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1.  Dissonance Between Parent-Selected Bedtimes and Young Children's Circadian Physiology Influences Nighttime Settling Difficulties 
Nighttime settling difficulties (i.e., bedtime resistance, sleep-onset delay) occur in about 25% of young children and are associated with attentional, behavioral, and emotional problems. We examined whether the timing of internal (endogenous) circadian melatonin phase (i.e., dim light melatonin onset; DLMO) and its relationship with parent-selected bedtimes were related to nighttime settling behaviors. Fourteen regularly napping preschoolers (8 females; 30–36 months) participated in a 6-day protocol (parent-report of nighttime settling, actigraphic assessment of sleep onset latency, evening salivary DLMO). Average DLMO clock time was 07:40 p.m. ± 00:48 minutes, occurring 29 minutes ± 32 minutes prior to bedtime (lights-out). Children with later DLMOs had longer sleep-onset latencies (r = .62) and poorer success in falling asleep (r = –.59). Children whose bedtimes were closer to their DLMO had longer sleep-onset latencies (r = .72) and increased bedtime resistance (r = –.54). We conclude that dissonance between parent-selected bedtimes and children's circadian physiology may contribute to the development of nighttime settling difficulties in early childhood.
doi:10.1111/mbe.12032
PMCID: PMC3925339  PMID: 24535929
2.  Circadian Phase and Its Relationship to Nighttime Sleep in Toddlers 
Journal of biological rhythms  2013;28(5):322-331.
Circadian phase and its relation to sleep are increasingly recognized as fundamental factors influencing human physiology and behavior. Dim light melatonin onset (DLMO) is a reliable marker of the timing of the circadian clock, which has been used in experimental, clinical, and descriptive studies in the past few decades. Although DLMO and its relationship to sleep have been well documented in school-aged children, adolescents, and adults, very little is known about these processes in early childhood. The purpose of this study was 1) to describe circadian phase and phase angles of entrainment in toddlers and 2) to examine associations between DLMO and actigraphic measures of children's nighttime sleep. Participants were 45 healthy toddlers aged 30 to 36 months (33.5 ± 2.2 months; 21 females). After sleeping on a parent-selected schedule for 5 days (assessed with actigraphy and diaries), children participated in an in-home DLMO assessment involving the collection of saliva samples every 30 minutes for 6 hours. Average bedtime was 2015 ± 0036 h, average sleep onset time was 2043 ± 0043 h, average midsleep time was 0143 ± 0038 h, and average wake time was 0644 ± 0042 h. Average DLMO was 1929 ± 0051 h, with a 3.5-hour range. DLMO was normally distributed; however, the distribution of the bedtime, sleep onset time, and midsleep phase angles of entrainment were skewed. On average, DLMO occurred 47.8 ± 47.6 minutes (median = 39.4 minutes) before bedtime, 74.6 ± 48.0 minutes (median = 65.4 minutes) before sleep onset time, 6.2 ± 0.7 hours (median = 6.1 hours) before midsleep time, and 11.3 ± 0.7 hours before wake time. Toddlers with later DLMOs had later bedtimes (r = 0.46), sleep onset times (r = 0.51), midsleep times (r = 0.66), and wake times (r = 0.65) (all p < 0.001). Interindividual differences in toddlers’ circadian phase are large and associated with their sleep timing. The early DLMOs of toddlers indicate a maturational delay in the circadian timing system between early childhood and adolescence. These findings are a first step in describing the fundamental properties of the circadian system in toddlers and have important implications for understanding the emergence of sleep problems and the consequences of circadian misalignment in early childhood.
doi:10.1177/0748730413506543
PMCID: PMC3925345  PMID: 24132058
circadian phase; melatonin; DLMO; sleep; phase angle of entrainment; early childhood; toddlers; children
3.  Acute Sleep Restriction Effects on Emotion Responses in 30- to 36-Month-Old Children 
Journal of Sleep Research  2011;21(3):235-246.
