When the approaching threat is uncertain: Dynamics of defensive motivation and attention in trait anxiety.

Uncertainty of threat has been linked to anxiety, but little is known about how neurophysiological responses change as uncertain threats approach and whether trait anxiety modulates these changes. The current study was designed to explore aspects of the dynamics of defensive motivation (startle reflex elicited by acoustic startle probes), attention (probe N100 component of event-related potentials elicited by acoustic startle probes), and autonomic nervous system activity (heart rate) when the approaching threat was certain or uncertain in a variant of the threat probability task. Behavioral results showed that high-trait anxious individuals reported higher levels of anxiety than low-trait anxious individuals only under the uncertain threat condition. Electromyographic data showed that high-trait anxious individuals tended to produce a more pronounced startle reflex, especially when the uncertain threat was proximal. This pattern was not observed in low-trait anxious individuals. By examining early attention engagement through probe N100, we observed a similar pattern in relation to defensive motivation. Moreover, under the uncertain threat condition, high-trait anxious individuals yielded a greater deceleration of heart rate than low-trait anxious individuals. These results indicate a distinct modulation effect of trait anxiety in the dynamics of defensive motivation, attention, and the autonomic nervous system during the anticipation of uncertain threats.