The neuroscience of positive memory deficits in depression

Emotion Regulation Under Stress: A Social Processing and Memory Perspective

Research on emotion regulation often focuses on cognitively effortful self-regulation strategies, but exposure to stress has been shown to interfere with the underlying mechanisms supporting such processes. Understanding alternative strategies that potentially bolster emotion regulation under stress is an important topic of investigation. Two potential alternatives involve everyday occurrences of social processing and memory recall. Social support and past emotional experiences may help in guiding us toward appropriate neurophysiological responses through overlapping circuitry with stress and reward systems, while also buttressing cognitive regulation strategies by expanding one's perspective and allowing multiple opportunities to regulate retrospectively. In recognition that ongoing social and emotional events are often at the beginning of a cascade of both emotion regulation and memory processes, this chapter focuses on the emerging role of social relationships and autobiographical memory recall in regulating emotions under stress, highlighting opportunities and challenges associated with this process.

Behavioral Animal Models and Neural-Circuit Framework of Depressive Disorder

Depressive disorder is a chronic, recurring, and potentially life-endangering neuropsychiatric disease. According to a report by the World Health Organization, the global population suffering from depression is experiencing a significant annual increase. Despite its prevalence and considerable impact on people, little is known about its pathogenesis. One major reason is the scarcity of reliable animal models due to the absence of consensus on the pathology and etiology of depression. Furthermore, the neural circuit mechanism of depression induced by various factors is particularly complex. Considering the variability in depressive behavior patterns and neurobiological mechanisms among different animal models of depression, a comparison between the neural circuits of depression induced by various factors is essential for its treatment. In this review, we mainly summarize the most widely used behavioral animal models and neural circuits under different triggers of depression, aiming to provide a theoretical basis for depression prevention.

The Functional Neuroimaging of Autobiographical Memory for Happy Events: A Coordinate-Based Meta-Analysis

Neuroimaging studies using autobiographical recall methods investigated the neural correlates of happy autobiographical memories (AMs). The scope of the present activation likelihood estimation (ALE) meta-analysis was to quantitatively analyze neuroimaging studies of happy AMs conducted with autobiographical recall paradigms. A total of 17 studies (12 fMRI; 5 PET) on healthy individuals were included in this meta-analysis. During recall of happy life events, consistent activation foci were found in the frontal gyrus, the cingulate cortex, the basal ganglia, the parahippocampus/hippocampus, the hypothalamus, and the thalamus. The result of this quantitative coordinate-based ALE meta-analysis provides an objective view of brain responses associated with AM recollection of happy events, thus identifying brain areas consistently activated across studies. This extended brain network included frontal and limbic regions involved in remembering emotionally relevant positive events. The frontal gyrus and the cingulate cortex may be responsible for cognitive appraisal processes during recollection of happy AMs, while the subthalamic nucleus and globus pallidus may be involved in pleasure reactions associated with recollection of happy life events. These findings shed light on the neural network involved in recalling positive AMs in healthy individuals, opening further avenues for future research in clinical populations with mood disorders.

The power of negative and positive episodic memories

The power of episodic memories is that they bring a past moment into the present, providing opportunities for us to recall details of the experiences, reframe or update the memory, and use the retrieved information to guide our decisions. In these regards, negative and positive memories can be especially powerful: Life’s highs and lows are disproportionately represented in memory, and when they are retrieved, they often impact our current mood and thoughts and influence various forms of behavior. Research rooted in neuroscience and cognitive psychology has historically focused on memory for negative emotional content. Yet the study of autobiographical memories has highlighted the importance of positive emotional memories, and more recently, cognitive neuroscience methods have begun to clarify why positive memories may show powerful relations to mental wellbeing. Here, we review the models that have been proposed to explain why emotional memories are long-lasting (durable) and likely to be retrieved (accessible), describing how in overlapping—but distinctly separable—ways, positive and negative memories can be easier to retrieve, and more likely to influence behavior. We end by identifying potential implications of this literature for broader topics related to mental wellbeing, education, and workplace environments.

