Retrieval orientation alters neural activity during autobiographical memory recollection

The Neural Corelates of Constructing Conceptual and Perceptual Representations of Autobiographical Memories

Contemporary neurocognitive frameworks propose that conceptual and perceptual content of autobiographical memories-personal past experiences-are processed by dissociable neural systems. Other work has proposed a central role of the anterior hippocampus in initially constructing autobiographical memories, regardless of the content. Here, we report on an fMRI study that utilized a repeated retrieval paradigm to test these ideas. In an MRI scanner, participants retrieved autobiographical memories at three timepoints. During the third retrieval, participants either shifted their focus to the conceptual content of the memory, the perceptual content of the memory, or retrieved the memory as they had done so on previous trials. We observed stronger anterior hippocampal activity for the first retrieval compared with later retrievals, regardless of whether there was a shift in content in those later trials. We also found evidence for separate cortical systems when constructing autobiographical memories with a focus on conceptual or perceptual content. Finally, we found that there was common engagement between later retrievals that required a shift toward conceptual content and the initial retrieval of a memory. This final finding was explored further with a behavioral experiment that provided evidence that focusing on conceptual content of a memory guides memory construction, whereas perceptual content adds precision to a memory. Together, these findings suggest there are distinct content-oriented cortical systems that work with the anterior hippocampus to construct representations of autobiographical memories.

Default mode network shows distinct emotional and contextual responses yet common effects of retrieval demands across tasks

The default mode network (DMN) lies towards the heteromodal end of the principal gradient of intrinsic connectivity, maximally separated from the sensory-motor cortex. It supports memory-based cognition, including the capacity to retrieve conceptual and evaluative information from sensory inputs, and to generate meaningful states internally; however, the functional organisation of DMN that can support these distinct modes of retrieval remains unclear. We used fMRI to examine whether activation within subsystems of DMN differed as a function of retrieval demands, or the type of association to be retrieved, or both. In a picture association task, participants retrieved semantic associations that were either contextual or emotional in nature. Participants were asked to avoid generating episodic associations. In the generate phase, these associations were retrieved from a novel picture, while in the switch phase, participants retrieved a new association for the same image. Semantic context and emotion trials were associated with dissociable DMN subnetworks, indicating that a key dimension of DMN organisation relates to the type of association being accessed. The frontotemporal and medial temporal DMN showed a preference for emotional and semantic contextual associations, respectively. Relative to the generate phase, the switch phase recruited clusters closer to the heteromodal apex of the principal gradient-a cortical hierarchy separating unimodal and heteromodal regions. There were no differences in this effect between association types. Instead, memory switching was associated with a distinct subnetwork associated with controlled internal cognition. These findings delineate distinct patterns of DMN recruitment for different kinds of associations yet common responses across tasks that reflect retrieval demands.

Spatial context scaffolds long-term episodic richness of weaker real-world autobiographical memories in both older and younger adults

Remembering life experiences involves recalling not only what occurred (episodic details), but also where an event took place (spatial context), both of which decline with age. Although spatial context can cue episodic detail recollection, it is unknown whether initially recalling an event alongside greater reinstatement of spatial context protects memory for episodic details in the long term, and whether this is affected by age. Here, we analysed 1079 personally-experienced, real-world events from 29 older adults and 12 younger adults. Events were recalled first on average 6 weeks after they occurred and then again on average 24 weeks after they occurred. We developed a novel scoring protocol to quantify spatial contextual details and used the established Autobiographical Interview to quantify episodic details. We found improved recall of episodic details after a delay if those details had initially been recalled situated in greater spatial context. Notably, for both older and younger adults, this preservation was observed for memories initially recalled with low, but not high, numbers of episodic details, suggesting that spatial context aided episodic retrieval for memories that required more support. This work supports the notion that spatial context scaffolds detail-rich event recollection and inspires memory interventions that leverage this spatial scaffold.

Brain connectivity patterns associated with individual differences in the access to experience-near personal semantics: a resting-state fMRI study

It has been proposed that a continuum of specificity exists between episodic and semantic autobiographical memory. Personal semantics have been theorized to situate intermediately on this continuum, with more "experience-near" personal semantics (enPS) closer to the episodic end. We used individual differences in behavior as a model to investigate brain networks associated with the access to episodic autobiographical (EAM) and enPS information, assessing the relation between performance in the EAM and enPS conditions of the Autobiographical Fluency Task (AFT) and intrinsic brain connectivity. Results of an intrinsic connectivity contrast analysis showed that the global connectivity of two clusters in the left and right posterior cingulate cortex (PCC) was predicted by performance in the enPS conditions. Moreover, enPS scores predicted the connectivity strength of the right PCC with the bilateral anterior hippocampus (aHC), anterior middle temporal gyrus (aMTG) and medial orbitofrontal cortex, and the left aMTG and PCC. enPS scores also predicted the connectivity strength of the left PCC with the bilateral HC and MTG. The network highlighted involves parts of the core and of the dorsal medial subsystems of the Default Mode Network, in line with the proposal that enPS represents an intermediate entity between episodic and semantic memory.

