Episodic memory: from mind to brain

Comparing episodic memory outcomes from walking augmented reality and stationary virtual reality encoding experiences

Episodic Memory (EM) is the neurocognitive capacity to consciously recollect personally experienced events in specific spatio-temporal contexts. Although the relevance of spatial and temporal information is widely acknowledged in the EM literature, it remains unclear whether and how EM performance and organisation is modulated by self-motion, and by motor- and visually- salient environmental features (EFs) of the encoding environment. This study examines whether and how EM is modulated by locomotion and the EFs encountered in a controlled lifelike learning route within a large-scale building. Twenty-eight healthy participants took part in a museum-tour encoding task implemented in walking Augmented Reality (AR) and stationary Virtual Reality (VR) conditions. EM performance and organisation were assessed immediately and 48-hours after trials using a Remember/Familiar recognition paradigm. Results showed a significant positive modulation effect of locomotion on distinctive EM aspects. Findings highlighted a significant performance enhancement effect of stairway-adjacent locations compared to dead-end and mid-route stimuli-presentation locations. The results of this study may serve as design criteria to facilitate neurocognitive rehabilitative interventions of EM. The underlying technological framework developed for this study represents a novel and ecologically sound method for evaluating EM processes in lifelike situations, allowing researchers a naturalistic perspective into the complex nature of EM.

A remote digital memory composite to detect cognitive impairment in memory clinic samples in unsupervised settings using mobile devices

Remote monitoring of cognition holds the promise to facilitate case-finding in clinical care and the individual detection of cognitive impairment in clinical and research settings. In the context of Alzheimer's disease, this is particularly relevant for patients who seek medical advice due to memory problems. Here, we develop a remote digital memory composite (RDMC) score from an unsupervised remote cognitive assessment battery focused on episodic memory and long-term recall and assess its construct validity, retest reliability, and diagnostic accuracy when predicting MCI-grade impairment in a memory clinic sample and healthy controls. A total of 199 participants were recruited from three cohorts and included as healthy controls (n = 97), individuals with subjective cognitive decline (n = 59), or patients with mild cognitive impairment (n = 43). Participants performed cognitive assessments in a fully remote and unsupervised setting via a smartphone app. The derived RDMC score is significantly correlated with the PACC5 score across participants and demonstrates good retest reliability. Diagnostic accuracy for discriminating memory impairment from no impairment is high (cross-validated AUC = 0.83, 95% CI [0.66, 0.99]) with a sensitivity of 0.82 and a specificity of 0.72. Thus, unsupervised remote cognitive assessments implemented in the neotiv digital platform show good discrimination between cognitively impaired and unimpaired individuals, further demonstrating that it is feasible to complement the neuropsychological assessment of episodic memory with unsupervised and remote assessments on mobile devices. This contributes to recent efforts to implement remote assessment of episodic memory for case-finding and monitoring in large research studies and clinical care.

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

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

Hippocampal-parietal cortex causal directed connectivity during human episodic memory formation: Replication across three experiments

Hippocampus-parietal cortex circuits are thought to play a crucial role in memory and attention, but their neural basis remains poorly understood. We employed intracranial EEG from 96 participants (51 females) to investigate the neurophysiological underpinning of these circuits across three memory tasks spanning verbal and spatial domains. We uncovered a consistent pattern of higher causal directed connectivity from the hippocampus to both lateral parietal cortex (supramarginal and angular gyrus) and medial parietal cortex (posterior cingulate cortex) in the delta-theta band during memory encoding and recall. This connectivity was independent of activation or suppression states in the hippocampus or parietal cortex. Crucially, directed connectivity from the supramarginal gyrus to the hippocampus was enhanced in participants with higher memory recall, highlighting its behavioral significance. Our findings align with the attention-to-memory model, which posits that attention directs cognitive resources toward pertinent information during memory formation. The robustness of these results was demonstrated through Bayesian replication analysis of the memory encoding and recall periods across the three tasks. Our study sheds light on the neural basis of casual signaling within hippocampus-parietal circuits, broadening our understanding of their critical roles in human cognition.

Temporal foundations of episodic memory

A fundamental question in the development of animal models of episodic memory concerns the role of temporal processes in episodic memory. Gallistel, (1990) developed a framework in which animals remember specific features about an event, including the time of occurrence of the event and its location in space. Gallistel proposed that timing is based on a series of biological oscillators, spanning a wide range of periods. Accordingly, a snapshot of the phases of multiple oscillators provides a representation of the time of occurrence of the event. I review research on basic timing mechanisms that may support memory for times of occurrence. These studies suggest that animals use biological oscillators to represent time. Next, I describe recently developed animal models of episodic memory that highlight the importance of temporal representations in memory. One line of research suggests that an oscillator representation of time supports episodic memory. A second line of research highlights the flow of events in time in episodic memory. Investigations that integrate time and memory may advance the development of animal models of episodic memory.

The formation of episodic autobiographical memory is predicted by mental imagery, self-reference, and anticipated details

Introduction

Despite the ecological nature of episodic memory (EM) and the importance of consolidation in its functioning, studies tackling both subjects are still scarce. Therefore, the present study aims at establishing predictions of the future of newly encoded information in EM in an ecological paradigm.

Methods

Participants recorded two personal events per day with a SenseCam portable camera, for 10 days, and characterized the events with different subjective scales (emotional valence and intensity, self-concept and self-relevance, perspective and anticipated details at a month, mental images…). They then performed a surprise free recall at 5 days and 1 month after encoding. Machine learning algorithms were used to predict the future of events (episodic or forgotten) in memory at 1 month.

Results

The best algorithm showed an accuracy of 78%, suggesting that such a prediction is reliably possible. Variables that best differentiated between episodic and forgotten memories at 1 month were mental imagery, self-reference, and prospection (anticipated details) at encoding and the first free recall.

