective factor for language development for children with DLD.

Adolescent circadian patterns link with psychiatric problems: A multimodal approach.

Circadian rhythms orchestrate brain function and mental wellbeing. We compared circadian patterns derived from continuous measurements of body temperature, sleep actigraphy and self-reported circadian preference in relation to different psychiatric disorders. 342 adolescents (70% females) aged 17.4y underwent M.I.N.I. psychiatric interviews, wore Ibutton 1922L skin temperature loggers (n = 281; 3 days), completed one-week GeneActiv Original actigraphy measurements (n = 306) and responded to Morningness-Eveningness Questionnaire (MEQ; n = 330). We derived circadian period length and amplitude from the temperature loggers. Actigraphy measures included sleep duration, midpoint, efficiency, and irregularity as well as Delayed Sleep Phase (DSP) characteristics (bedtime after 1 a.m. 3 times/week). M.I.N.I. psychiatric interviews suggested that 36% of participants had one or more psychiatric problem, with 21% suffering from comorbidity. Severe depression was associated with longer circadian period (p = 0.002). Suicidality was associated with later midpoint (p = 0.007) and more irregular sleep (p = 0.007). Those with agoraphobia slept longer (p = 0.013). Manic episodes and psychotic disorders were associated with irregular sleep (p-values <0.02). DSP was related to suicidality (p = 0.026), panic disorder (p = 0.022), and greater comorbidity (p = 0.026). Preference for eveningness was similarly related to higher prevalence of Generalized Anxiety Disorder (p = 0.014), social anxiety (p = 0.03), agoraphobia (p = 0.026), panic disorder (p = 0.004), suicidality (p = 0.018), severe depression (p < 0.001), and comorbidity (p < 0.001). Deviations in circadian rhythms were widely associated with psychiatric problems, whereas sleep duration was not. Especially suicidality linked with several markers of circadian disruption: later sleep midpoint, irregular sleep, and DSP characteristics. Longer circadian period length was associated with severe depression.

The association between overnight recognition accuracy and slow oscillation-spindle coupling is moderated by BDNF Val66Met.

During sleep, memories are consolidated via oscillatory events that occur in temporal and phasic synchrony. Several studies show that sleep spindles peaking close to the depolarized positive peaks of slow oscillations (SO) associate with better retention of memories. The exact timing of this synchrony presumably depends on the properties of the related neural network that, in turn, is affected by certain genetic variants associated with brain development and function. Brain-derived neurotrophic factor (BDNF) Val66Met and Catechol-O-methyltransferase (COMT) Val158Met are repeatedly reported to implicate the structure and function of prefrontal and hippocampal areas as well as molecular events promoting synaptic plasticity. In this study, we examined with a community-based sample of 153 adolescents (~17 years) whether these variants (1) affected the coupling properties between frontal SOs and spindles and (2) moderated the association between SO-spindle coupling and overnight recognition accuracy. We found SO-upstate-coupled fast (> 13 Hz) sleep spindles to associate with better recognition in the whole sample. Additionally, Val66Met moderated this association such that SO-spindle coupling was predictive of memory outcome only in those homozygous to ValBDNF alleles but not in MetBDNF carriers. Memory outcome was not associated with the SO-coupling properties of slow spindles nor affected by the interaction between Val158Met and coupling measures. Finally, in the whole sample we found that SO-upstate-coupled fast spindles were more strongly associated with the recognition of positive, relative to neutral, pictures. In conclusion, precise coupling of SOs and fast spindles associates with overnight recognition accuracy and this association is moderated by BDNF Val66Met.

Long-term cumulative light exposure from the natural environment and sleep: A cohort study.

We analysed (A) the association of short-term as well as long-term cumulative exposure to natural light, and (B) the association of detailed temporal patterns of natural light exposure history with three indicators of sleep: sleep duration, sleep problems, and diurnal preference. Data (N = 1,962; 55% women; mean age 41.4 years) were from the prospective Young Finns Study, which we linked to daily meteorological data on each participant's neighbourhood natural light exposure using residential postal codes. Sleep outcomes were self-reported in 2011. We first examined associations of the sleep outcomes with cumulative light exposure of 5-year, 2-year, 1-year, and 2-month periods prior to the sleep assessment using linear and Poisson regression models adjusting for potential confounders. We then used a data-driven time series approach to detect clusters of participants with different light exposure histories and assessed the associations of these clusters with the sleep outcomes using linear and Poisson regression analyses. A greater cumulative light exposure over ≥1 year was associated with a shorter sleep duration (ß = -0.10, 95% confidence interval [CI] -0.15 to -0.04), more sleep problems (incident rate ratio [IRR] 1.04, 95% CI 1.0-1.07) and diurnal preference towards eveningness (ß = -0.09, 95% CI -0.14 to -0.03). The data-driven exposure pattern of "slowly increasing" light exposure was associated with fewer overall sleep problems (IRR 0.93, 95% CI 0.88-0.98) compared to a "recently declining" light exposure group representing the "average-exposure" group. These findings suggest that living in an area with relatively more intense light exposure for a longer period of time influences sleep.

