Six-month-old infant long sleepers prefer a human face

The Architecture of Early Childhood Sleep Over the First Two Years

INTRODUCTION

The architecture and function of sleep during infancy and early childhood has not been fully described in the scientific literature. The impact of early sleep disruption on cognitive and physical development is also under-studied. The aim of this review was to investigate early childhood sleep development over the first two years and its association with neurodevelopment.

METHODS

This review was conducted according to the 2009 PRISMA guidelines. Four databases (OVID Medline, Pubmed, CINAHL, and Web of Science) were searched according to predefined search terms.

RESULTS

Ninety-three studies with approximately 90,000 subjects from demographically diverse backgrounds were included in this review. Sleep is the predominant state at birth. There is an increase in NREM and a decrease in REM sleep during the first two years. Changes in sleep architecture occur in tandem with development. There are more studies exploring sleep and early infancy compared to mid and late infancy and early childhood.

DISCUSSION

Sleep is critical for memory, learning, and socio-emotional development. Future longitudinal studies in infants and young children should focus on sleep architecture at each month of life to establish the emergence of key characteristics, especially from 7-24 months of age, during periods of rapid neurodevelopmental progress.

Habitual night waking associates with dynamics of waking cortical theta power in infancy

The implications of the substantial individual differences in infant sleep for early brain development remain unclear. Here, we examined whether night sleep quality relates to daytime brain activity, operationalized through measures of EEG theta power and its dynamic modulation, which have been previously linked to later cognitive development. For this longitudinal study, 76 typically developing infants were studied (age: 4-14 months, 166 individual study visits) over the course of 6 months with one, two, three, or four lab visits. Habitual sleep was measured with a 7-day sleep diary and actigraphy, and the Brief Infant Sleep Questionnaire. Twenty-channel EEG was recorded while infants watched multiple rounds of videos of women singing nursery rhymes; oscillatory power in the theta band was extracted. Key metrics were average theta across stimuli and the slope of change in theta within the first novel movie. Both objective and subjective sleep assessment methods showed a relationship between more night waking and higher overall theta power and reduced dynamic modulation of theta over the course of the novel video stimuli. These results may indicate altered learning and consolidation in infants with more disrupted night sleep, which may have implications for cognitive development.

Prior sleep timing and visual recognition of emotional faces in 6-month-old infants

Face recognition is an important mnemonic ability for infants when navigating the social world. While age-related changes in face processing abilities are relatively well documented, less is known about short-term intra-individual fluctuations in this ability. Given that sleep deprivation in adults leads to impairments in information processing, we assessed the role of prior sleep on 6-month-old infants' (N = 17) visual recognition of faces showing three emotional expressions (neutral, sad, angry). Visual recognition was inferred by assessing novelty preferences for unfamiliar relative to familiarized faces in a visual recognition memory paradigm. In a within-subject design, infants participated once after they had recently woken up from a nap (nap condition) and once after they had been awake for an extended period of time (awake condition). Infants failed to show visual recognition for the neutral faces in either condition. Infants showed recognition for the sad and angry faces when tested in the awake condition, but not in the nap condition. This suggests that timing of prior sleep shapes how effectively infants process emotionally relevant information in their environment.

Cross-cultural disparities of subjective sleep parameters and their age-related trends over the first three years of human life: A systematic review and meta-analysis

Changes in nighttime sleep consolidation and daytime discontinuation have been observed in early life. Yet information about societal or cultural factors remains scant for implementing sleep recommendations. We aimed to provide pooled estimates of subjective sleep duration, number of nightwakings and sleep timing; to describe their age-related trends; and to determine potential cross-cultural disparities between predominantly-Asian (PA) and predominantly-Caucasian (PC) regions during the first three years of life. We performed this review according to the PRISMA guidelines. Overall, 102 studies with 167,886 children aged 0-3 y from 26 different countries/regions were included. Compared to PC regions, PA toddlers had shorter sleep duration and more frequent nightwakings. When PC regions were further divided into Pacific Rim and Europe, differences were much more evident between PA and Pacific Rim for all nighttime sleep parameters. Trends of nighttime sleep duration and bedtime for PC regions showed rapid changes over the first 3-6 mo before stabilizing to a plateau, whereas a different change was found for PA regions. In conclusion, an apparent cross-cultural disparity of the subjective sleep parameters already exists in early childhood. Improved operationalization of sleep parameters and more objective evidence are needed to establish cultural-sensitive recommendations this early in life.

Association of Sleep and Circadian Activity Rhythm with Emotional Face Processing among 12-month-old Infants

Sleep and circadian rhythmicity both play an important role in human’s cognitive functioning, yet the way in which early development of sleep and circadian rhythm affects cognitive processes and social learning in infants remains less understood. We examined the association of sleep and circadian activity rhythm (CAR) with face and emotional information processing in 12-month old infants. Face processing was measured by eye tracking, whereby infants’ scanning patterns and pupil dilations were calculated when they were presented with neutral, pleasant and unpleasant faces. Infants with better sleep quality (i.e., less waking after sleep onset) and lower sleep-wake pattern variability (i.e., higher inter-daily stability) exhibited a higher eyes over mouth fixation ratio (EMR). Infants with longer total sleep time showed larger pupil diameter changes in response to emotional facial expressions, more closely resembling the responses of adults. Our findings suggest the role of sleep and circadian rhythm in waking cognition and have implications for understanding the early development of social learning in young children.