Stress effects on working memory, explicit memory, and implicit memory for neutral and emotional stimuli in healthy men

Luethi, Mathias · 2008 · OpenAlex-citations

DOI: 10.3389/neuro.08.005.2008

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Summary

This study investigates the differential effects of acute psychological stress on various memory systems, specifically examining working memory, explicit memory, and implicit memory for both neutral and emotional stimuli. Motivated by evidence that stress modulates memory in complex ways—often impairing hippocampus-dependent processes while facilitating amygdala-dependent ones—the researchers aimed to determine how stress impacts distinct memory phases and types in humans. The study focused on healthy male subjects to control for potential gender differences in stress responses. Thirty-five young adult male students were randomly assigned to either a stress group or a control group. Stress was induced in the experimental group using the Trier Social Stress Test (TSST), a standardized procedure involving public speaking and mental arithmetic tasks designed to elicit a cortisol response. Salivary cortisol levels were measured repeatedly to validate the stress induction. The control group underwent a relaxation phase instead. Both groups then completed a battery of memory tests: verbal and spatial explicit memory (using the LGT-3 test), working memory (using a reading span task), perceptual priming (fragmented pictures), contextual priming (visual search task), and classical conditioning (pairing neutral stimuli with positive or negative emotional stimuli). The results confirmed that the TSST successfully induced stress, evidenced by significantly elevated salivary cortisol levels in the stress group compared to controls. Stress had a pronounced negative impact on working memory, with the stressed group showing significantly lower reading span scores and fewer total correct responses. In contrast, stress did not impair verbal explicit memory; however, it significantly enhanced performance in spatial explicit memory. For implicit memory involving neutral stimuli, stress had no effect on either perceptual or contextual priming. Crucially, stress facilitated implicit learning for emotional stimuli, but only for negative content. In the classical conditioning task, stressed subjects showed significant conditioning for negative stimuli, whereas control subjects did not. No conditioning effects were observed for positive stimuli in either group. These findings demonstrate that acute stress disrupts working memory processing while selectively enhancing specific types of memory. The impairment of working memory aligns with previous evidence of stress-induced deficits in prefrontal cortex-dependent functions. The enhancement of spatial explicit memory and implicit conditioning for negative stimuli suggests that stress facilitates amygdala-dependent memory processes, particularly for emotionally salient, negative information. The authors conclude that these selective effects reinforce the view that stress is not uniformly detrimental to memory but rather modulates it based on the memory system and emotional valence involved. The results have implications for understanding psychiatric disorders such as post-traumatic stress disorder, where heightened sensitivity to negative emotional cues and impaired working memory are common features.

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• stress arousal performance