Stress Impairs Episodic Retrieval by Disrupting Hippocampal and Cortical Mechanisms of Remembering

Post-retrieval stress impairs subsequent memory depending on hippocampal memory trace reinstatement during reactivation

Upon retrieval, memories can become susceptible to meaningful events, such as stress. Post-retrieval memory changes may be attributed to an alteration of the original memory trace during reactivation-dependent reconsolidation or, alternatively, to the modification of retrieval-related memory traces that impact future remembering. Hence, how post-retrieval memory changes emerge in the human brain is unknown. In a 3-day functional magnetic resonance imaging study, we show that post-retrieval stress impairs subsequent memory depending on the strength of neural reinstatement of the original memory trace during reactivation, driven by the hippocampus and its cross-talk with neocortical representation areas. Comparison of neural patterns during immediate and final memory testing further revealed that successful retrieval was linked to pattern-dissimilarity in controls, suggesting the use of a different trace, whereas stressed participants relied on the original memory representation. These representation changes were again dependent on neocortical reinstatement during reactivation. Our findings show disruptive stress effects on the consolidation of retrieval-related memory traces that support future remembering.

Impaired free recall of neutral but not negative material tested 105 min after cortisol administration

Pharmacological studies have consistently shown memory retrieval impairment after administration of cortisol, particularly pronounced for emotional laboratory material (i.e. list of emotional words). However, it is unclear how pharmacological elevation of cortisol affects memory retrieval of ecologically-relevant emotional material (i.e. similar to a newspaper article about an emotional event). In the present study, we aimed to explore whether cortisol administration affects the recall of ecologically-relevant emotional and neutral material, and when memory retrieval occurs after a longer delay (105 min). In this double-blind, pseudo-randomized, placebo-control study, 79 participants learned a negative text and a neutral text. Twenty-four hours later, they were administrated either 10 mg of hydrocortisone or placebo. After 105 min, participants engaged in free recall of both texts. The group with cortisol administration showed significantly reduced free recall compared to the placebo group. Interestingly, this memory retrieval impairment was driven by significantly lower recall after cortisol vs. placebo administration for neutral texts, but not negative texts. The current finding suggests that cortisol administration impairs neutral ecologically-relevant material while leaving emotional material unaffected. These divergent findings, compared to existing literature, emphasize the necessity of employing more ecologically validated material to gain a more comprehensive understanding of the intricate interplay between cortisol administration and memory for ecological material.

Acute Stress Enhances Memory and Preference for Smoking-Related Associations in Smokers

INTRODUCTION

Nicotine dependence follows a chronic course that is characterized by repeated relapse, often driven by acute stress and rewarding memories of smoking retrieved from related contexts. These two triggers can also interact, with stress influencing retrieval of contextual memories. However, the roles of these processes in nicotine dependence remain unknown.

AIMS AND METHODS

We investigated how acute stress biases memory for smoking-associated contexts among smokers (N = 65) using a novel laboratory paradigm. On day 1, participants formed associations between visual stimuli of items (either neutral or related to smoking) and places (background scenes). On day 2 (24 hours later), participants were exposed to an acute laboratory-based stressor (socially evaluated cold pressor test; N = 32) or a matched control condition (N = 33) prior to being tested on their memory recognition and preferences for each item and place. We distinguished the accuracy of memory into specific (ie, precisely correct) or gist (ie, lure items with similar content) categories.

RESULTS

Results demonstrated that the stressor significantly induced physiological and subjective perceived stress responses, and that stressed smokers exhibited a memory bias in favor of smoking-related items. In addition, the stressed group displayed greater preference for both smoking-related items and places that had been paired with the smoking-related items. We also found suggestive evidence that stronger smoking-related memory biases were associated with more severe nicotine dependence (ie, years of smoking).

CONCLUSIONS

These results highlight the role of stress in biasing smokers toward remembering contexts associated with smoking, and amplifying their preference for these contexts.

