Individual differences in the activity of the hypothalamic pituitary adrenal axis: Relations to age and cumulative risk in early childhood.

This study examined individual differences in the function of the hypothalamic-pituitary-adrenal (HPA) axis with regard to age and cumulative risk during challenging laboratory tasks administered at 6, 12, 24, and 36 months. Saliva samples were collected from a majority-minority sample of N=185 children (57% African American, 50% female) prior to and following these tasks and later assayed for cortisol. Cumulative distal risk was indexed via a composite of maternal marital status, maternal education, income-to-needs ratio, the number of children in the household, and maternal age at childbirth. Probing of hierarchical models in which cortisol levels and age were nested within child revealed significant differences in cortisol as a function of both age and cumulative risk, such that children exposed to high levels of risk exhibited higher levels of cortisol both within and across age. These results highlight the sensitivity of the HPA axis to environmental context at the level of the individual, even as that sensitivity is manifest against the background of species-typical biological development.

Patterns of joint parasympathetic, sympathetic, and adrenocortical activity and their associations with temperament in early childhood.

Evidence has accrued to show that autonomic and adrenocortical systems act in coordination to facilitate responses to environmental opportunities and threats. In the current study, we used cluster analysis to examine whether individual differences in patterns of joint baseline activity among the parasympathetic and sympathetic branches of the autonomic nervous system with the hypothalamic-pituitary-adrenal axis are associated with parent-reported temperamental positive and negative affectivity in 36-month old children. The resulting clusters corresponded to the sensitive, buffered, and vigilant patterns as predicted by the adaptive calibration model of stress responsivity (Del Giudice et al., 2011) and included a novel pattern. Cluster memberships predicted differences in overall negative affectivity and its subscales, but no associations were found with positive affectivity. These results provide evidence that the joint activity of physiological systems at rest may underlie temperamental differences in negative affect.

The developmental course of salivary alpha-amylase and cortisol from 12 to 36 months: Relations with early poverty and later behavior problems.

This study examined the development of baseline autonomic nervous system (ANS) and hypothalamic-pituitary-adrenal (HPA) physiological activity from 12 to 36 months as well as antecedents (poverty) and consequents (behavior problems) of individual differences in physiological development. Children (N=179; 50% poor; 56% African American; 52% male) provided saliva samples at 12, 18, 24, 30, and 36 months of age. Latent growth curve models indicated that nonlinear change was evident for both sAA and cortisol, with sAA increasing and cortisol decreasing with age. Children residing in poor households exhibited lower initial levels of sAA, but not cortisol. African-American children showed slightly smaller decreases in cortisol over time. Initial levels of sAA predicted higher levels of internalizing behaviors at 36 months and both initial levels of and total change in sAA predicted higher levels of externalizing behaviors at 36 months. There was no evidence that sAA or cortisol mediated the relationship between poverty and later behavior problems.

Parenting behaviors and vagal tone at six months predict attachment disorganization at twelve months.

The authors investigated the relationships among parenting behaviors, infant vagal tone, and subsequent attachment classification. Vagal tone was assessed among 6-month olds (n = 95) during the still-face paradigm (SFP) via respiratory sinus arrhythmia (RSA), while attachment security and disorganization were measured at 12 months during the strange situation procedure (SSP). Infants demonstrating higher levels of RSA during the normal interaction and reunion episodes of the SFP whose mothers were also rated as negative-intrusive exhibited higher levels of attachment disorganization at 12 months, while infants with lower RSA and mothers who were negative-intrusive did not exhibit higher levels of disorganization. These results suggest that high levels of RSA may not be adaptive within the context of negative-intrusive parenting.

Systems theory and cascades in developmental psychopathology.

In the wake of prominent theoreticians in developmental science, whose contributions we review in this article, many developmental psychologists came to endorse a systems approach to understanding how the individual, as it develops, establishes functional relationships to social ecological contexts that from birth to school entry rapidly increase in complexity. The concept of developmental cascade has been introduced in this context to describe lawful processes by which antecedent conditions may be related with varying probabilities to specified outcomes. These are understood as processes by which function at one level or in one domain of behavior affect the organization of competency in later developing domains of general adaptation. Here we propose a developmental sequence by which the developing child acquires regulative capacities that are key to adjustment to a society that demands considerable control of emotional and cognitive functions early in life. We report empirical evidence showing that the acquisition of regulative capacities may be understood as a cascade of shifts in control parameters induced by the progressive integration of biological, transactional, and socioaffective systems over development. We conclude by suggesting how the developmental process may be accessed for effective intervention in populations deemed "at risk" for later problems of psychosocial adjustment.