Discussion

These results may establish the basis for the development of episodic autobiographical memory during daily experiences.

Effects of an acute bout of cycling on different domains of cognitive function

The literature suggesting acute exercise benefits cognitive function has been largely confined to single cognitive domains and measures of reliant on measures of central tendencies. Furthermore, studies suggest cognitive intra-individual variability (IIV) to reflect cognitive efficiency and provide unique insights into cognitive function, but there is limited knowledge on the effects of acute exercise on IIV. To this end, this study examined the effects of acute exercise on three different cognitive domains, executive function, implicit learning, and hippocampal-dependent memory function using behavioral performance and event-related potentials (ERPs). Furthermore, this study also sought to explore the effects of an acute bout of exercise on IIV using the RIDE algorithm to separate signals into individuals components based on latency variability. Healthy adult participants (N=20; 26.3±4.8years) completed a randomized cross-over trial with seated rest or 30min of high intensity cycling. Before and after each condition, participants completed a cognitive battery consisting of the Eriksen Flanker task, implicit statistical learning task, and a spatial reconstruction task. While exercise did not affect Flanker or spatial reconstruction performance, there were exercise related decreases in accuracy (F=5.47; P=0.040), slowed reaction time (F=5.18; P=0.036), and decreased late parietal positivity (F=4.26; P=0.046). However, upon adjusting for performance and ERP variability, there were exercise related decreases in Flanker reaction time (F=24.00; P<0.001), and reduced N2 amplitudes (F=13.03; P=0.002), and slower P3 latencies (F=3.57; P=0.065) for incongruent trials. These findings suggest that acute exercise may impact cognitive IIV as an adaptation to maintain function following exercise.

Bayesian evaluation of diverging theories of episodic and affective memory distortions in dysphoria

People suffering from dysphoria retrieve autobiographical memories distorted in content and affect, which may contribute to the aetiology and maintenance of depression. However, key memory difficulties in dysphoria remain elusive because theories disagree how memories of different valence are altered. Here, we assessed the psychophysiological expression of affect and retrieved episodic detail while participants with dysphoria (but without a diagnosed mental illness) and participants without dysphoria relived positive, negative, and neutral memories. We show that participants with dysphoria retrieve positive memories with diminished episodic detail and negative memories with enhanced detail, compared to participants without dysphoria. This is in line with negativity bias but not overgeneral memory bias theories. According to confirmatory analyses, participants with dysphoria also express diminished positive affect and enhanced negative affect when retrieving happy memories, but exploratory analyses suggest that this increase in negative affect may not be robust. Further confirmatory analyses showed that affective responses to memories are not related to episodic detail and already present during the experience of new emotional events. Our results indicate that affective memory distortions may not emerge from mnemonic processes but from general distortions in positive affect, which challenges assumptions of memory theories and therapeutics. Protocol registration: The Stage 1 protocol for this Registered Report was accepted in principle on the 18rd of March 2021. The protocol, as accepted by the journal, can be found at https://doi.org/10.6084/m9.figshare.14605374.v1 .

The Subjective Experience of Autobiographical Remembering: Conceptual and Methodological Advances and Challenges

The investigation of the phenomenology of autobiographical memories (i.e., how a memory is subjectively experienced and its meaning) has provided an important contribution to our understanding of autobiographical remembering. Over the last two decades, the study of phenomenology has received widespread scientific attention, and the field has undergone quite relevant conceptual and methodological changes. In the present work, we (1) review some basic and well-established research findings and methodological achievements; (2) discuss new theoretical and methodological challenges, with a special focus on the issue of the phenomenological experience of the retrieval process and its relationship with the phenomenology of the products of retrieval; and (3) propose an alternative way of conceptualizing and understanding it in the framework of experimental phenomenology.

A preliminary experimental test of the crossed influences between the valence of collective memory and collective future thinking

This research experimentally examined the crossed influences between the emotional valence of collective memory and collective future thinking. As remembering the past and imagining the future are shaped by the present, we additionally test whether perceived anomie (i.e., perceiving present society as disintegrated and disregulated) would moderate these influences. Study 1 (N = 228 French participants) manipulated the valence of collective memory (positive vs. negative French past) to test its effect on the valence of collective future thinking. Results showed that the salience of a negative (vs. positive) French past lead to the projection of a more negative French future only among participants who perceived present society as highly disregulated. Study 2 (N = 215) focused on the influence of the valence of collective future thinking (positive vs. negative French future) on the valence associated with the French past. Results showed that the salience of a negative (vs. positive) French future lead left-wing participants to rate more positively events/figures of the French past that are usually valued by conservatives. Taken together, these studies provided evidence of conditional effects in the crossed influences between the emotional valence of collective memory and collective future thinking, thus contributing to the recent literature on collective mental time travel.

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.

Writing about a stressful experience improves semantic clustering of memory in men, not women

Writing about negative experiences can produce multiple benefits, including improvements in mental and emotional health. However, writing about negative experiences potentially be detrimental, as reliving and reexperiencing a negative memory can be painful. Although the emotional effects of writing about negative experiences are well established, the cognitive effects are less heavily explored, and no work to date has examined how writing about a stressful experience might influence episodic memory. We addressed this issue in the present study (N = 520) by having participants encode a list of 16 words that were organised around four semantic clusters, randomly assigning participants to write about an unresolved stressful experience (n = 263) or the events of the previous day (n = 257), and assessing their memory in a free recall task. Writing about a stressful experience did not influence overall memory performance; however, the stressful writing manipulation increased semantic clustering of information within memory for men, whereas the stressful writing manipulation did not influence semantic clustering of information within memory in women. Additionally, writing with more positive sentiment improved semantic clustering and reduced serial recall. These results provide evidence for unique sex differences in writing about stressful experiences and the role of sentiment in the effects of expressive writing.