IMPLICATIONS

The current study elucidates the role of acute stress in promoting memory biases favoring smoking-related associations among smokers. The results suggest that the retrieval of smoking-biased associative memory could be a crucial factor in stress-related nicotine seeking. This may lead to a potential intervention targeting the extinction of smoking-related context memories as a preventive strategy for stress-induced relapse.

Using recognition testing to support semantic learning in developmental amnesia

ABSTRACTPatients with developmental amnesia (DA) have suffered hippocampal damage in infancy and subsequently shown poor episodic memory, but good semantic memory. It is not clear how patients with DA learn semantic information in the presence of episodic amnesia. However, patients with DA show good recognition memory and it is possible that semantic learning may be supported by recognition. Building on previous work, we compared two methods for supporting semantic learning in DA; recognition-learning and recall-learning. In each condition, a patient with DA (aged 8 years) was presented with semantic information in animated videos. After each presentation of a video, learning was supported by an immediate memory test. Two videos were paired with a cued recall test. Another two videos were paired with a multiple-choice test to enable recognition-based learning. The outcome measure was semantic recall performance after a short delay of 30 min and a long delay of one week. Results showed a benefit of recognition-learning compared to recall-learning on cued recall in the patient with DA (76% vs. 35%). This finding indicates that young people with severe hippocampal damage can utilize recognition to support semantic learning. This has implications for the support of school-aged children with episodic memory difficulties.

Strong but Fragmented Memory of a Stressful Episode

While it is commonly assumed that stressful events are vividly remembered, it remains largely unknown whether all aspects of memory for a stressful episode are enhanced. In this preregistered study, we tested whether stress enhances later remembering of individual elements of a stressful episode at the cost of impaired processing of the association between these elements. Therefore, male and female participants (N = 122) underwent a stressful (or control) episode during which they encoded a series of stimuli. To investigate stress effects on the memory for individual events and the links between these, we used temporal sequence effects in recognition memory tested 24 h after encoding. Specifically, we tested whether stress would affect the memory enhancement for a target item if this is preceded by another item that also preceded the target during encoding (recognition priming). Our results showed that participants recalled single events encoded under stress better than those encoded under nonstressful conditions, but were less able to leverage the temporal sequence of events encoded under stress to cue memory at delayed recall, reflected in reduced memory for items preceded by the item that preceded them also during encoding. Functional near-infrared spectroscopy further revealed that encoding under stress was accompanied by opposite changes in inferotemporal and dorsolateral prefrontal areas. Together, our data suggest that acute stress induces a mode of memory formation that results in strong but less integrated memories.

Neurocognitive effects of stress: a metaparadigm perspective

Stressful experiences, both physical and psychological, that are overwhelming (i.e., inescapable and unpredictable), can measurably affect subsequent neuronal properties and cognitive functioning of the hippocampus. At the cellular level, stress has been shown to alter hippocampal synaptic plasticity, spike and local field potential activity, dendritic morphology, neurogenesis, and neurodegeneration. At the behavioral level, stress has been found to impair learning and memory for declarative (or explicit) tasks that are based on cognition, such as verbal recall memory in humans and spatial memory in rodents, while facilitating those that are based on emotion, such as differential fear conditioning in humans and contextual fear conditioning in rodents. These vertically related alterations in the hippocampus, procedurally observed after subjects have undergone stress, are generally believed to be mediated by recurrently elevated circulating hypothalamic-pituitary-adrenal (HPA) axis effector hormones, glucocorticoids, directly acting on hippocampal neurons densely populated with corticosteroid receptors. The main purposes of this review are to (i) provide a synopsis of the neurocognitive effects of stress in a historical context that led to the contemporary HPA axis dogma of basic and translational stress research, (ii) critically reappraise the necessity and sufficiency of the glucocorticoid hypothesis of stress, and (iii) suggest an alternative metaparadigm approach to monitor and manipulate the progression of stress effects at the neural coding level. Real-time analyses can reveal neural activity markers of stress in the hippocampus that can be used to extrapolate neurocognitive effects across a range of stress paradigms (i.e., resolve scaling and dichotomous memory effects issues) and understand individual differences, thereby providing a novel neurophysiological scaffold for advancing future stress research.

