Influence of stress on fear memory processes in an aversive differential conditioning paradigm in humans

It is widely assumed that learning and memory processes play an important role in the pathogenesis, expression, maintenance and therapy of anxiety disorders, such as phobias or post-traumatic stress disorder (PTSD). Memory retrieval is involved in symptom expression and maintenance of these disorders, while memory extinction is believed to be the underlying mechanism of behavioral exposure therapy of anxiety disorders. There is abundant evidence that stress and stress hormones can reduce memory retrieval of emotional information, whereas they enhance memory consolidation of extinction training. In this study we aimed at investigating if stress affects these memory processes in a fear conditioning paradigm in healthy human subjects. On day 1, fear memory was acquired through a standard differential fear conditioning procedure. On day 2 (24h after fear acquisition), participants either underwent a stressful cold pressor test (CPT) or a control condition, 20min before memory retrieval testing and extinction training. Possible prolonged effects of the stress manipulation were investigated on day 3 (48h after fear acquisition), when memory retrieval and extinction were tested again. On day 2, men in the stress group showed a robust cortisol response to stress and showed lower unconditioned stimulus (US) expectancy ratings than men in the control group. This reduction in fear memory retrieval was maintained on day 3. In women, who showed a significantly smaller cortisol response to stress than men, no stress effects on fear memory retrieval were observed. No group differences were observed with respect to extinction. In conclusion, the present study provides evidence that stress can reduce memory retrieval of conditioned fear in men. Our findings may contribute to the understanding of the effects of stress and glucocorticoids on fear symptoms in anxiety disorders and suggest that such effects may be sex-specific

Associations between Basal Cortisol Levels and Memory Retrieval in Healthy Young Individuals

Cortisol is known to affect memory processes. On the one hand, stress-induced or pharmacologically induced elevations of cortisol levels enhance memory consolidation. On the other hand, such experimentally induced elevations of cortisol levels have been shown to impair memory retrieval. However, the effects of individual differences in basal cortisol levels on memory processes remain largely unknown. Here we tested whether individual differences in cortisol levels predict picture learning and recall in a large sample. A total of 1225 healthy young women and men viewed two different sets of emotional and neutral pictures on two consecutive days. Both sets were recalled after a short delay (10 min). On Day 2, the pictures seen on Day 1 were additionally recalled, resulting in a long-delay (20 hr) recall condition. Cortisol levels were measured three times on Days 1 and 2 via saliva samples before encoding, between encoding and recall as well as after recall testing. We show that stronger decreases in cortisol levels during retrieval testing were associated with better recall performance of pictures, regardless of emotional valence of the pictures or length of the retention interval (i.e., 10 min vs. 20 hr). In contrast, average cortisol levels during retrieval were not related to picture recall. Remarkably during encoding, individual differences in average cortisol levels as well as changes in cortisol did not predict memory recall. Our results support previous findings indicating that higher cortisol levels during retrieval testing hinders recall of episodic memories and extend this view onto interindividual changes in basal cortisol levels