When you look at your past: Eye movement during autobiographical retrieval

Until recently, little was known about whether or how autobiographical memory (i.e., memory of personal information) activates eye movement. This issue is now being addressed by several studies demonstrating not only how autobiographical memory activates eye movement, but also how eye movement influences the characteristics of autobiographical retrieval. This paper summarizes this research and presents a hypothesis according to which fixations and saccades during autobiographical retrieval mirror the construction of the visual image of the retrieved event. This hypothesis suggests that eye movements during autobiographical retrieval mirror the attempts of the visual system to generate and manipulate mental representations of autobiographical retrieval. It offers a theoretical framework for a burgeoning area of research that provides a rigorous behavioral evaluation of the phenomenological experience of memory.

Suppressing memory associations impacts decision-making preference: Evidence from the think/no-think paradigm

Recent research has suggested that episodic memory can guide our decision-making. Forgetting is one essential characteristic of memory. If certain memories are suppressed to be forgotten, decisions that rely on such memories should be impacted. So far, little research has examined whether suppression of episodic memory would impact decision-making. In the current pre-registered study, the effect of memory suppression on subsequent reinforcement decision-making was examined by combining the Think/No-think paradigm and a reinforcement decision-making task. We found that suppressing memories of learned associations significantly impaired recollected memories of those associations, and participants' decision bias disappeared after their memory associations were suppressed. Furthermore, the more memory associations participants recalled, the higher decision preferences they exhibited. Our findings provide additional support for the role of episodic memory in reinforcement decision-making, and suggest that suppressing memory associations can lead to behavioral consequences.

Dynamic predictive coding: A model of hierarchical sequence learning and prediction in the neocortex

We introduce dynamic predictive coding, a hierarchical model of spatiotemporal prediction and sequence learning in the neocortex. The model assumes that higher cortical levels modulate the temporal dynamics of lower levels, correcting their predictions of dynamics using prediction errors. As a result, lower levels form representations that encode sequences at shorter timescales (e.g., a single step) while higher levels form representations that encode sequences at longer timescales (e.g., an entire sequence). We tested this model using a two-level neural network, where the top-down modulation creates low-dimensional combinations of a set of learned temporal dynamics to explain input sequences. When trained on natural videos, the lower-level model neurons developed space-time receptive fields similar to those of simple cells in the primary visual cortex while the higher-level responses spanned longer timescales, mimicking temporal response hierarchies in the cortex. Additionally, the network's hierarchical sequence representation exhibited both predictive and postdictive effects resembling those observed in visual motion processing in humans (e.g., in the flash-lag illusion). When coupled with an associative memory emulating the role of the hippocampus, the model allowed episodic memories to be stored and retrieved, supporting cue-triggered recall of an input sequence similar to activity recall in the visual cortex. When extended to three hierarchical levels, the model learned progressively more abstract temporal representations along the hierarchy. Taken together, our results suggest that cortical processing and learning of sequences can be interpreted as dynamic predictive coding based on a hierarchical spatiotemporal generative model of the visual world.

Use of perceptual memory as a performance validity indicator: initial validation with simulated mild traumatic brain injury

INTRODUCTION

Many commonly employed performance validity tests (PVTs) are several decades old and vulnerable to compromise, leading to a need for novel instruments. Because implicit/non-declarative memory may be robust to brain damage, tasks that rely upon such memory may serve as an effective PVT. Using a simulation design, this experiment evaluated whether novel tasks that rely upon perceptual memory hold promise as PVTs.

METHOD

Sixty healthy participants were provided instructions to simulate symptoms of mild traumatic brain injury (TBI), and they were compared to a group of 20 honest responding individuals. Simulator groups received varying levels of information concerning TBI symptoms, resulting in naïve, sophisticated, and test-coached groups. The Word Memory Test, Test of Memory Malingering, and California Verbal Learning Test-II Forced Choice Recognition Test were administered. To assess perceptual memory, selected images from the Gollin Incomplete Figures and Mooney Closure Test were presented as visual perception tasks. After brief delays, memory for the images was assessed.

RESULTS

No group differences emerged on the perception trials of the Gollin and Mooney figures, but simulators remembered fewer images than the honest responders. Simulator groups differed on the standard PVTs, but they performed equivalently on the Gollin and Mooney figures, implying robustness to coaching. Relying upon a criterion of 90% specificity, the Gollin and Mooney figures achieved at least 90% sensitivity, comparing favorably to the standard PVTs.

CONCLUSIONS

The Gollin and Mooney figures hold promise as novel PVTs. As perceptual memory tests, they may be relatively robust to brain damage, but future research involving clinical samples is necessary to substantiate this assertion.

Decoding context memories for threat in large-scale neural networks

Humans are often tasked with determining the degree to which a given situation poses threat. Salient cues present during prior events help bring online memories for context, which plays an informative role in this process. However, it is relatively unknown whether and how individuals use features of the environment to retrieve context memories for threat, enabling accurate inferences about the current level of danger/threat (i.e. retrieve appropriate memory) when there is a degree of ambiguity surrounding the present context. We leveraged computational neuroscience approaches (i.e. independent component analysis and multivariate pattern analyses) to decode large-scale neural network activity patterns engaged during learning and inferring threat context during a novel functional magnetic resonance imaging task. Here, we report that individuals accurately infer threat contexts under ambiguous conditions through neural reinstatement of large-scale network activity patterns (specifically striatum, salience, and frontoparietal networks) that track the signal value of environmental cues, which, in turn, allows reinstatement of a mental representation, primarily within a ventral visual network, of the previously learned threat context. These results provide novel insight into distinct, but overlapping, neural mechanisms by which individuals may utilize prior learning to effectively make decisions about ambiguous threat-related contexts as they navigate the environment.