Effects of Acute Stress on Rigid Learning, Flexible Learning, and Value-Based Decision-Making in Spatial Navigation

The current study investigated how stress affects value-based decision-making during spatial navigation and different types of learning underlying decisions. Eighty-two adult participants (42 females) first learned to find object locations in a virtual environment from a fixed starting location (rigid learning) and then to find the same objects from unpredictable starting locations (flexible learning). Participants then decided whether to reach goal objects from the fixed or unpredictable starting location. We found that stress impairs rigid learning in females, and it does not impair, and even improves, flexible learning when performance with rigid learning is controlled for. Critically, examining how earlier learning influences subsequent decision-making using computational models, we found that stress reduces memory integration, making participants more likely to focus on recent memory and less likely to integrate information from other sources. Collectively, our results show how stress impacts different memory systems and the communication between memory and decision-making.

Toward an Understanding of Cognitive Mapping Ability Through Manipulations and Measurement of Schemas and Stress

Daily function depends on an ability to mentally map our environment. Environmental factors such as visibility and layout, and internal factors such as psychological stress, can challenge spatial memory and efficient navigation. Importantly, people vary dramatically in their ability to navigate flexibly and overcome such challenges. In this paper, we present an overview of "schema theory" and our view of its relevance to navigational memory research. We review several studies from our group and others, that integrate manipulations of environmental complexity and affective state in order to gain a richer understanding of the mechanisms that underlie individual differences in navigational memory. Our most recent data explicitly link such individual differences to ideas rooted in schema theory, and we discuss the potential for this work to advance our understanding of cognitive decline with aging. The data from this body of work highlight the powerful impacts of individual cognitive traits and affective states on the way people take advantage of environmental features and adopt navigational strategies.

Pharmacologically increased cortisol levels impair recall of associative background context memory in males, but not females

Laboratory studies have consistently shown that stress impairs memory retrieval of individual parts (items) of a memory. The stress-hormone cortisol has been particularly linked to this impairment. However, it is unclear whether cortisol similarly affects the binding of items to associative context information in memory, i.e. the constituents of episodic memory. Here, we examine memory retrieval of item and associative memory under pharmacologically elevated cortisol vs. normal levels. Given that previous studies have indicated potential sex differences in the stress- and cortisol-induced memory modulation, we additionally assessed whether there may be sex differences for the cortisol effect on memory retrieval. Eighty-four female and male participants were tested in a placebo controlled, double-blind between-subject design, assigned to either a cortisol (10 mg hydrocortisone) or a placebo group. Participants of both groups were presented foreground images of negative and neutral valence on different neutral background scenes. Twenty-four hours later, participants' memory for the images and their associated background scene was tested with a recognition task 20 min after substance administration. Among the 78 participants of both groups included in the final analysis, cortisol levels were higher in the cortisol group in comparison to the placebo group, and female participants had higher cortisol levels after hydrocortisone intake in comparison to male participants. Item memory did not differ between the placebo and cortisol group. In contrast, in males, but not females, associative memory for the background scene of emotional foreground images was lower in the cortisol vs. placebo group. Moreover, the individual cortisol increase during the recognition task was negatively correlated to memory for the background scenes of the emotional foreground images only in male participants of the cortisol group. This study shows that pharmacologically increased cortisol levels distinctly affect associative memory in female and male participants, but have no effect on item memory, indicating a complex interaction for the stress effects on memory.

