Study objectives

Limiting spindle activity via sleep restriction could explain some of the negative cognitive effects of sleep loss in adolescents. The current study evaluates how sleep restriction affects sleep spindle number, incidence, amplitude, duration, and wave frequency and tests whether sleep restriction effects on spindles change across the years of adolescence. The study determines whether sleep restriction effects on daytime sleepiness, vigilance, and cognition are related to changes in sleep spindles.

Methods

In each year of this 3-year longitudinal study, 77 participants, ranging in age from 10 to 16 years, each completed three different time in bed (TIB) schedules: 7, 8.5, or 10 hours in bed for 4 consecutive nights. A computer algorithm detected and analyzed sleep spindles in night four central and frontal electroencephalogram. Objective and self-reported daytime sleepiness and cognition were evaluated on the day following the 4th night.

Results

For 7 versus 10 hours TIB average all-night frontal and central spindle counts were reduced by 35% and 32%, respectively. Reducing TIB also significantly decreased spindle incidence in the first 5 hours of non-rapid eye movement sleep, produced small but significant reductions in spindle amplitude, and had little to no effect on spindle duration and spindle wave frequency. Sleep restriction effects did not change with age. The reductions in spindle count and incidence were related to daytime sleepiness on the following day but were not related to working memory.

Conclusions

The sleep loss effects on daytime functioning in adolescents are partially mediated by reduced sleep spindles impacting daytime sleepiness.

Native language statistical regularities about allowable phoneme combinations (i.e., phonotactic patterns) may provide learners with cues to support word learning. The current research investigated the association between infants' native language phonotactic knowledge and their word learning progress, as measured by vocabulary size. In the experiment, 19-month-old infants listened to a corpus of nonce words that contained novel phonotactic patterns. All words began with "illegal" consonant clusters that cannot occur in native (English) words. The rationale for the task was that infants with fragile phonotactic knowledge should exhibit stronger learning of the novel illegal phonotactic patterns than infants with robust phonotactic knowledge. We found that infants with smaller vocabularies showed stronger phonotactic learning than infants with larger vocabularies even after accounting for general cognition. We propose that learning about native language structure may promote vocabulary development by providing a foundation for word learning; infants with smaller vocabularies may have weaker support from phonotactics than infants with larger vocabularies. Furthermore, stored vocabulary knowledge may promote the detection of phonotactic patterns even during infancy.

Variation in the early environment has the potential to permanently alter offspring behavior and development. We have previously shown that naturally occurring variation in biparental care of offspring in the prairie vole is related to differences in social behavior of the offspring. It was not, however, clear whether the behavioral differences seen between offspring receiving high compared to low amounts of parental care were the result of different care experiences or were due to shared genetics with their high-contact or low-contact parents. Here we use cross-fostering methods to determine the mode of transmission of alloparental behavior and oxytocin receptor (OTR) and vasopressin V1a receptor (V1aR) binding from parent to offspring. Offspring were cross-fostered or in-fostered on postnatal day 1 and parental care received was quantified in the first week postpartum. At weaning, offspring underwent an alloparental care test and brains were then collected from all parents and offspring to examine OTR and V1aR binding. Results indicate that alloparental behavior of offspring was predicted by the parental behavior of their rearing parents. Receptor binding for both OTR and V1aR tended to be predicted by the genetic mothers for female offspring and by the genetic fathers for male offspring. These findings suggest a different, sex-dependent, role of early experience and genetics in shaping behavior compared to receptor distribution and support the notion of sex-dependent outcomes.

Empathic accuracy, the ability to accurately understand others' emotions, is typically viewed as beneficial for mental health. However, empathic accuracy may be problematic when a close relational partner is depressed because it promotes shared depression. Across two studies, we measured empathic accuracy using laboratory tasks that capture the ability to rate others' emotional valence accurately over time: first, in a sample of 156 neurotypical married couples (Study 1; Total N=312), and then in a sample of 102 informal caregivers of individuals with dementia (Study 2). Across both studies, the association between empathic accuracy and depressive symptoms varied as a function of a partner's level of depressive symptoms. Greater empathic accuracy was associated with (a) fewer depressive symptoms when a partner lacked depressive symptoms, but (b) more depressive symptoms when a partner had high levels of depressive symptoms. Accurately detecting changes in others' emotional valence may underpin shared depressive symptoms.

Study objectives

Daytime sleepiness increases across adolescence. This increase is commonly attributed to insufficient sleep durations resulting from increasingly limited time in bed. We tested the effects of 3 sleep schedules on daytime sleepiness and whether these effects changed with age in early adolescence.

Methods

In 77 children ranging in age from 9.9 to 14 years, objective (multiple sleep latency test [MSLT]) and subjective (Karolinska sleepiness scale [KSS]) sleepiness was measured following 4 consecutive nights of either 7, 8.5, or 10 hours in bed. All participants completed all 3 sleep schedules. The order in which they completed the schedules was not randomized but was accounted for in all statistical analyses.