The shared and unique neural correlates of personal semantic, general semantic, and episodic memory

One of the most common distinctions in long-term memory is that between semantic (i.e., general world knowledge) and episodic (i.e., recollection of contextually specific events from one's past). However, emerging cognitive neuroscience data suggest a surprisingly large overlap between the neural correlates of semantic and episodic memory. Moreover, personal semantic memories (i.e., knowledge about the self and one's life) have been studied little and do not easily fit into the standard semantic-episodic dichotomy. Here, we used fMRI to record brain activity while 48 participants verified statements concerning general facts, autobiographical facts, repeated events, and unique events. In multivariate analysis, all four types of memory involved activity within a common network bilaterally (e.g., frontal pole, paracingulate gyrus, medial frontal cortex, middle/superior temporal gyrus, precuneus, posterior cingulate, angular gyrus) and some areas of the medial temporal lobe. Yet the four memory types differentially engaged this network, increasing in activity from general to autobiographical facts, from autobiographical facts to repeated events, and from repeated to unique events. Our data are compatible with a component process model, in which declarative memory types rely on different weightings of the same elementary processes, such as perceptual imagery, spatial features, and self-reflection.

Common and distinct correlates of construction and elaboration of episodic-autobiographical memory: An ALE meta-analysis

The recollection of episodic-autobiographical memories (EAMs) entails a complex temporal dynamic, from initial "construction" to subsequent "elaboration" of memories. While there is consensus that EAM retrieval involves a distributed network of brain regions, it is still largely debated which regions specifically contribute to EAM construction and/or elaboration. To clarify this issue, we conducted an Activation Likelihood Estimation (ALE) meta-analysis based on the Preferred Reporting Items for Systematic-Reviews and Meta-Analyses (PRISMA) method. We found common recruitment of the left hippocampus and posterior cingulate cortex (PCC) during both phases. Additionally, EAM construction led to activations in the ventromedial prefrontal cortex, left angular gyrus (AG), right hippocampus, and precuneus, while the right inferior frontal gyrus was activated by EAM elaboration. Although most of these regions are distributed over the default mode network, the current findings highlight a differential contribution according to early (midline regions, left/right hippocampus, and left AG) versus later (left hippocampus, and PCC) recollection. Overall, these findings contribute to clarify the neural correlates that support the temporal dynamics of EAM recollection.

Cross-stage neural pattern similarity in the hippocampus predicts false memory derived from post-event inaccurate information

The misinformation effect occurs when people's memory of an event is altered by subsequent inaccurate information. No study has systematically tested theories about the dynamics of human hippocampal representations during the three stages of misinformation-induced false memory. This study replicates behavioral results of the misinformation effect, and investigates the cross-stage pattern similarity in the hippocampus and cortex using functional magnetic resonance imaging. Results show item-specific hippocampal pattern similarity between original-event and post-event stages. During the memory-test stage, hippocampal representations of original information are weakened for true memory, whereas hippocampal representations of misinformation compete with original information to create false memory. When false memory occurs, this conflict is resolved by the lateral prefrontal cortex. Individuals' memory traces of post-event information in the hippocampus predict false memory, whereas original information in the lateral parietal cortex predicts true memory. These findings support the multiple-trace model, and emphasize the reconstructive nature of human memory.

Autobiographical event memory and aging: older adults get the gist

We propose that older adults' ability to retrieve episodic autobiographical events, although often viewed through a lens of decline, reveals much about what is preserved and prioritized in cognitive aging. Central to our proposal is the idea that the so-called gist of an autobiographical event is not only spared with normal aging but also well adapted to serve memory-guided behavior in older age. To support our proposal, we review cognitive and brain evidence indicating an age-related shift toward gist memory. We then discuss why this shift likely arises from more than age-related decline and instead partly reflects a natural, arguably adaptive, outcome of experience, motivation, and mode-of-thinking factors. Our proposal reveals an upside of age-related memory changes and identifies important research questions.

