Salivary alpha-amylase as a longitudinal predictor of children's externalizing symptoms: respiratory sinus arrhythmia as a moderator of effects

Racial differences in sympathetic nervous system indicators: Implications and challenges for research

Growing evidence indicates the presence of racial differences in sympathetic nervous system (SNS) functioning, yet the nature of these differences is unclear and appears to vary across different indices of SNS activity. Moreover, racial differences among commonly used indices of SNS activity are under-investigated. This systematic review examines racial differences among widely used resting SNS indices, such as electrodermal activity (EDA), pre-ejection period (PEP), and salivary alpha-amylase (sAA). Our review reveals that Black participants have consistently been found to display lower resting EDA compared to White participants. The few studies that have investigated or reported racial differences in PEP and sAA yield mixed findings about whether racial differences exist. We discuss potential reasons for racial differences in SNS activity, such as index-specific factors, lab confounds, psychosocial environmental factors, and their interactions. We outline a framework characterizing possible contributors to racial differences in SNS functioning. Lastly, we highlight the implications of several definitional, analytic, and interpretive issues concerning the treatment of group differences in psychophysiological activity and provide future recommendations.

Autonomic nervous system reactivity and preschoolers' social dominance

The purpose of this study was to investigate the role of skin conductance level reactivity (SCLR) and respiratory sinus arrhythmia reactivity (RSAR) in preschoolers' social dominance, as well as potential gender differences in these associations. Reactivity was assessed in response to viewing videos of social exclusion and a post-aggression discussion. In a community sample of 94 preschool children followed over one calendar year, reactivity to the post-aggression discussion, but not exclusion, video was related to social dominance. Specifically, increased RSAR to the post-aggression discussion video was positively associated with concurrent social dominance for both boys and girls. Longitudinally, for boys only, coactivation (i.e., increases in SCLR accompanied by increases in RSAR) to the post-aggression discussion video, which may reflect dysregulated, emotionally labile reactions to stress, was associated with relatively low levels of social dominance across the course of the year. Overall, findings contribute to a growing literature documenting the role of autonomic reactivity in preschoolers' social adjustment and extend this work to their capacity to achieve and maintain socially dominant positions with peers.

Childhood violence exposure and externalizing behaviors: A systematic review of the role of physiological biomarkers

Childhood exposure to violence has been consistently linked to externalizing behaviors like delinquency and aggression. Growing evidence indicates that physiological biomarkers from the parasympathetic and sympathetic nervous systems (PNS and SNS) and hypothalamic-pituitary-adrenal (HPA) axis may moderate or mediate the relation between childhood violence exposure and externalizing behaviors. We conducted a systematic review to synthesize recent findings on physiological biomarkers as mediators and/or moderators of this association across the life course, using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Our search yielded 3878 articles, of which 44 met inclusion criteria (describing a total of 46 independent studies). We found consistent evidence for blunted HPA-axis reactivity as a mediator of the relation between childhood violence exposure and subsequent externalizing behaviors, and for non-reciprocal PNS/SNS activation as moderators exacerbating this relation. However, the results of the majority of included studies that demonstrated significant moderating effects of physiological biomarkers varied by participant sex, type of childhood violence exposure, and type of stimuli used to induce physiological reactivity. The observed mixed findings are consistent with some theories that emphasize that both high and low stress reactivity can be adaptive depending on one's early environment. These findings highlight the need for systematic explorations of heterogeneity, theory-driven research questions, and longitudinal studies that span multiple developmental periods and multiple biological systems. Clinical implications include the need to assess physiological biomarkers in treatment and intervention studies and the potential to target interventions based on both autonomic functioning and environmental contexts.

Developmental Pathways from Prenatal Substance Exposure to Reactive Aggression

Few studies have examined etiological pathways from prenatal substance exposure to adolescent reactive aggression. We tested a conceptual model that included hypothesized pathways from prenatal substance exposure to adolescent aggression via autonomic reactivity and violence exposure from infancy to early school age and maternal harshness across early childhood. The sample included 216 families (106 boys) who primarily self-identified as Black or Mixed Race. Results supported the hypothesized path from violence exposure across early childhood and early school age to school age autonomic reactivity and early adolescent reactive aggression. There was also a significant interaction effect of sympathetic and parasympathetic reactivity on adolescent reactive aggression, with sympathetic arousal and parasympathetic suppression at early school age associated with higher reactive relational and physical aggression in adolescence. Results emphasize the importance of early experiences and autonomic nervous system changes in contributing to the cascade of risk for reactive aggression in early adolescence.