Bittersweet memories and somatic marker hypothesis: adaptive control in emotional recall facilitates long-term decision-making in the Iowa Gambling Task

The somatic marker hypothesis states that emotional recall and its somatic influence guide long-term decision-making. However, the mechanism through which decision-making benefits from emotional recall is unclear; whether emotional recall and the induced affect increase the regulatory demand or amplify the affect state that requires inhibition. It is unclear if controlling the automatic flow of emotion in recall improves adaptive decision-making. Two studies examine the hypothesis that affect control in emotional recall facilitates inhibitory control and benefits long-term decision-making. In Experiment 1 (n = 137), affect control was assessed in emotional recall to examine if switching of affect in recall of positive and negative valence (order: positive-negative memory recall vs. negative-positive memory recall) is linked with long-term decision-making. Results for long-term decision-making showed that negative-positive recall sequence was associated with higher long-term decision-making, whereas automatic frequency-based decision-making remained unaffected by the recall sequence. In experiment 2 (n = 71, all male), emotional recall (positive vs. negative), recall specificity (i.e., specific vs. overgeneralized recall), and post-recall mood regulation (post-recall positive mood regulation vs. no regulation) was expected to facilitate long-term decision-making. Results showed that emotional recall and post-recall mood regulation (i.e., negative recall - positive mood and positive recall - negative mood) were associated with higher long-term decision-making (decks C' and D'). Results of frequency decision-making showed that positive emotional recall, and poor recall specificity led to infrequent punishment deck choices (decks B' and D'). Hierarchical regression indicated that emotional recall increased infrequent deck choices and accounted for 10% of choices made, recall specificity increased the explanatory power to 19%, and higher recall specificity was associated with fewer infrequent punishment deck choices. Affect control engaged via negative emotional recall, post-recall mood regulation, and recall specificity might be a potential mechanism through which affect control in emotional recall might facilitate long-term decision-making.

A neurological foundation for peaceful negotiations

Glowacki explored the conditions required for peace and argued its preconditions arose only within the last 100,000 years. The present commentary addresses some major brain changes that occurred only in Homo sapiens within that period of time and the verbal and nonverbal cognitive sequelae of those neurological changes that may have aided the diplomatic negotiations required for peaceful solutions.

Neural correlates of fanhood: the role of fan identity and team brand strength

Introduction

We analyzed the importance of fan identity and brand strength on fans' neural reactions to different team-related stimuli.

Methods

A total of 53 fMRI scans with fans of two professional sport teams were conducted. Following up on a previous study we focused on the differences between fandom levels as well as the contrast between two team "brand" strength. Neural responses were compared among individuals based on their levels of fan identity. In sum, group comparisons between relatively high and lower identity and between weak and strong teams were made based on the notion that the latter reflects team brand strength (strong brand and weak brand).

Results

Findings indicate that brain activity in emotion regulation, memory, and cognitive control circuits is influenced by the relative level of fan identity.

Discussion

Higher-level identified fans showed increased reactivity to positive stimuli and the under-recruitment of their cognitive appraisal circuits, suggesting more vulnerability to marketers' messages. The strength of the team brand activates different neural mechanisms. Interestingly, the posterior cingulate showed larger recruitment both for weaker brands and lower fan identification, suggesting that visual memory processes are more active in these cases. Neurally processed content depends on the relative brand's strength, highlighting the importance of brand-focused communications.

Episodic Thinking in Alzheimer's Disease Through the Lens of Language: Linguistic Analysis and Transformer-Based Classification

PURPOSE

Episodic memory decline is a hallmark of Alzheimer's disease (AD) and linked to deficits in episodic thinking directed to the future. We addressed the question whether a deficit in episodic thinking can be picked up directly from connected speech and its detection can be automatized.

METHOD

We linguistically classified 2,809 utterances (including embedded clauses in the utterances) from picture descriptions from 70 healthy older controls, 82 people with mild probable AD (pAD), and 46 people with moderate pAD for whether they were episodic, nonepisodic, or "other" (e.g., off-task). Generalized linear regression models were used to investigate how ratios of these categories change in AD, controlling for age, gender, and education. Finally, we applied deep learning technique to explore the feasibility of automating the episodicity analysis.

RESULTS

Decline in episodicity significantly distinguished controls from both mild pAD and moderate pAD. Correlation analysis suggested this decline not to be an effect of age, gender, and education but of cognitive ability. The decline was not compensated by an increase of nonepisodic utterances but mainly of off-task expressions. A transformer-based classifier to explore the possibility of automatizing the classification of episodicity achieved a macro F1 score of 0.913 in the ternary classification.

CONCLUSION

These results show that a loss of episodicity is an early effect in AD that is manifested in spontaneous speech and can be reliably measured by both humans and machines.

Altered EEG Microstates Dynamics in Individuals with Subthreshold Depression When Generating Negative Future Events

Negative bias in prospection may play a crucial role in driving and maintaining depression. Recent research suggests abnormal activation and functional connectivity in regions of the default mode network (DMN) during future event generation in depressed individuals. However, the neural dynamics during prospection in these individuals remain unknown. To capture network dynamics at high temporal resolution, we employed electroencephalogram (EEG) microstate analysis. We examined microstate properties during both positive and negative prospection in 35 individuals with subthreshold depression (SD) and 35 controls. We identified similar sets of four canonical microstates (A-D) across groups and conditions. Source analysis indicated that each microstate map partially overlapped with a subsystem of the DMN (A: verbal; B: visual-spatial; C: self-referential; and D: modulation). Notably, alterations in EEG microstates were primarily observed in negative prospection of individuals with SD. Specifically, when generating negative future events, the coverage, occurrence, and duration of microstate A increased, while the coverage and duration of microstates B and D decreased in the SD group compared to controls. Furthermore, we observed altered transitions, particularly involving microstate C, during negative prospection in the SD group. These altered dynamics suggest dysconnectivity between subsystems of the DMN during negative prospection in individuals with SD. In conclusion, we provide novel insights into the neural mechanisms of negative bias in depression. These alterations could serve as specific markers for depression and potential targets for future interventions.