Sluggish retrieval of positive memories in depressed adults

Although depression is associated with poor memory for positive material, the underlying mechanisms remain unclear. We used the Hierarchical Drift Diffusion Model (HDDM) to determine whether slow evidence accumulation at retrieval contributes to depressed individuals' difficulty remembering positive events. Participants completed the Beck Depression Inventory-II and were stratified into High BDI (HBDI; BDI-II > 20, n = 49) and Low BDI (LBDI; BDI-II < 6, n = 46) groups. Next, participants completed an oddball task in which neutral, negative, and positive pictures served as rare targets. One day later, recognition memory was tested by presenting the encoded ("old") pictures along with closely matched ("new") lures. Recognition accuracy was analyzed with a generalized linear model, and choice and response time data were analyzed with the HDDM. Recognition accuracy for old positive pictures was lower in HBDI versus LBDI participants, and the HDDM highlighted slow evidence accumulation during positive memory retrieval in the HBDI group. Impaired memory for positive material in depressed adults was related to slow evidence accumulation at retrieval. Because oddballs should elicit prediction errors that normally strengthen memory formation, these retrieval findings may reflect weak positive prediction errors, at encoding, in depressed adults.

Resting-state functional connectivity relates to interindividual variations in positive memory

Individual differences in positive memory recollection are of interest in mental health, as positive memories can help protect people against stress and depression. However, it is unclear how individual differences in positive memory recollection are reflected in brain activity in the resting state. Here, we investigate the resting-state functional connectivity (FC) associated with interindividual variations in positive memory by employing cluster-level inferences based on randomization/permutation region of interest (ROI)-to-ROI analyses. We identified a cluster of FCs that was positively associated with positive memory performance, including the frontal operculum, central operculum, parietal operculum, Heschl's gyrus, and planum temporale. The current results suggest that positive memory is innervated by frontotemporal network connectivity, which may have implications for future investigations of vulnerability to stress and depression.

Win, lose, or draw: Examining salience, reward memory, and depression with the reward positivity

The reward positivity (RewP) is a putative biomarker of depression. Careful control of stimulus properties and manipulation of both stimulus valence and salience could facilitate interpretation of the RewP. RewP interpretation could further be improved by investigating functional outcomes of a blunted RewP in depression, such as reduced memory for rewarding outcomes. This study sought to advance RewP interpretation first by advancing task design through use of neutral (i.e., draw) control trials and counterbalanced feedback stimuli. Second, we examined the RewP's association with memory and the impact of depression. Undergraduates completed self-report measures of depression and anhedonia prior to a modified doors task in which words were displayed in colored fonts that indicated win, loss, or draw feedback. Memory of the feedback associated with each word (i.e., source memory) was tested. Results showed that RewP response to wins was more positive than to losses, which was more positive than to draws. The RewP was not associated with depression or anhedonia. The low depression group showed a source memory advantage for win words, but the high depression group did not. Source memory showed small relations to the RewP, but these did not survive Bonferroni correction. Results suggest the RewP is sensitive to salience and highlight challenges in detecting an association between the RewP and depression in modified doors tasks. Findings indicate that depression is related to dysfunctional source memory for reward but not loss and that future research should probe the possible associations between the RewP and memory in depression.

Examining Maternal Elaborative Reminiscing as a Protective Factor in the Intergenerational Transmission of Psychopathology

Most research examining the impact of early parental depression on the developing child has focused on the nature of parenting practices observed in depressed adults. Maternal elaborative reminiscing, or the extent to which mothers elaboratively discuss past shared experiences with their children, has a considerable influence on children's emotional and social development and is understudied within the context of maternal depression. The current study is the first to examine whether maternal elaborative reminiscing in middle childhood mediates the association between exposure to maternal depressive symptoms in infancy and later internalizing and externalizing problems. The study included 206 mother-child dyads recruited from the community who participated in a prospective longitudinal study. Maternal depressive symptoms were assessed when offspring were 6-months old. At 5-years old, dyads were observed during a free play task to measure sensitive and harsh-intrusive parenting and during a reminiscing task to measure maternal elaboration. Teacher-reported internalizing and externalizing problems were collected at age 7. A saturated path model revealed that maternal elaborative reminiscing, but not sensitive or harsh-intrusive parenting, fully mediated the association between maternal depression in infancy and externalizing, but not internalizing, problems. Reduced maternal elaboration during parent-child reminiscing constitutes one way in which risk from early maternal depression is associated with later externalizing problems.