Parental Self-Efficacy and Physiological Responses to Stress among Mothers of Early Adolescents

Little research addresses how parental self-efficacy is related to stress responses, and no research does so among parents of early adolescents. To fill this research gap, the current study examined the association between maternal self-efficacy and physiological stress responses during early adolescence. Participants were 68 mother-early adolescent dyads with youth in the 6th grade (M = 11 years; 56% female). Physiological responses (i.e., skin conductance, respiratory sinus arrythmia, cortisol) were measured before and after mothers observed their children engage in a modified Trier Social Stress Test for Children. Mothers reported on parental self-efficacy. Mothers with higher parental self-efficacy exhibited a more moderate skin conductance response to the speech portion of the task, and a smaller increase in cortisol, compared to mothers with lower parental self-efficacy. Respiratory sinus arrhythmia change was not related to parental self-efficacy. The findings are consistent with a "caring but confident" physiological profile among mothers with high parental self-efficacy, suggesting that greater confidence about parental influence might reduce parents' experience of stress/anxiety as they observe children face certain challenges.

Externalizing behavior and stress system functioning in infants exposed to early adversity: A multi-system exploration

Children who experience early adversity often show alterations across multiple stress response systems, including the hypothalamic-pituitary-adrenal (HPA) axis and autonomic nervous system (ANS). Changes in the diurnal rhythm of salivary cortisol (a marker of HPA axis functioning) and alpha-amylase (a marker of ANS functioning) may increase their probability of developing behavior problems. The goal of this study is to examine how these analytes may interact to predict externalizing behavior in infants exposed to early stress. Participants included 179 parents and their 6- to 20-month old infants recruited from a low-income neighborhood. Parents reported on their infants' externalizing behaviors and collected saliva samples from their children at wake-up and bedtime over three days. Diurnal cortisol and alpha-amylase were modeled using latent difference scores. Four models were tested examining the effects of cortisol and alpha-amylase morning values and slopes, as well as their interactions, on externalizing behavior. Results showed a significant interaction effect of cortisol and alpha-amylase morning values, such that low morning cortisol was associated with decreased externalizing behavior when morning alpha-amylase was high but not low. These findings highlight the importance of examining multiple systems when characterizing the physiological correlates of externalizing behavior among infants experiencing adversity.

Latent profiles of children's autonomic nervous system reactivity early in life predict later externalizing problems

Prior researchers have observed relations between children's autonomic nervous system reactivity and externalizing behavior problems, but rarely considers the role of developmentally regulated changes in children's stress response systems. Using growth mixture modeling, the present study derived profiles of parasympathetic nervous system reactivity (as indicated by respiratory sinus arrhythmia (RSA)) and sympathetic nervous system reactivity (as indicated by pre-ejection period (PEP)) from low income, primarily Mexican American children measured repeatedly from infancy through age 5 (N = 383) and investigated whether profiles were associated with externalizing problems at age 7. Analyses identified two profiles of RSA reactivity (reactive decreasing and U-shaped reactivity) and three profiles of PEP reactivity (blunted/anticipatory reactivity, reactive decreasing, non-reactive increasing). Compared to children with an RSA profile of reactive decreasing, those with an RSA profile of U-shaped reactivity had marginally higher externalizing problems, however, this difference was not statistically significant. Children who demonstrated a profile of blunted/anticipatory PEP reactivity had significantly higher externalizing problems compared to those with a profile of non-reactive increasing, likely related to the predominantly male composition of the former profile and predominantly female composition of the latter profile. Findings contribute to our understanding of developmental trajectories of ANS reactivity and highlight the utility of a longitudinal framework for understanding the effects of physiological risk factors on later behavior problems.

