The effects of stress on different stages of memory
Research suggests that memory is influenced by stress and the associated rise of glucocorticoids, such as cortisol. While human studies have generally found a negative effect of stress and elevated cortisol on memory, animal studies have demonstrated a dose-dependent facilitative effect. These discrepant findings may be a result of methodological limitations in the human literature, which often confound the different stages of memory by elevating cortisol levels prior to encoding, consolidation and retrieval. The purpose of the current study was to parse the effects of an acute psychosocial stressor on these separate memory processes by varying the timing of the stressor. Based on recent evidence, we predicted that stress would enhance encoding and consolidation, but impair retrieval. 208 college students (63 male, 138 female, mean age = 18.9) were randomly assigned to a no-stress control group (n = 51) or one of three groups stressed at different time points: prior to stimulus presentation (encoding/ consolidation, n = 51), immediately after stimuli presentation (consolidation, n = 56), or just before memory testing 48 hours later (retrieval, n = 50). Salivary cortisol was measured at baseline and 20 minutes after the stressor. Both verbal and visual memory was measured at the 48-hr delay using a film stimulus developed by the investigator and with the WMS-III narrative. Results demonstrated that the group stressed prior to consolidation significantly outperformed controls on the film recognition at delay for verbal and total scores. This effect may have been related to cortisol response, as this was the only stress group to exhibit a significant increase in cortisol (40%) following the stressor. No significant differences in memory were found between the other stress conditions and controls. Within-group correlations between change in cortisol and memory were not significant, but exploratory analyses revealed a small but significant positive correlation for cortisol and verbal scores on the film recognition test across all groups (rxy = .18). Results support the hypothesis that stress enhances consolidation of new information, and provides the first evidence of this for verbal memory. Findings did not support a detrimental effect of stress on retrieval.