Fractal Analysis of Autonomic Nervous System Function in ASD
Objectives: To investigate ASD-related alterations in the fractal structure of interbeat intervals during baseline and response to an anxiogenic stimulus.
Methods: A sample of typically-developing children (n=33, age: 12.5 +/-2.9 years, full-scale IQ: 112.9 +/- 14.1, 19 male), and those with a diagnosis of ASD (n=40, age: 12.0 +/- 2.9 years, full-scale IQ: 92.9 +/- 20.6, 33 male) completed an anxiogenic task (Stroop test), preceded and followed by a 15-minute and 5-minute baseline task (movie watching), respectively. Throughout the experimental session, electrocardiogram (ECG) was measured and used to extract inter-beat interval time-series. Deterended fluctuation analysis (DFA) was used to obtain the scaling exponent, an index of complexity in the signal. Repeated measures multiple regression analysis was performed to examine the effect of group and group x time interaction on the scaling exponent while controlling for age, gender, and full-scale IQ.
Results: Multiple regression analysis revealed a significant group x time interaction for the scaling exponent (p=0.04 ) (Figure 1), suggesting atypical fractal dynamics in the ASD group.
Conclusions: Our results suggest that ASD may be associated with atypical fractal structure in the cardiac interbeat sequences. Specifically, the results point to altered, and possibility decreased, flexibility and adaptability of the autonomic response in ASD. This study adds to the body of evidence supporting atypical ANS function in ASD. Future studies with longer time-series are needed to further characterize the nature of nonlinear atypicalities in this domain.