A latent change score approach to understanding dynamic autonomic coordination

Children's self-regulation is a core adaptive system in child development. Physiological indices of regulation, particularly the autonomic nervous system (ANS), have garnered increased attention as an informative level of analysis in regulation research. Cardiography supports the simultaneous examination of both ANS branches via measures of pre-ejection period (PEP) and respiratory sinus arrhythmia (RSA) as indicators of sympathetic and parasympathetic activity, respectively. However, despite their heavily intertwined functions, research examining autonomic coordination across sympathetic and parasympathetic systems is scarce. Moreover, extant efforts have favored static, mean level reactivity analyses, despite the dynamic nature of ANS regulation and the availability of analytic tools that can model these processes across time. This study drew on a sample of 198 six-year-old children from a diverse community sample (49.5% female, 43.9% Latinx) to examine dynamic autonomic coordination using bivariate latent change score modeling to evaluate bidirectional influences of sympathetic and parasympathetic activity over the course of a challenging puzzle completion task. Results indicated that children evidenced reciprocal sympathetic activation (i.e., PEP attenuation and RSA withdrawal) across the challenge task, and these regulatory responses were characterized by a temporally leading influence of PEP on lagging changes in RSA. The current findings contribute to our understanding of children's autonomic coordination while illustrating a novel analytic technique to advance ongoing efforts to understand the etiology and developmental significance of children's physiological self-regulation.

A process model linking physiological arousal and fear recognition to aggression via guilt in middle childhood

Aggression coincides with emotional underarousal in childhood, but we still lack an understanding of how underarousal contributes to aggression. With an ethnically diverse sample of 8-year-olds (N = 150), we tested whether physiological underarousal and lower fear recognition were indirectly associated with heightened aggression through dampened guilt feelings. Caregivers rated children's aggressive behavior. We assessed children's skin conductance (SC) and respiratory sinus arrhythmia (RSA) while they imagined transgressing norms and measured their fear recognition with a facial morph task. Children reported guilt or lack thereof after hypothetically transgressing. The interaction of decreasing SC and increasing RSA (i.e., physiological underarousal) and poor fear recognition were indirectly associated with higher aggression through their associations with lower guilt. Emotional underarousal may contribute to aggression by disrupting the normative development of guilt. We discuss strategies to improve social-emotional acuity and reduce aggression in children with blunted physiological arousal and fear recognition.

Trait impulsiveness and response inhibition in young adults: Moderating role of resting respiratory sinus arrhythmia

Trait impulsiveness is a multifaceted construct that includes motor-, attention/cognitive- and non-planning facets, but how specific impulsiveness facets are associated with the deficit of response inhibition is not well understood. Resting respiratory sinus arrhythmia (RSA), which is considered as an index of cardiac vagal tone has been demonstrated to play a moderating role in the associations between many individual's variables. Whether resting RSA moderates the relationships between the facets of trait impulsiveness and response inhibition remains unknown. To examine these issues, data of self-reported trait impulsiveness, as assessed using the Barratt Impulsiveness Scale (BIS-II), 5-min resting RSA, and response accuracy (ACC) on a modified Go/NoGo task were collected from 132 college students. Results indicated that ACC of NoGo condition on the Go/NoGo task was negatively correlated with BIS motor and BIS total. Trait motor impulsiveness negatively predicted ACC of NoGo condition on the Go/NoGo task in the low resting RSA group but not in the high resting RSA group. This finding suggests that cardiac vagal tone could moderate the association between trait impulsiveness, especially motor impulsiveness, and deficits of response inhibition.

The simultaneous assessment of and relations between children's sympathetic and parasympathetic psychophysiology and their reactive and proactive aggression

The goal of the current study was to examine the link between children's psychophysiology and aggression when both constructs were assessed simultaneously in scenarios designed to provide the opportunity to aggress for either a reactive reason or a proactive reason. Both sympathetic nervous system (SNS) activity (skin conductance) and parasympathetic nervous system (PNS) activity (respiratory sinus arrhythmia or RSA), as well as their interaction, were included as physiological measures. Participants were 35 5th-grade children who were placed in two virtual-peer scenarios; one scenario provided the opportunity to aggress in response to peer provocation (i.e., reactive aggression) and the other scenario provided the opportunity to aggress for instrumental gain (i.e., proactive aggression). Both skin conductance and RSA were assessed at the time that children were given the opportunity to aggress; this simultaneous assessment of psychophysiology and aggression allowed for an examination of in-the-moment relations between the two constructs. For the reactive scenario, RSA moderated the in-the-moment relation between skin conductance and aggression such that the association was positive at low RSA but negative at high RSA. For the proactive scenario, skin conductance negatively predicted aggression in-the-moment, and RSA positively predicted aggression in-the-moment, but their interaction was not a significant predictor of aggression. Theoretical implications for reactive and proactive aggression and underlying physiological processes are discussed.