SUMMARY
Early childhood is a period of dramatic change in sleep and emotion processing, as well as a time when disturbance in both domains are first detected. Although sleep is recognized as central in emotion processing and psychopathology, the great majority of experimental data have been collected in adults. We examined the effects of acute sleep restriction (nap deprivation) on toddlers’ emotion expression. Ten healthy children (7 females; 30–36 months) followed a strict sleep schedule (≥12.5 hrs time in bed/24 hrs) for 5 days before each of two randomly-assigned afternoon emotion assessments following Nap and No-Nap conditions (resulting in an 11-day protocol). Children viewed emotion-eliciting pictures (5 positive, 3 neutral, 3 negative) and completed puzzles (1 solvable, 1 unsolvable). Children’s faces were video-recorded, and emotion displays were coded. When sleep restricted, children displayed less confusion in response to neutral pictures, more negativity to neutral and negative pictures, and less positivity to positive pictures. Sleep restriction also resulted in a 34% reduction in positive emotion responses (solvable puzzle), as well as a 31% increase in negative emotion responses and a 39% decrease in confused responses (unsolvable puzzle). These findings suggest sleep is a key factor in how young children respond to their world. When sleep restricted, toddlers are neither able to take full advantage of positive experiences nor are they as adaptive in challenging contexts. If insufficient sleep consistently “taxes” young children’s emotion responses, they may not manage emotion regulation challenges effectively, potentially placing them at risk for future emotional/behavioral problems.
doi:10.1111/j.1365-2869.2011.00962.x
PMCID: PMC3258474  PMID: 21988087
Sleep Restriction; Napping; Emotion; Facial Coding; Early Childhood; Toddlers
4.  The Cortisol Awakening Response (CAR) in 2- to 4-Year Old Children: Effects of Acute Nighttime Sleep Restriction, Wake Time, and Daytime Napping 
Developmental Psychobiology  2011;54(4):412-422.
The cortisol awakening response (CAR) is presumed critically important for healthy adaptation. The current literature, however, is hampered by systematic measurement difficulties relative to awakening, especially with young children. While reports suggest the CAR is smaller in children than adults, well-controlled research in early childhood is scarce. We examined whether robust CARs exist in 2- to 4-year-old children and if sleep restriction, wake timing, and napping influence the CAR (n=7). During a 25-day in-home protocol, researchers collected four salivary cortisol samples (0, 15, 30, 45 min post-wake) following five polysomnographic sleep recordings on non-consecutive days after 4 hrs (morning nap), 7 hrs (afternoon nap), 10 hrs (evening nap), 13 hrs (baseline night), and 16 hrs (sleep restriction night) of wakefulness (20 samples/child). The CAR was robust after nighttime sleep, diminished after sleep restriction, and smaller but distinct after morning and afternoon (not evening) naps. Cortisol remained elevated 45 min after morning and afternoon naps.
doi:10.1002/dev.20599
PMCID: PMC3249011  PMID: 21953381
CAR; Cortisol; Children; Sleep; Polysomnography
5.  Poorer sleep quality is associated with lower emotion-regulation ability in a laboratory paradigm 
Cognition & emotion  2012;27(3):567-576.
Theoretical models suggest a positive relationship between sleep quality and individuals' ability to regulate emotion. However, few studies have empirically tested this hypothesized link using standardized laboratory measures of emotion-regulation ability. The present research examined the relationship between sleep quality and the ability to implement a type of emotion regulation that has particularly important implications for psychological health: cognitive reappraisal (cognitively reframing an emotional event so as to dampen its impact). To do so, 156 participants (86 male) reported on their past week's sleep quality. Their ability to implement cognitive reappraisal (CRA) was then measured with a standardized laboratory challenge. Participants with poorer self-reported sleep quality exhibited lower CRA, even after controlling for fourteen potential key confounds (e.g., age, negative affect, mood disorder symptoms, stress). This finding is consistent with the idea that poorer sleep quality may impair individuals' ability to engage in the crucial task of regulating negative emotions.
doi:10.1080/02699931.2012.727783
PMCID: PMC3931554  PMID: 23025547
Sleep quality; emotion-regulation ability; cognitive reappraisal
6.  The Relationship Between Reported Sleep Quality and Sleep Hygiene in Italian and American Adolescents 
Pediatrics  2005;115(1 0):257-265.
Objective
The purpose of the study was to examine the relationship between self-reported sleep quality and sleep hygiene in Italian and American adolescents and to assess whether sleep-hygiene practices mediate the relationship between culture and sleep quality.
Methods
Two nonprobability samples were collected from public schools in Rome, Italy, and Hattiesburg, Mississippi. Students completed the following self-report measures: Adolescent Sleep-Wake Scale, Adolescent Sleep Hygiene Scale, Pubertal Developmental Scale, and Morningness/Eveningness Scale.
Results
The final sample included 776 Italian and 572 American adolescents 12 to 17 years old. Italian adolescents reported much better sleep hygiene and substantially better sleep quality than American adolescents. A moderate-to-strong linear relationship was found between sleep hygiene and sleep quality in both samples. Separate hierarchical multiple regression analyses were performed on both samples. Demographic and individual characteristics explained a significant proportion of the variance in sleep quality (Italians: 18%; Americans: 25%), and the addition of sleep-hygiene domains explained significantly more variance in sleep quality (Italians: 17%; Americans: 16%). A final hierarchical multiple regression analysis with both samples combined showed that culture (Italy versus United States) only explained 0.8% of the variance in sleep quality after controlling for sleep hygiene and all other variables.
