Subsequent Episodic Memory Research Articles

The impact of working memory testing on long-term associative memory.

The long-term fate of to-be-remembered information depends in part on the conditions of initial learning, including mental operations engaged via working memory. However, the mechanistic role of working memory (WM) processes in subsequent episodic memory (EM) remains unclear. Does re-exposure to word-pairs during WM recognition testing improve EM for those associations? Are benefits from WM re-exposure greater after an opportunity for retrieval practice compared to mere re-exposure to the memoranda? These questions are addressed in three experiments (N = 460) designed to assess whether WM-based recognition testing benefits long-term associative memory relative to WM-based restudying. Our results show null or negative benefits of WM recognition testing minutes later when initial WM accuracy was not considered. An EM benefit of WM recognition testing only emerges when the analyses are limited to pairs responded to correctly during WM. However, even when compared with accurate WM recognition, restudying can lead to similar associative EM benefits in specific experimental conditions. Taken together, the present results suggest that while WM re-exposure to studied pairs is beneficial to long-term associative memory, successful retrieval on initial tests may be a necessary but insufficient condition for the emergence of a "WM-based testing effect." We consider these results in relation to several hypotheses proposed to explain the testing effect in long-term memory (LTM). In view of empirical parallels with the LTM testing effect, we propose that similar processes influence the benefits of practice tests administered within the canonical boundaries of WM, suggesting continuities in memory over the short and long term.

Mismatch negativity as a marker of auditory pattern separation.

To what extent does incidental encoding of auditory stimuli influence subsequent episodic memory for the same stimuli? We examined whether the mismatch negativity (MMN), an event-related potential generated by auditory change detection, is correlated with participants' ability to discriminate those stimuli (i.e. targets) from highly similar lures and from dissimilar foils. We measured the MMN in 30 young adults (18-32years, 18 females) using a passive auditory oddball task with standard and deviant 5-tone sequences differing in pitch contour. After exposure, all participants completed an incidental memory test for old targets, lures, and foils. As expected, participants at test exhibited high sensitivity in recognizing target items relative to foils and lower sensitivity in recognizing target items relative to lures. Notably, we found a significant correlation between MMN amplitude and lure discrimination, but not foil discrimination. Our investigation shows that our capacity to discriminate sensory inputs at encoding, as measured by the MMN, translates into precision in memory for those inputs.

Association of Sleep-Disordered Breathing and Medial Temporal Lobe Atrophy in Cognitively Unimpaired Amyloid-Positive Older Adults.

Sleep disordered breathing (SDB) has been related to amyloid deposition and an increased dementia risk. However, how SDB relates to medial temporal lobe neurodegeneration and subsequent episodic memory impairment is unclear. Our objective was to investigate the impact of amyloid positivity on the associations between SDB severity, medial temporal lobe subregions, and episodic memory performance in cognitively unimpaired older adults. Data were acquired between 2016 and 2020 in the context of the Age-Well randomized controlled trial of the Medit-Aging European project. Participants older than 65 years who were free of neurologic, psychiatric, or chronic medical diseases were recruited from the community. They completed a neuropsychological evaluation, in-home polysomnography, a Florbetapir PET, and an MRI, including a specific high-resolution assessment of the medial temporal lobe and hippocampal subfields. Multiple linear regressions were conducted to test interactions between amyloid status and SDB severity on the volume of MTL subregions, controlling for age, sex, education, and the ApoE4 status. Secondary analyses aimed at investigating the links between SDB, MTL subregional atrophy, and episodic memory performance at baseline and at a mean follow-up of 20.66 months in the whole cohort and in subgroups stratified according to amyloid status. We included 122 cognitively intact community-dwelling older adults (mean age ± SD: 69.40 ± 3.85 years, 77 women, 26 Aβ+ individuals) in baseline analyses and 111 at follow-up. The apnea-hypopnea index interacted with entorhinal (β = -0.81, p < 0.001, pη2 = 0.19), whole hippocampal (β = -0.61, p < 0.001, pη2 = 0.10), subiculum (β = -0.56, p = 0.002, pη2 = 0.08), CA1 (β = -0.55, p = 0.002, pη2 = 0.08), and DG (β = -0.53, p = 0.003, pη2 = 0.08) volumes such that a higher sleep apnea severity was related to lower MTL subregion volumes in amyloid-positive individuals, but not in those who were amyloid negative. In the whole cohort, lower whole hippocampal (r = 0.27, p = 0.005) and CA1 (r = 0.28, p = 0.003) volumes at baseline were associated with worse episodic memory performance at follow-up. Overall, we showed that SDB was associated with MTL atrophy in cognitively asymptomatic older adults engaged in the Alzheimer continuum, which may increase the risk of developing memory impairment over time. ClinicalTrials.gov Identifier: NCT02977819.