Evening salivary cortisol and alpha-amylase at 14months and neurodevelopment at 4years: Sex differences

Stress system activity in early life can have long-term effects on neurodevelopment. The main aim of this study was to assess the association of child evening salivary cortisol and alpha-amylase basal levels at 14months of age with longer-term neuropsychological development at 4years in a low-risk population-based birth cohort derived from the INMA (Environment and Childhood) project in Spain. We included 186 parent-children pairs with information on both stress system activity and neurodevelopment. Both stress markers at 14months of age showed an association with neuropsychological development at 4years. Salivary cortisol showed a sex-specific pattern of association. In girls, cortisol levels at 14months were negatively associated with cognitive development [long-term declarative memory (β=-17.8, p=0.028; 95% CI=-33.2 to -2.5); executive function (β=-9.8, p=0.08; 95% CI=-21 to 1)] and gross motor development (β=-13; p=0.022; 95% CI=-24 to -2), whereas in boys cortisol levels were negatively associated with socioemotional development [autistic-like behaviours: Incidence Rate Ratio (IRR)=1.6, p=0.039; 95% CI=1.01 to 2.41]. Salivary alpha-amylase was positively associated with socioemotional development in boys only [social competence (β=2.11, p=0.013; 95% CI=0.47 to 3.72), autistic-like behaviours (IRR=0.93, p=0.042; 95% CI=0.87 to 0.99) and hyperactivity symptoms (IRR=0.81, p=0.021; 95% CI=0.69 to 0.97)]. These results suggest that stress system activity in early life is associated with longer-term neurodevelopment and that sex is an important factor in this relationship.

Test-Retest Reliability of Pediatric Heart Rate Variability: A Meta-Analysis

Heart rate variability (HRV), an established index of autonomic cardiovascular modulation, is associated with health outcomes (e.g., obesity, diabetes) and mortality risk. Time- and frequency-domain HRV measures are commonly reported in longitudinal adult and pediatric studies of health. While test-retest reliability has been established among adults, less is known about the psychometric properties of HRV among infants, children, and adolescents. The objective was to conduct a meta-analysis of the test-retest reliability of time- and frequency-domain HRV measures from infancy to adolescence. Electronic searches (PubMed, PsycINFO; January 1970-December 2014) identified studies with nonclinical samples aged ≤ 18 years; ≥ 2 baseline HRV recordings separated by ≥ 1 day; and sufficient data for effect size computation. Forty-nine studies (N = 5,170) met inclusion criteria. Methodological variables coded included factors relevant to study protocol, sample characteristics, electrocardiogram (ECG) signal acquisition and preprocessing, and HRV analytical decisions. Fisher's Z was derived as the common effect size. Analyses were age-stratified (infant/toddler < 5 years, n = 3,329; child/adolescent 5-18 years, n = 1,841) due to marked methodological differences across the pediatric literature. Meta-analytic results revealed HRV demonstrated moderate reliability; child/adolescent studies (Z = 0.62, r = 0.55) had significantly higher reliability than infant/toddler studies (Z = 0.42, r = 0.40). Relative to other reported measures, HF exhibited the highest reliability among infant/toddler studies (Z = 0.42, r = 0.40), while rMSSD exhibited the highest reliability among child/adolescent studies (Z = 1.00, r = 0.76). Moderator analyses indicated greater reliability with shorter test-retest interval length, reported exclusion criteria based on medical illness/condition, lower proportion of males, prerecording acclimatization period, and longer recording duration; differences were noted across age groups. HRV is reliable among pediatric samples. Reliability is sensitive to pertinent methodological decisions that require careful consideration by the researcher. Limited methodological reporting precluded several a priori moderator analyses. Suggestions for future research, including standards specified by Task Force Guidelines, are discussed.

