Acute stress has been observed to induce hormonal alterations in animals and humans. One of the perceived effects is the increased glucocorticoid concentrations in the blood and saliva. Moreover, a large percentage of animal research have pointed out that significant increases in the levels of circulating glucocorticoids are said to have improved memory storage. Aversive conditioning paradigms and water-maze experiments have consistently shown the association of the memory enhancing effect of glucocorticoids with a significant increase in emotional arousal. This suggests a relationship between arousal and glucocorticoids on memory formation.
Similarly, it was found that the memory enhancing effect of cortisol was particular to emotionally arousing material. The findings corroborate previous animal studies which found that glucocorticoids do relate to arousal in improving memory for emotionally significant stimuli among individuals.
On the other hand, a number of human studies have presented the positive effects of post-learning stress and stress hormones, while others were not able to observe any relationship between the amount of cortisol and memory arousal or found the opposite effect. Meanwhile, other studies show the contrary, observing that stress and glucocorticoids have impaired memory in both animals and humans in specific conditions.
In addition, some studies were able to discover a parallel effect in terms of verbal recovery of material. They found that individuals who received 25 mg of cortisone had weakened memory performances when the drug was given prior to the act of remembering, but not when the same was given prior to or immediately after understanding. This indicates that both externally administered and naturally occurring glucocorticoids in the body do not seem to indicate any damage to memory acquisition, but rather to the recovery of previously gained memories.
A number of studies have produced conflicting results regarding the effects of both stress-induced elevations in cortisol secretions and those due to the administration of externally administered glucocorticoids. Some found a reduction in declarative memory performance when the stressor was introduced immediately prior to learning. On the contrary, some did not show the same effect while employing a similar stressor. The disparity noted may be due to the differences in timing of the stressor and valence of the verbal material used.
The existence of mood disorders supports the claim that stimulus valence is likewise a controlling factor in the effect of stress and stress-induced cortisol secretion on memory performance. Specifically, it was seen that stress-induced cortisol secretions mainly disrupted the memory retrieval of positively valenced material, while leaving that of neutral or negatively valenced material unchanged.
This led the authors to investigate whether psychosocial stress and the increased endogenous cortisol secretion associated with it have varying effects on the recovery of words with different valences.
Specifically, the following hypotheses would be tested: a) the negative effect of cute psychosocial stress on retrieval than on acquisition; b) that elevations in cortisol secretions due to acute stress would disrupt the retrieval of long-term memory for positive words, while leaving that for neutral or negative words unchanged; and c) that individuals with significant increases in cortisol secretions due to stress would experience greater disruption in the retrieval of positive memories.
Male participants were employed for the study. They had to be free from any serious physical and mental illness for the past 12 months. In addition, they also had to be non-smoking individuals.
They were randomly classified into three conditions, namely: a) exposure to a brief laboratory stressor prior to word presentation on the first day (pre-learning stress; n=20); b) exposure to the stressor prior to recovery on the second day (pre-retrieval stress; n=20); and c) no stress exposure.
Psychosocial stress was employed using the Trier Social Stress Test (TSST). This test is composed of two activities, an impromptu speech and the conduct of a mental computation exercise in front of an audience. Both activities were held for five minutes.
Samples of the subjects’ saliva were collected prior to the administration of the TSST and four times after exposure to the stressor. The Salivette sampling device was used for this. The said samples were immediately stored and frozen at -20°C until the conduct of biochemical analysis.
Mood changes associated with the administration of the TSST were evaluated using a standardized 6-item 5-point Likert scale. This mood scale was administered before and after exposure to the stressor. Post-stress values were then deducted from the pre-stress values, to correlate the experimentally induced mood changes on both the first and second days.
Results and Conclusion
Regarding stress-induced cortisol secretion, the pre-learning stress group indicated a significant increase in cortisol concentration as a reaction to the stressor on the first day, while the two other groups did not present the same reaction. On the other hand, the pre-retrieval stress group showed a significant reaction on the second day.
Moreover, the two groups did not show significant differences regarding post-stress cortisol concentrations, but the pre-retrieval stress group indicated a considerably higher relative increase in cortisol concentration as a reaction to the stressor.
On the effects of the stressors on memory acquisition and retrieval, no significant valence interaction, nor a main effect of group, was observed. Moreover, word recognition was greatly affected by stimulus valence, but exposure to the stressor did not have a significant effect in terms of a main effect of group.
Overall, exposure to the psychosocial stressor had no effect on both free recall and recognition, when stimulus valence was not taken into account.
The findings support the hypothesis indicating that the effect of acute psychosocial stress on previously stored declarative memory is dependent on the stimulus valence and as to when the stressor is administered. Specifically, exposure to the stressor decreased memory performance for positive stimuli. Moreover, it was observed that the decrease in performance was greater for participants who were exposed to stress before retrieval compared to those before acquisition.
It was also found that the subjects’ change in cortisol levels, as a response to stress, greatly affected memory performance. Specifically, those with higher cortisol responses had more errors of commission or false alarms in recognition, compared to those with low cortisol levels. However, contrary to one of the hypotheses, it was not specific to positive stimuli. Nevertheless, as a whole, the trends in the relationships support the hypothesis that certain phases of memory performance are hindered under high cortisol concentrations, while the other parts remain unaffected. As such, it is safe to conclude that higher cortisol responses in the pre-learning stress group would most likely lead to greater memory impairment.
In conclusion, the findings do not reinforce the hypothesis of memory impairment as a result or reaction to stress, but instead indicate that acute stress hinders memory performance for positive stimuli. On the other hand, stress-induced cortisol secretions were shown to have decreased the accuracy of memory retrieval, such as the ability to discern memories from false ones.
Significance of the Study
The indicated findings have significant implications. First is along the lines of determining false memories during a testimony. This includes mistakes in remembering stressful events. It also indicates the effect of stress-induced cortisol concentrations during retrieval may also contribute to a decreased memory performance. These are likewise important because the findings could provide possible explanations for the inconsistent literature regarding stress, cortisol levels and memory.
Domes, G., Heinrichs, M., Rimmele, U., Reichwald, U. and Hautzinger, M. (2004). Acute stress impairs recognition for positive words—Association with Stress-induced Cortisol Secretion. Stress, 7 (3), 173-181.