Stress differentially modulates fear conditioning in healthy men and women.

BACKGROUND Stress and stress hormones modulate emotional learning in rats and might have similar effects in humans. Theoretic accounts of posttraumatic stress disorder (PTSD), for example, implicate the stress-induced modulation of fear conditioning in the development of intrusive emotional reactions. The present study examined the impact of acute stress and cortisol (CORT) on classically conditioned fear in men and women. METHODS Ninety-four healthy undergraduates were exposed to a mild stressor (or control condition) while subjective anxiety and glucocorticoid stress responses (salivary CORT) were measured. One hour later, all participants participated in a differential fear conditioning procedure while conditioned skin conductance responses (SCR) were recorded. RESULTS Exposure to the stressor increased subjective anxiety and elevated CORT levels. In men, stress exposure facilitated fear conditioning; whereas in women, stress appeared to inhibit fear conditioning. The impact of stress on differential conditioning in men was associated with increased CORT levels. CONCLUSIONS Consistent with animal models, these results demonstrate that stress exposure can modulate classical conditioning in humans, possibly via hormonal mechanisms. The enhancing effects of stress on the formation of conditioned fear might provide a useful model for the formation of pathological emotional reactions, such as those found in PTSD.