Greater sleep variance related to decrements in memory performance and event-specific neural similarity: a racially/ethnically diverse lifespan sample

Successful memory performance depends on overlap between neural representations at encoding and retrieval. With older age, neural similarity, memory performance, and sleep quality decline. Regardless of age, racial/ethnic minorities tend to experience poor sleep, which may contribute to poor memory. Previous studies have not investigated memory performance, neural similarity, sleep quality, and age in diverse participants. Here, we recruited racially/ethnically diverse adults across the lifespan and examined night-to-night sleep quality in relation to memory performance and encoding-retrieval similarity. We employed item-specific, representational similarity analysis (not confounded by effort, word perception, or differences in electroencephalography signal amplitude) to assess neural similarity for intact and recombined paired associates. Greater sleep variance and poorer memory performance were more strongly associated with older age. Interestingly, sleep variance was positively associated with neural similarity for intact pairs. This relationship was stronger with younger age and for racial/ethnic minorities. For recombined pairs, greater sleep variance was associated with reduced neural similarity. Thus, varied sleep may induce greater reliance on familiarity, while consistent sleep may support recollection.

Neural reactivation and judgements of vividness reveal separable contributions to mnemonic representation

Mnemonic representations vary in fidelity, sharpness, and strength-qualities that can be examined using both introspective judgements of mental states and objective measures of brain activity. Subjective and objective measures are both valid ways of "reading out" the content of someone's internal mnemonic states, each with different strengths and weaknesses. St-Laurent and colleagues (2015) compared the neural correlates of memory vividness ratings with patterns of neural reactivation evoked during memory recall and found considerable overlap between the two, suggesting a common neural basis underlying these different markers of representational quality. Here we extended this work with meta-analytic methods by pooling together four neuroimaging datasets in order to contrast the neural substrates of neural reactivation and those of vividness judgements. While reactivation and vividness judgements correlated positively with one another and were associated with common univariate activity in the dorsal attention network and anterior hippocampus, some notable differences were also observed. Vividness judgments were tied to stronger activation in the striatum and dorsal attention network, together with activity suppression in default mode network nodes. We also observed a trend for reactivation to be more closely associated with early visual cortex activity. A mediation analysis found support for the hypothesis that neural reactivation is necessary for memory vividness, with activity in the anterior hippocampus associated with greater reactivation. Our results suggest that neural reactivation and vividness judgements reflect common mnemonic processes but differ in the extent to which they engage effortful, attentional processes. Additionally, the similarity between reactivation and vividness appears to arise, partly, through hippocampal engagement during memory retrieval.

Mechanisms of memory under stress

It is well established that stress has a major impact on memory, driven by the concerted action of various stress mediators on the brain. Recent years, however, have seen considerable advances in our understanding of the cellular, neural network, and cognitive mechanisms through which stress alters memory. These novel insights highlight the intricate interplay of multiple stress mediators, including-beyond corticosteroids, catecholamines, and peptides-for instance, endocannabinoids, which results in time-dependent shifts in large-scale neural networks. Such stress-induced network shifts enable highly specific memories of the stressful experience in the long run at the cost of transient impairments in mnemonic flexibility during and shortly after a stressful event. Based on these recent discoveries, we provide a new integrative framework that links the cellular, systems, and cognitive mechanisms underlying acute stress effects on memory processes and points to potential targets for treating aberrant memory in stress-related mental disorders.

Ethnoracial disparities in cognition are associated with multiple socioeconomic status-stress pathways

