Enhanced Startle Responsivity 24 Hours After Acute Stress Exposure

Cortisol release in a stressful situation can be beneficial for memory encoding and memory consolidation. Stimuli, such as odors, related to the stressful episode may successfully cue memory contents of the stress experience. The current investigation aimed at testing the potency of stress to influence startle responsivity 24 hr later and to implicitly reactivate emotional memory traces triggered by an odor involved. Participants were assigned to either a stress (Trier Social Stress Test [TSST]) or control (friendly TSST [f-TSST]) condition featuring an ambient odor. On the next day, participants underwent an auditory startle paradigm while their eyeblink reflex was recorded by an electrooculogram. Three different olfactory stimuli were delivered, one being the target odor presented the day before. Additionally, negative, positive, and pictures of the committee members were included for comparing general startle responsivity and fear-potentiated startle. Participants of the stress group demonstrated an enhanced startle response across all stimuli compared to participants of the control group. There were no specific effects with regard to the target odor. The typical fear-potentiated startle response occurred. Stressed participants tended to rate the target odor more aversive than control participants. Odor recognition memory did not differ between the groups, suggesting an implicit effect on odor valence. Our results show that acute stress exposure enhances startle responsivity 24 hr later. This effect might be caused by a shift of amygdala function causing heightened sensitivity, but lower levels of specificity.