The Bidirectional Association Between Cognitive Function and Gait Speed in Chinese Older Adults: Longitudinal Observational Study.

Cognitive and gait speed decline are common conditions in older adults and are often associated with future adverse consequences. Although an association between cognitive function and gait speed has been demonstrated, its temporal sequence remains unclear, especially in older Chinese adults. Clarifying this could help identify interventions to improve public health in older adults. This study aims to examine the longitudinal reciprocal association between gait speed and cognitive function and the possible temporal sequence of changes in both factors in a national longitudinal cohort. Data were derived from 2 waves (2011 baseline and 2015 follow-up) of the China Health and Retirement Longitudinal Study (CHARLS). Participants 60 years or older, without dementia or Parkinson disease at baseline, and with completed data on gait speed and cognition at both baseline and follow-up were included. Usual gait speed was measured over two 2.5-m walks. Mental intactness and episodic memory were used to assess global cognitive function. Cross-lagged panel models and linear mixed-effects models were used to examine the association between cognition and gait speed over time. Standardized coefficients were reported. A total of 3009 participants (mean age 66.4 years, SD 5.4 years; 1422/3009, 47.26%, female participants) were eligible for inclusion in our analyses. Cross-lagged panel analyses revealed that after accounting for baseline gait speed, cognition, and potential confounders, baseline global cognition (β=.117, 95% CI 0.082-0.152; P<.001), mental intactness (β=.082, 95% CI 0.047-0.118; P<.001), and episodic memory (β=.102, 95% CI 0.067-0.137; P<.001) were associated with subsequent gait speed. Simultaneously, baseline gait speed was also associated with subsequent global cognition (β=.056, 95% CI 0.024-0.087; P=.001), mental intactness (β=.039, 95% CI 0.008-0.069; P=.01), and episodic memory (β=.057, 95% CI 0.023-0.092; P=.001). The comparison of standardized cross-lagged coefficients suggested that the effect size of baseline global cognition on subsequent gait speed was significantly larger than the reverse effect (χ12=6.50, P for difference=.01). However, the effects of both mental intactness and episodic memory on subsequent gait speed were not significantly stronger than those of the reverse pathway (χ12=3.33, P for difference=.07 and χ12=3.21, P for difference=.07). Linear mixed-effects analyses further supported these bidirectional relationships, revealing that lower baseline cognitive scores predicted steeper declines in gait speed trajectory, and slower baseline gait speed predicted more declines in cognitive trajectory over time. There is a longitudinal bidirectional association between usual gait speed and both global cognitive function and specific domains of mental intactness and episodic memory among Chinese older adults. Baseline global cognition is likely to have a stronger association with subsequent gait speed than the reverse pathway. This interlinkage is noteworthy and may have implications for public health. Maintaining normal cognitive function may be an important interventional strategy for mitigating age-related gait speed reduction.

Left Prefrontal tDCS during Learning Does Not Enhance Subsequent Verbal Episodic Memory in Young Adults: Results from Two Double-Blind and Sham-Controlled Experiments.

Recent studies suggest that transcranial direct current stimulation (tDCS) applied over the prefrontal cortex (PFaC) may enhance episodic memory ability. As such, there is ongoing interest in the therapeutic potential of this technique in age-related memory decline. At the same time, the findings are not yet conclusive regarding the magnitude of this effect, and assumptions regarding underlying brain mechanisms of stimulation-induced changes in behaviour are yet to be tested in detail. Here, we evaluated the effect of tDCS over left PFC on verbal episodic memory in young adults. Two separate randomized, double-blind, sham-controlled experiments were carried out using (1) incidental learning followed by a recognition test and (2) intentional learning followed by a free recall. In both studies, participants performed a learning task with active or sham tDCS during the encoding period, followed by retrieval tasks on the same day and the next day. The results suggest that, contrary to expectations, active tDCS did not enhance memory performance relative to sham tDCS. Possible reasons behind the lack of enhancement effects are discussed, including the possibility that memory enhancement effects of tDCS may be smaller than first thought. Scientific practices that could improve estimation accuracy in the field are also discussed.