Systemic racism can have broad impacts on health in ethnoracial minorities. One way is by suppressing socioeconomic status (SES) levels through barriers to achieve higher income, wealth, and educational attainment. Additionally, the weathering hypothesis proposes that the various stressful adversities faced by ethnoracial minorities lead to greater wear and tear on the body, known as allostatic load. In the present study, we extend these ideas to cognitive health in a tri-ethnic sample of young adults-when cognition and brain health is arguably at their peak. Specifically, we tested competing mediation models that might shed light on how two key factors caused by systemic racism-SES and perceived stress-intersect to explain ethnoracial disparities in cognition. We found evidence for partial mediation via a pathway from SES to stress on episodic memory, working memory capacity, and executive function in Black Americans relative to non-Hispanic White Americans. Additionally, we found that stress partially mediated the ethnoracial disparities in working memory updating for lower SES Black and Hispanic Americans relative to non-Hispanic White Americans, showing that higher SES can sometimes reduce the negative effects stress has on these disparities in some cognitive domains. Overall, these findings suggest that multiple pathways exist in which lower SES creates a stressful environment to impact ethnoracial disparities cognition. These pathways differ depending on the specific ethnoracial category and cognitive domain. The present results may offer insight into strategies to help mitigate the late-life risk for neurocognitive disorders in ethnoracial minorities.

Brain Activity-Based Metrics for Assessing Learning States in VR under Stress among Firefighters: An Explorative Machine Learning Approach in Neuroergonomics

The nature of firefighters` duties requires them to work for long periods under unfavorable conditions. To perform their jobs effectively, they are required to endure long hours of extensive, stressful training. Creating such training environments is very expensive and it is difficult to guarantee trainees' safety. In this study, firefighters are trained in a virtual environment that includes virtual perturbations such as fires, alarms, and smoke. The objective of this paper is to use machine learning methods to discern encoding and retrieval states in firefighters during a visuospatial episodic memory task and explore which regions of the brain provide suitable signals to solve this classification problem. Our results show that the Random Forest algorithm could be used to distinguish between information encoding and retrieval using features extracted from fNIRS data. Our algorithm achieved an F-1 score of 0.844 and an accuracy of 79.10% if the training and testing data are obtained at similar environmental conditions. However, the algorithm's performance dropped to an F-1 score of 0.723 and accuracy of 60.61% when evaluated on data collected under different environmental conditions than the training data. We also found that if the training and evaluation data were recorded under the same environmental conditions, the RPM, LDLPFC, RDLPFC were the most relevant brain regions under non-stressful, stressful, and a mix of stressful and non-stressful conditions, respectively.

When the brain, but not the person, remembers: Cortical reinstatement is modulated by retrieval goal in developmental amnesia

Developmental amnesia (DA) is associated with early hippocampal damage and subsequent episodic amnesia emerging in childhood alongside age-appropriate development of semantic knowledge. We employed fMRI to assess whether patients with DA show evidence of 'cortical reinstatement', a neural correlate of episodic memory, despite their amnesia. At study, 23 participants (5 patients) were presented with words overlaid on a scene or a scrambled image for later recognition. Scene reinstatement was indexed by scene memory effects (greater activity for previously presented words paired with a scene rather than scrambled images) that overlapped with scene perception effects. Patients with DA demonstrated scene reinstatement effects in the parahippocampal and retrosplenial cortex that were equivalent to those shown by healthy controls. Behaviourally, however, patients with DA showed markedly impaired scene memory. The data indicate that reinstatement can occur despite hippocampal damage, but that cortical reinstatement is insufficient to support accurate memory performance. Furthermore, scene reinstatement effects were diminished during a retrieval task in which scene information was not relevant for accurate responding, indicating that strategic mnemonic processes operate normally in DA. The data suggest that cortical reinstatement of trial-specific contextual information is decoupled from the experience of recollection in the presence of severe hippocampal atrophy.

