Is autonomic function during resting-state atypical in Autism: A systematic review of evidence

Theories of differences in resting-state arousal in autistic individuals are influential. Differences in arousal during resting-state would impact engagement and adaptation to the environment, having a cascading effect on development of attentional and social skills. In this review, we evaluate the evidence for differences in autonomic arousal during resting-state in autistic individuals, and importantly, whether there are contextual or methodological factors that impact reports of such differences. We carried out a systematic review of the literature on 60 studies, which measured autonomic function (using indices of heart rate, pupillometry or electrodermal activity) during rest or a pre-task baseline. Of the 51 studies that investigated group differences between neurotypical and autistic participants, 60.8% of the studies found evidence of group differences. While findings of hyperarousal were more common, particularly using indices of parasympathetic function, findings of hypoarousal and autonomic dysregulation were also consistently present. Importantly, experimental context played a role in revealing such differences. The evidence is discussed with regard to important methodological factors and implications for future research are described.