Temporal Dynamics of Competition between Statistical Learning and Episodic Memory in Intracranial Recordings of Human Visual Cortex.

The function of long-term memory is not just to reminisce about the past, but also to make predictions that help us behave appropriately and efficiently in the future. This predictive function of memory provides a new perspective on the classic question from memory research of why we remember some things but not others. If prediction is a key outcome of memory, then the extent to which an item generates a prediction signifies that this information already exists in memory and need not be encoded. We tested this principle using human intracranial EEG as a time-resolved method to quantify prediction in visual cortex during a statistical learning task and link the strength of these predictions to subsequent episodic memory behavior. Epilepsy patients of both sexes viewed rapid streams of scenes, some of which contained regularities that allowed the category of the next scene to be predicted. We verified that statistical learning occurred using neural frequency tagging and measured category prediction with multivariate pattern analysis. Although neural prediction was robust overall, this was driven entirely by predictive items that were subsequently forgotten. Such interference provides a mechanism by which prediction can regulate memory formation to prioritize encoding of information that could help learn new predictive relationships.SIGNIFICANCE STATEMENT When faced with a new experience, we are rarely at a loss for what to do. Rather, because many aspects of the world are stable over time, we rely on past experiences to generate expectations that guide behavior. Here we show that these expectations during a new experience come at the expense of memory for that experience. From intracranial recordings of visual cortex, we decoded what humans expected to see next in a series of photographs based on patterns of neural activity. Photographs that generated strong neural expectations were more likely to be forgotten in a later behavioral memory test. Prioritizing the storage of experiences that currently lead to weak expectations could help improve these expectations in future encounters.

The reciprocal relationship between episodic memory and future thinking: How the outcome of predictions is subsequently remembered.

Evidence suggests that memory is involved in making simulations and predictions about the future (i.e., future thinking), but less work has examined how the outcome of those predictions (whether events play out as predicted or expected) subsequently affects episodic memory. In this investigation, we examine whether memory is better for outcomes that are consistent with predictions, or whether memory is enhanced for outcomes that are inconsistent with predictions, after the predicted event occurs. In this experiment, participants learned a core trait associated with social targets (e.g., high in extroversion), before making predictions about behaviors targets would perform. Participants then were shown behaviors the social targets actually performed (i.e., prediction outcome), which was either consistent or inconsistent with predictions. After that, participants completed a memory test (recognition; recall) for the prediction outcomes. For recognition, the results revealed better memory for outcomes that were consistent with traits associated with targets (i.e., trait‐consistent outcomes), compared to outcomes that were inconsistent (i.e., trait‐inconsistent outcomes). Finding a memory advantage for trait‐consistent outcomes suggests that outcomes that are in line with the contents of memory (e.g., what one knows; schemas) are more readily remembered than those that are inconsistent with memory, which may reflect an adaptive memory process. For recall, memory did not differ between trait‐consistent and trait‐inconsistent outcomes. Altogether, the results of this experiment advance understanding of the reciprocal relationship between episodic memory and future thinking and show that outcome of predictions has an influence on subsequent episodic memory, at least as measured by recognition.

Subjective memory, objective memory, and race over a 10-year period: Findings from the ACTIVE study.

The longitudinal associations between subjective and objective memory functioning in later life remain unclear. This may be due, in part, to sociodemographic differences across studies, given the hypothesis that these associations differ across racial groups. Using data from the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE; N = 2,694; 26% African American), multiple-group, parallel-process latent growth curve models were used to explore relationships between subjective and objective memory over 10 years and assess racial differences in these associations. Across African Americans and whites, we found bidirectional associations between subjective and objective memory such that greater self-reported forgetting at baseline predicted faster subsequent verbal episodic memory declines, and higher baseline objective memory scores predicted less increase in self-reported forgetting over time. However, rates of change in self-reported frequency of forgetting were correlated with rates of change in verbal episodic memory in whites, but not in African Americans. Subjective memory complaints may be a harbinger of future memory declines across African Americans and whites but may not track with objective memory in the same way across these racial groups. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Associations between life course marital biography and late-life memory decline.

