Many adolescents used multiple forms of technology late into the night and concurrently consumed caffeinated beverages. Subsequently, their ability to stay alert and fully functional throughout the day was impaired by excessive daytime sleepiness. Future studies should measure more than television hours when evaluating the impact of nighttime activities on sleep patterns in adolescents.

Neuregulin-1 (NRG-1) signaling has been implicated in inductive interactions between pre- and postsynaptic partners during synaptogenesis. We used gene targeting to selectively disrupt cysteine-rich domain-(CRD-) containing NRG-1 isoforms. In CRD-NRG-1-/-mice, peripheral projections defasciculated and displayed aberrant branching patterns within their targets. Motor nerve terminals were transiently associated with broad bands of postsynaptic ACh receptor (AChR) clusters. Initially, Schwann cell precursors accompanied peripheral projections, but later, Schwann cells were absent from axons in the periphery. Following initial stages of synapse formation, sensory and motor nerves withdrew and degenerated. Our data demonstrate the essential role of CRD-NRG-1-mediated signaling for coordinating nerve, target, and Schwann cell interactions in the normal maintenance of peripheral synapses, and ultimately in the survival of CRD-NRG-1-expressing neurons.

SUMMAR Y Obesity continues to be a major public health issue. In adolescents, there are limited studies on the relationship between obesity and sleep duration. We found hypothesized that an average sleep duration of <6 h in adolescents was associated with obesity. Data were from the National Longitudinal Study of Adolescent Health (ADD Health); a survey of 90 000 youths, aged 12-18 years; surveyed in several waves. The sample population for our study was 13 568. Weighted multiple logistic regression was used to identify the relationship between obesity at Wave II and sleep duration, having adjusted for skipping breakfast ‡ 2 ⁄ week; race, gender, parental income, TV ‡ 2 h per day, depression, and obesity at Wave I. At Wave I, the mean age was 15.96 ± 0.11 years; mean sleep hours were 7.91 ± 0.04. At Waves I and II, respectively, 10.6 and 11.2% of adolescents were obese. Adjusted analyses suggest that the effect of shortened sleep duration in Wave I was not significantly predictive of obesity in Wave II (P < 0.218). Longitudinally, depression and TV ‡ 2 h per day at Wave I was associated with a higher risk of obesity at Wave II in adjusted analyses. Depressed adolescents were almost twice as likely to be obese (OR = 1.84, 95% CI = 1.25-2.72); adolescents who watched TV ‡ 2 h per day were 37% more likely to be obese (OR = 1.37, 95% CI = 1.09-1.72). Environmental factors including TV ‡ 2 h per day and depression were significantly associated with obesity; shortened sleep duration was not. Future longitudinal studies in adolescents are needed to determine whether timing of television watching directly influences sleep patterns and, ultimately, obesity.k e y w o r d s add health, adolescents, fast food, obesity, sleep, television

Objective-To determine the relationship between napping and cognitive function in preschoolaged children.Methods-Daytime napping, nighttime sleep and cognitive function were assessed in fifty-nine typically developing children ages 3-5 years, who were enrolled in full-time childcare. Participants wore an actigraphy watch for 7 days to measure sleep and napping patterns, and completed neuropsychological testing emphasizing attention, response control, and vocabulary. Parents of participants completed behavior ratings and sleep logs during the study. Sleep/wake cycles were scored with the Sadeh algorithm.Results-Children who napped more on weekdays were also more likely to nap during weekends. Weekday napping and nighttime sleep were inversely correlated, such that those who napped more slept less at night, while total weekday sleep remained relatively constant. Weekday napping was significantly (negatively) correlated with vocabulary and auditory attention span, and weekday nighttime sleep was positively correlated with vocabulary. Nighttime sleep was also significantly negatively correlated with performance, such that those who slept less at night made more impulsive errors on a computerized go/no-go test.Conclusions-Daytime napping is actually negatively correlated with neurocognitive function in preschoolers. Nighttime sleep appears to be more critical for development of cognitive performance. Cessation of napping may serve as a developmental milestone of brain maturation. Children who nap less do not appear to be sleep deprived, especially if they compensate with increased nighttime sleep. An alternative explanation is that children who sleep less at night are sleep deprived and require a nap. A randomized trial of nap restriction would be the next step in understanding the relationship between napping and neurocognitive performance. Keywords childhood; attention; sleep; cognition; actigraphy; preschool The frequency of afternoon naps in children declines between the ages of 2 and 5 years as the biphasic sleep/wake pattern gives rise to a consolidated rest period at night [1][2][3] . Even during infancy, maturation of the sleep/wake cycles is suggested by sleep consolidation. Among premature infants, for example, those with longer, uninterrupted sleep had higher developmental scores on the Bayley-2 Developmental Scales 4 . Nevertheless, the role of napping in cognitive development has not been studied in preschoolers. Based on the trends in napping 1-3 , it may be speculated that preschool children have an increased diurnal sleep A meta-analysis of sleep deprivation studies in adults found that sleep deprivation has profound detrimental effects on cognitive functioning 9 . At the same time, daytime naps have been shown to restore wakefulness and promote performance and learning in adults [10][11][12] . Older children with nighttime sleep restriction have been shown to have increased inattentive behaviors 13 . Similarly, there is an increased incidence of sleep problems in preschool-aged children with ...