Human infants devote the majority of their time to sleeping. However, very little is known about the role of sleep in early memory processing. Here we test 6-and 12-mo-old infants' declarative memory for novel actions after a 4-h [Experiment (Exp.) 1] and 24-h delay (Exp. 2). Infants in a nap condition took an extended nap (≥30 min) within 4 h after learning, whereas infants in a no-nap condition did not. A comparison with age-matched control groups revealed that after both delays, only infants who had napped after learning remembered the target actions at the test. Additionally, after the 24-h delay, memory performance of infants in the nap condition was significantly higher than that of infants in the nonap condition. This is the first experimental evidence to our knowledge for an enhancing role of sleep in the consolidation of declarative memories in the first year of life.sleep-dependent memory | infant development | daytime naps | deferred imitation

The influence of a model's age on young children's behaviour has been a subject of considerable debate among developmental theorists. Despite the recent surge of interest, controversy remains about the nature of peer influence in early life. This article reviews studies that investigated the influence of a model's age on young children's behaviour in the first 5 years of life, and presents an account of seemingly mixed results. We propose that children imitate familiar behaviour for social reasons, such as in order to identify with the model or to communicate likeness. Since age is an important indicator of the degree of being alike, we propose that children are more likely to imitate familiar behaviour from peers. In contrast, we propose that children primarily imitate novel behaviour for learning reasons. Since adults are perceived as being more competent than children, children are more likely to learn from adults. We further suggest that increased peer experience leads children to evaluate peers as valuable resources for learning novel behaviour in domains in which peers are knowledgeable. Copyright © 2013 John Wiley & Sons, Ltd.

Rumination and worrying are relevant to the onset and maintenance of depression and anxiety. Yet, it is unclear, whether depressive rumination and worrying are predictive for depressive and anxious symptomatology during pregnancy. Likewise, the potential role of depressive rumination and worrying for maternal-foetal attachment has been rarely explored. In the present longitudinal study, N = 215 pregnant women were assessed within the first 4 months of pregnancy and again in the last 4 months of pregnancy. Using regression analysis, associations between worrying and depressive rumination on the one hand and maternal-foetal attachment, depression and anxiety on the other were studied-controlling for age, number of children, social support and baseline antenatal depressive and anxious symptoms. Baseline rumination was a significant predictor of impairments in maternal-foetal attachment in later pregnancy. Baseline worrying was a significant predictor of heightened depressive symptoms and anxiety. These effects were of modest magnitude. Nonetheless, our findings reveal that different types of perseverative thinking (i.e., rumination vs. worry) might have differential effects on maternal well-being and maternal-foetal attachment.

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Developmental changes in learning from peers and adults during the second year of life were assessed using an imitation paradigm. Independent groups of 15-and 24-month-old infants watched a prerecorded video of an unfamiliar child or adult model demonstrating a series of actions with objects. When learning was assessed immediately, 15-month-old infants imitated the target actions from the adult, but not the peer whereas 24-month-old infants imitated the target actions from both models. When infants' retention was assessed after a 10-min delay, only 24-month-old infants who had observed the peer model exhibited imitation. Across both ages, there was a significant positive correlation between the number of actions imitated from the peer and the length of regular peer exposure reported by caregivers. Length of peer exposure was not related to imitation from the adult model. Taken together, these findings indicate that a peer-model advantage develops as a function of age and experience during the second year of life.

In human adults, learning and memory under acute stress are characterized by an increased use of rigid habitual response strategies at the cost of flexible cognitive strategies. The immediate effects of stress on cognitive functioning early in life are not well understood. Here we show experimentally that acute stress leads human infants to perform habitual behavior rigidly. We found that 15-mo-old infants exposed to stress thereafter kept performing a previously effective action, even after the action suddenly became ineffective. Infants in a no-stress control group flexibly adjusted their behavior by disengaging from the newly ineffective action in favor of exploring an alternative action. This finding demonstrates that stress impairs infants' ability to adjust their behavior to changing circumstances.S tress is pervasive in modern society. It is by definition aversive, but how potentially stressful experiences affect a person depends on a variety of factors, such as the person's age, developmental history, temperament, and the type of stressor (1, 2). Thus, the very same set of challenges that inspires peak performance in some people might leave others drained. In addition to its relevance for mental and physical well-being, stress alters the way human adults think. Learning and memory under acute stress are characterized by increased use of rigid habitual response strategies at the cost of flexible cognitive strategies (3-5). For example, stressed adults continue to select a particular beverage even after they have become satiated with its flavor, whereas satiated nonstressed adults select a new beverage (4). This shift from hippocampus-dependent to dorsal striatum-dependent memory is mediated by an increase of the stress hormone cortisol (6-8).In the first years of life, core characteristics of the human brain are its rapid development and high plasticity (9). Providing infants with a caring and stimulating environment is generally considered ideal for fostering cognitive development (10). One reason is that infants growing up in such an environment are protected from frequent stress exposure. However, the immediate consequences of stress exposure on infant cognition are not well understood. In a number of previous studies, children between 1 and 5 y of age were unlikely to show a physiological response (i.e., an increase in cortisol levels) to mildly threatening situations, such as being in an unfamiliar environment or being approached by an unfamiliar person (11,12). This human equivalent to the so-called hyporesponsive phase reported in rodents is thought to protect the developing brain from potentially harmful effects of acute stress (13). However, this idea is somewhat at odds with a minority of studies in which stress induction did lead to increased cortisol levels in young children (14,15). Furthermore, chronic stress exposure early in life is associated with long-term impairments in cognitive functioning (16). Thus, even if a cortisol response can be difficult to elicit, it seems unlikely that early...

We examined whether sleep quality during the night and naps during the day preceding a learning event are related to memory encoding in human infants. Twenty-four 6-and twenty-four 12-month-old infants' natural sleeping behavior was monitored for 24 hr using actigraphy. After the recording period, encoding was assessed using an imitation paradigm. In an initial baseline phase, infants were allowed to interact with the stimulus to assess spontaneous production of any target actions. Infants then watched an experimenter demonstrate a sequence of three target actions and were immediately given the opportunity to reproduce the demonstrated target actions to assess memory encoding. Analyses revealed significant correlations between nighttime sleep quality variables (sleep efficiency, sleep fragmentation) and immediate imitation in 6-month-olds, but not in 12-month-olds. High sleep quality in the preceding night was thus positively associated with next day's memory encoding in 6-month-old infants

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