Regulation of overnight sleep on negative emotion memory with moral-violation

Abstract

The processing of negative emotion memory is a key factor influencing human mental health and the ability to manipulate negative emotion memory is crucial for mental health. It is beneficial for individuals to be highly motivated to successfully forget an unpleasant experience. However, people with post‐traumatic stress disorder (PTSD) often show an imbalance in voluntary memory manipulation. They are unable to regulate memories of emotions and are exposed to negative emotions for a longer time, which over time will lead to greater damage to both physical and mental health. Witnessing moral violation may induce negative emotions in real life, but it is still unknown if when faced with memories of negative emotions associated with moral violation content, whether the process of suppression and recall manipulation would be different for non-moral content. A previous study found that overnight sleep could weaken the effect of suppression on memory. In the present study, we first selected 120 pictures and recruited participants to rate their emotional arousal, valence, and morality on a 9-point scale in an online survey. After selecting and matching negative emotional stimuli with similar emotional arousal and valence and distinguishable morality (non-moral vs. moral-violation) in the online ratings, 28 participants were required to remember the stimuli paired with the cue objects after two days’ training (overnight sleep vs. newly acquired condition) and then they had a think/no-think task (TNT) (recall vs. suppression vs. baseline) to intuitively suppress and recall these pairs. After the TNT task, a recall test was conducted to record vocal memory performance, which was scored by three scorers. The scorer reliability was measured, and showed high quality. We determined the recall score by computing the difference between recall accuracy and baseline accuracy, and found the suppression score to be the difference between suppression accuracy and baseline accuracy. Then a 2×2×2 repeated measures ANOVA with within-subject factors of training time, cue manipulation, and morality was performed. The results of the repeated measures ANOVA and the paired t -test analyses showed that memory could be adjusted through conscious cue manipulation, and negative memory with different moral content had significantly different manipulation effects. Specifically, in the newly acquired condition, the recall score in non-moral memory was significantly higher than both zero and the recall score in moral violation, while the suppression score in moral violation memory was both significantly lower than zero and marginally lower than the suppression score in non-moral pairs. Additionally, compared with the newly acquired condition, both the memory enhanced effect in the non-moral pairs and the memory forgotten effect in the moral violation memory pairs faded in the overnight sleep condition. Our findings revealed that both the retrieval of non-moral content and the suppression of moral violation content in negative emotion memories were significant when newly acquired; and overnight sleep could eliminate the influences of retrieval and suppression manipulation. These results manifest the effects of morality on negative emotion memory which can be weakened by overnight sleep consolidation. The present study extends our understanding of how moral emotional memories are stored, retrieved, and repressed after sleep.