Conclusions
Cross-cultural differences in sleep quality, for the most part, were due to differences in sleep-hygiene practices. Sleep hygiene is an important predictor of sleep quality in Italian and American adolescents, thus supporting the implementation and evaluation of educational programs on good sleep-hygiene practices.
doi:10.1542/peds.2004-0815H
PMCID: PMC3928632  PMID: 15866860
Pediatrics; adolescence; sleep quality; sleep hygiene; cultural differences
7.  Development of Brain EEG Connectivity across Early Childhood: Does Sleep Play a Role? 
Brain sciences  2013;3(4):1445-1460.
Sleep has beneficial effects on brain function and learning, which are reflected in plastic changes in the cortex. Early childhood is a time of rapid maturation in fundamental skills—e.g., language, cognitive control, working memory—that are predictive of future functioning. Little is currently known about the interactions between sleep and brain maturation during this developmental period. We propose coherent electroencephalogram (EEG) activity during sleep may provide unique insight into maturational processes of functional brain connectivity. Longitudinal sleep EEG assessments were performed in eight healthy subjects at ages 2, 3 and 5 years. Sleep EEG coherence increased across development in a region- and frequency-specific manner. Moreover, although connectivity primarily decreased intra-hemispherically across a night of sleep, an inter-hemispheric overnight increase occurred in the frequency range of slow waves (0.8–2 Hz), theta (4.8–7.8 Hz) and sleep spindles (10–14 Hz), with connectivity changes of up to 20% across a night of sleep. These findings indicate sleep EEG coherence reflects processes of brain maturation—i.e., programmed unfolding of neuronal networks—and moreover, sleep-related alterations of brain connectivity during the sensitive maturational window of early childhood.
doi:10.3390/brainsci3041445
PMCID: PMC3925344  PMID: 24535935
sleep EEG; coherence; development; maturation; children; early childhood
8.  Sleep Hygiene and Sleep Quality in Italian and American Adolescents 
This study investigated cross-cultural differences in adolescent sleep hygiene and sleep quality. Participants were 1348 students (655 males; 693 females) aged 12–17 years from public school systems in Rome, Italy (n = 776) and Southern Mississippi (n = 572). Participants completed the Adolescent Sleep-Wake Scale and the Adolescent Sleep Hygiene Scale. Reported sleep hygiene and sleep quality were significantly better for Italian than American adolescents. A moderate linear relationship was observed between sleep hygiene and sleep quality in both samples (Italians: R = .40; Americans: R = .46). Separate hierarchical multiple regression analyses showed that sleep hygiene accounted for significant variance in sleep quality, even after controlling for demographic and health variables (Italians: R2 = .38; Americans: R2 = .44). The results of this study suggest that there are cultural differences in sleep quality and sleep hygiene practices, and that sleep hygiene practices are importantly related to adolescent sleep quality.
doi:10.1196/annals.1308.044
PMCID: PMC2981826  PMID: 15251909
adolescence; sleep hygiene; sleep quality
9.  Development of Brain EEG Connectivity across Early Childhood: Does Sleep Play a Role? 
Brain Sciences  2013;3(4):1445-1460.
Sleep has beneficial effects on brain function and learning, which are reflected in plastic changes in the cortex. Early childhood is a time of rapid maturation in fundamental skills—e.g., language, cognitive control, working memory—that are predictive of future functioning. Little is currently known about the interactions between sleep and brain maturation during this developmental period. We propose coherent electroencephalogram (EEG) activity during sleep may provide unique insight into maturational processes of functional brain connectivity. Longitudinal sleep EEG assessments were performed in eight healthy subjects at ages 2, 3 and 5 years. Sleep EEG coherence increased across development in a region- and frequency-specific manner. Moreover, although connectivity primarily decreased intra-hemispherically across a night of sleep, an inter-hemispheric overnight increase occurred in the frequency range of slow waves (0.8–2 Hz), theta (4.8–7.8 Hz) and sleep spindles (10–14 Hz), with connectivity changes of up to 20% across a night of sleep. These findings indicate sleep EEG coherence reflects processes of brain maturation—i.e., programmed unfolding of neuronal networks—and moreover, sleep-related alterations of brain connectivity during the sensitive maturational window of early childhood.
doi:10.3390/brainsci3041445
PMCID: PMC3925344  PMID: 24535935
sleep EEG; coherence; development; maturation; children; early childhood
10.  A Longitudinal Study of Preschoolers' Language-Based Bedtime Routines, Sleep Duration, and Wellbeing 
Objective
To investigate the associations of caregiver-reported use of language-based bedtime routines among preschoolers at age 3 with children's nighttime sleep duration, and cognitive, behavioral and health outcomes at age 5. Further, to identify if parental or household characteristics help explain these associations.
