There is evidence that glucocorticoids have an impact on intrusive memories in patients with posttraumatic stress disorder (PTSD). Hydrocortisone impairs intrusive memory retrieval whereas dexamethasone should strengthen intrusions in PTSD. We, the investigators, want to investigate (1) the effect of these two glucocorticoids on traumatic memories and (2) assess the neural correlates using the script-driven imagery paradigm in the functional magnetic resonance imaging (fMRI) scanner. We hypothesize that intrusive memories are less intensive under hydrocortisone-administration and more intense under dexamethasone-administration comparing both to a placebo-condition. Regarding the neural activation pattern we expect higher activation in the hydrocortisone condition in the amygdala, the hippocampus and the medial prefrontal cortex compared to the placebo-condition and less activation in the dexamethasone-condition compared to the placebo-condition.