Noradrenergic stimulation increases fear memory expression

Fear responses are typically not limited to the actual threatening stimulus but generalize to other stimuli resembling the threatening stimulus. Although this fear generalization is generally adaptive, fear overgeneralization is maladaptive and assumed to contribute to anxiety disorders. Despite the clinical relevance of fear (over)generalization, how the extent of fear generalization is modulated remains not well understood. Based on the known effects of stress on learning and memory, we tested here the impact of major stress mediators, glucocorticoids and noradrenergic arousal, on fear generalization. In a laboratory-based, placebo-controlled, double-blind, between-subject design, 125 healthy participants first underwent a fear conditioning procedure. About 24 h later, participants received orally either a placebo, hydrocortisone, the α2-adrenoceptor antagonist yohimbine, leading to increased noradrenergic stimulation, or both drugs before a test of fear generalization. Skin conductance responses as well as explicit rating data revealed that yohimbine intake led to enhanced fear memory expression, i.e. an enhanced responding to the CS+ but not to stimuli resembling the CS+. Moreover, neither enhanced safety learning nor a mere enhancement of perceptual discrimination ability could explain this result. In contrast to yohimbine, hydrocortisone had no significant effect on fear memory. These findings suggest that noradrenergic arousal strengthens fear memory expression and have important implications for mental disorders in which the overgeneralization of conditioned fear is prominent.

Stress-induced cortisol modulates the control of memory retrieval towards the dorsal striatum

Stress can modulate the recruitment of multiple memory systems during learning, favouring dorsal striatal "habit" learning over hippocampal "cognitive" learning. Here, we tested whether stress may also bias the engagement of "cognitive" and "habit" systems during retrieval and thereby affect the nature of remembering. To this end, participants first performed a probabilistic classification learning task that can be solved by both the "cognitive" and the "habit" system. Twenty-four hours later, participants underwent either a stress manipulation or a non-stressful control procedure before they completed a retention test for the previously learned task in the MRI scanner. During this retention test, stress-induced cortisol levels were linked to a relative bias towards behavioural strategies indicative for the "habit" system. At the neural level, stress led to increased dorsal striatal activity during retrieval. Elevated cortisol levels were directly correlated with increased activity in the dorsal striatum and further linked to reduced functional connectivity between the hippocampus and the amygdala, which is assumed to orchestrate the stress-related shift from "cognitive" to "habitual" control. Together, our data suggest that stress may bias the contributions of multiple memory systems also at retrieval, in a manner that promotes dorsal striatal "habit" processes and most likely driven by cortisol.

Acute psychosocial stress during retrieval impairs pattern separation processes on an episodic memory task

Numerous studies have shown that the presence of psychosocial stress impairs the ability to retrieve episodic memories, which raise questions about the specific cognitive processes that underlie this impairment. Here, we tested the hypothesis that stress targets retrieval processes needed to reliability discriminate previously learned from new information within episodic memory, pattern separation processing by measuring the effects of retrieval-induced stress on a modified version of the Mnemonic Similarity Task. In a two-part between-subjects design, all participants studied a series of object images in an initial testing session. In a second session, held 24 h later, half of the participants completed a stress induction task (stress group) and half performed a similarly structured but non-stressful task (control group) and all were then given a recognition memory test for the previously studied images which included new images similar to those studied (lures), and images that were completely novel (foils). Both groups performed equally well in terms of overall recognition memory, but the stress group was significantly impaired in discriminating new and similar (lure) items from studied items. This pattern of results suggests that stress specifically targets pattern separation processing when retrieving information from episodic memory. We discuss the implications of this effect, specifically how stress at retrieval reduces the ability to discriminate new from learned information.

Hippocampal and cortical mechanisms at retrieval explain variability in episodic remembering in older adults

Age-related episodic memory decline is characterized by striking heterogeneity across individuals. Hippocampal pattern completion is a fundamental process supporting episodic memory. Yet, the degree to which this mechanism is impaired with age, and contributes to variability in episodic memory, remains unclear. We combine univariate and multivariate analyses of fMRI data from a large cohort of cognitively normal older adults (N=100) to measure hippocampal activity and cortical reinstatement during retrieval of trial-unique associations. Trial-wise analyses revealed that (a) hippocampal activity scaled with reinstatement strength, (b) cortical reinstatement partially mediated the relationship between hippocampal activity and associative retrieval, (c) older age weakened cortical reinstatement and its relationship to memory behaviour. Moreover, individual differences in the strength of hippocampal activity and cortical reinstatement explained unique variance in performance across multiple assays of episodic memory. These results indicate that fMRI indices of hippocampal pattern completion explain within- and across-individual memory variability in older adults.

