Quantifying the dynamic nature of vagal responsivity in infancy: Methodological innovations and theoretical implications

Abstract

According to polyvagal theory, rapid modulation of the vagal brake develops early in infancy and supports social interactions. Despite being viewed as a dynamic system, researchers typically assess vagal regulation using global measures of respiratory sinus arrhythmia (RSA; an index of vagal tone). This study sought to capture the dynamic property of RSA and evaluate individual differences in within-infant RSA responsivity during mother-infant interaction. RSA was evaluated in a sample of 135 6-month-old Mexican-American infants during a 5-min free play task. Mothers reported on their children's behavioral problems and competence at 18 months using the Brief Infant-Toddler Social and Emotional Assessment. Time-varying estimates of infant RSA during the interaction were obtained using a multiple window technique and spectrogram analysis. Using structural equation modeling, we evaluated whether within-infant SD of RSA predicted infants' behavioral problems and competence at 18 months, after adjusting for infants' mean RSA and covariates. Greater within-infant SD of RSA predicted more behavior problems at 18 months. This study demonstrates that assessing intra-individual variability in RSA, or the extent to which infants fluctuate around their average level of RSA during a task, enhances our ability to test polyvagal theory's central tenet: vagal regulation supports well-regulated social interaction. K E Y W O R D S infant, respiratory sinus arrhythmia, vagal functioning | 583 SOMERS Et al. biomarkers that either increase risk for poor socioemotional well-being or confer resilience among high-risk populations (Cicchetti & Toth, 2009; Sroufe, 2007). Although polyvagal theory posits that dynamic, moment-to-moment changes in vagal functioning support social engagement and behavioral regulation, the majority of empirical work testing these predictions has focused on global measures of vagal responsivity during stressful situations. According to polyvagal theory, withdrawal of the vagal brake modulates heart rate, allowing for increases in cardiometabolic output to support emotional and attentional demands from environmental stimuli. For example, the vagal brake is released during periods that require active regulatory coping, such as when one experiences pain or frustration. In contrast, activation of the vagal brake supports behaviorally calm states and social engagement during less stressful times. Despite theory-driven expectations about vagal regulation as it occurs within a task, on the time scale during which social processes unfold, vagal reactivity is typically calculated by subtracting average respiratory sinus arrhythmia (RSA; the degree of change in heart rate during the respiratory cycle) during a resting task from average RSA during a challenge task, which precludes directly examining dynamic within-task vagal responsivity. Thus, common methodical approaches are ill-equipped to test a central tenet of polyvagal theory: rapid changes in vagal influences on cardiac output in response to environmental demands ...

Within‐mother variability in vagal functioning and concurrent socioemotional dysregulation

“…Rather than focusing on trajectories of change in RSA across varying social contexts (e.g., change from play to stressful interactions, i.e., reactivity, or return to play, i.e., recovery), examining within‐person variability in RSA during a task offers insight into dynamic changes in RSA that are thought to facilitate real‐time socioemotional responding during a specific interactive context. Consistent with polyvagal theory (e.g., Porges, 2007) and the assertion that greater temporal variability around one’s own mean level of RSA in the absence of psychosocial challenge suggests difficulties maintaining homeostasis in vagal functioning, prior work from our group demonstrated that more second‐by‐second variability (within‐infant SD ) in infant RSA during free play predicted elevated behavior problems in toddlerhood (Somers et al., 2020). Similarly, Berry et al.…”

Second-by-second infant and mother emotion regulation and coregulation processes

“…By contrast, lower baseline infant RSA and smaller decreases in infant RSA (i.e., change in average RSA from baseline to a stressor task) in response to stress have been associated with deficits in self-regulation, and social, emotional, and behavioral problems in childhood (Feldman, 2009; Field & Diego, 2008; Porges, 2001; Porges et al, 1996). Prior work from our group demonstrated that higher within-infant variability (standard deviation, SD ) of RSA during free play, suggestive of difficulties maintaining homeostasis in vagal functioning in the absence of environmental challenges, predicted elevated behavior problems in toddlerhood (Somers, Curci, & Luecken, 2020). Context-appropriate infant RSA (indicated by higher within-infant mean and lower within-infant SD of RSA during free play) may enable infants to more effectively participate in social interactions, leading to smoother Parent × Child interactions and more sensitive caregiving (e.g., Perry, Mackler, Calkins, & Keane, 2014).…”

Introduction to the SEED Science special issue

“…describe another novel approach: stressing caregivers during caregiver-child face-toface interactions. They find that while caregiver behavior was not rated differently between stress and non-stressed caregivers, infant cortisol responses and infant distress reflected the stress condition, and caregivers rated themselves more negatively following the stress exposure Somers et al (2022). present data suggesting more nuanced measurement of respiratory sinus arythmia (RSA, specifically, intraindividual variability in RSA during a task at 6 months) offers predictive value.…”

“…Somers et al. (2022) present data suggesting more nuanced measurement of respiratory sinus arythmia (RSA, specifically, intraindividual variability in RSA during a task at 6 months) offers predictive value. In their article, Mexican‐American infants with greater RSA variability at 6 months were reported by parents to have more behavior problems at 18 months.…”