The generative grammar of the brain: a critique of internally generated representations

The past decade of progress in neurobiology has uncovered important organizational principles for network preconfiguration and neuronal selection that suggest a generative grammar exists in the brain. In this Perspective, I discuss the competence of the hippocampal neural network to generically express temporally compressed sequences of neuronal firing that represent novel experiences, which is envisioned as a form of generative neural syntax supporting a neurobiological perspective on brain function. I compare this neural competence with the hippocampal network performance that represents specific experiences with higher fidelity after new learning during replay, which is envisioned as a form of neural semantic that supports a complementary neuropsychological perspective. I also demonstrate how the syntax of network competence emerges a priori during early postnatal life and is followed by the later development of network performance that enables rapid encoding and memory consolidation. Thus, I propose that this generative grammar of the brain is essential for internally generated representations, which are crucial for the cognitive processes underlying learning and memory, prospection, and inference, which ultimately underlie our reason and representation of the world.

Autonoesis and episodicity: Perspectives from philosophy of memory

The idea that episodic memory is distinguished from semantic memory by the fact that it involves autonoetic consciousness, initially introduced by Tulving, has been influential not only in psychology but also in philosophy, where a variety of approaches to autonoesis and to its relationship to episodicity have been developed. This article provides a critical review of the available philosophical approaches. Distinguishing among representational, metacognitive, and epistemic accounts of autonoesis, it considers these in relation to objective and subjective conceptions of episodicity and assesses them against immediacy and source criteria that any philosophical account of autonoesis should arguably aim to satisfy. This article is categorized under: Philosophy > Psychological Capacities Philosophy > Consciousness Psychology > Memory.

Artificial sharp-wave-ripples to support memory and counter neurodegeneration

Information processed in our sensory neocortical areas is transported to the hippocampus during memory encoding, and between hippocampus and neocortex during memory consolidation, and retrieval. Short bursts of high-frequency oscillations, so called sharp-wave-ripples, have been proposed as a potential mechanism for this information transfer: They can synchronize neural activity to support the formation of local neural networks to store information, and between distant cortical sites to act as a bridge to transfer information between sensory cortical areas and hippocampus. In neurodegenerative diseases like Alzheimer's Disease, different neuropathological processes impair normal neural functioning and neural synchronization as well as sharp-wave-ripples, which impairs consolidation and retrieval of information, and compromises memory. Here, we formulate a new hypothesis, that artificially inducing sharp-wave-ripples with noninvasive high-frequency visual stimulation could potentially support memory functioning, as well as target the neuropathological processes underlying neurodegenerative diseases. We also outline key challenges for empirical tests of the hypothesis.

Engrams: From Behavior to Brain-Wide Networks

Animals utilize a repertoire of behavioral responses during everyday experiences. During a potentially dangerous encounter, defensive actions such as "fight, flight, or freeze" are selected for survival. The successful use of behavior is determined by a series of real-time computations combining an animal's internal (i.e., body) and external (i.e., environment) state. Brain-wide neural pathways are engaged throughout this process to detect stimuli, integrate information, and command behavioral output. The hippocampus, in particular, plays a role in the encoding and storing of the episodic information surrounding these encounters as putative "engram" or experience-modified cellular ensembles. Recalling a negative experience then reactivates a dedicated engram ensemble and elicits a behavioral response. How hippocampus-based engrams modulate brain-wide states and an animal's internal/external milieu to influence behavior is an exciting area of investigation for contemporary neuroscience. In this chapter, we provide an overview of recent technological advancements that allow researchers to tag, manipulate, and visualize putative engram ensembles, with an overarching goal of casually connecting their brain-wide underpinnings to behavior. We then discuss how hippocampal fear engrams alter behavior in a manner that is contingent on an environment's physical features as well as how they influence brain-wide patterns of cellular activity. Overall, we propose here that studies on memory engrams offer an exciting avenue for contemporary neuroscience to casually link the activity of cells to cognition and behavior while also offering testable theoretical and experimental frameworks for how the brain organizes experience.

Journeying to the past: time travel and mental time travel, how far apart?

Spatial models dominated memory research throughout much of the twentieth century, but in recent decades, the concept of memory as a form of mental time travel (MTT) to the past has gained prominence. Initially introduced as a metaphor, the MTT perspective shifted the focus from internal memory processes to the subjective conscious experience of remembering. Despite its significant impact on empirical and theoretical memory research, there has been limited discussion regarding the meaning and adequacy of the MTT metaphor in accounting for memory. While in previous work I have addressed the general limitations of the MTT metaphor in explaining memory, the objective of this article is more focused and modest: to gain a better understanding of what constitutes MTT to the past. To achieve this objective, a detailed analysis of the characteristics of MTT to the past is presented through a comparison with time travel (TT) to the past. Although acknowledging that TT does not refer to an existing physical phenomenon, it is an older concept extensively discussed in the philosophical literature and provides commonly accepted grounds, particularly within orthodox theories of time, that can offer insights into the nature of MTT. Six specific characteristics serve as points of comparison: (1) a destination distinct from the present, (2) the distinction between subjective time and objective time, (3) the subjective experience of the time traveler, (4) their differentiation from the past self, (5) the existence of the past, and (6) its unchangeability. Through this research, a detailed exploration of the phenomenal and metaphysical aspects of MTT to the past is undertaken, shedding light on the distinct features that mental time travel to the past acquires when it occurs within the realm of the mind rather than as a physical phenomenon. By examining these characteristics, a deeper understanding of the nature of mental time travel is achieved, offering insights into how it operates in relation to memory and the past.