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.

The contributions of early adverse experiences and trajectories of respiratory sinus arrhythmia on the development of neurobehavioral disinhibition among children with prenatal substance exposure

Neurobehavioral disinhibition (ND) is a complex condition reflecting a wide range of problems involving difficulties with emotion regulation and behavior control. Respiratory sinus arrhythmia (RSA) is a physiological correlate of emotion regulation that has been studied in a variety of at-risk populations; however, there are no studies of RSA in children with ND. Data were drawn from a prospective longitudinal study of prenatal substance exposure that included 1,073 participants. Baseline RSA and RSA reactivity to an attention-demanding task were assessed at 3, 4, 5, and 6 years. ND was assessed at ages 8/9, 11, and 13/14 years via behavioral dysregulation and executive dysfunction composite measures. Greater exposure to early adversity was related to less RSA reactivity at 3 years, increases in RSA reactivity from ages 3 to 6 years, and increased behavioral dysregulation from ages 8/9 to 13/14. RSA reactivity was examined as a moderator of the association between early adversity and changes in ND. A significant Early Adversity × RSA Reactivity quadratic interaction revealed that children with decelerations in RSA reactivity exhibited increases in behavioral dysregulation, regardless of their exposure to early adversity. However, greater exposure to early adversity was related to greater increases in behavioral dysregulation, but only if children exhibited accelerations in RSA reactivity from ages 3 to 6 years. The results contribute to our understanding of how interactions across multiple levels of analysis contribute to the development of ND.

Family conflict, autonomic nervous system functioning, and child adaptation: state of the science and future directions

The family is one of the primary contexts of child development. Marital and parent-child conflict (family conflict) are common and predict a wide range of negative behavioral and emotional outcomes in children. Thus, an important task for developmental researchers is to identify the processes through which family conflict contributes to children's psychological maladjustment, as well as vulnerability and protective factors in the context of family conflict. In the current paper, we aim to advance a conceptual model that focuses on indices of children's autonomic nervous system (ANS) functioning that increase vulnerability or provide protection against psychological maladjustment in the context of family conflict. In doing so, we provide a selective review that reflects the state of the science linking family conflict, children's ANS activity, and child psychological adjustment, and offer directions and guidance for future research. Our hope is to accelerate research at the intersection of family conflict and ANS functioning to advance understanding of risk and resilience among children.

Asymmetry in children's salivary cortisol and alpha-amylase in the context of marital conflict: links to children's emotional security and adjustment

Recent research supports the promise of examining interactive models of physiological processes on children's adjustment. The present study investigates interactions between children's autonomic nervous system activity and adrenocortical functioning in the context of marital discord; specifically, testing models of concurrent responses proposed by Bauer et al. ([2002] Developmental and Behavioral Pediatrics 23:102-113) in the prediction of children's behavioral responses to conflict and adjustment. Asymmetry and symmetry in children's salivary alpha-amylase and cortisol were examined in 195 children (M age = 8 years) in response to viewing conflict vignettes. Results were partially consistent with an interactive model in the context of high marital discord; asymmetry among higher alpha-amylase and lower cortisol related to higher emotional insecurity and concurrent and subsequent maladjustment. In contrast, patterns of symmetrical responses were related to greater maladjustment for children exposed to lower levels of marital discord, supporting an additive model. Findings support the importance of a multisystem approach to investigating the adaptiveness of children's physiological stress responses, while also highlighting the value of considering physiological responses in the context of family risk.

The role of prenatal substance exposure and early adversity on parasympathetic functioning from 3 to 6 years of age

We employed latent growth curve analysis to examine trajectories of respiratory sinus arrhythmia (RSA) from 3 to 6 years among children with varying levels of prenatal substance exposure and early adversity. Data were drawn from a prospective longitudinal study of prenatal substance exposure that included 1,121 participants. Baseline RSA and RSA reactivity to an attention-demanding task were assessed at 3, 4, 5, and 6 years. Overall, there were significant individual differences in the trajectories of RSA reactivity, but not baseline RSA, across development. Greater levels of prenatal substance exposure, and less exposure to early adversity, were associated with increased RSA reactivity at 3 years, but by 6 years, both were associated with greater RSA reactivity. Prenatal substance exposure had an indirect influence through early adversity on growth in RSA reactivity. Results are in support of and contribute to the framework of allostatic load.