Self-Conscious Affect Is Modulated by Rapid Eye Movement Sleep but Not by Targeted Memory Reactivation-A Pilot Study.

The neurophysiological properties of rapid eye movement sleep (REMS) are believed to tune down stressor-related emotional responses. While prior experimental findings are controversial, evidence suggests that affective habituation is hindered if REMS is fragmented. To elucidate the topic, we evoked self-conscious negative affect in the participants (N = 32) by exposing them to their own out-of-tune singing in the evening. Affective response to the stressor was measured with skin conductance response and subjectively reported embarrassment. To address possible inter-individual variance toward the stressor, we measured the shame-proneness of participants with an established questionnaire. The stressor was paired with a sound cue to pilot a targeted memory reactivation (TMR) protocol during the subsequent night's sleep. The sample was divided into three conditions: control (no TMR), TMR during slow-wave sleep, and TMR during REMS. We found that pre- to post-sleep change in affective response was not influenced by TMR. However, REMS percentage was associated negatively with overnight skin conductance response habituation, especially in those individuals whose REMS was fragmented. Moreover, shame-proneness interacted with REM fragmentation such that the higher the shame-proneness, the more the affective habituation was dependent on non-fragmented REMS. In summary, the potential of REMS in affective processing may depend on the quality of REMS as well as on individual vulnerability toward the stressor type.

Is It Time We Stop Discouraging Evening Physical Activity? New Real-World Evidence From 150,000 Nights.

Professional and colloquial sleep hygiene guidelines advise against evening physical activity, despite meta-analyses of laboratory studies concluding that evening exercise does not impair sleep. This study is the first to investigate the association between objectively measured evening physical activity and sleep within a real-world big-data sample. A total of 153,154 nights from 12,638 individuals aged 18-60 years (M = 40.1 SD = 10.1; 44.5% female) were analyzed. Nighttime sleep and minutes of physical activity were assessed using Polar wearable devices for 14 consecutive days. Thirty minutes or more of moderate-to-near maximal physical activity during the 3 h before sleep onset were recorded in 12.4% of evenings, and were more frequent on weekdays than weekends (13.3 vs. 10.2% respectively, p < 0.001). Linear mixed modeling revealed that sleep efficiency was not significantly associated with evening physical activity, and that sleep duration was 3.4 min longer on average on nights following evenings in which participants engaged in 30 min or more of moderate-intense physical activity. Effects were found for sleep timing metrics, as evening physical activity was linked with earlier sleep onset and offset times (-13.7 and -9.3 min, respectively). Overall, these effects were greater- but still very small- on weekdays compared to weekends. The present study provides further evidence for the lack of meaningful links between sleep duration or quality and physical activity in the hours preceding sleep. Taken together with recent meta-analytic findings, these findings suggest that changes in public health recommendations are warranted regarding evening physical activity and its relation to sleep.

The Overnight Retention of Novel Metaphors Associates With Slow Oscillation-Spindle Coupling but Not With Respiratory Phase at Encoding.

Accumulating evidence emphasizes the relevance of oscillatory synchrony in memory consolidation during sleep. Sleep spindles promote memory retention, especially when occurring in the depolarized upstate of slow oscillation (SO). A less studied topic is the inter-spindle synchrony, i.e. the temporal overlap and phasic coherence between spindles perceived in different electroencephalography channels. In this study, we examined how synchrony between SOs and spindles, as well as between simultaneous spindles, is associated with the retention of novel verbal metaphors. Moreover, we combined the encoding of the metaphors with respiratory phase (inhalation/exhalation) with the aim of modulating the strength of memorized items, as previous studies have shown that inhalation entrains neural activity, thereby benefiting memory in a waking condition. In the current study, 27 young adults underwent a two-night mixed-design study with a 12-h delayed memory task during both sleep and waking conditions. As expected, we found better retention over the delay containing sleep, and this outcome was strongly associated with the timing of SO-spindle coupling. However, no associations were observed regarding inter-spindle synchrony or respiratory phase. These findings contribute to a better understanding of the importance of SO-spindle coupling for memory. In contrast, the observed lack of association with inter-spindle synchrony may emphasize the local nature of spindle-related plasticity.

Data-driven modelling approach to circadian temperature rhythm profiles in free-living conditions.