Association Study of a Comprehensive Panel of Neuropeptide-Related Polymorphisms Suggest Potential Roles in Verbal Learning and Memory

Neuropeptides are mostly expressed in regions of the brain responsible for learning and memory and are centrally involved in cognitive pathways. The majority of neuropeptide research has been performed in animal models; with acknowledged differences between species, more research into the role of neuropeptides in humans is necessary to understand their contribution to higher cognitive function. In this study, we investigated the influence of genetic polymorphisms in neuropeptide genes on verbal learning and memory. Variants in genes encoding neuropeptides and neuropeptide receptors were tested for association with learning and memory measures using the Hopkins Verbal Learning Test-Revised (HVLT-R) in a healthy cohort of individuals (n = 597). The HVLT-R is a widely used task for verbal learning and memory assessment and provides five sub-scores: recall, delay, learning, retention, and discrimination. To determine the effect of candidate variants on learning and memory performance, genetic association analyses were performed for each HVLT-R sub-score with over 1300 genetic variants from 124 neuropeptide and neuropeptide receptor genes, genotyped on Illumina OmniExpress BeadChip arrays. This targeted analysis revealed numerous suggestive associations between HVLT-R test scores and neuropeptide and neuropeptide receptor gene variants; candidates include the SCG5, IGFR1, GALR1, OXTR, CCK, and VIPR1 genes. Further characterization of these genes and their variants will improve our understanding of the genetic contribution to learning and memory and provide insight into the importance of the neuropeptide network in humans.

Engram cell connectivity as a mechanism for information encoding and memory function

Information derived from experiences is incorporated into the brain as changes to ensembles of cells, termed engram cells, which allow memory storage and recall. The mechanism by which those changes hold specific information is unclear. Here, we test the hypothesis that the specific synaptic wiring between engram cells is the substrate of information storage. First, we monitor how learning modifies the connectivity pattern between engram cells at a monosynaptic connection involving the hippocampal ventral CA1 (vCA1) region and the amygdala. Then, we assess the functional significance of these connectivity changes by artificially activating or inhibiting its presynaptic and postsynaptic components, respectively. Finally, we identify a synaptic plasticity mechanism mediated by postsynaptic density protein 95 (PSD-95), which impacts the connectivity pattern among engram cells and contributes to the long-term stability of the memory. These findings impact our theory of learning and memory by helping us explain the translation of specific information into engram cells and how these connections shape brain function.

Memory and creativity: A meta-analytic examination of the relationship between memory systems and creative cognition

Increasing evidence suggests that specific memory systems (e.g., semantic vs. episodic) may support specific creative thought processes. However, there are a number of inconsistencies in the literature regarding the strength, direction, and influence of different memory (semantic, episodic, working, and short-term) and creativity (divergent and convergent thinking) types, as well as the influence of external factors (age, stimuli modality) on this purported relationship. In this meta-analysis, we examined 525 correlations from 79 published studies and unpublished datasets, representing data from 12,846 individual participants. We found a small but significant (r = .19) correlation between memory and creative cognition. Among semantic, episodic, working, and short-term memory, all correlations were significant, but semantic memory - particularly verbal fluency, the ability to strategically retrieve information from long-term memory - was found to drive this relationship. Further, working memory capacity was found to be more strongly related to convergent than divergent creative thinking. We also found that within visual creativity, the relationship with visual memory was greater than that of verbal memory, but within verbal creativity, the relationship with verbal memory was greater than that of visual memory. Finally, the memory-creativity correlation was larger for children compared to young adults despite no impact of age on the overall effect size. These results yield three key conclusions: (1) semantic memory supports both verbal and nonverbal creative thinking, (2) working memory supports convergent creative thinking, and (3) the cognitive control of memory is central to performance on creative thinking tasks.

Temporal regularity in autobiographical memory: A single case fMRI study

Using fMRI, precise temporal control was extracted from routine activities in a female blind subject. Findings reveal a specific neural machinery for temporal control of recalled sequential events in episodic memory.

Prediction error and memory across the lifespan

The influence of Prediction Errors (PEs) on episodic memory has generated growing empirical and theoretical interest. This review explores how the relationship between PE and memory may evolve throughout lifespan. Drawing upon the predictive processing framework and the Predictive, Interactive Multiple Memory System (PIMMS) model in particular, the paper highlights the hierarchical organization of memory systems and the interaction between top-down predictions and bottom-up sensory input, proposing that PEs promote synaptic change and improve encoding and consolidation processes. We discuss the neuroscientific mechanisms underlying PE-driven memory enhancement, focusing on the involvement of the hippocampus, the entorhinal cortex-hippocampus pathway, and the noradrenergic sympathetic system. Recognizing the divergent trajectories of episodic and semantic memory across the lifespan is crucial when examining the effects of PEs on memory. This review underscores the heterogeneity of memory processes and neurocognitive mechanisms underlying PE-driven memory enhancement across age. Future research is suggested to directly compare neural networks involved in learning from PEs across different age groups and to contribute to a deeper understanding of PE-driven learning across age.

