# Nocturnal Risk Assessment and Its Association With Anxiety Symptoms

## TL;DR

This study finds that nighttime enhances threat-related attention and is linked to higher anxiety symptoms, suggesting that our body's response to danger varies with the time of day.

## Contribution

The study introduces a novel task to show that nighttime selectively enhances attentional threat responses and their link to anxiety.

## Key findings

- Nighttime, but not daytime, groups showed sustained cardiac deceleration to infection threat images.
- Higher cardiac deceleration to infection images at night was associated with elevated anxiety symptoms.
- Time-of-day modulates threat responses and anxiety phenotype expression, particularly for ambiguous illness-related threats.

## Abstract

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.

The current study provides novel evidence that the night period amplifies both: (i) cardiac deceleration towards image‐based threat and (ii) the inter‐person association between such cardiac decelerations and anxiety symptoms. Situating threat responses in an evolutionary‐ecological framework, findings suggest that time‐of‐day modulates cardiac threat responding and the expression of an anxiety phenotype related to autonomic/attentional functioning.