Reinstatement of item-specific contextual details during retrieval supports recombination-related false memories

Age-Related differences in the relationship between sustained attention and associative memory and Memory-Guided inference

Episodic memory enables the encoding and retrieval of novel associations, as well as the bridging across learned associations to draw novel inferences. A fundamental goal of memory science is to understand the factors that give rise to individual and age-related differences in memory-dependent cognition. Variability in episodic memory could arise, in part, from both individual differences in sustained attention and diminished attention in aging. We first report that, relative to young adults (N = 23; M = 20.0 years), older adults (N = 26, M = 68.7 years) demonstrated lower associative memory and memory-guided associative inference performance and that this age-related reduction in associative inference occurs even when controlling for associative memory performance. Next, we confirm these age-related memory differences by using a high-powered, online replication study (young adults: N = 143, M = 26.2 years; older adults N = 133, M = 67.7 years), further demonstrating that age-related differences in memory do not reflect group differences in sustained attention (as assayed by the gradual-onset continuous performance task; gradCPT). Finally, we report that individual differences in sustained attention explain between-person variability in associative memory and inference performance in the present, online young adult sample, but not in the older adult sample. These findings extend understanding of the links between attention and memory in young adults, demonstrating that differences in sustained attention was related to differences in memory-guided inference. By contrast, our data suggest that the present age-related differences in memory-dependent behavior and the memory differences between older adults are due to attention-independent mechanisms.

The effects of episodic context on memory integration

Information encountered in different events, such as people and objects, can be interlinked in memory. Such memory integration supports novel inferences about the world. This study investigates the role of episodic context on memory integration in two experiments using an associative inference task. Participants encoded events with overlapping (AB and BC) and non-overlapping associations (XY) presented in the same or different episodic contexts. Inference performance across events (AC) was tested in the absence (Experiment 1) and in the presence (Experiment 2) of the encoding context. Our data show that inferences across events encoded in the same context were more accurate, faster, and made with greater confidence compared to those encoded in different contexts. However, this effect was observed only when the context was presented during testing, suggesting that context enhances associative inferences by facilitating retrieval of events associated with that context. These findings demonstrate that revisiting the encoding context promotes memory integration by providing privileged access to contextually associated memory traces and facilitating their flexible recombination to form novel inferences.

Episodic recombination and the role of time in mental travel

Mental time travel is often presented as a singular mechanism, but theoretical and empirical considerations suggest that it is composed of component processes. What are these components? Three hypotheses about the major components of mental time travel are commonly considered: (i) remembering and imagining might, respectively, rely on different processes, (ii) past- and future-directed forms of mental time travel might, respectively, rely on different processes, and (iii) the creation of episodic representations and the determination of their temporal orientation might, respectively, rely on different processes. Here, we flesh out the last of these proposals. First, we argue for 'representational continuism': the view that different forms of mental travel are continuous with regard to their core representational contents. Next, we propose an updated account of episodic recombination (the mechanism generating these episodic contents) and review evidence in its support. On this view, episodic recombination is a natural kind best viewed as a form of compositional computation. Finally, we argue that episodic recombination should be distinguished from mechanisms determining the temporal orientation of episodic representations. Thus, we suggest that mental travel is a singular capacity, while mental time travel has at least two major components: episodic representations and their temporal orientation. This article is part of the theme issue 'Elements of episodic memory: lessons from 40 years of research'.

Disrupted cognitive network revealed by task-induced brain entropy in schizophrenia

Brain entropy (BEN), which measures the amount of information in brain activity, provides a novel perspective for evaluating brain function. Recent studies using resting-state functional magnetic resonance imaging (fMRI) have shown that BEN during rest can help characterize brain function alterations in schizophrenia (SCZ). However, there is a lack of research on BEN using task-evoked fMRI to explore task-dependent cognitive deficits in SCZ. In this study, we evaluate whether the reduced working memory (WM) capacity in SCZ is possibly associated with dynamic changes in task BEN during tasks with high cognitive demands. We analyzed data from 15 patients with SCZ and 15 healthy controls (HC), calculating task BEN from their N-back task fMRI scans. We then examined correlations between task BEN values, clinical symptoms, 2-back task performance, and neuropsychological test scores. Patients with SCZ exhibited significantly reduced task BEN in the cerebellum, hippocampus, parahippocampal gyrus, thalamus, and the middle and superior frontal gyrus (MFG and SFG) compared to HC. In HC, significant positive correlations were observed between task BEN and 2-back accuracy in several brain regions, including the MFG and SFG; such correlations were absent in patients with SCZ. Additionally, task BEN was negatively associated with scores for both positive and negative symptoms in areas including the parahippocampal gyrus among patients with SCZ. In conclusion, our findings indicate that a reduction in BEN within prefrontal and hippocampal regions during cognitively demanding tasks may serve as a neuroimaging marker for SCZ.