Brain Volume Abnormalities in Youth at High Risk for Depression: Adolescent Brain and Cognitive Development Study

OBJECTIVE

Children of parents with depression are two to three times more likely to develop major depressive disorder than children without parental history; however, subcortical brain volume abnormalities characterizing major depressive disorder risk remain unclear. The Adolescent Brain and Cognitive Development (ABCD) Study provides an opportunity to identify subcortical differences associated with parental depressive history.

METHOD

Structural magnetic resonance data were acquired from 9- and 10-year-old children (N = 11,876; release 1.1, n = 4,521; release 2.0.1, n = 7,355). Approximately one-third of the children had a parental depressive history, providing sufficient power to test differences in subcortical brain volume between low- and high-risk youths. Children from release 1.1 were examined as a discovery sample, and we sought to replicate effects in release 2.0.1. Secondary analyses tested group differences in the prevalence of depressive disorders and clarified whether subcortical brain differences were present in youths with a lifetime depressive disorder history.

RESULTS

Parental depressive history was related to smaller right putamen volume in the discovery (release 1.1; d = -0.10) and replication (release 2.0.1; d = -0.10) samples. However, in release 1.1, this effect was driven by maternal depressive history (d = -0.14), whereas in release 2.0.1, paternal depressive history showed a stronger relationship with putamen volume (d = -0.09). Furthermore, high-risk children exhibited a near twofold greater occurrence of depressive disorders relative to low-risk youths (maternal history odds ratio =1.99; paternal history odds ratio = 1.45), but youths with a lifetime depressive history did not exhibit significant subcortical abnormalities.

CONCLUSION

A parental depressive history was associated with smaller putamen volume, which may affect reward learning processes that confer increased risk for major depressive disorder.

Trauma, posttraumatic stress disorder severity, and positive memories

Positive memories play an important role in the aetiology and maintenance of posttraumatic stress disorder (PTSD). However, most trauma research/clinical work has focused solely on the role of traumatic memories. Thus, we examined the relationship between count of retrieved positive memories and PTSD severity, factors associated with count of retrieved positive memories (i.e., rumination, negative/positive emotion dysregulation, fear of positive emotions), and the relationship between positive memory phenomenological domains and PTSD severity. The sample included 185 trauma-exposed participants recruited through Amazon's Mechanical Turk (Mage = 35.69 years; 63.80% female). Results of linear/hierarchical regressions showed that (1) PTSD severity did not predict count of (specific) positive memories; (2) greater positive emotion dysregulation predicted fewer retrieved positive memories controlling for PTSD severity; and (3) greater PTSD severity predicted more negative valence, less vividness, less coherence, less accessibility, less clear time perspective, fewer sensory details, and greater distancing ratings of the retrieved positive memory, controlling for sleep quantity/quality. Findings add to the literature by informing PTSD theoretical perspectives; enhancing an understanding of positive memories in PTSD/trauma treatments; and highlighting potential clinical targets (e.g., positive emotion regulation), when integrating a focus on positive memories into PTSD intervention.

Multimodal Abnormalities of Brain Structure and Function in Major Depressive Disorder: A Meta-Analysis of Neuroimaging Studies

OBJECTIVE

Imaging studies of major depressive disorder have reported structural and functional abnormalities in a variety of spatially diverse brain regions. Quantitative meta-analyses of this literature, however, have failed to find statistically significant between-study spatial convergence, other than transdiagnostic-only effects. In the present study, the authors applied a novel multimodal meta-analytic approach to test the hypothesis that major depression exhibits spatially convergent structural and functional brain abnormalities.

METHODS

This coordinate-based meta-analysis included voxel-based morphometry (VBM) studies and resting-state voxel-based pathophysiology (VBP) studies of blood flow, glucose metabolism, regional homogeneity, and amplitude of low-frequency fluctuations (ALFF) and fractional ALFF (fALFF). Input data were grouped into three primary meta-analytic classes: gray matter atrophy, increased function, and decreased function in patients with major depression relative to healthy control subjects. In secondary meta-analyses, the data were grouped across primary categories, and in tertiary analyses, by medication status and absence of psychiatric comorbidity. Activation likelihood estimation was used for all analyses.