Late-life marital status is associated with cognitive aging; however, the influence of life course marital biography (i.e., changes in marital status) on late-life cognitive trajectories, as well as gender differences in the effects of marital biography, remain to be explored. Associations between (a) marital status at study baseline (currently married, previously married, never married) and (b) retrospectively reported life course marital biography (i.e., age at first marriage, time spent unmarried following initial marriage, history of divorce, history of widowhood) and up to 20 years of subsequent episodic memory trajectories were examined using latent growth curve models in 3,061 participants aged 51 + in the Health and Retirement Study 2017 Life History Mail Survey. Gender differences were examined with multiplicative interaction terms and stratified models. Participants who were married at study baseline demonstrated higher initial memory than previously and never married individuals. Older age at first marriage and shorter duration spent unmarried were each associated with better initial episodic memory among previously married individuals only; longer duration spent unmarried was associated with slower memory decline. Stratified models suggested that these associations may be driven by women. These results highlight the importance of considering multiple aspects of marital biography, not just current marital status, in cognitive aging research. Marital biography may have an enduring influence on cognitive aging, particularly among previously married older women. Future work is needed to identify mechanisms (e.g., socioeconomic resources, cognitive stimulation, self and spousal health, emotional support) through which marital histories influence cognitive aging. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Baseline cognition is the best predictor of 4-year cognitive change in cognitively intact older adults

BackgroundWe examined in cognitively intact older adults the relative weight of cognitive, genetic, structural and amyloid brain imaging variables for predicting cognitive change over a 4-year time course.MethodsOne hundred-eighty community-recruited cognitively intact older adults (mean age 68 years, range 52–80 years, 81 women) belonging to the Flemish Prevent Alzheimer’s Disease Cohort KU Leuven (F-PACK) longitudinal observational cohort underwent a baseline evaluation consisting of detailed cognitive assessment, structural MRI and 18F-flutemetamol PET. At inclusion, subjects were stratified based on Apolipoprotein E (APOE) ε4 and Brain-Derived Neurotrophic Factor (BDNF) val66met polymorphism according to a factorial design. At inclusion, 15% were amyloid-PET positive (Centiloid >23.4). All subjects underwent 2-yearly follow-up of cognitive performance for a 4-year time period. Baseline cognitive scores were analysed using factor analysis. The slope of cognitive change over time was modelled using latent growth curve analysis. Using correlation analysis, hierarchical regression and mediation analysis, we examined the effect of demographic (age, sex, education) and genetic variables, baseline cognition, MRI volumetric (both voxelwise and region-based) as well as amyloid imaging measures on the longitudinal slope of cognitive change.ResultsA base model of age and sex explained 18.5% of variance in episodic memory decline. This increased to 41.6% by adding baseline episodic memory scores. Adding amyloid load or volumetric measures explained only a negligible additional amount of variance (increase to 42.2%). A mediation analysis indicated that the effect of age on episodic memory scores was partly direct and partly mediated via hippocampal volume. Amyloid load did not play a significant role as mediator between age, hippocampal volume and episodic memory decline.ConclusionIn cognitively intact older adults, the strongest baseline predictor of subsequent episodic memory decline was the baseline episodic memory score. When this score was included, only very limited explanatory power was added by brain volume or amyloid load measures. The data warn against classifications that are purely biomarker-based and highlight the value of baseline cognitive performance levels in predictive models.

Age moderation of the association between negative subsequent memory effects and episodic memory performance.

Negative subsequent memory effects in functional MRI studies of memory formation have been linked to individual differences in memory performance, yet the effect of age on this association is currently unclear. To provide insight into the brain systems related to memory across the lifespan, we examined functional neuroimaging data acquired during episodic memory formation and behavioral performance from a memory recognition task in a sample of 109 participants, including three developmental age groups (8-12, 13-17, 18-25 year-olds) and one additional group of older adults (55-85 year-olds). Young adults showed the highest memory performance and strongest negative subsequent memory effects, while older adults showed reduced negative subsequent memory effects relative to young adults. Across the sample, negative subsequent memory effects were associated with better memory performance, and there was a significant interaction between negative subsequent memory effects and memory performance by age group. Posthoc analyses revealed that this moderation effect was driven by a stronger association between negative subsequent memory effects and memory performance in young adults than children, and that neither children nor older adults showed a significant association. These findings suggest that negative subsequent memory effects may differentially support memory performance across a lifespan trajectory characterized by developmental maturation and support further investigation of this effect in aging.