Prefrontal reinstatement of contextual task demand is predicted by separable hippocampal patterns

Goal-directed behavior requires the representation of a task-set that defines the task-relevance of stimuli and guides stimulus-action mappings. Past experience provides one source of knowledge about likely task demands in the present, with learning enabling future predictions about anticipated demands. We examine whether spatial contexts serve to cue retrieval of associated task demands (e.g., context A and B probabilistically cue retrieval of task demands X and Y, respectively), and the role of the hippocampus and dorsolateral prefrontal cortex (dlPFC) in mediating such retrieval. Using 3D virtual environments, we induce context-task demand probabilistic associations and find that learned associations affect goal-directed behavior. Concurrent fMRI data reveal that, upon entering a context, differences between hippocampal representations of contexts (i.e., neural pattern separability) predict proactive retrieval of the probabilistically dominant associated task demand, which is reinstated in dlPFC. These findings reveal how hippocampal-prefrontal interactions support memory-guided cognitive control and adaptive behavior.

Spatial contexts are often predictive of the tasks to be performed in them (e.g., a kitchen predicts cooking). Here the authors show that the retrieval of task demand when encountering a spatial context depends on hippocampal-prefrontal interactions.

Stress Disrupts Human Hippocampal-Prefrontal Function during Prospective Spatial Navigation and Hinders Flexible Behavior

The ability to anticipate and flexibly plan for the future is critical for achieving goal-directed outcomes. Extant data suggest that neural and cognitive stress mechanisms may disrupt memory retrieval and restrict prospective planning, with deleterious impacts on behavior. Here, we examined whether and how acute psychological stress influences goal-directed navigational planning and efficient, flexible behavior. Our methods combined fMRI, neuroendocrinology, and machine learning with a virtual navigation planning task. Human participants were trained to navigate familiar paths in virtual environments and then (concurrent with fMRI) performed a planning and navigation task that could be most efficiently solved by taking novel shortcut paths. Strikingly, relative to non-stressed control participants, participants who performed the planning task under experimentally induced acute psychological stress demonstrated (1) disrupted neural activity critical for mnemonic retrieval and mental simulation and (2) reduced traversal of shortcuts and greater reliance on familiar paths. These neural and behavioral changes under psychological stress were tied to evidence for disrupted neural replay of memory for future locations in the spatial environment, providing mechanistic insight into why and how stress can alter planning and foster inefficient behavior.

Mild acute stress improves response speed without impairing accuracy or interference control in two selective attention tasks: Implications for theories of stress and cognition

Acute stress is generally thought to impair performance on tasks thought to rely on selective attention. This effect has been well established for moderate to severe stressors, but no study has examined how a mild stressor-the most common type of stressor-influences selective attention. In addition, no study to date has examined how stress influences the component processes involved in overall selective attention task performance, such as controlled attention, automatic attentional activation, decision-making, and motor abilities. To address these issues, we randomly assigned 107 participants to a mild acute stress or control condition. As expected, the mild acute stress condition showed a small but significant increase in cortisol relative to the control condition. Following the stressor, we assessed attention with two separate flanker tasks. One of these tasks was optimized to investigate component attentional processes using computational cognitive modeling, whereas the other task employed mouse-tracking to illustrate how response conflict unfolded over time. The results for both tasks showed that mild acute stress decreased response time (i.e., increased response speed) without influencing accuracy or interference control. Further, computational modeling and mouse-tracking analyses indicated that these effects were due to faster motor action execution time for chosen actions. Intriguingly, however, cortisol responses were unrelated to any of the observed effects of mild stress. These results have implications for theories of stress and cognition, and highlight the importance of considering motor processes in understanding the effects of stress on cognitive task performance.