Constructive Memory and Conscious Experience

Episodic memory relies on constructive processes that support simulating novel future events by flexibly recombining elements of past experiences, and that can also give rise to memory errors. In recent studies, we have developed methods to characterize the cognitive and neural processes that support conscious experiences linked to this process of episodic recombination, both when people simulate novel future events and commit recombination-related memory errors. In this Perspective, we summarize recent studies that illustrate these phenomena, and discuss broader implications for characterizing the basis of conscious experiences associated with constructive memory from a cognitive neuroscience perspective.

Ingroup sources enhance associative inference

Episodic memory encompasses flexible processes that enable us to create and update knowledge by making novel inferences across overlapping but distinct events. Here we examined whether an ingroup source enhances the capacity to draw such inferences. In three studies with US-American samples (NStudy1 = 53, NStudy2 = 68, NStudy3 = 68), we investigated the ability to make indirect associations, inferable from overlapping events, presented by ingroup or outgroup sources. Participants were better at making inferences based on events presented by ingroup compared to outgroup sources (Studies 1 and 3). When the sources did not form a team, the effect was not replicated (Study 2). Furthermore, we show that this ingroup advantage may be linked to differing source monitoring resources allocated to ingroup and outgroup sources. Altogether, our findings demonstrate that inferential processes are facilitated for ingroup information, potentially contributing to spreading biased information from ingroup sources into expanding knowledge networks, ultimately maintaining and strengthening polarized beliefs.

Neural distinctiveness and discriminability underlying unitization and associative memory in aging

Previous work has suggested unitized pairs behave as a single unit and more critically, are processed neurally different than those of associative memories. The current works examines the neural differences between unitization and non-unitized memory using fMRI and multivoxel analyses. Specifically, we examined the differences across face-occupation pairings as a function of whether the pairing was viewed as a person performing the given job (unitized binding) or a person saying they knew someone who had a particular job (non-unitized binding). The results show that at encoding and retrieval, the angular gyrus can discriminate between unitized and non-unitized target trials. Additionally, during encoding, the medial temporal lobe (hippocampus and perirhinal cortex), frontal parietal regions (angular gyrus and medial frontal gyrus) and visual regions (middle occipital cortex) exhibit distinct neural patterns to recollected unitized and non-unitized targets. Furthermore, the perirhinal cortex and medial frontal gyrus show greater neural similarity within subsequently recollected unitized trials compared to non-unitized trials. We conclude that an encoding based strategy to elicit unitization can produce greater associative memory compared to non-unitized trials in older adults. Additionally, when unitized trials are subsequently recollected in the perirhinal cortex older adults show greater neural similarity within unitized trials compared to non-unitized trials.

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.

Neural distinctiveness and reinstatement of hippocampal representations support unitization for associations

The medial temporal lobe (MTL) is critical to associative memory success, yet not all types of associations may be processed in a similar manner within MTL subregions. In particular, previous work suggests intra- and inter-item associations not only exhibit differences in overall rates of recollection, but also recruit different MTL subregions. Whereas intra-item associations, akin to unitization, take advantage of associations between within-item features, inter-item associations form links across discrete items. The current work examines the neural differences between these two types of associations using fMRI and multivoxel analyses. Specifically, the current study examines differences across face-occupation as a function of whether the pairing was viewed as a person performing the given job (intra-item binding) or a person saying they knew someone who had a particular job (inter-item binding). The results show that at encoding, successfully recollected neural patterns related to intra- and inter-item associations are distinct from one another in the hippocampus, parahippocampal and perirhinal cortex. Additionally, the two trial types are reinstated distinctly such that inter-item trials have higher neural reinstatement from encoding to retrieval compared to intra-item trials in the hippocampus. We conclude that intra- and inter- associative pairs may utilize similar neural regions that represent patterns of activation differentially at encoding. However, to reinstate information to the same degree (i.e., subsequently successfully recollected) inter-item associations, that are all encoded in the same manner, may be reinstated more similarly compared to intra-item associations that are encoded by imagining pairs differently and occupation specific. This may indicate that intra-item associations promote more efficient reinstatement.