RESULTS

A total of 92 publications reporting 152 experiments were identified, collectively representing 2,928 patients with major depressive disorder. The primary analyses detected no convergence across studies. The secondary analyses identified portions of the subgenual cingulate cortex, hippocampus, amygdala, and putamen as demonstrating convergent abnormalities. The tertiary analyses (clinical subtypes) showed improved convergence relative to the secondary analyses.

CONCLUSIONS

Coordinate-based meta-analysis identified spatially convergent structural (VBM) and functional (VBP) abnormalities in major depression. The findings suggest replicable neuroimaging features associated with major depression, beyond the transdiagnostic effects reported in previous meta-analyses, and support a continued research focus on the subgenual cingulate and other selected regions' role in depression.

Links between autobiographical memory richness and temporal discounting in older adults

When making choices between smaller, sooner rewards and larger, later ones, people tend to discount future outcomes. Individual differences in temporal discounting in older adults have been associated with episodic memory abilities and entorhinal cortical thickness. The cause of this association between better memory and more future-oriented choice remains unclear, however. One possibility is that people with perceptually richer recollections are more patient because they also imagine the future more vividly. Alternatively, perhaps people whose memories focus more on the meaning of events (i.e., are more "gist-based") show reduced temporal discounting, since imagining the future depends on interactions between semantic and episodic memory. We examined which categories of episodic details - perception-based or gist-based - are associated with temporal discounting in older adults. Older adults whose autobiographical memories were richer in perception-based details showed reduced temporal discounting. Furthermore, in an exploratory neuroanatomical analysis, both discount rates and perception-based details correlated with entorhinal cortical thickness. Retrieving autobiographical memories before choice did not affect temporal discounting, however, suggesting that activating episodic memory circuitry at the time of choice is insufficient to alter discounting in older adults. These findings elucidate the role of episodic memory in decision making, which will inform interventions to nudge intertemporal choices.

Pro-neurogenic effect of fluoxetine in the olfactory bulb is concomitant to improvements in social memory and depressive-like behavior of socially isolated mice

Although loneliness is a human experience, it can be estimated in laboratory animals deprived from physical contact with conspecifics. Rodents under social isolation (SI) tend to develop emotional distress and cognitive impairment. However, it is still to be determined whether those conditions present a common neural mechanism. Here, we conducted a series of behavioral, morphological, and neurochemical analyses in adult mice that underwent to 1 week of SI. We observed that SI mice display a depressive-like state that can be prevented by enriched environment, and the antidepressants fluoxetine (FLX) and desipramine (DES). Interestingly, chronic administration of FLX, but not DES, was able to counteract the deleterious effect of SI on social memory. We also analyzed cell proliferation, neurogenesis, and astrogenesis after the treatment with antidepressants. Our results showed that the olfactory bulb (OB) was the neurogenic niche with the highest increase in neurogenesis after the treatment with FLX. Considering that after FLX treatment social memory was rescued and depressive-like behavior decreased, we propose neurogenesis in the OB as a possible mechanism to unify the FLX ability to counteract the deleterious effect of SI.

Machine Learning Identifies Large-Scale Reward-Related Activity Modulated by Dopaminergic Enhancement in Major Depression

BACKGROUND

Theoretical models have emphasized systems-level abnormalities in major depressive disorder (MDD). For unbiased yet rigorous evaluations of pathophysiological mechanisms underlying MDD, it is critically important to develop data-driven approaches that harness whole-brain data to classify MDD and evaluate possible normalizing effects of targeted interventions. Here, using an experimental therapeutics approach coupled with machine learning, we investigated the effect of a pharmacological challenge aiming to enhance dopaminergic signaling on whole-brain response to reward-related stimuli in MDD.

