Does maternal care-giving behavior modulate the cortisol response to an acute stressor in 5-week-old human infants?

In previous studies, a higher quality of care-giving behavior reduced the cortisol response to acute stressors in infants aged 3 months and older. Here, we investigated whether the quality of maternal care-giving behavior affected the cortisol response to being bathed in 5-week-old infants (N = 141). Mothers and infants were observed during a bathing routine. Infant saliva samples were collected before and after bathing to assess cortisol concentrations, and the quality of maternal care-giving behavior was scored from videotapes. Bathing elicited a significant increase in infant salivary cortisol level (reactivity), and cortisol concentrations returned to pre-stressor values 40 min after bathing (recovery). In contrast, with previous findings in older infants, the quality of maternal care giving was not associated with either cortisol reactivity or recovery. This finding suggests that the quality of maternal care-giving behavior is not effective in modulating 5-week-old infants' cortisol responses to a (mild) physical stressor. Although a satisfactory neurophysiological explanation for this inference is still lacking, current knowledge of the behavioral development of very young infants supports this suggestion.

Spatial learning in pigs: effects of environmental enrichment and individual characteristics on behaviour and performance.

This study investigated the effects of both environmental enrichment and individual behavioural characteristics on spatial cognitive capabilities of pigs, using a novel latent spatial learning paradigm based on Tolman's detour experiments (1948). Pigs were housed either in 'barren' pens or in pens enriched with straw bedding from birth. Pigs were restrained in a Backtest at 10 and 17 days postpartum. Based on their escape behaviour in this test, which has been shown to reflect their behavioural style, six 'high-resisting'(HR) and six 'low-resisting' (LR) pigs were selected from each housing environment (n = 24 in total). At 12 weeks of age, pairs of pen mates (LR and HR) were exposed to a maze three times (exploration trials). Pigs were then placed individually in the maze, and social reinstatement proved to be a strong incentive to find the exit leading to the home pen. We subsequently blocked the direct route to the exit, forcing animals to find a detour (memory test 1, MT1). This test was repeated once to investigate the relative improvement, i.e. detour learning (memory test 2, MT2). Housing condition and Backtest response strongly affected exploration patterns. In spite of this, no effects on performance during the subsequent memory tests were found. Performance was substantially improved in MT2, indicating that once a goal is apparent, pigs are able to solve a complex spatial memory task easily. In conclusion, social reinstatement provided a good incentive to complete a spatial task, and the substantial improvement in performance between MT1 and MT2 stresses the need for task complexity when testing spatial memory in pigs. Housing conditions or individual behavioural style did not affect spatial memory during MT1 or MT2. However, housing environment and behavioural style strongly affected explorative behaviour of pigs in an unfamiliar maze during both exploration trials and memory tests. This implicates that apparent effects of environmental enrichment on spatial learning and memory in pigs might reflect differences in explorative patterns rather than in cognitive processes.

A new device for collecting saliva for cortisol determination.

Saliva for measurement of cortisol is generally sampled by swabbing the mouth with a cotton roll, but this method has drawbacks. In the present study, we evaluated the use of an eye sponge as an oral collection device for saliva cortisol. The eye sponge was compared with commercial cotton rolls, and tested for use in infants as well as adults. Our results show that the eye sponge has adequate cortisol recoveries, even after samples have been kept at 4-8 degrees C for up to a week. In adults, volumes of 200-250 microl are obtained without problem; although smaller volumes are obtained in young infants, they are sufficient for assays requiring only 50-100 microl of saliva. In conclusion, the eye sponge is a valid and adequate collection device for saliva cortisol. Additional advantages as compared to cotton rolls are: more comfortable sampling, tastelessness, no need to manipulate the absorbing material, and the ease with which the untrained eye can determine that enough saliva has been collected.

Functioning within a relationship: mother-infant synchrony and infant sleep.

The aim of this study was to investigate the coupling of the biological system of infant sleep and the social system of mother-infant synchrony. Before birth and shortly after birth the systems appear to be connected, but it is unclear whether this remains the case over time. This study therefore examined whether infant sleep measured at 6 weeks and 5 months could predict mother-infant gaze synchrony after a social challenge at 5 months (N=84). Infant sleep was measured in terms of sleep bout duration, which normally increases during this period. Gaze was defined in terms of looking at each other's head simultaneously, known as gaze synchrony, or looking elsewhere. Results showed that infant sleep could predict the temporal dynamics of the mother-infant interaction in terms of flexibility of gaze pattern shifts. The larger the increase in sleep bout duration over age, the more flexible the interaction appeared to be. Maternal Age, type of feeding and change of feeding appeared to function as confounding variables in this relation. Infant sleep could not predict percentage of synchrony (central tendency measure) or the average sequence length of gaze patterns (temporal dynamic measure).

Nonparental care and infant health: do number of hours and number of concurrent arrangements matter?

