Enhanced mnemonic discrimination for emotional memories: the role of arousal in interference resolution

A daytime nap with REM sleep is linked to enhanced generalization of emotional stimuli

How memory representations are shaped during and after their encoding is a central question in the study of human memory. Recognition responses to stimuli that are similar to those observed previously can hint at the fidelity of the memories or point to processes of generalization at the expense of precise memory representations. Experimental studies utilizing this approach showed that emotions and sleep both influence these responses. Sleep, and more specifically rapid eye movement sleep, is assumed to facilitate the generalization of emotional memories. We studied mnemonic discrimination by the emotional variant of the Mnemonic Separation Task in participants (N = 113) who spent a daytime nap between learning and testing compared with another group that spent an equivalent time awake between the two sessions. Our findings indicate that the discrimination of similar but previously not seen items from previously seen ones is enhanced in case of negative compared with neutral and positive stimuli. Moreover, whereas the sleep and the wake groups did not differ in memory performance, participants entering rapid eye movement sleep exhibited increased generalization of emotional memories. Our findings indicate that entering into rapid eye movement sleep during a daytime nap shapes emotional memories in a way that enhances recognition at the expense of detailed memory representations.

Awake ripples enhance emotional memory encoding in the human brain

Enhanced memory for emotional experiences is hypothesized to depend on amygdala-hippocampal interactions during memory consolidation. Here we show using intracranial recordings from the human amygdala and the hippocampus during an emotional memory encoding and discrimination task increased awake ripples after encoding of emotional, compared to neutrally-valenced stimuli. Further, post-encoding ripple-locked stimulus similarity is predictive of later memory discrimination. Ripple-locked stimulus similarity appears earlier in the amygdala than in hippocampus and mutual information analysis confirms amygdala influence on hippocampal activity. Finally, the joint ripple-locked stimulus similarity in the amygdala and hippocampus is predictive of correct memory discrimination. These findings provide electrophysiological evidence that post-encoding ripples enhance memory for emotional events.

Neurocognitive predictors of food memory in healthy adults - A preregistered analysis

Memory processes have long been known to determine food choices (Rozin & Zellner, 1985) but recognition memory of food and its cognitive, homeostatic and neuroanatomical predictors are still largely understudied. 60 healthy, overweight, non-restrictive eating adults (20 females) took part in a food wanting and subsequent food recognition and lure discrimination task at four time points after a standardized breakfast shake. With advanced tractography of 3 T diffusion-weighted imaging data, we investigated the influence of the uncinate fasciculus' (UF) brain microstructure on the interplay of food wanting and memory processes. The analysis was preregistered in detail and conducted with Bayesian multilevel regression modeling. Target recognition (d') and lure discrimination (LDI) performance of food tended to be higher than of art images while single image food memory accuracy evidently dominated art memory. On this single item level, wanting enhanced recognition accuracy and caloric content enhanced food memory accuracy. The enhancement by reward anticipation was most pronounced during memory encoding. Subjective hunger level did not predict performance on the memory task. The microstructure of the UF did neither evidently affect memory performance outcomes nor moderate the wanting enhancement of the recognition accuracy. Interestingly, female participants outperformed males on the memory task, and individuals with stronger neuroticism showed poorer memory performance. We shed light on to date understudied processes in food decision-making: reward anticipation influenced recognition accuracy and food memory was enhanced by higher caloric content, both effects might shape food decisions. Our findings indicate that brain microstructure does not affect food decision processes in adult populations with overweight. We suggest extending investigation of this interplay to brain activity as well as to populations with eating behaviour disorders.