The individual variation in the circadian rhythms at the physiological level is not well understood. Albeit self-reported circadian preference profiles have been consolidated, their premises are grounded on human experience, not on physiology. We used data-driven, unsupervised time series modelling to characterize distinct profiles of the circadian rhythm measured from skin surface temperature in free-living conditions. We demonstrate the existence of three distinct clusters of individuals which differed in their circadian temperature profiles. The cluster with the highest temperature amplitude and the lowest midline estimating statistic of rhythm, or rhythm-adjusted mean, had the most regular and early-timed sleep-wake rhythm, and was the least probable for those with a concurrent delayed sleep phase, or eveningness chronotype. While the clusters associated with the observed sleep and circadian preference patterns, the entirely unsupervised modelling of physiological data provides a novel basis for modelling and understanding the human circadian functions in free-living conditions.

Genetic variants for morningness in relation to habitual sleep-wake behavior and diurnal preference in a population-based sample of 17,243 adults.

OBJECTIVE: Associations of eveningness with health hazards benefit from analyzing to what extent the polygenic score for morningness correlates with the assessments of the behavioral trait of morningness-eveningness and chronotype. METHODS: With a population-based sample of 17,243 Finnish adults, aged 25-74 years, this study examines the associations of four feasible assessment methods of chronotype, a) biological the genetic liability based on the polygenic score for morningness (PGSmorn), b) the widely-used single item for self-assessed morningness/eveningness (MEQi19) of the original Morningness-Eveningness Questionnaire (MEQ), c) the behavioral trait of morningness-eveningness as assessed with the score on the shortened version (sMEQ) of the original MEQ, and d) the phase of entrainment as assessed with the habitual midpoint of sleep based on the self-reported sleep-wake schedule during weekend (Sleepmid-wknd) as well as the sleep debt corrected midpoint of sleep (Sleepmid-corr). RESULTS: All self-report measures correlated with each other, but very weakly with the PGSmorn, which explained 1-2% of the variation in diurnal preference or habitual sleep-wake schedule. The influence of age was greater on Sleepmid-wknd and Sleepmid-corr than on the sMEQ or MEQi19, indicating that the diurnal preference might be a more stable indicator for morningness-eveningness than the sleep-wake schedule. Analyses of the discrepancies between sMEQ and MEQi19 indicated that eveningness can be over-estimated when relying on only the single-item self-assessment. CONCLUSIONS: The current polygenic score for morningness explains only a small proportion of the variation in diurnal preference or habitual sleep-wake schedule. The molecular genetic basis for morningness-eveningness needs further elucidation.

Heart Rate Variability and Firstbeat Method for Detecting Sleep Stages in Healthy Young Adults: Feasibility Study.

BACKGROUND: Polysomnography (PSG) is considered the only reliable way to distinguish between different sleep stages. Wearable devices provide objective markers of sleep; however, these devices often rely only on accelerometer data, which do not enable reliable sleep stage detection. The alteration between sleep stages correlates with changes in physiological measures such as heart rate variability (HRV). Utilizing HRV measures may thus increase accuracy in wearable algorithms. OBJECTIVE: We examined the validity of the Firstbeat sleep analysis method, which is based on HRV and accelerometer measurements. The Firstbeat method was compared against PSG in a sample of healthy adults. Our aim was to evaluate how well Firstbeat distinguishes sleep stages, and which stages are most accurately detected with this method. METHODS: Twenty healthy adults (mean age 24.5 years, SD 3.5, range 20-37 years; 50% women) wore a Firstbeat Bodyguard 2 measurement device and a Geneactiv actigraph, along with taking ambulatory SomnoMedics PSG measurements for two consecutive nights, resulting in 40 nights of sleep comparisons. We compared the measures of sleep onset, wake, combined stage 1 and stage 2 (light sleep), stage 3 (slow wave sleep), and rapid eye movement (REM) sleep between Firstbeat and PSG. We calculated the sensitivity, specificity, and accuracy from the 30-second epoch-by-epoch data. RESULTS: In detecting wake, Firstbeat yielded good specificity (0.77), and excellent sensitivity (0.95) and accuracy (0.93) against PSG. Light sleep was detected with 0.69 specificity, 0.67 sensitivity, and 0.69 accuracy. Slow wave sleep was detected with 0.91 specificity, 0.72 sensitivity, and 0.87 accuracy. REM sleep was detected with 0.92 specificity, 0.60 sensitivity, and 0.84 accuracy. There were two measures that differed significantly between Firstbeat and PSG: Firstbeat underestimated REM sleep (mean 18 minutes, P=.03) and overestimated wake time (mean 14 minutes, P<.001). CONCLUSIONS: This study supports utilizing HRV alongside an accelerometer as a means for distinguishing sleep from wake and for identifying sleep stages. The Firstbeat method was able to detect light sleep and slow wave sleep with no statistically significant difference to PSG. Firstbeat underestimated REM sleep and overestimated wake time. This study suggests that Firstbeat is a feasible method with sufficient validity to measure nocturnal sleep stage variation.

