Nocturnal Risk Assessment and Its Association With Anxiety Symptoms.

Human risk assessment (RA), the attentional and behavioral activities involved in detecting and analyzing threat, is feasibly enhanced at night to protect against hidden danger. However, this enhanced RA at night might come at a cost and thus signal increased risk for anxiety disorders. To test the hypothesis that the nighttime enhances RA and its associations with anxiety, the current study randomly assigned healthy volunteers (N = 87, Mean age = 22.4; 69% Female) to visit the laboratory at day or night. Participants completed a novel task that presented images depicting neutral content, injury threat (e.g., weapon) or infection threat (e.g., person sneezing). Each image was followed by a lottery decision. The task estimated RA's attentional component as threat-induced bradycardia-cardiac deceleration to threat images. RA's behavioral component was estimated as threat-induced risk aversion-decrease in risky choice following threat images. Anxiety symptoms were self-reported on the Depression, Anxiety, and Stress Scale (DASS-21). The cardiac results partially supported the "nocturnal enhancement" hypothesis: (1) The night but not the day group exhibited a sustained, non-habituating pattern of threat-induced bradycardia to infection threat images. (2) In the night but not the day group, individuals with higher bradycardia to infection images had a higher likelihood of elevated anxiety. Contrary to predictions, bradycardia to injury threat and risk aversion metrics, as well as their relations to anxiety symptoms, were not higher at night. Overall, time-of-day is shown to be an important variable to consider in studies of human threat responses and anxiety disorder risk. Based on our findings, the intuitive idea that humans have elevated RA at night is not straightforward; instead, the nighttime may selectively activate attentional orienting (vis-à-vis bradycardia) to ambiguous stimuli like those signaling risk of illness, with these nocturnal enhancements being subject to individual differences in anxiety.