The serotonin transporter gene variants modulate acute stress-induced hippocampus and dorsomedial prefrontal cortex activity during memory retrieval

The short (s) allele of a polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR) is related to reduced serotonin transporter efficiency and an increased vulnerability to stress and mental disorders. In the present study, we investigated how 5-HTTLPR impacts on memory retrieval under stress and related neural activity by reanalyzing a small genetic neuroimaging data set. Twenty-seven healthy male volunteers participated in both the Trier Social Stress Test (TSST) and a respective control procedure and then their brain activity was measured with functional MRI (fMRI) while they performed an emotional-face-recognition task. Sixteen participants were carriers of the short allele (ss/sl carriers) and 11 were homozygous for the long allele (ll carriers). Genotype groups were compared with respect to stress-related physiological changes, memory performance, and brain activity. No significant genotype-dependent effects on memory performance or cortisol levels were found. The ss/sl carriers showed significantly higher systolic and diastolic blood pressure than the ll carriers, independent of stress. The ss/sl carriers reported stronger stress-induced nervous mood than the ll carriers. Our fMRI data revealed that the ss/sl carriers showed significantly weaker left hippocampus activation and stronger dorsomedial prefrontal cortex (dmPFC) deactivation when retrieving memories under stress as compared with the ll carriers. Subsequent analyses revealed that the distinct hippocampal activation pattern in both genotypes was associated with stress-induced cortisol elevation, while the distinct dmPFC activation pattern in both genotypes was associated with stress-induced changes in reaction times. Our results thus add new evidence that serotonin signaling modulates neural activity in the hippocampus and dmPFC during memory retrieval under acute psychosocial stress.

An oral presentation causes stress and memory impairments

Laboratory experiments revealed the stress hormone cortisol to decrease memory retrieval of emotional material, but a translation to real-life settings is missing so far. In this study, 51 students encoded a list of neutral, positive, and negative words as well as two neutral, biographical notes one day before attendance at a seminar at the university. In the stress condition, students gave a graded oral presentation, whereas they just attended the same seminar in the control condition immediately before retrieval took place. Measures of state anxiety, salivary cortisol and alpha-amylase confirmed the oral presentation to constitute a potent stressor. Importantly, stress significantly impaired retrieval of negative words, but not retrieval of the biographical notes. These results indicate that a real-life stressor decreases memory retrieval for negative items. In contrast, delayed memory retrieval of neutral information and interrelated details of biographical notes seems to be less prone to stress effects. These results have critical implications for educational settings.

Acute stress-induced cortisol elevation during memory consolidation enhances pattern separation

Stress is a potent modulator of brain function and particularly mnemonic processes. While chronic stress is associated with long-term deficits in memory, the effects of acute stress on mnemonic functions are less clear as previous reports have been inconsistent. Some studies suggest that cortisol, a stress hormone that modulates biological changes in response to stress, may enhance memory consolidation and impair memory retrieval. However, other studies report no effect of cortisol on either memory consolidation or retrieval. These discrepancies could be due to differences in the timing and sequencing of the experimental procedures or individual differences in participants’ stress response. In the present study, we examined the effect of increased cortisol levels due to acute stress, induced by the Trier Social Stress Test (TSST), on a pattern separation memory task while differentiating the distinct stages of memory processing and controlling for the effects of diurnal variation. Sixty-nine young adults completed a 2-d study in which subjects either underwent the TSST immediately following the encoding part of the memory task, targeting memory consolidation, or immediately prior to the recognition part of the memory task on the second day, targeting memory retrieval. Control subjects completed the same study procedures but underwent a control version of the TSST that did not induce a stress response. Mnemonic discrimination of highly similar stimuli was enhanced by stress induced during consolidation with better discrimination showing a significant correlation with increased cortisol responses. Stress induced during memory retrieval showed no significant effect on memory performance. These findings suggest that stress induced changes in cortisol differentially affect the consolidation and retrieval stages of memory function.