Acute Stress Enhances Individual Processing Of Threat Stimuli

In our daily life, we might encounter stress situation The stressor change the homeostasis whereby enhance threat processing while impair executive control. The acute stress has significant effect on the working memory and long-term memory. Furthermore, the ability to resolve threat interference and maintain goal-directed behavior is a cardinal feature of rapid behavioral adaption in face of changing environmental demands. The attentional bias towards threat stimuli is highly correlated with anxiety disorder. Many previous studies focus on the processing of threat stimuli and the effect of threat stimuli on cognitive processing. Generally speaking, threat stimuli affect attention, cognitive evaluation and response output phases. However, how the acute stress modulates attentional bias towards threat is still unclear. In addition, the neural mechanism of interaction between threat and working memory is less known In this thesis, we will explore the acute stress effect on the attentional bias towards threat as well as the neural mechanism of emotional working memory.In the first study, we investigated how the acute stress affects the attentional bias towards threat. Participants were randomly assigned to stress or control group, and performed a spatial threat cueing task. The salivary cortisol and subjective emotional experience were measured. We expected that acute stress would enhance the facilitation of attention towards threat as well as impair the disengaging attention from the threat stimuli. The stress manipulation was successfully induced stress in stress group. Participants showed difficultly disengaged attention from a threat cue compare to a neutral cue. Furthermore, acute stress exacerbates the difficultly disengage attention from cue regardless of cue valence. These results suggest that the cognitive mechanism of attentional bias towards threat is difficult disengage attention from threat. The acute stress exacerbates this effect due to the impaired top-down control.The second study was focus on the neural mechanism of improvement and impairment effect of threat stimuli on working memory. Participants performed an emotional working memory task when doing brain activation scanning. The task was a within-subject design with stimuli valence (fearful and neutral) as well as working memory load (0-and2-back) as within-subject factors. We expected that the fearful faces, comparing to neutral ones, would impair working memory performance in the0-back task, while fearful faces would enhanced working memory performance in the2-back task. Furthermore, the behavioral effect is associated with the activation of salience network including anterior insula and anterior cingulated cortex The results consistent with our hypothesis which the threat effect on working memory depends on working memory load. The hinder effect was related to the high activation of salience network, whereas the enhancement effect was related to the higher activation of the amygdala and temporal-occipital cortex. These results provide the behavioral and neural evidences to the emerging dual competition model for emotion-cognitive interactionThe third study investigated how acute stress affects the threat effects on attention and how it affects distracters memory in a24hours’ time frame. This study included two experiments. In experiment1, the social evaluation cold pressure test was used to induce acute stress or control situation Participants performed a letter search task after the stress manipulation In the letter search task, a six letters consisted string superimpose on a distracter face. Participants identified the target letter by pressing a left or a right button. The experiment was a2perceptual load (low and high) by2face valence (fearful and neutral) by2treatment (stress and control) mixed design with perceptual load and face valence as within-subject factors and treatment as between-subjects factor. We expected the similar effect as study2, and furthermore, the acute stress would enhance these effects. The results of salivary cortisol and negative emotion experiences as well as heart beat suggested successfully stress induction in stress group. Participants in stress group were response slower than control group, which suggested that the acute stress impaired the behavioral response. Moreover, the performance of the high cortisol responders to the stress manipulation was impaired when compare fearful to neutral distracter, which suggested acute stress hindered visual search when there was threat distracters. In addition, the trait anxiety enhances the impairment effect of threat in high perceptual load conditionIn the experiment2, participants of experiment1were come back on day2at the same time of day1. They were performed a surprise memory recognition task for the face distracters on day1. The salivary cortisol and subjective negative emotion experience were measured. We expected that the memory performance for the distracter in low load condition on day1would be better than the faces in high load condition Furthermore, acute stress would enhance the encoding and consolidation of fearful faces. The results were confirmed our hypothesis, which participants remember better for the faces in low load condition regardless of face valence. More important, the acute stress enhance the memory for fearful distracter in the low perceptual load condition, which suggest the acute stress effect on threat distracter memory is modulated by the cognitive load.All in all, this thesis investigated the effects of acute stress on processing of threat stimuli as well as the interaction between threat stimuli and working memory. The acute stress impairs the ability to disengaging attention from a cue position. The acute stress enhances the memory fora threat distracter. The enhancement or hindered effect of threat on working memory depends on the working memory load, and the activation of salience network is the neural mechanism of these effects.