Children’s vagal flexibility is a predictor and moderator of treatment response to early parenting interventions for inhibited youth

Behavioral inhibition (BI), a dispositional trait characterized by fear and withdrawal in the face of novelty, is a risk factor for the later diagnosis of anxiety; yet, not all inhibited children go on to develop anxiety disorders. Certain parenting behaviors moderate risk for anxiety among temperamentally inhibited youth, which has motivated the creation of early parenting interventions to mitigate this risk among young children high in BI. These programs vary in complexity, begging the question of who needs more or less intensive intervention. In addition, variability in children’s parasympathetic nervous system (PNS) functioning may provide insight into the substantial heterogeneity in anxiety outcomes for children high in BI. The current study investigates the role of vagal flexibility (VF), an index of non-linear change in PNS functioning, in children’s response to an early intervention for anxiety (ClinicalTrials.gov registration: NCT02308826). Participants ( n = 151, ages of 45–64 months) were randomized to participate in the Turtle Program (“Turtle”), a multi-component intervention comprising an adaptation of parent–child interaction therapy and social skills training, or Cool Little Kids (CLK), an established psychoeducational parenting intervention. Child participants also completed pre-, mid-, and post-treatment laboratory visits, which included a series of social stressor tasks preceded by a non-stressful but emotionally engaging video, during which cardiac physiology was recorded. Longitudinal latent profile analyses were used to identify latent non-linear trajectories of VF across the entire intervention (i.e., pre-, mid-, and post-treatment visits). Two latent classes were distinguished by the presence of high or low child VF across the treatment. Although VF class membership was not associated with intervention group membership, auxiliary within-class prediction models suggest that children who exhibited consistently greater VF demonstrated lower post-treatment clinician severity ratings of anxiety in Turtle, β = −0.21, p = .01, but not in CLK, β = 0.13, p = .39. Findings contribute to a broad literature demonstrating the utility of indices of PNS functioning in providing insight into risk for psychopathology and suggest that children’s VF moderates treatment response by supporting children’s ability to effectively engage in and extract benefits from intervention protocols. Implications for our understanding of the role children’s physiological regulation plays in the links between BI, parenting, risk for anxiety, and treatment response are discussed.