Post-traumatic stress disorder (PTSD) is characterised by alterations in the function of the autonomic nervous system. However, it is unclear if this dysfunction is threat-related or related to arousing stimuli in general. Pupillometry offers a simple non-invasive measure of ANS activity that can separate parasympathetic and sympathetic arousal. Participants viewed images with emotional or neutral content: 20 met diagnostic criteria for PTSD, 28 were trauma-exposed (but with no PTSD), and 17 were controls. Initial pupil constriction (a marker of parasympathetic function) was reduced for the PTSD group, while dilation due to the emotional content of the image (a marker of sympathetic activity) was greater in the PTSD group. Individuals with PTSD demonstrated enhanced physiological arousal to both threat-related and positive images. The results suggest reduced parasympathetic arousal and increased sympathetic arousal in the autonomic nervous system, which has been linked to a range of adverse health outcomes in PTSD
