Diminished Autonomic Response to Social Partners in Infants Later Diagnosed with Autism Spectrum Disorder

Background:   The core behavioral symptoms of autism spectrum disorder (ASD) emerge developmentally and are not reliably observed within the first year of life (Jones et al., 2014).  Even sensitive measures, like those generated from eye-tracking techniques, have not yet identified consistent reliable differences between children with and without ASD until the second year of life. Biological measures, such as respiratory sinus arrhythmia (RSA), hold great potential for detecting predictors of an ASD outcome before behavioral differences emerge.  RSA is a measure of heart rate variability that indicates the body’s readiness to engage with environmental stimuli (Grossman & Taylor, 2007).  RSA response patterns have been linked to social functioning in children with ASD (Sheinkopf et al., 2009).  Differential patterns of RSA response may be part of the underlying biology of ASD and, therefore, be detectable within early infancy.    

Objectives: To identify early patterns of behavioral and RSA responses in infants later diagnosed with ASD.

Methods:   Two groups of infants were compared: infants with an ASD outcome (N = 8) and matched controls (N = 186).  Infants were seen as part of their participation in the Maternal Lifestyle Study (MLS), a longitudinal study of the effects of drug exposures on long term developmental outcomes.  At four months infants completed the face-to-face still-face (FFSF) protocol with their mother.  The FFSF begins with the caregiver and infant in face to face interaction (play), followed by a period when the caregiver is instructed to face the infant relatively expressionless (still face), and ending with a reunion episode of normal face to face interaction (reunion). Infants were also observed in a face to face play interaction with a novel female examiner immediately following the caregiver interaction (stranger).   ECG was collected to measure RSA. ECG post-processing incorporated automated artifact detection and correction routines. RSA was calculated from the resulting “cleaned” time series data using Porges’ method.  Infant behaviors (passive-withdrawn, protest, object-environment, social monitor, and social positive engagement) were coded from video.

Results: A general linear mixed model of the FFSF paradigm revealed no significant group differences on RSA during interactions with the mothers between infants with an ASD outcome and controls.  Both groups of infants demonstrated a decrease in RSA during the still face phase compared to the play phase (p <.05).  No significant behavioral differences were detected.  However, in response to play with a stranger, an ANOVA revealed that the infants with an ASD outcome had lower RSA than controls (p < .05).  During the interaction with a stranger, lower RSA response was associated with more protesting behaviors (p <.01), whereas higher RSA response was associated with more social monitoring (p = .001).

Conclusions: Infants later diagnosed with ASD exhibited greater autonomic reactivity during interactions with an unfamiliar adult than did comparison infants. There were no differences between groups during interactions with mothers.  Physiological dysregulation, as indicated here by a lower RSA response, may function as an early biological marker of difficulties with social interactions before differences in behavioral responses are detectable.