Prestimulus alpha power signals attention to retrieval

The human brain is in distinct processing modes at different times. Specifically, a distinction can be made between encoding and retrieval modes, which refer to the brain's state when it is storing new information or searching for old information, respectively. Recent research proposed the idea of a "ready-to-encode" mode, which describes a prestimulus effect in brain activity that signals (external) attention to encoding and predicts subsequent memory performance. Whether there is also a corresponding "ready-to-retrieve" mode in human brain activity is currently unclear. In this study, we examined whether prestimulus oscillations can be linked to (internal) attention to retrieval. We show that task cues to prepare for retrieval (or testing) in comparison with restudy of previously studied vocabulary word pairs led to a significant decrease of prestimulus alpha power just before the onset of word stimuli. Beamformer analysis localized this effect in the right secondary visual cortex (Brodmann area 18). Correlation analysis showed that the task cue-induced, prestimulus alpha power effect is positively related to stimulus-induced alpha/beta power, which in turn predicted participants' memory performance. The results are consistent with the idea that prestimulus alpha power signals internal attention to retrieval, which promotes the elaborative processing of episodic memories. Future research on brain-computer interfaces may find the findings interesting regarding the potential of using online measures of fluctuating alpha oscillations to trigger the presentation and sequencing of restudy and testing trials, ultimately enhancing instructional learning strategies.

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.

Cognitive Neuroscience Perspectives on Language Acquisition and Processing

The earliest investigations of the neural implementation of language started with examining patients with various types of disorders and underlying brain damage [...].

From jamais to déjà vu: The respective roles of semantic and episodic memory in novelty monitoring and involuntary memory retrieval

Barzykowski and Moulin's model proposes that déjà vu and involuntary autobiographical memories are the result of a continuously active memory system that tracks the novelty of situations. Déjà vu would only have episodic content and concern interpretation of prior experiences. We argue that these aspects of the model would gain to be clarified and explored further and we suggest possible directions.

Hippocampal neurons code individual episodic memories in humans

The hippocampus is an essential hub for episodic memory processing. However, how human hippocampal single neurons code multi-element associations remains unknown. In particular, it is debated whether each hippocampal neuron represents an invariant element within an episode or whether single neurons bind together all the elements of a discrete episodic memory. Here we provide evidence for the latter hypothesis. Using single-neuron recordings from a total of 30 participants, we show that individual neurons, which we term episode-specific neurons, code discrete episodic memories using either a rate code or a temporal firing code. These neurons were observed exclusively in the hippocampus. Importantly, these episode-specific neurons do not reflect the coding of a particular element in the episode (that is, concept or time). Instead, they code for the conjunction of the different elements that make up the episode.

Preparing children to cope with earthquakes: Building emotional competence

Natural disasters, including earthquakes, can have a traumatic impact on children's psychological wellbeing and development. The efficacy of interventions aimed at enhancing children's socio-emotional learning has been documented in the literature. At the same time, these techniques are the key for training children for possible future disasters by enhancing their knowledge about behavioural preparedness and emotional competence. However, research on evidence-based training programs on earthquakes combining digital and traditional activities is scarce. We tested the efficacy of a 10-unit training program for primary school children, developed within the Emotional Prevention and Earthquakes in Primary School (PrEmT) project. The program aimed at increasing knowledge of and metacognition about earthquakes, safety behaviours, emotions, and coping strategies, through digital (using the web-application HEMOT® , Helmet for EMOTions, developed ad-hoc) and traditional activities (completing paper-and-pencil tasks). The participants were 548 second and fourth-graders from Italian schools. They were divided into an experimental group (participating in the training program) and a control group. Both groups participated in pretests and posttests to evaluate changes in their knowledge of training-related contents. For ethical reasons, we also measured children's wellbeing. Generalized linear mixed models indicated an improvement in the experimental group's knowledge and metacognition about earthquakes, safety behaviours, emotions, and coping strategies after the training program, compared to the control group. Children's general wellbeing did not deteriorate during participation in the project. The results documented the efficacy of the evidence-based training program developed within the PrEmT project. The program provides a preventive method for enhancing earthquake-related resilience that could be generalized to other kinds of disasters.

Minor Changes Change Memories: Functional Magnetic Resonance Imaging and Behavioral Reflections of Episodic Prediction Errors

Episodic memories can be modified, a process that is potentially driven by mnemonic prediction errors. In the present study, we used modified cues to induce prediction errors of different episodic relevance. Participants encoded episodes in the form of short toy stories and then returned for an fMRI session on the subsequent day. Here, participants were presented either original episodes or slightly modified versions thereof. Modifications consisted of replacing a single object within the episode and either challenged the gist of an episode (gist modifications) or left it intact (surface modifications). On the next day, participants completed a post-fMRI memory test that probed memories for originally encoded episodes. Both types of modifications triggered brain activation in regions we previously found to be involved in the processing of content-based mnemonic prediction errors (i.e., the exchange of an object). Specifically, these were ventrolateral pFC, intraparietal cortex, and lateral occipitotemporal cortex. In addition, gist modifications triggered pronounced brain responses, whereas those for surface modification were only significant in the right inferior frontal sulcus. Processing of gist modifications also involved the posterior temporal cortex and the precuneus. Interestingly, our findings confirmed the posterior hippocampal role of detail processing in episodic memory, as evidenced by increased posterior hippocampal activity for surface modifications compared with gist modifications. In the post-fMRI memory test, previous experience with surface modified, but not gist-modified episodes, increased erroneous acceptance of the same modified versions as originally encoded. Whereas surface-level prediction errors might increase uncertainty and facilitate confusion of alternative episode representations, gist-level prediction errors seem to trigger the clear distinction of independent episodes.

Keeping track of reality: embedding visual memory in natural behaviour

Since immersive virtual reality (IVR) emerged as a research method in the 1980s, the focus has been on the similarities between IVR and actual reality. In this vein, it has been suggested that IVR methodology might fill the gap between laboratory studies and real life. IVR allows for high internal validity (i.e., a high degree of experimental control and experimental replicability), as well as high external validity by letting participants engage with the environment in an almost natural manner. Despite internal validity being crucial to experimental designs, external validity also matters in terms of the generalizability of results. In this paper, we first highlight and summarise the similarities and differences between IVR, desktop situations (both non-immersive VR and computer experiments), and reality. In the second step, we propose that IVR is a promising tool for visual memory research in terms of investigating the representation of visual information embedded in natural behaviour. We encourage researchers to carry out experiments on both two-dimensional computer screens and in immersive virtual environments to investigate visual memory and validate and replicate the findings. IVR is valuable because of its potential to improve theoretical understanding and increase the psychological relevance of the findings.

