The effects of acute stress on episodic memory: A meta-analysis and integrative review

Abstract

A growing body of research has indicated that acute stress can critically impact memory. However, there are a number of inconsistencies in the literature, and important questions remain regarding the conditions under which stress effects emerge as well as basic questions about how stress impacts different phases of memory. In this meta-analysis, we examined 113 independent studies in humans with 6,216 participants that explored effects of stress on encoding, postencoding, retrieval, or postreactivation phases of episodic memory. The results indicated that when stress occurred prior to or during encoding it impaired memory, unless both the delay between the stressor and encoding was very short and the study materials were directly related to the stressor, in which case stress improved encoding. In contrast, postencoding stress improved memory unless the stressor occurred in a different physical context than the study materials. When stress occurred just prior to or during retrieval, memory was impaired, and these effects were larger for emotionally valenced materials than neutral materials. Although stress consistently increased cortisol, the magnitude of the cortisol response was not related to the effects of stress on memory. Nonetheless, the effects of stress on memory were generally reduced in magnitude for women taking hormonal contraceptives. These analyses indicate that stress disrupts some episodic memory processes while enhancing others, and that the effects of stress are modulated by a number of critical factors. These results provide important constraints on current theories of stress and memory, and point to new questions for future research. (PsycINFO Database Record

Figure 1

Flow diagram illustrating the process of our review, screening, and article selections.

Figure 2

Effect of stress on cortisol. Size of the square indicates the relative weight assigned to that study in the analysis. Error bars represent the 95% confidence interval of the effect. This meta-analysis indicates that stress significantly increased cortisol from baseline to post-manipulation relative to a control condition.

Figure 3

Effect of stress on encoding. Size of the square indicates the relative weight assigned to that study in the analysis. Error bars represent the 95% confidence interval of the effect. Points to the left of zero indicate a study-average impairment of encoding, and points to the right of zero indicate a study-average enhancement of encoding. This meta-analysis indicated that stress did not significantly influence encoding across all studies and paradigms.

Figure 4

Significant moderators of stress effects on encoding. Size of circles in the continuous plot indicates the relative weight given to that study in the analysis. Effects of stress on encoding were moderated by the stress-encoding delay as well as the relevance of the learned items to the stressor.

Figure 5

Depiction of the interrelations of stressor type, item relevance, and stress-encoding delay. Size of the dots indicates the relative weight given to each study in the analysis. This graph illustrates that at a study-average level it is difficult to disentangle item relevance to the stressor from delay, especially once stressor type is also taken into account.

Figure 6

Effect of post-encoding stress on memory. Size of the square indicates the relative weight assigned to that study in the analysis. Error bars represent the 95% confidence interval of the effect. Points to the left of zero indicate a study-average impairment in memory, and points to the right of zero indicate a study-average enhancement in memory. This meta-analysis indicated that post-encoding stress significantly enhanced memory across all studies and paradigms.

Figure 7

Significant moderators of post-encoding stress effects. Size of circles in the continuous plot indicates the relative weight given to that study in the analysis. Effects of post-encoding stress were moderated by whether the encoding task and stressor were conducted in the same physical context, the inclusion of hormonal contraceptives, and the time of day the study began.

Figure 8

Effect of retrieval stress on memory. Size of the square indicates the relative weight assigned to that study in the analysis. Error bars represent the 95% confidence interval of the effect. Points to the left of zero indicate a study-average impairment in retrieval, and points to the right of zero indicate a study-average enhancement in retrieval. This meta-analysis indicated that stress significantly impaired retrieval across all studies and paradigms.

Figure 9

Significant moderators of stress effects on retrieval. Effects of stress on retrieval were greater for negative and positive items than for neutral items. In addition, effects of stress on retrieval were greater when women using hormonal contraceptives were excluded from the study.

Figure 10

Effects of post-encoding/retrieval stress on memory. Size of the square indicates the relative weight assigned to that study in the analysis. Error bars represent the 95% confidence interval of the effect. Points to the left of zero indicate a study-average impairment in memory, and points to the right of zero indicate a study-average enhancement in memory. This meta-analysis indicated that stress that impacted both the post-encoding and retrieval phases of memory did not influence memory across all studies and paradigms.

Figure 11

Effect encoding/retrieval stress on memory. Size of the square indicates the relative weight assigned to that study in the analysis. Error bars represent the 95% confidence interval of the effect. Points to the left of zero indicate a study-average impairment in memory, and points to the right of zero indicate a study-average enhancement in memory. This meta-analysis indicated that stress that impacted encoding, post-encoding, and retrieval phases of memory marginally impaired memory across all studies and paradigms.

Figure 12

Delay between encoding and retrieval moderated effects of stress on memory when the stressor occurred within a timeframe to influence encoding, post-encoding, and retrieval phases. With less time between encoding and retrieval, stress at encoding/retrieval impaired memory to a greater extent than with more time.

Figure 13

Effects of reactivation stress on memory. Size of the square indicates the relative weight assigned to that study in the analysis. Error bars represent the 95% confidence interval of the effect. Points to the left of zero indicate a study-average impairment in memory, and points to the right of zero indicate a study-average enhancement in memory. This meta-analysis indicated that post-reactivation stress did not influence memory across all studies and paradigms.