How shifting visual perspective during autobiographical memory retrieval influences emotion: A change in retrieval orientation

Visual perspective during autobiographical memory (AM) retrieval influences how people remember the emotional aspects of memories. Prior research in emotion regulation has also shown that shifting from an own eyes to an observer-like perspective is an efficient way of regulating the affect elicited by emotional AMs. However, the impact of shifting visual perspective is also dependent on the nature of the emotion associated with the event. The current review synthesizes behavioral and functional neuroimaging findings from the event memory and emotion regulation literature that examine how adopting particular visual perspectives and actively shifting across them during retrieval alters emotional experience, by primarily focusing on emotional intensity. We review current theories explaining why shifts in perspectives may or may not change the emotional characteristics of memories, then propose a new theory, suggesting that the own eyes and observer-like perspectives are two different retrieval orientations supported by differential neural activations that lead episodic details to be reconstructed in specific ways.

Readiness to remember: predicting variability in episodic memory

Learning and remembering are fundamental to our lives, so what causes us to forget? Answers often highlight preparatory processes that precede learning, as well as mnemonic processes during the act of encoding or retrieval. Importantly, evidence now indicates that preparatory processes that precede retrieval attempts also have powerful influences on memory success or failure. Here, we review recent work from neuroimaging, electroencephalography, pupillometry, and behavioral science to propose an integrative framework of retrieval-period dynamics that explains variance in remembering in the moment and across individuals as a function of interactions among preparatory attention, goal coding, and mnemonic processes. Extending this approach, we consider how a 'readiness to remember' (R2R) framework explains variance in high-level functions of memory and mnemonic disruptions in aging.

Volume of the posterior hippocampus mediates age-related differences in spatial context memory and is correlated with increased activity in lateral frontal, parietal and occipital regions in healthy aging

Healthy aging is associated with episodic memory decline, particularly in the ability to encode and retrieve object-context associations (context memory). Neuropsychological and neuroimaging studies have highlighted the importance of the medial temporal lobes (MTL) in supporting episodic memory across the lifespan. However, given the functional heterogeneity of the MTL, volumetric declines in distinct regions may impact performance on specific episodic memory tasks, and affect the function of the large-scale neurocognitive networks supporting episodic memory encoding and retrieval. In the current study, we investigated how MTL structure may mediate age-related differences in performance on spatial and temporal context memory tasks, in a sample of 125 healthy adults aged 19-76 years old. Standard T1-weighted MRIs were segmented into the perirhinal, entorhinal and parahippocampal cortices, as well as the anterior and posterior hippocampal subregions. We observed negative linear and quadratic associations between age and volume of the parahippocampal cortex, and anterior and posterior hippocampal subregions. We also found that volume of the posterior hippocampus fully mediated the association between age and spatial, but not temporal context memory performance. Further, we employed a multivariate behavior partial-least-squares analysis to assess how age and regional MTL volumes correlated with brain activity during the encoding and retrieval of spatial context memories. We found that greater activity within lateral prefrontal, parietal, and occipital regions, as well as within the anterior MTL was related to older age and smaller volume of the posterior hippocampus. Our results highlight the heterogeneity of MTL contributions to episodic memory across the lifespan and provide support for the posterior-anterior shift in aging, and scaffolding theory of aging and cognition.

Individual differences in the relationship between episodic detail generation and resting state functional connectivity vary with age

The ability to generate episodic details while recollecting autobiographical events is believed to depend on a collection of brain regions that form a posterior medial network (PMN). How age-related differences in episodic detail generation relate to the PMN, however, remains unclear. The present study sought to examine individual differences, and the role of age, in PMN resting state functional connectivity (rsFC) associations with episodic detail generation. Late middle-aged and older adults (N = 41, ages 52-81), and young adults (N = 21, ages 19-35) were asked to describe recent personal events, and these memory narratives were coded for episodic, semantic and 'miscellaneous' details. Independent components analysis and regions-of-interest analyses were used to assess rsFC within the PMN separately for anterior connections (hippocampal and medial prefrontal) and posterior connections (hippocampal, parahippocampal and parieto-occipital), as these connections purportedly serve different functional roles in episodic detail generation. Compared to younger adults, older adults produced memory narratives with lower episodic specificity (ratio of episodic:total details) and a greater amount of semantic detail. Among the older adults, episodic detail amounts and episodic specificity were reduced with increasing age. There were no significant age differences in PMN rsFC. Stronger anterior PMN rsFC was related to lower episodic detail in the older adult group, but not in the young. Among the older adults, increasing age brought on an association between increased anterior PMN rsFC and reduced episodic specificity. In contrast, increasing age brought on an association between increased posterior PMN rsFC and increased semantic detail. The present study provides evidence that functional connectivity within the PMN, particularly anterior PMN, tracks individual differences in the amount of episodic details retrieved by older adults. Furthermore, these brain-behavior relationships appear to be age-specific, indicating that some process within aging alters the nature of how anterior PMN rsFC and episodic detail relate to each other. Whether this process entails an age-related loss of integrity to the PMN, or an age-related shift toward semantic retrieval, remains to be determined.

