Children with autism spectrum disorders (ASD) have difficulties modulating social behavior, including eye gaze, vocalizations, and facial affect (American Psychiatric Association, 2000). Children with ASD also demonstrate more physiological “defensiveness” - a mobilized autonomic state at baseline when compared to their typically developing peers (Bal et al., 2010; Van Hecke et al., 2009). The neurobehavioral link between physiological defensiveness and social engagement difficulties has been suggested in the Polyvagal Theory (e.g., Porges, 2007), which specifies neural circuits that promote social communication, mobilization, and immobilization. Unlike typically developing children, who exhibit effective social communication paired with a soothed physiological state, children with ASD demonstrate social engagement difficulties paired with a mobilized/defensive physiological state. We examined the relationship between baseline measures of heart rate variability (HRV; respiratory sinus arrhythmia, RSA; heart period, HP) and social symptoms associated with ASD measured via the Social Responsiveness Scale (SRS; Constantino, 2002).
Objectives:
We predicted that lower baseline RSA (greater heart rate variability) and lower baseline HP (faster heart rate) would be associated with more severe sub-scale and total scores on the SRS.
Methods:
Data were collected from 23 children (18 boys, 5 girls), aged 4 years 3 months to 7 years 9 months (M = 5.72, SD = 1.17) with prior ASD diagnoses. HP data were edited with CardioEdit and CardioBatch (Brain-Body Center, University of Illinois at Chicago; Porges, 1985). Baseline HP data were collected during a neutral 3-minute video with the LifeShirt® heart monitor. Parents completed the SRS, a 65-item questionnaire used to measure severity of ASD symptoms, including the following sub-scales: social awareness, social information processing, capacity for reciprocal social communication, social anxiety, and autistic preoccupations.
Results:
Due to non-significant RSA findings when participants were not grouped by SRS severity cutoffs, we examined the prediction of RSA and HP when participants were grouped by SRS cutoffs (severe n = 17; mild-moderate n = 6). Age was used as a covariate in all analyses. In the severe group (Mtotal = 84.76; SDtotal = 5.460) lower baseline RSA and lower baseline HP predicted higher SRS total scores, b -2.281, t(16) = -3.424, p = .005 and b= -.042, t(16) = -3.416, p = .005. Lower RSA and lower HP also predicted the autistic mannerisms sub-scale, b= -2.803, t(16) = -3.911, p = .002 and b= -.056, t(16) = -4.643, p < .001. In the mild-moderate group (Mtotal = 70.83; SDtotal = 4.119), total SRS score was not predicted from baseline RSA or HP. Baseline RSA only predicted social information processing in the mild-moderate group, b= -8.831, t(6) = -6.664, p = .007.
Conclusions:
Lower baseline RSA and HP were related to more severe social deficits in children whose SRS total score was in the severe range. Importantly, baseline RSA and HP did not predict total score for children whose SRS total score was in the mild-moderate range. This suggests that physiological defensiveness or activation may be related to severity of social symptoms of ASD in children with SRS total scores in the severe range.