Cardiac vagal control and children's adaptive functioning: a meta-analysis

Polyvagal theory has influenced research on the role of cardiac vagal control, indexed by respiratory sinus arrhythmia withdrawal (RSA-W) during challenging states, in children's self-regulation. However, it remains unclear how well RSA-W predicts adaptive functioning (AF) outcomes and whether certain caveats of measuring RSA (e.g., respiration) significantly impact these associations. A meta-analysis of 44 studies (n=4996 children) revealed small effect sizes such that greater levels of RSA-W were related to fewer externalizing, internalizing, and cognitive/academic problems. In contrast, RSA-W was differentially related to children's social problems according to sample type (community vs. clinical/at-risk). The relations between RSA-W and children's AF outcomes were stronger among studies that co-varied baseline RSA and in Caucasian children (no effect was found for respiration). Children from clinical/at-risk samples displayed lower levels of baseline RSA and RSA-W compared to children from community samples. Theoretical/practical implications for the study of cardiac vagal control are discussed.

Is salivary alpha-amylase an indicator of autonomic nervous system dysregulations in mental disorders?--a review of preliminary findings and the interactions with cortisol

During recent years, a growing interest emerged in using salivary alpha-amylase (sAA) as a non-invasive, surrogate marker for sympathetic activity. Numerous studies applying stress protocols have demonstrated that sAA is highly sensitive to stress-related changes (in healthy subjects). Additionally, it was suggested that sAA might moreover serve as an index for pathological dysregulation of the autonomic nervous system (ANS) in patients showing psychopathology. Since then, a small but growing literature investigated sAA in patients with mental disorders. This review aims to give an overview of preliminary findings in this field of research. The results of n=15 studies are described in detail and implications for further research are discussed. Although the number of studies and the samples examined were rather small, changes in sAA, reflecting adrenergic dysregulation, could be demonstrated in psychopathology, especially in anxiety-related disorders. This field of research is still in its early stages. However, the studies included in this review revealed first evidence that the employment of sAA, as an indicator of ANS dysregulation in mental disorders, is promising.

How can the study of physiological reactivity contribute to our understanding of adversity and resilience processes in development?

The focus of this article is to present current progress in understanding the interplay among adversity, physiological sensitivity to context, and adaptive functioning, with an emphasis on implications and future directions for resilience researchers. It includes a review of current literature that demonstrates (a) links between various levels of adversity exposure and variability in physiological reactivity, (b) how the interplay between children's physiological reactivity and different sources of risk and adversity relates to variability in adaptive functioning, and (c) various approaches for capturing a more dynamic nature of physiological reactivity and related processes. Throughout, important conceptual and empirical issues are highlighted.

Adaptive patterns of stress responsivity: a preliminary investigation

The adaptive calibration model (ACM) is an evolutionary-developmental theory of individual differences in stress responsivity. In this article, we tested some key predictions of the ACM in a middle childhood sample (N = 256). Measures of autonomic nervous system activity across the sympathetic and parasympathetic branches validated the 4-pattern taxonomy of the ACM via finite mixture modeling. Moreover, the 4 patterns of responsivity showed the predicted associations with family stress levels but no association with measures of ecological stress. Our hypotheses concerning sex differences in responsivity were only partly confirmed. This preliminary study provides initial support for the key predictions of the ACM and highlights some of the methodological challenges that will need to be considered in future research on this topic.

Interactions between salivary cortisol and alpha-amylase as predictors of children's cognitive functioning and academic performance

We examined relations between salivary cortisol, alpha-amylase (sAA), and children's cognitive and academic functioning. Of interest were curvilinear and interactive effects of these salivary measures on cognitive and academic performance. Data were based on a sample of 28 boys and 36 girls (ages 8 and 9) in the Southeastern U.S.A. Children provided resting afternoon saliva samples. Children completed standardized tests of Intellectual Ability and schools provided academic achievement information. Regression analyses demonstrated significant curvilinear relations and interactions between cortisol and sAA in the prediction of child functioning. Contrary to current models of interactions among biological systems, findings indicated some of the highest and lowest scores were predicted at moderate levels of physiological arousal. For example, children with moderate sAA and either higher or lower cortisol had low predicted scores for Reading Ability. Children with moderate cortisol and lower sAA had the highest predicted scores for Intellectual Ability. Findings suggest that the study of interactions between biological stress response systems should not be based on models of rectilinear interactions.