Psychophysiological correlates of parenting behavior in mothers of young children.

This study investigated HPA and vagal functioning as correlates of parenting in mothers of 175 six-month-old children. Salivary cortisol indexed HPA functioning and respiratory sinus arrhythmia (RSA) reduction indexed vagal regulation. Positive engagement and negative intrusiveness were observed during the Face-to-Face Still Face Paradigm (FFSFP) reunion and a semi-structured free play episode. Mixed modeling was used to examine differences in maternal behaviors across contexts as a function of psychophysiology. Main effects of cortisol levels, as well as interactions with RSA reduction and context, predicted negative intrusiveness. Mothers with high cortisol exhibited more negative intrusiveness if they also had lower RSA reduction. Mothers were also less negatively intrusive during the FFSFP than the free play if they had lower cortisol levels. There were no associations between psychophysiological measures and positive engagement. The findings suggest: (1) that parenting behaviors are associated with maternal stress physiology; (2) considerations of single physiological systems related to parenting behaviors may be incomplete; and (3) type and context of behaviors must be considered when examining biobehavioral associations with parenting.

An anxiety-like phenotype in mice selectively bred for aggression.

Using selective bi-directional breeding procedures, two different lines of mice were developed. The NC900 line is highly reactive and attacks their social partners without provocation, whereas aggression in NC100 animals is uncommon in social environments. The enhanced reactivity of NC900 mice suggests that emotionality may have been selected with aggression. As certain forms of anxiety promote exaggerated defensive responses, we tested NC900 mice for the presence of an anxiety-like phenotype. In the open field, light-dark exploration, and zero maze tests, NC900 mice displayed anxiety-like responses. These animals were less responsive to the anxiolytic actions of diazepam in the zero maze than NC100 animals; diazepam also reduced the reactivity and attack behaviors of NC900 mice. The NC900 mice had reduced diazepam-sensitive GABA(A) receptor binding in brain regions associated with aggression and anxiety. Importantly, there was a selective reduction in levels of the GABA(A) receptor alpha(2) subunit protein in NC900 frontal cortex and amygdala; no changes in alpha(1) or gamma(2) subunit proteins were observed. These findings suggest that reductions in the alpha(2) subunit protein in selected brain regions may underlie the anxiety and aggressive phenotype of NC900 mice. Since anxiety and aggression are comorbid in certain psychiatric conditions, such as borderline personality and posttraumatic stress disorder, investigations with NC900 mice may provide new insights into basic mechanisms that underlie these and related psychiatric conditions.

Changes in maternal sensitivity across the first three years: are mothers from different attachment dyads differentially influenced by depressive symptomatology?

Hierarchical linear modeling was used to describe longitudinal relations between maternal sensitivity and depressive symptomatology for mothers of children with differing attachment classifications at 36 months of child age using data from the NICHD Study of Early Child Care. Attachment during toddlerhood was assessed using a modified Strange Situation Paradigm developed by the MacArthur Working Group on Attachment. On average, maternal sensitivity increased longitudinally from 6 to 36 months for groups with children classified as secure or resistant, but not for groups classified as avoidant or disorganized. Higher maternal depressive symptoms were associated with lower levels of sensitivity for all mothers, although this effect was significantly less severe for mothers of securely attached children. In addition, higher maternal depressive symptoms were associated with decreases in sensitivity from 6 to 36 months for mothers of children who at 36 months showed disorganized attachments combined with underlying patterns of avoidant or resistant behavior.

Parasympathetic and sympathetic responses to the strange situation in infants and mothers from avoidant and securely attached dyads.

