استرس و بازیابی حافظه هیجانی: اثر جنسیت و واکنش کورتیزول

In some situations, memory is enhanced by stressful experience, while in others, it is impaired. The specific components of the stress–response that may result in these differing effects remain unclear, and the current study sought to address this knowledge gap. Forty healthy participants (20 women, 20 men) were exposed to emotionally arousing and neutral pictures. Twenty-four hours later, 20 participants underwent a social stressor (speech and math tests), and 20 underwent a control reading task, both followed by a delayed free recall task. Cortisol responders to the stress condition (5 men and 1 woman) showed reduced memory retrieval for both neutral and emotionally arousing pictures. Men and women in the stress condition who did not produce a cortisol response showed increased retrieval of unpleasant pictures compared to controls. The results provide further evidence that cortisol is a primary effector in the stress-induced memory retrieval deficit. At the same time, stress can enhance memory retrieval performance, especially for emotional stimuli, when the cortisol response is absent.

Memory performance is affected by stress. The direction of this effect, however, depends on many factors: the nature of the stressor, the emotional arousal of the to-be-remembered material, sex of the stressed individuals, and interactions among these factors. Such factors have led to mixed findings with regard to the effects of stress on memory. Stress after learning can improve memory consolidation (see Roozendaal, 2000 for review). By contrast, stress before memory testing can impair memory retrieval performance ( Buchanan et al., 2006, de Quervain et al., 1998 and Kuhlmann et al., 2005). Roozendaal and colleagues have documented that these differences in the effects of stress on the different phases of memory are dependent on the amygdala. Specifically, the stress enhancement of consolidation as well as the impairing effects of stress on retrieval is dependent on the integrity of the basolateral amygdala (see Roozendaal, 2000 for review). This discrepancy in how stress affects memory—enhancing consolidation while impairing retrieval—may help explain some of the discrepant findings on stress and memory. While a stress response is typically defined by an increase in corticosteroid release, there are considerable individual differences in this response, which have been well-documented in human studies (Pruessner et al., 1997). Some individuals show persistent, large cortisol increases in response to stress while others show little or no such response (Kirschbaum et al., 1995). In addition to individual differences in the cortisol stress response, situational factors inherent in stress tasks influence whether or not a cortisol response will be elicited. These situational factors are a perceived lack of control and experience of distress (Dickerson and Kemeny, 2004 and Lundberg and Frankenhaeuser, 1980). Situations associated with challenge, such as moderate physical exercise, may result in autonomic nervous system (ANS) activity, but not a corticosteroid response (Lovallo et al., 1985). In situations associated with challenge, but without a cortisol response, mild stress may have a different effect on memory performance than a more severe stressful situation. Studies have documented differential effects of moderate stress on memory. We recently showed that subjects who produced a cortisol response to a cold pressor task showed impaired memory retrieval performance for words learned one hour before the stressor (Buchanan et al., 2006). Subjects who produced a skin conductance response to the cold pressor (indicative of ANS activity), but not a cortisol response did not show reduced retrieval performance. These results suggest that cortisol, and not activation of the sympathetic nervous system, is the primary actor in the stress-induced retrieval deficit. There are important nuances to this effect, though. Some studies have shown that a mild stressor or a small dose of corticosterone can actually improve memory performance. Domes and colleagues (2005) showed that subjects who had lower salivary cortisol levels after a 25 mg dose of cortisol showed improved memory retrieval performance compared to both a placebo group and a high responder group, demonstrating the so-called inverted-U pattern of cortisol on performance (ala, Yerkes & Dodson, 1908). Sex differences are often reported both in responses to stress (Kudielka & Kirschbaum, 2005) and in studies of learning and memory (Cahill, 2005 and Wolf, 2006, among many other domains that are beyond the scope of our review). Men tend to show a greater cortisol stress response than women in laboratory studies (Kirschbaum, Kudielka, Gaab, Schommer, & Hellhammer, 1999). Studies examining sex differences have shown that men are more affected by stress than women on both declarative memory retrieval (Wolf, Schommer, Hellhammer, McEwen, & Kirschbaum, 2001) as well as in fear conditioning (Jackson et al., 2006, Zorawski et al., 2006 and Zorawski et al., 2005). The reason for this sex difference is unclear, although there has been speculation on the potential beneficial effects of female sex hormones (Wolf, 2006) and sex differences in cortisol response to stress (Kudielka & Kirschbaum, 2005). The current study was designed to examine the effects of stress on memory retrieval in men and women. If corticosteroids are the main actor in producing a stress-induced retrieval deficit, then individuals who do not produce a cortisol response may show no effect (or even a beneficial effect, if the stress is not severe) of stress on memory retrieval. Additionally, if sex differences in cortisol response to stress are responsible for the sex differences in stress-induced memory effects, then it would be predicted that in the absence of a cortisol response, men and women may show similar memory performance. Finally, we investigated how this stress–effect interacted with the emotional arousal of the memory material, by using emotional and neutral pictures as to-be-remembered stimuli.