Memories for traumatic events are fundamentally different from typical memories. Individuals who witness or are involved in an extremely stressful event, such as a robbery or a violent act, retain highly accurate memories for the information directly related to the trauma (e.g., a gun or verbal threat), while surrounding details are poorly remembered. This so-called weapon focus phenomenon has been found in both naturalistic and laboratory studies with humans. However, difficulties with the control of naturalistic studies and approximating trauma in the lab limit the validity of these findings.

Neurophysiologically, cortisol and norepinephrine are principal mediators of the stress response, and both influence memory function. In particular, cortisol improves memory at low levels but impairs memory at higher doses. Similarly, some evidence indicates that norepinephrine also enhances memory in low doses and either impairs or does not influence memory at high doses. Much of the experimental work in this area has been conducted with animals. Studies have recently begun to extend these paradigms to humans.

To better understand memory processing during trauma, hydrocortisone and/or yohimbine (a stimulator of central norepinephrine) will be administered to healthy adults in two experiments in order to pharmacologically model the stress response. Following infusion, participants will hear a story with emotional and nonemotional segments in one experiment (N = 80) and emotional as well as nonemotional stimuli (faces and scenes) in another experiment (N = 80). It is predicted that relative to the placebo, hydrocortisone will impair memory for both emotional and nonemotional information, yohimbine will improve memory for both types of information, and the combination of hydrocortisone and yohimbine will enhance memory for emotional aspects and impair memory for the nonemotional segments of the story. Results from this study will permit a better understanding of how emotionally charged memories are encoded and will potentially lead to treatments to mitigate the psychological effects of traumatic exposure.