Memory Sins in Applied Settings: What Kind of Progress?

Over two decades ago, I proposed that memory errors could be classified into seven basic categories or sins (Schacter, 1999, 2001), comprising three sins of omission (transience, absentmindedness, and blocking) and four sins of commission (misattribution, suggestibility, bias, and persistence). In the past two decades, much has been learned about the nature and basis of the memory sins. Here, I assess the extent of progress that has been made during that time regarding applied implications of five of the sins: transience, absentmindedness, misattribution, suggestibility, and persistence. The manifestations of these sins have been examined in a variety of applied settings, including educational, clinical, legal, and technological domains. I argue that considerable progress has been made in characterizing the impact of memory sins in each domain, identify gaps in and limitations of our current knowledge, and briefly consider how these developments bear on broad questions regarding the reliability of human memory.

Dynamic changes in neural representations underlie the repetition effect on false memory

Restudying word lists (e.g., dream, awake, and bed) strengthens true memory of the studied words and reduces false memory for unstudied but semantically related lures (e.g., sleep). Yet, the neural mechanisms involved in this repetition effect on false memory remain unclear. Possible mechanisms involve item-specific and semantic neural representations at encoding, and the memory strength between encoding and retrieval. This study first replicated the behavioral results (Exp. 1) and then investigated various neural mechanisms by using slow event-related functional magnetic resonance imaging (fMRI) and representational similarity analysis (Exp. 2). Behavioral results confirmed that restudy improved true memory and reduced false memory. The fMRI results showed that restudy induced item-specific neural representations at encoding in the left occipital pole, but reduced neural overlap between semantic representations at encoding in the left temporal pole. Individual differences in these two encoding neural mechanisms were correlated with the behavioral measure of false memory, with greater restudy-induced representational changes at encoding (item-specific neural representations and reduced neural overlap between semantic representations) being associated with lower false memory. Moreover, restudy enhanced the memory strength between encoding and retrieval in the visuoparietal cortex but reduced it in the frontal cortex. These findings suggest that dynamic changes in neural representations underlie the repetition effect on false memory, supporting a dual-coding neural framework.

Mnemonic construction and representation of temporal structure in the hippocampal formation

The hippocampal-entorhinal region supports memory for episodic details, such as temporal relations of sequential events, and mnemonic constructions combining experiences for inferential reasoning. However, it is unclear whether hippocampal event memories reflect temporal relations derived from mnemonic constructions, event order, or elapsing time, and whether these sequence representations generalize temporal relations across similar sequences. Here, participants mnemonically constructed times of events from multiple sequences using infrequent cues and their experience of passing time. After learning, event representations in the anterior hippocampus reflected temporal relations based on constructed times. Temporal relations were generalized across sequences, revealing distinct representational formats for events from the same or different sequences. Structural knowledge about time patterns, abstracted from different sequences, biased the construction of specific event times. These findings demonstrate that mnemonic construction and the generalization of relational knowledge combine in the hippocampus, consistent with the simulation of scenarios from episodic details and structural knowledge.

