Autonomic modulation of pain perception in autism spectrum disorder: unraveling the role of parasympathetic activity among autistic adults

Autonomic dysfunction in autism spectrum disorder (ASD) is well-documented, yet its role in pain processing remains unclear. Given the established link between vagal tone and pain inhibition in neurotypical individuals, we hypothesized that autistic individuals would show reduced vagal tone associated with diminished pain inhibition capacities. This was measured via heart rate variability (HRV) and experimental pain intensity ratings. Forty-nine autistic adults diagnosed with level 1 severity of ASD and 39 typically developing controls (TDC), all with IQ above 80, underwent pain quantitative sensory testing and HRV assessments. Vagal tone indices, root mean square of successive differences (RMSSD), and the percentage of successive RR intervals that differ by more than 50 milliseconds (pNN50) were measured during resting-state, pain exposure to the individually tailored pain stimuli, and recovery. The ASD group demonstrated lower resting vagal tone (RMSSD: P = 0.019; pNN50: P = 0.017) but, similar to the TDC, responded with increased vagal tone both during pain exposure (RMSSD: P = 0.003; pNN50: P = 0.008) and recovery (RMSSD: P = 0.003; pNN50: P = 0.033). No significant main effects of RMSSD or pNN50 on psychophysical parameters were observed. However, only within the ASD group, higher resting vagal tone correlated with lower pain ratings to individually tailored stimuli (RMSSD: r = -0.389, P = 0.012; pNN50: r = -0.383, P = 0.013). Our findings suggest a potential protective role of parasympathetic activity in pain processing of autistic adults, although the complex nature of pain perception and study limitations warrant further investigation.