METHODS

Using a double-blind, placebo-controlled design, we analyzed functional magnetic resonance imaging data from 31 unmedicated MDD participants receiving a single dose of 50 mg amisulpride (MDD_Amisulpride), 26 MDD participants receiving placebo (MDD_Placebo), and 28 healthy control subjects receiving placebo (HC_Placebo) recruited through two independent studies. An importance-guided machine learning technique for model selection was used on whole-brain functional magnetic resonance imaging data probing reward anticipation and consumption to identify features linked to MDD (MDD_Placebo vs. HC_Placebo) and dopaminergic enhancement (MDD_Amisulpride vs. MDD_Placebo).

RESULTS

Highly predictive classification models emerged that distinguished MDD_Placebo from HC_Placebo (area under the curve = 0.87) and MDD_Placebo from MDD_Amisulpride (area under the curve = 0.89). Although reward-related striatal activation and connectivity were among the most predictive features, the best truncated models based on whole-brain features were significantly better relative to models trained using striatal features only.

CONCLUSIONS

Results indicate that in MDD, enhanced dopaminergic signaling restores abnormal activation and connectivity in a widespread network of regions. These findings provide new insights into the pathophysiology of MDD and pharmacological mechanism of antidepressants at the system level in addressing reward processing deficits among depressed individuals.

Depression Detection Using Relative EEG Power Induced by Emotionally Positive Images and a Conformal Kernel Support Vector Machine

Electroencephalography (EEG) can assist with the detection of major depressive disorder (MDD). However, the ability to distinguish adults with MDD from healthy individuals using resting-state EEG features has reached a bottleneck. To address this limitation, we collected EEG data as participants engaged with positive pictures from the International Affective Picture System. Because MDD is associated with blunted positive emotions, we reasoned that this approach would yield highly dissimilar EEG features in healthy versus depressed adults. We extracted three types of relative EEG power features from different frequency bands (delta, theta, alpha, beta, and gamma) during the emotion task and resting state. We also applied a novel classifier, called a conformal kernel support vector machine (CK-SVM), to try to improve the generalization performance of conventional SVMs. We then compared CK-SVM performance with three machine learning classifiers: linear discriminant analysis (LDA), conventional SVM, and quadratic discriminant analysis. The results from the initial analyses using the LDA classifier on 55 participants (24 MDD, 31 healthy controls) showed that the participant-independent classification accuracy obtained by leave-one-participant-out cross-validation (LOPO-CV) was higher for the EEG recorded during the positive emotion induction versus the resting state for all types of relative EEG power. Furthermore, the CK-SVM classifier achieved higher LOPO-CV accuracy than the other classifiers. The best accuracy (83.64%; sensitivity = 87.50%, specificity = 80.65%) was achieved by the CK-SVM, using seven relative power features extracted from seven electrodes. Overall, combining positive emotion induction with the CK-SVM classifier proved useful for detecting MDD on the basis of EEG signals. In the future, this approach might be used to develop a brain–computer interface system to assist with the detection of MDD in the clinic. Importantly, such a system could be implemented with a low-density electrode montage (seven electrodes), highlighting its practical utility.

Modulation of GSK-3β/β-Catenin Signaling Contributes to Learning and Memory Impairment in a Rat Model of Depression

BACKGROUND

It is widely accepted that cognitive processes, such as learning and memory, are affected in depression, but the molecular mechanisms underlying the interactions of these 2 disorders are not clearly understood. Recently, glycogen synthase kinase-3 beta (GSK-3β)/β-catenin signaling was shown to play an important role in the regulation of learning and memory.

METHODS

The present study used a rat model of depression, chronic unpredictable stress, to determine whether hippocampal GSK-3β/β-catenin signaling was involved in learning and memory alterations.

RESULTS

Our results demonstrated that chronic unpredictable stress had a dramatic influence on spatial cognitive performance in the Morris water maze task and reduced the phosphorylation of Ser9 of GSK-3β as well as the total and nuclear levels of β-catenin in the hippocampus. Inhibition of GSK3β by SB216763 significantly ameliorated the cognitive deficits induced by chronic unpredictable stress, while overexpression of GSK3β by AAV-mediated gene transfer significantly decreased cognitive performance in adult rats. In addition, chronic unpredictable stress exposure increased the expression of the canonical Wnt antagonist Dkk-1. Furthermore, chronic administration of corticosterone significantly increased Dkk-1 expression, decreased the phosphorylation of Ser9 of GSK-3β, and resulted in the impairment of hippocampal learning and memory.