Presleep physiological stress is associated with a higher cortical arousal in sleep and more consolidated REM sleep.

How sleep regulates physiological stress in healthy individuals is not well understood. We explored the associations between naturally occurring pre-sleep physiological arousal and EEG power spectral density together with rapid eye movement sleep (REMS) continuity. One hundred and fifty-four individuals (mean age 16.9, SD 0.1 years) collected five samples of saliva between the evening (mean time 18:20) and bedtime (mean 23:00) by using swabs, and underwent an overnight in-home polysomnography. We calculated spectral density for REMS and non-rapid eye movement sleep (non-REMS), and the number and duration of REMS arousals (<15 s) during sleep. An observational design allowed for measurement of natural variation in physiological and sleep arousal. Increasing cortisol levels toward bedtime were associated with higher EEG power spectral density at all frequency ranges in frontal locations, the highest association being for the beta1 frequency band. In central locations, the associations were pronounced for beta1 and beta2 bands. Higher overall cortisol levels in the evening were associated with less fragmented REMS. Presleep arousal was not associated with sleep staging. Physiological arousal toward bedtime was associated with EEG power spectral density values during sleep specifically at high EEG frequencies. This may represent a compensatory mechanism that serves as an adaptation to stress, since the REMS was more continuous along a higher physiological arousal level in the evening. Although causality cannot be inferred, a design with nonmanipulated physiological stress followed by naturally timed sleep at home provides new insights into stress regulation homeostasis.

Is moderate depression associated with sleep stage architecture in adolescence? Testing the stage type associations using network and transition probability approaches.

BACKGROUND: Depression even at the subclinical level is often accompanied by sleep disturbances, but little is known about the dynamics of the sleep stages in relation to depressive symptoms. We examined whether the amount, associations, and transition probabilities of various sleep stages were associated with depressive symptoms in a community sample of adolescents. METHODS: The participants (N = 172, 59% girls, mean age 16.9 years) underwent overnight polysomnography and provided data on depressive symptoms (Beck Depression Inventory II). The association between depression status and total duration of each stage type was analyzed using ANOVA and survival analyses. The associations between the number of different sleep stage types were analyzed using graphical Gaussian models, mixed graphical models, and relative importance networks. A Markov chain algorithm was used to estimate the transition probabilities between each state and these probabilities were further compared between depression status groups. RESULTS: The associations between N1 and N3 were significantly stronger in both directions of the association (p-values for interactions 0.012 and 0.006) in those with more depressive symptoms. Similarly, a stronger association was observed from N1 to wake stage in those with more depressive symptoms (p-value for interaction 0.002). In those with more depressive symptoms, it was more likely to transition from N2 to N3 and from REM to N2 compared to others. CONCLUSIONS: These findings indicate that changes in sleep architecture are not limited to clinical depression and that the transitional dynamics of sleep stages are an important marker of subclinical depression.

The association between sleep-wake ratio and overnight picture recognition is moderated by BDNF genotype.

A wealth of studies supports the role of sleep in memory performance. Experimentally controlled studies indicate that prolonged wake after memory encoding is detrimental for memory outcome whereas sleep protects from wake-time interference and promotes memory consolidation. We examined how the natural distribution of wake and sleep between encoding and retrieval associated with overnight picture recognition accuracy among 161 adolescents following their typical sleep schedule with an in-home polysomnography. The memorized pictures varied in their level of arousal (calm to exciting) and valence (negative to positive). Suspecting genotypic influence on the sensitivity for sleep/wake dynamics, we also assessed if these associations were affected by known gene polymorphisms involved in neural plasticity and sleep homeostasis: brain-derived neurotrophic factor (BDNF) Val66Met and Catechol-O-methyltransferase (COMT) Val158Met. In the whole sample, overnight recognition accuracy was associated with the levels of arousal and valence of the pictures, but not with sleep percentage (i.e. the percentage of time spent asleep between memory encoding and retrieval). While the allelic status of BDNF or COMT did not have any main effect on recognition accuracy, a significant moderation by BDNF Val66Met was found (p = .004): the subgroup homozygous for valine allele showed positive association between sleep percentage and recognition accuracy. This was underlain by detrimental influence of wake, rather than by any memory benefit of sleep. Our results complement the mounting evidence that the relation between sleep and memory performance is moderated by BDNF Val66Met. Further studies are needed to clarify the specific mechanisms.