Positive, But Not Negative, Emotion Retroactively Enhances Memory via Neural Reactivation

Emotion profoundly influences our memory for neutral events. For instance, positive emotions elicited by well-timed humor in a classroom can lead to stronger retention of the just-preceding lesson. This retroactive enhancement effect is well established: in animals, novel or emotional events (e.g., exploring a new environment or receiving a shock) can enhance memory for neutral stimuli encountered minutes to hours earlier (Dunsmoor et al., 2022). Similarly, in humans, emotional stimuli (e.g., frightening or pleasant pictures) can boost memory for neutral information presented seconds before those stimuli (Anderson et al., 2006). These findings indicate that emotional stimuli retroactively strengthen memory for immediately preceding neutral information. The ability of both positive and negative emotional stimuli to retroactively enhance memory for a preceding neutral item is often attributed to emotional arousal, which strengthens recent memories by enhancing attention (Anderson et al., 2006; Mather and Sutherland, 2011). However, different emotional valences may influence memory via different attentional mechanisms. According to attentional theories, negative emotion narrows attention to salient details, potentially intensifying the encoding of the item's core features (Easterbrook, 1959). In contrast, positive emotion broadens attentional scope, potentially enriching the item's encoding with a wider array of contextual and associative details (Fredrickson and Branigan, 2005). This divergence raises a key question: Do these distinct attentional modes enhance memory through the same neural mechanism? This question relates to two competing accounts of memory stabilization. The encoding variability hypothesis contends that superior memory arises from greater dissimilarity in neural representations across study episodes. This variability is proposed to result in the incorporation of diverse contextual information, thereby creating multiple retrieval routes and enhancing memory performance (Wirebring et al., 2015). In contrast, the neural pattern similarity hypothesis, supported by a growing body of empirical data, posits that memory … Correspondence should be addressed to Luzi Xu at luzixu{at}polyu.edu.hk.