Signed Reward Prediction Errors in the Ventral Striatum Drive Episodic Memory.

Recent behavioral evidence implicates reward prediction errors (RPEs) as a key factor in the acquisition of episodic memory. Yet, important neural predictions related to the role of RPEs in episodic memory acquisition remain to be tested. Humans (both sexes) performed a novel variable-choice task where we experimentally manipulated RPEs and found support for key neural predictions with fMRI. Our results show that in line with previous behavioral observations, episodic memory accuracy increases with the magnitude of signed (i.e., better/worse-than-expected) RPEs (SRPEs). Neurally, we observe that SRPEs are encoded in the ventral striatum (VS). Crucially, we demonstrate through mediation analysis that activation in the VS mediates the experimental manipulation of SRPEs on episodic memory accuracy. In particular, SRPE-based responses in the VS (during learning) predict the strength of subsequent episodic memory (during recollection). Furthermore, functional connectivity between task-relevant processing areas (i.e., face-selective areas) and hippocampus and ventral striatum increased as a function of RPE value (during learning), suggesting a central role of these areas in episodic memory formation. Our results consolidate reinforcement learning theory and striatal RPEs as key factors subtending the formation of episodic memory.SIGNIFICANCE STATEMENT Recent behavioral research has shown that reward prediction errors (RPEs), a key concept of reinforcement learning theory, are crucial to the formation of episodic memories. In this study, we reveal the neural underpinnings of this process. Using fMRI, we show that signed RPEs (SRPEs) are encoded in the ventral striatum (VS), and crucially, that SRPE VS activity is responsible for the subsequent recollection accuracy of one-shot learned episodic memory associations.

Depressive Symptoms Longitudinally Mediate the Negative Effects of HbA1c on Memory Change Over 6 Years

Elevated glycated hemoglobin (HbA1c) has been associated with worse episodic memory in Type 2 diabetes. Prospective links between HbA1c and incident depressive symptoms suggest that behavioral mechanisms may underlie this association. Elevations in HbA1c may lead to depressive symptoms via biochemical changes directly caused by Type 2 diabetes or through distress associated with managing the treatment demands of the disease. This study aimed to determine whether depressive symptoms longitudinally mediate associations between HbA1c and episodic memory over 6 years. Participants (N=2,155) comprised adults aged 51+ with self-reported Type 2 diabetes and clinically elevated HbA1c (≥5.7%) at the time the Health and Retirement Study initiated blood collection. A longitudinal mediation model quantified associations between baseline HbA1c and 6-year change in episodic memory through 4-year change in depressive symptoms, controlling for baseline socio-demographics, other health conditions, and medication adherence. HbA1c was assayed from dried blood spots. Depressive symptoms were self-reported twice over four years. Episodic memory, assessed three times over six years, was a z-score composite of immediate and delayed recall of a word list. Increased depressive symptoms four years after baseline partially mediated the negative association between baseline HbA1c and 6-year memory decline. Depressive symptoms partially mediated the concurrent association between HbA1c and memory at baseline. This longitudinal study provides evidence that the deleterious effects of HbA1c on subsequent episodic memory may operate partly through behavioral mechanisms. Depressive symptoms may represent a critical target for interventions to reduce the enduring negative effects of hyperglycemia on memory aging in Type 2 diabetes.

Frontal ERP slow waves during memory encoding are associated with affective attitude formation

