Uncertainty contributes to stress and anxiety-like behaviors by impairing the ability of participants to objectively estimate threat. Our study used the cue-picture paradigm in conjunction with the event-related potential (ERP) technique to explore the temporal dynamics of anticipation for and response to uncertain threat in healthy individuals. This task used two types of cue. While ‘certain’ cues precisely forecasted the valence of the subsequent pictures (negative or neutral), the valence of pictures following ‘uncertain’ cues was not predictable. ERP data showed that, during anticipation, uncertain cues elicited similar Stimulus-Preceding Negativity (SPN) to certain-negative cues, while both of them elicited larger SPN than certain-neutral cues. During affective processing, uncertainty enlarged the mean amplitude of late positive potential (LPP) for both negative and neutral pictures. Behavioral data showed that participants reported more negative mood ratings of uncertain-neutral pictures relative to certain-neutral pictures and overestimated the probability of negative pictures following uncertain cues. Importantly, the enlarged anticipatory activity evoked by uncertain cues relative to that evoked by certain-neutral cues positively modulated the more negative mood ratings of uncertain-neutral pictures relative to certain-neutral pictures. Further, this more negative mood ratings and the general arousal anticipation during anticipatory stage contributed to the covariation bias. These results can provide a novel insight into understanding the neural mechanism and pathological basis of 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.