CONCLUSIONS

Our results indicate that impairment of learning and memory in response to chronic unpredictable stress may be attributed to the dysfunction of GSK-3β/β-catenin signaling mediated by increased glucocorticoid signaling via Dkk-1.

MDMA Impairs Both the Encoding and Retrieval of Emotional Recollections

The psychoactive drug ±3,4-methylenedioxymethamphetamine (MDMA) is increasingly used for its perceived emotional effects (eg, prosociality, empathy, psychotherapy), but surprisingly little research has been aimed at identifying the effect of the drug on emotional episodic memory in humans. Here, we report the first double-blind placebo-controlled study to examine the effects of MDMA on emotional memory separately during encoding and retrieval in healthy participants. Participants viewed emotionally negative, neutral, and positive pictures and their labels. Forty-eight hours later, they were given cued recollection and recognition memory tests designed to assess recollection and familiarity for the studied pictures. Participants were randomly assigned to one of three groups who received MDMA (1 mg/kg) either during encoding (Encoding group; N=20), retrieval (Retrieval group; N=20), or neither (Placebo group; N=20). Although MDMA administered at either phase did not affect overall memory accuracy, it did alter the recollection of details associated specifically with emotional memories as estimated using a dual process signal detection analysis of confidence judgments and subjective 'remember' judgments. In the Encoding group, MDMA reduced recollection estimates for negative and positive pictures but had little to no effect on neutral items or familiarity estimates. There was evidence for similar trends in the Retrieval group. These findings indicate that MDMA attenuates the encoding and retrieval of salient details from emotional events, consistent with the idea that its potential therapeutic effects for treating posttraumatic stress disorder are related to altering emotional memory.

Mechanisms of Memory Disruption in Depression

Depressed individuals typically show poor memory for positive events, potentiated memory for negative events, and impaired recollection. These phenomena are clinically important but poorly understood. Compelling links between stress and depression suggest promising candidate mechanisms. Stress can suppress hippocampal neurogenesis, inhibit dopamine neurons, and sensitize the amygdala. We argue that these phenomena may impair pattern separation, disrupt the encoding of positive experiences, and bias retrieval toward negative events, respectively, thus recapitulating core aspects of memory disruption in depression. Encouragingly, optogenetic reactivation of cells engaged during the encoding of positive memories rapidly reduces depressive behavior in preclinical models. Thus, many memory deficits in depression appear to be downstream consequences of chronic stress, and addressing memory disruption can have therapeutic value.

Disruption of amygdala-entorhinal-hippocampal network in late-life depression

Episodic memory deficits are evident in late-life depression (LLD) and are associated with subtle synaptic and neurochemical changes in the medial temporal lobes (MTL). However, the particular mechanisms by which memory impairment occurs in LLD are currently unknown. We tested older adults with (DS+) and without (DS-) depressive symptoms using high-resolution fMRI that is capable of discerning signals in hippocampal subfields and amygdala nuclei. Scanning was conducted during performance of an emotional discrimination task used previously to examine the relationship between depressive symptoms and amygdala-mediated emotional modulation of hippocampal pattern separation in young adults. We found that hippocampal dentate gyrus (DG)/CA3 activity was reduced during correct discrimination of negative stimuli and increased during correct discrimination of neutral items in DS+ compared to DS- adults. The extent of the latter increase was correlated with symptom severity. Furthermore, DG/CA3 and basolateral amygdala (BLA) activity predicted discrimination performance on negative trials, a relationship that depended on symptom severity. The impact of the BLA on depressive symptom severity was mediated by the DG/CA3 during discrimination of neutral items, and by the lateral entorhinal cortex (LEC) during false recognition of positive items. These results shed light on a novel mechanistic account for amygdala-hippocampal network changes and concurrent alterations in emotional episodic memory in LLD. The BLA-LEC-DG/CA3 network, which comprises a key pathway by which emotion modulates memory, is specifically implicated in LLD. © 2017 Wiley Periodicals, Inc.