Patients and Methods
We use data on 4,274 children from birth to age 5, drawn from the Fragile Families and Child Wellbeing Study (FFCW), a longitudinal birth cohort study of at-risk children born between 1998 and 2000 in 20 US cities. We use ordinary least squares (for continuous outcomes) and logistic regressions (for dichotomous outcomes) to estimate associations of language-based bedtime routines at age 3 with sleep duration, and cognitive, behavioral and health outcomes at age 5, net of a host of child and family background characteristics.
Results
After adjustment for child and family characteristics, we observed a positive association between language-based bedtime routines and both nighttime sleep duration and verbal test scores. Language-based bedtime routines were also inversely associated with behavior problems (anxious, withdrawn, and aggressive behaviors) and positively associated with better general health, yet adjustment for family background characteristics attenuated these associations. No associations were found between language-based bedtime routines and obesity. Results were confirmed using propensity score matching.
Conclusions
This research suggests regular use of language-based bedtime routines including singing, reading, and/or story-telling at bedtime may have a lasting positive benefit for children's sleep duration and cognitive development; we find little evidence of such a benefit for child behavior or health.
doi:10.1037/a0023564
PMCID: PMC3134391  PMID: 21517173
Bedtime Routines; Preschoolers; Cognitive Development; Behavioral Outcomes; Health Outcomes
11.  Circadian and wakefulness-sleep modulation of cognition in humans 
Cognitive and affective processes vary over the course of the 24 h day. Time of day dependent changes in human cognition are modulated by an internal circadian timekeeping system with a near-24 h period. The human circadian timekeeping system interacts with sleep-wakefulness regulatory processes to modulate brain arousal, neurocognitive and affective function. Brain arousal is regulated by ascending brain stem, basal forebrain (BF) and hypothalamic arousal systems and inhibition or disruption of these systems reduces brain arousal, impairs cognition, and promotes sleep. The internal circadian timekeeping system modulates cognition and affective function by projections from the master circadian clock, located in the hypothalamic suprachiasmatic nuclei (SCN), to arousal and sleep systems and via clock gene oscillations in brain tissues. Understanding the basic principles of circadian and wakefulness-sleep physiology can help to recognize how the circadian system modulates human cognition and influences learning, memory and emotion. Developmental changes in sleep and circadian processes and circadian misalignment in circadian rhythm sleep disorders have important implications for learning, memory and emotion. Overall, when wakefulness occurs at appropriate internal biological times, circadian clockwork benefits human cognitive and emotion function throughout the lifespan. Yet, when wakefulness occurs at inappropriate biological times because of environmental pressures (e.g., early school start times, long work hours that include work at night, shift work, jet lag) or because of circadian rhythm sleep disorders, the resulting misalignment between circadian and wakefulness-sleep physiology leads to impaired cognitive performance, learning, emotion, and safety.
doi:10.3389/fnmol.2012.00050
PMCID: PMC3328852  PMID: 22529774
circadian phase; sleep homeostasis; performance; forced desynchrony; circadian sleep disorders
12.  ASSESSMENT OF CHRONOTYPE IN FOUR- TO ELEVEN-YEAR-OLD CHILDREN: RELIABILITY AND VALIDITY OF THE CHILDREN’S CHRONOTYPE QUESTIONNAIRE (CCTQ) 
Chronobiology international  2009;26(5):992-1014.
Individual differences in circadian phase preference (“chronotype”) are linked to sleep schedule variability, psychosocial functioning, and specific properties of the circadian clock. While much is known about the development, distribution, and variability of chronotype in adolescents and adults, assessment in prepubertal children has been hindered by a lack of appropriate, reliable, and valid measures. This study presents a detailed description of the assessment of children’s chronotype by the Children’s ChronoType Questionnaire (CCTQ). The CCTQ is a parent-report, 27-item mixed-format questionnaire resulting in multiple measures of chronotype in 4- to 11-yr-old children: the midsleep point on free days (MSF), a morningness/eveningness scale (M/E) score, and a five-point chronotype (CT) score. The study provides validity data using actigraphy as well as test-retest reliability data for all three chronotype measures and sleep/wake parameters. Overall, the findings indicate moderate to strong agreement between the three measures, adequate associations between chronotype measures and sleep/wake parameters assessed by actigraphy, and excellent temporal stability (reliability). (Author correspondence: oskar.jenni@kispi.uzh.ch)
doi:10.1080/07420520903044505
PMCID: PMC2988284  PMID: 19637055
Chronotype; Midsleep point; Morningness/eveningness; Validity; Children
13.  Racial Differences in Reported Napping and Nocturnal Sleep in 2- to 8-Year-Old Children 
Pediatrics  2005;115(1 Suppl):225-232.