Vagal reactivity and salivary alpha-amylase (sAA) were assessed in infants (M age = 13.55 months) and their mothers during the Strange Situation Paradigm (SSP) to investigate differences in physiological responses in a sample of insecure-avoidant and securely-attached dyads (N = 132). Infants classified as insecure-avoidant had significantly higher vagal withdrawal during the SSP and higher sAA overall, suggesting that the avoidant attachment pattern is associated with a greater allostatic load. During separation episodes of the SSP, all mothers showed significant vagal withdrawal, suggesting greater attempts at regulation. During the last reunion, typically the most stressful episode for infants, mothers of secure infants showed greater vagal withdrawal than mothers of insecure-avoidant infants, suggesting greater attempts by these mothers at interactive repair. Results for mothers and infants supported the allostatic load theory.

A biological window on psychological development.

The articles in this special issue of Developmental Psychobiology were presented in May 2005 at an international institute on developmental science hosted by the University of North Carolina at Chapel Hill. Conducted annually at one of the participating universities, these meetings are intended to foster collaboration and build consensus on specific theoretical, methodological, and analytical issues faced by developmentally oriented researchers. The overall goal of the 2005 meeting, titled "Integrating Biology and Developmental Science," was to identify different ways by which a developmental study of psychological phenomena in their joint biological and behavioral aspects may shed new light on their organization in the individual. The six contributions to this special issue illustrate how a biological window on developmental processes can further this scientific endeavor.

Bidirectional genetic and environmental influences on mother and child behavior: the family system as the unit of analyses.

Family systems theory proposes that an individual's functioning depends on interactive processes within the self and within the context of dyadic family subsystems. Previous research on these processes has focused largely on behavioral, cognitive, and psychophysiological properties of the individual and the dyad. The goals of this study were to explore genetic and environmental interactions within the family system by examining how the dopamine receptor D2 gene (DRD2) A1+ polymorphism in mothers and children relates to maternal sensitivity, how maternal and child characteristics might mediate those effects, and whether maternal sensitivity moderates the association between DRD2 A1+ and child affective problems. Evidence is found for an evocative effect of child polymorphism on parenting behavior, and for a moderating effect of child polymorphism on the association between maternal sensitivity and later child affective problems. Findings are discussed from a family systems perspective, highlighting the role of the family as a context for gene expression in both mothers and children.

Infant and parent factors associated with early maternal sensitivity: a caregiver-attachment systems approach.

We examined variations in maternal sensitivity at 6 months of child age as a function of child negativity and maternal physiology. We expected maternal vagal withdrawal in response to infant negative affect to facilitate the maintenance of sensitivity, but only for mothers of securely attached children. One hundred and forty-eight infant-mother dyads were observed in multiple contexts at 6 months of child age, and associations among maternal and child variables were examined with respect to 12-month attachment quality. Mothers of later securely attached children were more sensitive than mothers of avoidant children. However, sensitivity decreased for all mothers at high levels of infant negative affect. Furthermore, for mothers of avoidant children, vagal withdrawal was associated with sensitivity to child distress. No association was found between vagal withdrawal and sensitivity for mothers of securely attached children. This suggests that mothers of avoidant children may be uniquely challenged by the affective demands of their infants.

Handling, genetic and housing effects on the mouse stress system, dopamine function, and behavior.

This research was designed to examine how early stimulation (i.e., handling), subsequent housing conditions and genetic factors interact to produce adult differences in stress regulation. High-aggressive (NC900) and low-aggressive (NC100) mice were handled for 3 weeks potspartum and were subsequently isolated or grouped until observed as adults in an open field or a dyadic test. In NC100, handling abolished the temporal variations seen in open-field activity among the nonhandled subjects and reduced corticosterone (CORT) activation. In NC900, these two measures were unaffected by handling. Only among handled NC100 did subsequent group rearing further reduce CORT activation. By contrast, handling caused an up-regulation of D1 dopamine receptors in both lines, and, in NC100, this effect was increased by group rearing. In a dyadic encounter with another male mouse, subjects of both lines showed handling effects. NC100 froze less rapidly and NC900 attacked more rapidly. This multifactorial design showed that the systemic effects of handling are modulated by genetic background, and that measures of these effects are affected by experience beyond infancy. Our findings also showed that the effects of handling vary when assessed across different physiological systems and across social and nonsocial testing conditions.