Evidence for a pervasive autobiographical memory impairment in Logopenic Progressive Aphasia

Although characterized primarily as a language disorder, mounting evidence indicates episodic amnesia in Logopenic Progressive Aphasia (LPA). Whether such memory disturbances extend to information encoded pre-disease onset remains unclear. To address this question, we examined autobiographical memory in 10 LPA patients, contrasted with 18 typical amnestic Alzheimer's disease and 16 healthy Control participants. A validated assessment, the Autobiographical Interview, was employed to explore autobiographical memory performance across the lifespan under free and probed recall conditions. Relative to Controls, LPA patients showed global impairments across all time periods for free recall, scoring at the same level as disease-matched cases of Alzheimer's disease. Importantly, these retrieval deficits persisted in LPA, even when structured probing was provided, and could not be explained by overall level of language disruption or amount of information generated during autobiographical narration. Autobiographical memory impairments in LPA related to gray matter intensity decrease in predominantly posterior parietal brain regions implicated in memory retrieval. Together, our results suggest that episodic memory disturbances may be an under-appreciated clinical feature of LPA.

The effect of retrieval goals on the content recalled from complex narratives

Memories are not always accurately recalled, and one factor that influences memory is the goal of retrieval. Evidence suggests that retrieving a memory to fit a social goal affects the content that is recollected, yet the nature of this effect, and whether this effect remains stable over time, is not fully understood. To this end, we compared the effect of retrieving a complex event (i.e., a narrative) motivated by a social versus an accuracy goal both immediately and after a 24-hour consolidation period. Three groups of young adults encoded audio narratives and recalled these narratives immediately (Session 1) and again after a 24-hour delay (Session 2). One group recalled the narratives to meet a social goal across both sessions (social); another group recalled the narratives for an accuracy goal across both sessions (accuracy); and a final group initially recalled the narratives for a social goal (Session 1) and then for an accuracy goal (Session 2; mixed). We found no effect of group on the number of details that described the overall theme (central details); however, a social goal significantly reduced the number of specific (episodic) details and altered the order in which the details were described. When the goal of retrieval changed across session (i.e., mixed group), the reduction in specific details remained but not the effect on detail order. These results demonstrate that socially motivated memory retrieval selectively alters the specific episodic content contained in the memory, leaving intact the thematic knowledge and overall structure of the memory.

Intrinsic connectivity reveals functionally distinct cortico-hippocampal networks in the human brain

Episodic memory depends on interactions between the hippocampus and interconnected neocortical regions. Here, using data-driven analyses of resting-state functional magnetic resonance imaging (fMRI) data, we identified the networks that interact with the hippocampus-the default mode network (DMN) and a "medial temporal network" (MTN) that included regions in the medial temporal lobe (MTL) and precuneus. We observed that the MTN plays a critical role in connecting the visual network to the DMN and hippocampus. The DMN could be further divided into 3 subnetworks: a "posterior medial" (PM) subnetwork comprised of posterior cingulate and lateral parietal cortices; an "anterior temporal" (AT) subnetwork comprised of regions in the temporopolar and dorsomedial prefrontal cortex; and a "medial prefrontal" (MP) subnetwork comprised of regions primarily in the medial prefrontal cortex (mPFC). These networks vary in their functional connectivity (FC) along the hippocampal long axis and represent different kinds of information during memory-guided decision-making. Finally, a Neurosynth meta-analysis of fMRI studies suggests new hypotheses regarding the functions of the MTN and DMN subnetworks, providing a framework to guide future research on the neural architecture of episodic memory.