Objectives
The objectives of this study were to examine racial differences in reported napping and nighttime sleep of 2- to 8-year-old children, to identify factors accounting for these differences, and to determine if variability in napping was related to psychosocial functioning.
Methods
Caretakers of 1043 children (73.5% non-Hispanic white; 50.4% male) 2 to 8 years old from a community sample reported on their children’s napping behavior and nighttime sleep. Caretakers of 255 preschool children (3–5 years old) also completed the Behavior Assessment System for Children.
Results
A more gradual age-related decline in napping was found for black children. At age 8, 39.1% of black children were reported to nap, compared with only 4.9% of white children. Black children also napped significantly more days per week, had shorter average nocturnal sleep durations, and slept significantly less on weekdays than on weekend nights. Despite differences in sleep distribution, total weekly sleep duration (diurnal and nocturnal) was nearly identical for the 2 racial groups at each year of age. Logistic regression analysis revealed that demographic variables were related to but did not fully explain napping differences. Napping in a subset of preschoolers was not significantly related to psychosocial functioning.
Conclusions
There are remarkable racial differences in reported napping and nighttime sleep patterns beginning as early as age 3 and extending to at least 8 years of age. These differences are independent of commonly investigated demographic factors. Differences in napping behavior do not seem to have psychosocial significance in a sample of preschool children.
doi:10.1542/peds.2004-0815D
PMCID: PMC2987587  PMID: 15866856
racial differences; napping; sleep; children; psychosocial functioning
14.  Understanding sleep–wake behavior and sleep disorders in children: the value of a model 
Current opinion in psychiatry  2006;19(3):282-287.
Purpose of review
Sleep–wake problems such as night wakings, excessive crying, or difficulties in falling asleep are frequent behavioral issues during childhood. Maturational changes in sleep and circadian regulation likely contribute to the development and maintenance of such problems. This review highlights the recent research examining bioregulatory sleep mechanisms during development and provides a model for predicting sleep–wake behavior in young humans.
Recent findings
Findings demonstrate that circadian and sleep homeostatic processes exhibit maturational changes during the first two decades of life. The developing interaction of both processes may be a key determinant of sleep–wake and crying behavior in infancy. Evidence shows that the dynamics of sleep homeostatic processes slow down in the course of childhood (i.e., sleep pressure accumulates more slowly with increasing age) enabling children to be awake for consolidated periods during the day. Another current topic is the adolescent sleep phase delay, which appears to be driven primarily by maturational changes in sleep homeostatic and circadian processes.
Summary
The two-process model of sleep regulation is a valuable framework for understanding and predicting sleep–wake behavior in young humans. Such knowledge is important for improving anticipatory guidance, parental education, and patient care, as well as for developing appropriate social policies.
doi:10.1097/01.yco.0000218599.32969.03
PMCID: PMC2980811  PMID: 16612214
adolescence; children; excessive crying; sleep behavior; sleep homeostasis
15.  Social and Demographic Predictors of Preschoolers’ Bedtime Routines 
Objective
To examine associations of child and family sociodemographic characteristics with preschooler bedtime routines.
Method
We use parent-report data on 3,217 3-year-old children (48% black; 26% Hispanic; 26% white) from the Fragile Families and Child Wellbeing Study to examine whether child and family characteristics are associated with the presence, time, and consistency of bedtime routines.
Results
Over 80% of sample children have a bedtime yet only two-thirds follow it. After extensive controls for maternal education, family structure, and other household characteristics, Black and Hispanic children have later bedtimes than white children and reduced odds of using regular bedtimes (by 22% and 29%, respectively) and using bedtime routines (by 47% and 33%, respectively). Low maternal education, increased household size, and poverty are associated with decreased use of parent-child interactive and hygiene-related bedtime routines.
Conclusion
Children from disadvantaged households are less likely to have consistent bedtime routines than their more advantaged counterparts. This may contribute to later disparities in sleep quality, duration and timing, factors known to be associated with adverse behavioral, cognitive, and health outcomes.
doi:10.1097/DBP.0b013e3181ba0e64
PMCID: PMC2793084  PMID: 19745760
bedtimes; bedtime routines; children; sleep

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