A neutral stimulus can acquire valence by being paired with a valenced stimulus, leading to a new attitude towards the previously neutral stimulus. There is, however, considerable debate about the mechanisms that underlie this process of affective attitude formation. Therefore, in the present study we employed a single-trial, intentional learning procedure that paired neutral with valenced words while recording ERP activity, and measured subsequent memory and subsequent attitudes for the pre-experimentally neutral words immediately following learning. Using traditional as well as single-trial ERP analyses, we found that frontal slow wave (FSW) activity, elicited while stimuli were being paired, was associated with both subsequent memory for the word pairs and subsequent attitudes towards the pre-experimentally neutral words. Specifically, FSW activity during the pairing of neutral with positive words was related to more positive subsequent attitudes, while during the pairing of neutral with negative words, it was associated with more negative subsequent attitudes, towards the pre-experimentally neutral words. Given that this FSW activity was also related to successful subsequent episodic memory retrieval for the word pairs, these findings provide evidence that the transfer of valence may depend on a process that supports associative episodic encoding during word paring. Further, a single-trial, mixed-effects model indicated that the relationship between encoding FSW activity and subsequent attitudes depended on the strength of the episodic memory trace. Thus, the present study provides novel evidence that a common mechanism contributes to both episodic memory encoding and affective attitude formation.

Visual and Semantic Representations Predict Subsequent Memory in Perceptual and Conceptual Memory Tests.

It is generally assumed that the encoding of a single event generates multiple memory representations, which contribute differently to subsequent episodic memory. We used functional magnetic resonance imaging (fMRI) and representational similarity analysis to examine how visual and semantic representations predicted subsequent memory for single item encoding (e.g., seeing an orange). Three levels of visual representations corresponding to early, middle, and late visual processing stages were based on a deep neural network. Three levels of semantic representations were based on normative observed ("is round"), taxonomic ("is a fruit"), and encyclopedic features ("is sweet"). We identified brain regions where each representation type predicted later perceptual memory, conceptual memory, or both (general memory). Participants encoded objects during fMRI, and then completed both a word-based conceptual and picture-based perceptual memory test. Visual representations predicted subsequent perceptual memory in visual cortices, but also facilitated conceptual and general memory in more anterior regions. Semantic representations, in turn, predicted perceptual memory in visual cortex, conceptual memory in the perirhinal and inferior prefrontal cortex, and general memory in the angular gyrus. These results suggest that the contribution of visual and semantic representations to subsequent memory effects depends on a complex interaction between representation, test type, and storage location.

Positive Psychosocial Factors and Cognitive Decline in Ethnically Diverse Older Adults.

Previous cross-sectional studies have documented associations between positive psychosocial factors, such as self-efficacy and emotional support, and late-life cognition. Further, the magnitudes of concurrent associations may differ across racial and ethnic groups that differ in Alzheimer's disease risk. The goals of this longitudinal study were to characterize prospective associations between positive psychosocial factors and cognitive decline and explicitly test for differential impact across race and ethnicity. 578 older adults (42% non-Hispanic Black, 31% non-Hispanic White, and 28% Hispanic) in the Washington Heights-Inwood Columbia Aging Project completed cognitive and psychosocial measures from the NIH Toolbox and standard neuropsychological tests over 2.4 years. Latent difference scores were used to model associations between positive psychosocial factors and cognitive decline controlling for baseline cognition, sociodemographics, depressive symptoms, physical health, and other positive psychosocial factors. Multiple-group modeling was used to test interactions between the positive psychosocial factors and race/ethnicity. Higher NIH Toolbox Friendship scores predicted less episodic memory decline. One standard deviation increase in friendship corresponded to 6 fewer years of memory aging. This association did not significantly differ across racial/ethnic groups. This longitudinal study provides support for the potential importance of friendships for subsequent episodic memory trajectories among older adults from three ethnic groups. Further study into culturally informed interventions is needed to investigate whether and how friend networks may be targeted to promote cognitive health in late life.

Automatic Encoding of a View-Centered Background Image in the Macaque Temporal Lobe.

Perceptual processing along the ventral visual pathway to the hippocampus (HPC) is hypothesized to be substantiated by signal transformation from retinotopic space to relational space, which represents interrelations among constituent visual elements. However, our visual perception necessarily reflects the first person's perspective based on the retinotopic space. To investigate this two-facedness of visual perception, we compared neural activities in the temporal lobe (anterior inferotemporal cortex, perirhinal and parahippocampal cortices, and HPC) between when monkeys gazed on an object and when they fixated on the screen center with an object in their peripheral vision. We found that in addition to the spatially invariant object signal, the temporal lobe areas automatically represent a large-scale background image, which specify the subject's viewing location. These results suggest that a combination of two distinct visual signals on relational space and retinotopic space may provide the first person's perspective serving for perception and presumably subsequent episodic memory.

Priming Effects on Subsequent Episodic Memory: Testing Attentional Accounts.

