Available online 13 April 2024, 107928

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Memory for inherently neutral elements of emotional events is often enhanced on delayed tests - an effect that has been attributed to noradrenergic arousal. Reactivation of a memory is thought to return its corresponding neural ensemble to a state that is similar to when it was originally experienced. Therefore, we hypothesized that neutral elements of memories, too, can be enhanced through reactivation concurrent with heightened arousal. Participants (n = 94) visited the lab for three sessions. During the first session, they encoded 120 neutral memories consisting of an object presented in unique context images. In session two, the 80 objects were reactivated by presenting their corresponding context images, 40 of which were immediately followed by an arousal-inducing shock. Finally, recognition memory for all objects was tested. It was found that memory for reactivated objects was enhanced, but even though the shocks elicited elevations in arousal as indexed by skin conductance, there was no difference between memory of objects reactivated with and without heightened arousal. We thus conclude that arousal, when isolated from other cognitive and affective variables that might impact memory, has no enhancing effect on reactivated memories.

Section snippetsNo evidence that arousal affects reactivated memories

The capacity to remember previous experiences has been shaped by evolution to prioritize information that is relevant to survival (Klein et al., 2002, Nairne and Pandeirada, 2008). This is why elements of emotionally charged events, such as a car’s head lights in near-fatal accidents or a gun in violent encounters, leave particularly vivid and long-lasting memories (Hirst et al., 2010, Talmi, 2013). As the capacity to store memories is presumed to be limited, it needs to be decided for each

Participants

Previous studies have demonstrated noradrenergic memory enhancements of initial encoding with sample sizes of around 20 participants (e.g. Schwarze et al., 2012), but did not consistently report effect sizes on which power analysis can be based. We sought to include a substantially larger sample for two reasons. First, it has been demonstrated that effect sizes of published studies are, on average, twice as large as direct replications (Camerer et al., 2018). Second, instead of direct

Vividness and reliving ratings did not differ across groups and conditions

A mixed ANOVA of mean vividness ratings given on day one of the experiment with Group (immediate test, delayed test) as between-subjects factor and Reactivation Condition (no reactivation, reactivation, reactivation with shock) as within-subjects factor revealed no significant effects (all F < 0.774, all p > 0.463). Similarly, a mixed ANOVA of mean reliving ratings given on day two with the same factors, but without the level ‘no reactivation’ as those trials were not presented during session

Discussion

The present study was conducted to test whether the strength of declarative memories can be retroactively altered when reactivated in the presence of heightened noradrenergic arousal, but finds no evidence for this hypothesis. Recognition accuracy of objects that were reactivated followed by a shock was similar to objects reactivated without a shock, independent of the magnitude of the arousal response as indexed via skin conductance responses, and regardless of reactivation strength as indexed

CRediT authorship contribution statement

Olivier T. de Vries: Data curation, Formal analysis, Methodology, Writing – original draft. Sascha B. Duken: Data curation, Validation. Merel Kindt: Conceptualization, Writing – review & editing. Vanessa A. van Ast: Conceptualization, Funding acquisition, Methodology, Software, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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