Direct and moderating links of salivary alpha-amylase and cortisol stress-reactivity to youth behavioral and emotional adjustment

Recent studies have revealed evidence for interactions between autonomic nervous system (ANS) activity, indexed by saliva alpha amylase (sAA), and hypothalamic-pituitary-adrenocortical activity, in predicting psychological functioning. The present study extends this work by examining individual differences in sAA and cortisol stress reactivity in relation to behavioral and emotional adjustment in youth. Participants were 56 healthy children (age 7-16). sAA, cortisol, and other physiological and affective responses were measured before, during, and after stressor tasks (either performance or peer rejection). Basal and stress responsive sAA and cortisol as well as their interactions were assessed in relation to externalizing and internalizing behaviors and trait anxiety. sAA was positively related to anxiety, while sAA reactivity moderated associations between cortisol reactivity and problem behavior. Results highlight the importance of measuring multiple physiological systems to elucidate mechanisms underlying behavioral and emotional dysregulation.

Children's and adults' salivary alpha-amylase responses to a laboratory stressor and to verbal recall of the stressor

Salivary alpha-amylase (sAA), an enzyme produced by the salivary glands, increases in response to physical and psychosocial stressors in adults. Whether similar increases are evident among children, though, is less clear, and there is a lack of studies directly comparing children's and adults' sAA responses to an identical stressor. In this study, 24 children (9-12 years; 12 female) and 26 adults (18-23 years; 16 female) were exposed to an identical psychosocial laboratory stressor and a recall interview regarding that stressor after a 2-week delay. Saliva was collected before and 1, 10, 20, and 30 min after the stressor/recall interview. Among adults, concentrations of sAA increased on both study days, but similar increases were not detected among children. Findings suggest developmental differences in sAA reactivity, and underscore the need to characterize the confluence of elements that will reliably elicit sAA responses to mild stress in youth.

Children's internalizing symptoms: the role of interactions between cortisol and respiratory sinus arrhythmia

We examined interactions between children's physiological activity across two systems, the hypothalamic-pituitary-adrenal (HPA)-axis and the parasympathetic nervous system (PNS), as predictors of child-reported internalizing symptoms (depression, anxiety). HPA activity was indexed by baseline salivary cortisol, and PNS activity was indexed by baseline respiratory sinus arrhythmia (RSA). Study 1 consisted of 57 children (54% girls; M age=8.81 years ±.34), and Study 2 included 219 children (51% girls; M age=9.31 years ±.79). Cortisol interacted with RSA to explain unique variance in children's internalizing symptoms. Across the two studies, children with higher cortisol levels in conjunction with higher RSA levels tended to exhibit the lowest levels of depression and anxiety symptoms. Findings demonstrate that contemporaneous consideration of physiological activity across multiple systems can advance understanding of internalizing symptoms in children.

Peer victimization and aggression: moderation by individual differences in salivary cortisol and alpha-amylase

This research examined whether variations in salivary measures of the hypothalamic-pituitary-adrenal axis (cortisol) and autonomic nervous system (alpha amylase [sAA]) contribute to individual differences in the association between peer victimization and aggression. Children (N = 132; M age = 9.46 years, SD = 0.33) completed a measure of peer victimization, teachers rated children's aggression, and children's saliva was collected prior to, and following, participation in a laboratory-based peer-oriented social challenge task. Children rated their level of frustration at the end of the task. Results revealed that victimization interacted with cortisol and sAA measured in anticipation of the task to predict aggression; the victimization x cortisol contribution to aggression was partly mediated by children's self-reported frustration level. Victimization also was associated with heightened frustration in girls with high task-related sAA reactivity. Task-related sAA reactivity was associated with heightened aggression, but only for girls. These findings suggest that associations between peer victimization and aggression are moderated by variation in the activity of the major components of the psychobiology of stress; results are discussed in relation to theoretical models of individual differences in biological sensitivity to context.