Reduced anterior hippocampal and ventromedial prefrontal activity when repeatedly retrieving autobiographical memories

Research has reported that repeatedly retrieving a novel or imagined event representation reduces activity within brain regions critical for constructing mental scenarios, namely the anterior hippocampus and ventromedial prefrontal cortex (vmPFC). The primary aim of this investigation was to test if this pattern reported for imagined events would be found when repeatedly recollecting autobiographical memories. Twenty-four participants retrieved 12 pre-selected autobiographical memories four times while undergoing an fMRI scan. We used a region of interest approach to investigate how the anterior and posterior hippocampus as well as cortical regions critical for memory retrieval-the vmPFC and the posterior cingulate cortex (PCC)-are affected by repeated retrievals. This analysis revealed an effect in the bilateral anterior hippocampi and vmPFC, but not the posterior hippocampus nor the PCC, with activity decreasing in these regions as a function of repeated retrievals. A multivariate analytic approach (Partial Least Squares) was used to assess whole-brain patterns of neural activity associated with repeated retrievals. This analysis revealed one pattern of neural activity associated with the initial retrieval of a memory (e.g., inferior frontal and temporal lobe regions) and a separate pattern of activity associated with later retrievals that was distributed primarily across the lateral parietal cortices. These findings suggest that the anterior hippocampus and the vmPFC support the episodic construction of an autobiographical memory the first time it is retrieved and that alternate nonconstructive processes support its subsequent retrieval shortly thereafter.

Mapping the imaginative mind: Charting new paths forward

The fields of psychology and neuroscience are in the midst of an explosion of research seeking to understand human imagination - the ability to form thoughts and mental images that stretch beyond what is currently available to the senses. Imaginative thought is proving to be remarkably diverse, capturing the capacity to recall past experiences, consider what lies ahead, and understand others' minds, in addition to other forms of creative and spontaneous thinking. In the first part of this article, we introduce an integrative framework that attempts to explain how components of a core brain network facilitate interacting features of imagination that we refer to as the "mind's eye" and "mind's mind." We then highlight three emerging research directions that could inform our understanding of how imagination arises and unfolds in everyday life.

Deconstructing the Posterior Medial Episodic Network

Our ability to remember or imagine specific events involves the construction of complex mental representations, a process that engages cortical and hippocampal regions in a core posterior medial (PM) brain network. Existing theoretical approaches have described the overarching contributions of the PM network, but less is known about how episodic content is represented and transformed throughout this system. Here, we review evidence of key functional interactions among PM regions and their relation to the core cognitive operations and representations supporting episodic construction. Recent demonstrations of intranetwork functional diversity are integrated with existing accounts to inform a network-based model of episodic construction, in which PM regions flexibly share and manipulate event information to support the variable phenomenology of episodic memory and simulation.

The Neural Dynamics of Individual Differences in Episodic Autobiographical Memory

The ability to mentally travel to specific events from one's past, dubbed episodic autobiographical memory (E-AM), contributes to adaptive functioning. Nonetheless, the mechanisms underlying its typical interindividual variation remain poorly understood. To address this issue, we capitalize on existing evidence that successful performance on E-AM tasks draws on the ability to visualize past episodes and reinstate their unique spatiotemporal context. Hence, here, we test whether features of the brain's functional architecture relevant to perceptual versus conceptual processes shape individual differences in both self-rated E-AM and laboratory-based episodic memory (EM) for random visual scene sequences (visual EM). We propose that superior subjective E-AM and visual EM are associated with greater similarity in static neural organization patterns, potentially indicating greater efficiency in switching, between rest and mental states relevant to encoding perceptual information. Complementarily, we postulate that impoverished subjective E-AM and visual EM are linked to dynamic brain organization patterns implying a predisposition towards semanticizing novel perceptual information. Analyses were conducted on resting state and task-based fMRI data from 329 participants (160 women) in the Human Connectome Project (HCP) who completed visual and verbal EM assessments, and an independent gender diverse sample (N = 59) who self-rated their E-AM. Interindividual differences in subjective E-AM were linked to the same neural mechanisms underlying visual, but not verbal, EM, in general agreement with the hypothesized static and dynamic brain organization patterns. Our results suggest that higher E-AM entails more efficient processing of temporally extended information sequences, whereas lower E-AM entails more efficient semantic or gist-based processing.

Human hippocampal CA3 damage disrupts both recent and remote episodic memories

Neocortical-hippocampal interactions support new episodic (event) memories, but there is conflicting evidence about the dependence of remote episodic memories on the hippocampus. In line with systems consolidation and computational theories of episodic memory, evidence from model organisms suggests that the cornu ammonis 3 (CA3) hippocampal subfield supports recent, but not remote, episodic retrieval. In this study, we demonstrated that recent and remote memories were susceptible to a loss of episodic detail in human participants with focal bilateral damage to CA3. Graph theoretic analyses of 7.0-Tesla resting-state fMRI data revealed that CA3 damage disrupted functional integration across the medial temporal lobe (MTL) subsystem of the default network. The loss of functional integration in MTL subsystem regions was predictive of autobiographical episodic retrieval performance. We conclude that human CA3 is necessary for the retrieval of episodic memories long after their initial acquisition and functional integration of the default network is important for autobiographical episodic memory performance.