Results

Time in bed restriction decreased sleep duration and increased objective and subjective daytime sleepiness. Although the sleep durations did not change with age, the likelihood of falling asleep during the MSLT increased with age. Nevertheless, sleep restriction produced a greater increase in MSLT-measured sleepiness in younger participants. Subjective sleepiness measured with the KSS increased with shorter sleep duration, but this effect did not change with age.

Conclusions

Increasing objective daytime sleepiness in early adolescence cannot simply be attributed to reduced sleep due to restricted sleep schedules. We propose that some of the increased daytime sleepiness of adolescents is a consequence of adolescent brain reorganization driven by synaptic pruning which decreases the intensity of waking brain activity.

The current study investigated longitudinal change in hippocampal and prefrontal contribution to episodic retrieval. Functional neuroimaging data were collected during an item-context association memory task for children between the ages of 8 and 14 with individuals scanned 1-3 times over the course of 0.75-3.7 years (Timepoint 1 N = 90; Timepoint 2 N = 83, Timepoint 3 N = 75). We investigated developmental changes in functional activation associated with episodic retrieval (correct item-context > incorrect item-context contrast) and asked whether pubertal changes contributed to developmental changes in pattern of activation. Non-linear developmental trajectories were observed. In the hippocampus, activation decreased with age during childhood and then increased into early adolescence. In the dorsolateral prefrontal cortex, activation was largely absent initially, but quickly accelerated over time. Independent of age, changes in pubertal status additionally predicted increases in item-context activation in initially older children, and decreases in initially younger children across both regions and two indicators of puberty: the Pubertal Development Scale and salivary testosterone. These findings suggest that changes in both age and pubertal status uniquely contribute to memory-related activation, and the timing of pubertal onset may play an important role in the neural mechanisms supporting memory retrieval.

Metamemory monitoring, or the ability to introspect on the accuracy of one's memories, improves considerably during childhood, but the underlying neural changes and implications for intellectual development are largely unknown. The present study examined whether cortical changes in key brain areas hypothesized to support metacognition contribute to the development of metamemory monitoring from late childhood into early adolescence. Metamemory monitoring was assessed among 7- to 12-y-old children (n = 145) and adults (n = 31). Children returned for up to two additional assessments at 8 to 14 y of age (n = 120) and at 9 to 15 y of age (n = 107) (n = 347 longitudinal scans). Results showed that metamemory monitoring continues to improve from childhood into adolescence. More pronounced cortical thinning in the anterior insula and a greater increase in the thickness of the ventromedial prefrontal cortex over the three assessment points predicted these improvements. Thus, performance benefits are linked to the unique patterns of regional cortical change during development. Metamemory monitoring at the first time point predicted intelligence at the third time point and vice versa, suggesting parallel development of these abilities and their reciprocal influence. Together, these results provide insights into the neuroanatomical correlates supporting the development of the capacity to self-reflect, and highlight the role of this capacity for general intellectual development.

Integrative data analysis (IDA) involves obtaining multiple datasets, scaling the data to a common metric, and jointly analyzing the data. The first step in IDA is to scale the multisample item-level data to a common metric, which is often done with multiple group item response models (MGM). With invariance constraints tested and imposed, the estimated latent variable scores from the MGM serve as an observed variable in subsequent analyses. This approach was used with empirical multiple group data and different latent variable estimates were obtained for individuals with the same response pattern from different studies. A Monte Carlo simulation study was then conducted to compare the accuracy of latent variable estimates from the MGM, a single-group item response model, and an MGM where group differences are ignored. Results suggest that these alternative approaches led to consistent and equally accurate latent variable estimates. Implications for IDA are discussed.

Patterns of pubertal maturation have been linked to vulnerability for emotion dysregulation disorders in girls, as well as white matter (WM) development, suggestive of a potential mechanism between pubertal maturation and emotional health. Because pubertal processes begin at varying ages (i.e., status, timing) and proceed at varying rates (i.e., tempo), identifying individual differences in the pubertal course associated with subsequent WM microstructure development may reveal clues about neurobiological mechanisms of girls' emotional well-being. In a prospective cohort study of 107 girls, we examined associations between pubertal status at age 9, pubertal timing and tempo from ages 9-15, and WM microstructure at age 19. Tract-based spatial statistics revealed that girls with more advanced pubertal status at age 9, specific to gonadal-related physical changes, had higher fractional anisotropy, and lower mean diffusivity (MD) and radial diffusivity in tracts relevant to cognitive control and emotion regulation (e.g., the superior longitudinal fasciculus, external capsule, and uncinate fasciculus). Additionally, girls with earlier pubertal timing showed lower MD in the left anterior cingulum bundle. Tempo was unrelated to WM measures. These findings implicate specific aspects of pubertal maturation in subsequent neural signatures, suggesting possible neuroendocrine mechanisms relevant to emotional development. Future work incorporating longitudinal neuroimaging in parallel with pubertal measures may contribute to the understanding of individual variation in pubertal course and WM development.