The Social Engagement System: Functional Differences in Individuals with Autism

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The Polyvagal Theory links the evolution of the autonomic nervous system to affective experience, emotional expression, facial gestures, vocalization and social engagement behavior. Therefore, the theory provides a plausible explanation for the bio-behavioral indices of several psychiatric disorders. The vagus as a "system" provides a rich organizing principle to investigate several of the behavioral, psychological, and physiological features associated with compromised social behavior in several psychiatric disorders. The Polyvagal Theory describes this integrated system as the Social Engagement System. Observations of the behaviors and physiological responses of autistic individuals suggest that they have great difficulties in recruiting the neural circuit that regulates the social engagement system. This model predicts that a deficit in the system would produce atypical social behaviors such as social withdrawal; improper communication (i.e., poor intonation and prosody); difficulty listening (inability to extract human voice from background noise); poor eye contact; inappropriate facial expressivity (i.e., flat affect); and atypical visceral functioning (i.e., low cardiac vagal tone). These indices are directly related to the atypical behaviors associated with autism, and several other psychiatric disorders. In the current study, measures related to the functioning of these components were obtained to test the hypothesis that autistic individuals have a compromised social engagement system. Forty subjects participated in the study (20 autistic, 31 males, ages 9-24). Data were collected to assess autonomic functioning (i.e., cardiac vagal tone), the ability to extract human voice from a compromised environment, an estimate of right ear advantage, and looking behavior (i.e., eye contact). Analyses showed that autistic individuals scored poorer on all measures assessing social engagement system functioning. Compared to controls, the autistic group had lower mean cardiac vagal tone and shorter heart periods, performed poorer on extracting human voice from a compromised environment, on a dichotic listening task, and on a measure of right ear advantage. They also spent significantly less time fixating on the eyes and more time fixating off of the face when viewing a movie of a person telling them a story. Results support the hypothesized relation between a compromised social engagement system and the atypical features associated with autism.