Baseline cortisol level moderated the effect of stress on associative memory: Pre-encoding and pre-retrieval manipulations.

Stress has powerful effects on memory, but previous studies have yielded mixed findings regarding its impact on associative memory and the relationship between cortisol response and memory performance. Whether stress affects both encoding and retrieval of associative memory through a common mechanism remains unclear. In addition, an individual's baseline cortisol level should be considered to clarify the cortisol reactivity - memory relationship. In this study, we recruited 63 participants for Experiment 1 and 56 participants for Experiment 2 to learn unrelated word pairs with negative and neutral valence and complete an associative recognition task. They were exposed to a stress or control condition before either the encoding phase (Experiment 1) or the retrieval phase (Experiment 2). The results showed that pre-retrieval stress significantly impaired associative memory. For pre-encoding stress, the group difference was not significant, but stress significantly predicted the corrected recognition and FA rate in the regression analysis. Regardless of whether stress was induced at pre-encoding or pre-retrieval, cortisol reactivity positively predicted the false alarm (FA) rate, while baseline cortisol levels negatively predicted the FA rate. In addition, baseline cortisol levels moderated the effect of stress on memory performance. When the baseline cortisol levels were lower, a greater cortisol reactivity was associated with a higher FA rate in both experiments. These results suggest that stress impairs the ability to distinguish old memories from lures, which is a common mechanism across memory phases. They also highlight the role of baseline cortisol in moderating the relationship between cortisol reactivity and associative memory.