Perceived antidepressant efficacy associated with reduced negative and enhanced neutral mnemonic discrimination

Introduction

While antidepressants are one of the first-line treatments for depression, the mechanisms underlying antidepressant action are unclear. Furthermore, the extent to which antidepressants impact emotional and cognitive dysfunction in depression requires more fine-grained approaches toward measuring these impacts in humans. Depression is associated with emotion and mood dysregulation in addition to cognitive deficits. Depressed individuals experience general memory impairment as well as a negativity bias in episodic memory, where negative events are better remembered than positive or neutral events. One potential mechanism hypothesized to underlie the negativity bias in memory is dysfunctional hippocampal pattern separation, in which depressed individuals tend to show impaired general pattern separation but enhanced negative pattern separation. Mnemonic discrimination tasks have been designed to tax hippocampal pattern separation in humans and provide a powerful approach to develop a mechanistic account for cognitive dysfunction in depression. While antidepressants have been examined primarily in rodent models in the context of hippocampal pattern separation, this has yet to be examined in humans.

Methods

Here, we investigated how antidepressant usage and their perceived efficacy was associated with emotional mnemonic discrimination, given our prior work indicating a negativity bias for mnemonic discrimination in individuals with greater depressive symptoms.

Results

We found that individuals who reported a greater improvement in their depressive symptoms after taking antidepressants (responders) showed reduced negative and enhanced neutral mnemonic discrimination compared to those with little to no improvement (non-responders). Perceived antidepressant efficacy was the strongest predictor of a reduction in the negativity bias for mnemonic discrimination, even when controlling for current depressive symptoms, antidepressant type, and other relevant factors.

Discussion

These results suggest that antidepressants, when effective, can shift memory dynamics toward healthy function.

The key to superior memory encoding under stress: the relationship between cortisol response and mnemonic discrimination

Some previous studies have shown that increased stress hormone levels have beneficial effects on memory encoding; however, there is no clear consensus on which encoding-related processes are affected by stress hormones. In the present study, we investigated the relationship between interindividual differences in neuroendocrine response to acute stress and interference resolution (i.e., mnemonic discrimination). Participants were healthy young adults who were exposed to physical and psychological stressors (Socially Evaluated Cold Pressor Test). Then participants completed the modified version of the Mnemonic Similarity Task. Specifically, they were presented with photographs of emotionally arousing (negative and positive) and nonarousing (neutral) scenes followed by a recognition memory test where they saw a mixture of old and new stimuli. Crucially, participants were also presented with critical lure items, that is, visually similar stimuli to ones presented at encoding. We found that participants who had higher cortisol response to the stressors were better in discriminating between the studied items and their visually similar lures. This effect was present for the arousing and nonarousing materials as well. These findings suggest that increased hormonal response to acute stress has a beneficial impact on the formation of distinct, nonoverlapping, unique memory representations, and consequently, on episodic memory encoding processes.

Emotional memories are (usually) harder to forget: A meta-analysis of the item-method directed forgetting literature

The current meta-analysis explored whether emotional memories are less susceptible to item-method directed forgetting than neutral memories. Basic analyses revealed superior memory for remember (R) than forget (F) items in both the neutral, M = 19.6%, CI_95% [16.1, 23.1], and the emotional, M = 15.1%, CI_95% [12.4, 17.7], conditions. Directed forgetting in either valence condition was larger for (a) words than for other stimuli; (b) recall than recognition tests; (c) studies that used recall prior to recognition testing; (d) shorter lists; and (e) studies that included buffer items. Direct comparison of the magnitude of the directed forgetting effect across neutral and emotional conditions within studies revealed relatively diminished directed forgetting of emotional items compared to neutral items, with an average difference of 4.2%, CI_95% [2.0, 6.4]. However, the nature of this finding varied broadly across studies, meaning that whether - and to what degree - emotional memories are more resilient than neutral memories likely depends on the methodological features of the study in question. Moderator analyses revealed larger differences (a) in studies for which the emotional items were more arousing than the neutral items, and (b) when buffer items were included. Together, these findings suggest that emotional memories are often more resilient to intentional forgetting than neutral memories, although further research is necessary to characterize the circumstances under which these differences emerge.