Representing the Good and Bad: fMRI signatures during the encoding of multisensory positive, negative, and neutral events

Few studies have examined how multisensory emotional experiences are processed and encoded into memory. Here, we aimed to determine whether, at encoding, activity within functionally-defined visual- and auditory-processing brain regions discriminated the emotional category (i.e., positive, negative, or neutral) of the multisensory (audio-visual) events. Participants incidentally encoded positive, negative, and neutral multisensory stimuli during event-related functional magnetic resonance imaging (fMRI). Following a 3-h post-encoding delay, their memory for studied stimuli was tested, allowing us to identify emotion-category-specific subsequent-memory effects focusing on medial temporal lobe regions (i.e., amygdala, hippocampus) and visual- and auditory-processing regions. We used a combination of univariate and multivoxel pattern fMRI analyses (MVPA) to examine emotion-category-specificity in mean activity levels and neural patterning, respectively. Univariate analyses revealed many more visual regions that showed negative-category-specificity relative to positive-category-specificity, and auditory regions only showed negative-category-specificity. These results suggest that negative emotion is more closely tied to information contained within sensory regions, a conclusion that was supported by the MVPA analyses. Functional connectivity analyses further revealed that the visual amplification of category-selective processing is driven, in part, by mean signal from the amygdala. Interestingly, while stronger representations in visuo-auditory regions were related to subsequent-memory for neutral multisensory stimuli, they were related to subsequent-forgetting of positive and negative stimuli. Neural patterning in the hippocampus and amygdala were related to memory for negative multisensory stimuli. These results provide new evidence that negative emotional stimuli are processed with increased engagement of visuosensory regions, but that this sensory engagement-that generalizes across the entire emotion category-is not the type of sensory encoding that is most beneficial for later retrieval.

Neural correlates of transitive inference: An SDM meta-analysis on 32 fMRI studies

Transitive inference (TI) is a critical capacity involving the integration of relevant information into prior knowledge structure for drawing novel inferences on unobserved relationships. To date, the neural correlates of TI remain unclear due to the small sample size and heterogeneity of various experimental tasks from individual studies. Here, the meta-analysis on 32 fMRI studies was performed to detect brain activation patterns of TI and its three paradigms (spatial inference, hierarchical inference, and associative inference). We found the hippocampus, prefrontal cortex (PFC), putamen, posterior parietal cortex (PPC), retrosplenial cortex (RSC), supplementary motor area (SMA), precentral gyrus (PreCG), and median cingulate cortex (MCC) were engaged in TI. Specifically, the RSC was implicated in the associative inference, whereas PPC, SMA, PreCG, and MCC were implicated in the hierarchical inference. In addition, the hierarchical inference and associative inference both evoked activation in the hippocampus, medial PFC, and PCC. Although the meta-analysis on spatial inference did not generate a reliable result due to insufficient amount of investigations, the present work still offers a new insight for better understanding the neural basis underlying TI.

Neural Reinstatement of Overlapping Memories in Young and Older Adults

When we update our episodic memories with new information, mnemonic competition between old and new memories may result because of the presence of shared features. Behavioral studies suggest that this competition can lead to proactive interference, resulting in unsuccessful memory updating, particularly for older adults. It is difficult with behavioral data alone to measure the reactivation of old, overlapping memories during retrieval and its impact on memory for new memories. Here, we applied encoding-retrieval representational similarity (ERS) analysis to EEG data to estimate event-specific encoding-related neural reinstatement of old associations during the retrieval of new ones and its impact on memory for new associations in young and older adults. Our results showed that older adults' new associative memory performance was more negatively impacted by proactive interference from old memories than that of young adults. In both age groups, ERS for old associative memories was greater for trials for which new associative memories were forgotten than remembered. In contrast, ERS for new associative memories was greater when they were remembered than forgotten. In addition, older adults showed relatively attenuated target (i.e., new associates) and lure (i.e., old associates) ERS effects compared to younger adults. Collectively, these results suggest that the neural reinstatement of interfering memories during retrieval contributes to proactive interference across age, whereas overall attenuated ERS effect in older adults might reflect their reduced memory fidelity.

On the evolution of a functional approach to memory

In an analysis of memory systems, Sherry and Schacter (Psychological Review, 94, 439-454, 1987) emphasized the importance of functional and evolutionary considerations for characterizing mechanisms of memory. The present article considers four different yet closely related topics from more recent research in which similar considerations have played a prominent role in shaping both experiment and theory: the seven sins of memory, mechanisms underlying memory misattribution errors, the role of memory in imagining future experiences, and the relation between associative inference and memory errors. These lines of research illustrate the usefulness of attempting to integrate functional and mechanistic considerations, in line with the general approach articulated by Sherry and Schacter.