Prior work has shown that priming improves subsequent episodic memory, i.e., memory for the context in which an item is presented is improved if that item has been seen previously. We previously attributed this effect of "Priming on Subsequent Episodic Memory" (PSEM) to a sharpening of the perceptual/conceptual representation of an item, which improves its associability with an (arbitrary) background context, by virtue of increasing prediction error (Greve et al, 2017). However, an alternative explanation is that priming reduces the attentional resources needed to process an item, leaving more residual resources to encode its context. We report four experiments that tested this alternative, resource-based hypothesis, based on the assumption that reducing the available attentional resources by a concurrent load would reduce the size of the PSEM. In no experiment was there an interaction between attentional load and priming on mean memory performance, nor a consistent correlation across participants between priming and PSEM, failing to support the resource account. However, formal modelling revealed that a resource account is not, in fact, inconsistent with our data, by confirming that nonlinear (sigmoidal) resource-performance functions can reproduce any interaction with load, and, more strikingly, any pattern of correlation between priming and PSEM. This work reinforces not only the difficulty of refuting attentional resource accounts of memory encoding, but also questions the value of load manipulations more generally.

Systematic Review and Network Meta-Analysis of Anodal tDCS Effects on Verbal Episodic Memory

Abstract. There is growing interest in the study of transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, as an effective intervention to improve memory. In order to evaluate the relative efficacy of tDCS based on the location of anodal electrode sites, we conducted a systematic review examining the effect of stimulation applied during encoding on subsequent verbal episodic memory in healthy adults. We performed a network meta-analysis of 20 studies (23 experiments) with N = 978 participants. Left ventrolateral prefrontal and temporo-parietal sites appeared most likely to enhance episodic memory, although any significant effects were based on findings from single studies only. We did not find evidence for verbal retrieval enhancement of tDCS versus sham stimulation where the effect was based on more than one experimental paper. More frequent replication efforts and stricter reporting standards may improve the quality of evidence and allow more precise estimation of population-level effects of tDCS.

Exposure to fine particulate matter and temporal dynamics of episodic memory and depressive symptoms in older women

BackgroundEmerging data suggests PM2.5 (particulate matter with aerodynamic diameter <2.5 μm) may be associated with both earlier declines in episodic memory (EM) and increased depressive symptoms in older adults. Although late-life depressive symptoms are associated with EM, no longitudinal studies have examined the inter-relationship among PM2.5, depressive symptoms and EM. MethodsOlder women (n = 2,202; aged 67–83 in 1999) enrolled in the Women’s Health Initiative Study of Cognitive Aging completed up to eight annual assessments of depressive symptoms (15-item Geriatric Depression Scale) and EM (California Verbal Learning Test). A nationwide spatiotemporal model (1999–2010) was used to estimate ambient PM2.5 exposure at residential locations. Univariate and bivariate structural equation models (SEMs) for latent-change scores were used to examine how 3-year average PM2.5 preceding each assessment affects the temporal dynamics and bidirectional relations of annual changes in depressive symptoms and EM. ResultsIn univariate SEMs, one inter-quartile (4.04 μg/m3) increment of 3-year PM2.5 was significantly (p < 0.05) associated with accelerated declines in verbal learning (List A trials 1–3: β = −1.48) and free-recall memory (short-delay: β = −1.43; long-delay: β = −1.11), but not with change in depressive symptoms (β = 0.12; p = 0.71). In bivariate SEMs, significant associations were observed between PM2.5 and accelerated declines in EM measures (β = −1.44 to −0.99; p < 0.05) and between EM performance and changes in depressive symptoms (β = −0.08 to −0.05; p < 0.05), with significant indirect PM2.5 effects on changes in depressive symptoms (β = 0.08–0.10; p < 0.05). These findings were robust with adjustment for multiple demographic, lifestyle, and clinical factors, and remained after excluding subjects with dementia or mild cognitive impairment. No associations were found between PM2.5 and change in depressive symptoms or depressive symptoms and subsequent EM decline. ConclusionsFindings suggest that PM2.5 neurotoxicity may damage brain areas implicated in EM, followed by manifestation of depressive symptoms. Our data did not support depressive symptoms as the neuropsychological mediator of accelerated brain aging associated with PM2.5 exposure.