OBJECTIVES: Previous research found that centre-based childcare is related to more illnesses early in life. The goal of this longitudinal study is to determine whether infant health in the first year of life is also related to the amount of time spent in non-parental care and the number of concurrent non-parental care arrangements. METHODS: Information on infant health and non-parental care was obtained through monthly maternal interviews across the first year of life. The occurrences of respiratory, digestive, general, and skin illnesses and complaints were used as dependent variables, while the number of hours and the number of arrangements per week were used as predictors. Analyses were done separately in infants for whom centre-based childcare is included in their arrangements (n=107), and for those which it is not (n=61). RESULTS: Infants spending more hours in non-parental care had more respiratory and general illnesses. Infants who were cared for in more concurrent arrangements had fewer respiratory and general, but more skin illnesses. These results only applied to infants that included centre-based childcare in their arrangements. In the group of infants that did not attend centre-based childcare, health was not related to either the number of hours or the number of arrangements. CONCLUSIONS: Number of hours and number of arrangements do matter in relation to infant health early in life, but only for infants who attend centre-based childcare. While more hours were related to more illnesses, more arrangements were related to both fewer and more illnesses, depending on the type of illnesses.

Attachment and infant night waking: a longitudinal study from birth through the first year of life.

OBJECTIVE: : Night wakings are common in infancy. Although a link between infant night wakings and attachment to the primary caregiver has been previously proposed, empirical support is limited so far. The aim of this longitudinal study was to examine the early history of night waking in infants who were later classified as securely or insecurely (avoidantly, resistantly, or disorganized) attached. METHODS: : Participants in the study were 193 infants and their mothers. Information on infant night wakings was collected with the use of daily sleep diaries for the first 6 months of life and again for 2 weeks at 12 months of age. Infant-mother attachment was assessed using the Strange Situation (Ainsworth et al, Patterns of Attachment: A Psychological Study of the Strange Situation. New York: Hillsdale; 1978) when the infants were 12 months of age. RESULTS: : Longitudinal regression analyses showed that, after controlling for many covariates, infants with an insecure-resistant attachment at 12 months of age awoke more during the night in their first 6 months of life than the other infants. Furthermore, infants with different attachment classifications developed different patterns of night wakings over the first 6 months, with the insecure-avoidant infants waking the least toward the end of the 6 months. Hierarchical multiple regression analyses showed no associations between attachment and night wakings at 12 months of age. CONCLUSION: : This study is the first in showing that attachment at 12 months of age is related to infant night waking patterns in the first 6 months of life. Patterns of infant night wakings early in life apparently reflect the emerging attachment relationship.

Cortisol reactivity in young infants.

In this systematic review on empirical studies of cortisol reactivity to acute stressors in infants, we specifically focus on the role of infant age in the early development of cortisol reactivity to stressors. Our findings indicate that many psychological stressors do not provoke a cortisol reaction, but in response to physical stressors, the infant HPA-axis mostly reacts with a moderate increase in post-stressor cortisol. Furthermore, for physical stressors only, cortisol reactivity effect sizes decrease with infant age, although relatively little is known for infants older than 6 months. These data provide more insight in the role of infant age in the development of cortisol reactivity in response to acute stressors. We discuss the role of caregivers in buffering the cortisol response to both psychological and physical stressors, and recommend extending the current knowledge on infant cortisol reactivity.

Maternal prenatal anxiety and stress predict infant illnesses and health complaints.

OBJECTIVES: Evidence from both animals and humans suggests that maternal prenatal anxiety and stress can have adverse consequences on the offspring's development. Animal models also show that prenatal stress has programming effects on the physical health of the offspring, such as immune functioning. In human studies, however, physical health outcomes are often restricted to birth complications; studies on the effects of acquiring illnesses are scarce. This study aimed to examine whether maternal prenatal anxiety and stress, measured both by self-report and by cortisol physiology, are related to more infant illnesses and antibiotic use during the first year of life. METHODS: Participants in the study were 174 mothers with normal pregnancies and term deliveries (71 firstborns; 91 boys). The mothers filled out third-trimester questionnaires on general and pregnancy-specific anxiety and stress and provided saliva samples for circadian cortisol. Information on infant illnesses and antibiotic use was obtained through monthly maternal interviews across the infant's first year of life. RESULTS: Hierarchical multiple regressions showed that, even after controlling for many relevant confounders, prenatal anxiety and stress predicted a considerable amount of variance in infant illnesses and antibiotic use: 9.3% for respiratory, 10.7% for general, 8.9% for skin, and 7.6% for antibiotic use. Digestive illnesses were not related to prenatal anxiety and stress. CONCLUSIONS: Although replication is warranted, to our knowledge, this is the first evidence linking maternal prenatal anxiety and stress to infant illnesses and antibiotic use early in life.

Cortisol in the first year of life: normative values and intra-individual variability.

INTRODUCTION: Many studies have incorporated cortisol measurements when studying infant development, but descriptions of normal development of basal cortisol levels in large study populations are scarce. The present study aimed to establish norm values for infant basal cortisol levels and to examine the development of intra-individual variability in the first year of life. METHODS: More than 2500 cortisol samples were collected in 300 infants at three different ages. At each age four 1100h samples were collected to determine average cortisol levels and intra-individual variability. The development of basal cortisol levels and intra-individual variability was analyzed with multilevel growth curve modeling. RESULTS: Norm tables with 90 and 95% intervals are presented. Basal cortisol levels decreased gradually over the year. Intra-individual variability was relatively large and stable in the first half year but decreased towards the end of the year. CONCLUSIONS: The results of this study will aid researchers in evaluating cortisol data collected in early infancy. It also underscores the importance of taking intra-individual cortisol variability into account in studies involving infants.