The effect of visual perspective on episodic memory in aging: A virtual reality study

The possibility of flexibly retrieving our memories using a first-person or a third-person perspective (1PP or 3PP) has been extensively investigated in episodic memory research. Here, we used a Virtual Reality-based paradigm to manipulate the visual perspective used during the encoding stage to investigate age-related differences in the formation of memories experienced from 1PP vs. 3PP. 32 young adults and 32 seniors participated in the study. Participants navigated through two virtual cities to encode complex real-life virtual events, from either a 1PP (as if from their egocentric viewpoint) or a 3PP, while actively controlling an avatar. While recognition accuracy was higher in young adults after encoding in 1PP compared to 3PP, there was no benefit in memory formation in 1PP for older adults. These findings are discussed in terms of both age-related changes in episodic memory functioning and self-referencing processes.

Cracking the neuronal code of episodic memory

Hierarchical organization of memory is observed in the brains of rats.

Context reexposure to bolster contextual dependency of emotional episodic memory

Contextual overgeneralization of emotional memory is a core aspect of anxiety disorders. Identifying methods to enhance contextual dependency of emotional memory is therefore of significant clinical interest. Animal research points to a promising approach: reexposure to the context in which fear is acquired reduces generalization to other contexts. However, the exact conditions for this effect are unknown, complicating translation to effective interventions. Most notably, exposure to a context that resembles-but is not identical to-the learning context may diminish contextual dependency of memory by integration of additional contextual cues. Here, we therefore assessed in a large-scale study (N = 180) whether context reexposure enhances contextual dependency of emotional episodic memory whereas exposure to a similar context impairs it. We also tested whether relatively strong memory retrieval during context (re)exposure amplifies these effects. We replicated prior research showing that correct recognition depends on context and contextual dependency is lower for emotional than neutral memories. However, exposure to the encoding context or a similar context did not affect contextual dependency of memory, and retrieval strength did not interact with such effects. Thorough insight into factors underlying the effects of context (re)exposure on contextual dependency seems key to eventually attain a memory recontextualization intervention.

Flexible coding of time or distance in hippocampal cells

Analysis of neuronal activity in the hippocampus of behaving animals has revealed cells acting as 'Time Cells', which exhibit selective spiking patterns at specific time intervals since a triggering event, and 'Distance Cells', which encode the traversal of specific distances. Other neurons exhibit a combination of these features, alongside place selectivity. This study aims to investigate how the task performed by animals during recording sessions influences the formation of these representations. We analyzed data from a treadmill running study conducted by Kraus et al., 2013, in which rats were trained to run at different velocities. The rats were recorded in two trial contexts: a 'fixed time' condition, where the animal ran on the treadmill for a predetermined duration before proceeding, and a 'fixed distance' condition, where the animal ran a specific distance on the treadmill. Our findings indicate that the type of experimental condition significantly influenced the encoding of hippocampal cells. Specifically, distance-encoding cells dominated in fixed-distance experiments, whereas time-encoding cells dominated in fixed-time experiments. These results underscore the flexible coding capabilities of the hippocampus, which are shaped by over-representation of salient variables associated with reward conditions.

Lived Experiences of Everyday Memory in Adults with Dyslexia: A Thematic Analysis

Dyslexia-related difficulties with memory are well documented under laboratory conditions and via self-report questionnaires. However, the voice of the individual with dyslexia regarding the lived experience of memory across different memory systems and different daily settings is currently lacking. To address this gap in the literature, semi-structured in-depth interviews were conducted with 12 adult female university students with dyslexia. Questions probed different memory systems and experiences across different settings, with interviewees also being asked about their use of technology to support their memory. Two overarching themes were identified in the subsequent thematic analysis. The theme of fallibility of memory had two sub-themes of (i) a lack of trust and confidence in memory and (ii) factors contributing to memory failure. The second theme, facilitators of memory, also consisted of two sub-themes, relating to (i) a preference for traditional tools to support memory and (ii) the use of digital tools to support memory: benefits and limitations. The current study gives insights into the rich and complex extended and distributed cognitive systems of adults with dyslexia. The implications of the findings for dyslexia theory, support in educational and work settings as well as assistive technology development are considered.

The role of bodily self-consciousness in episodic memory of naturalistic events: an immersive virtual reality study

Recent studies suggest that the human body plays a critical role in episodic memory. Still, the precise relationship between bodily self-consciousness (BSC) and memory formation of specific events, especially in real-life contexts, remains a topic of ongoing research. The present study investigated the relationship between BSC and episodic memory (EM) using immersive virtual reality (VR) technology. Participants were immersed in an urban environment with naturalistic events, while their visuomotor feedback was manipulated in three within-subjects conditions: Synchronous, Asynchronous, and No-body. Our results show that asynchronous visuomotor feedback and not seeing one's body, compared to synchronous feedback, decrease the sense of self-identification, self-location and agency, and sense of presence. Moreover, navigating in the Asynchronous condition had a detrimental impact on incidental event memory, perceptual details, contextual association, subjective sense of remembering, and memory consolidation. In contrast, participants in the No-Body condition were only impaired in egocentric spatial memory and the sense of remembering at ten-day delay. We discuss these findings in relation to the role of bodily self-representation in space during event memory encoding. This study sheds light on the complex interplay between BSC, sense of presence, and episodic memory processes, and strengthens the potential of embodiment and VR technology in studying and enhancing human cognition.

Individual differences in the frequency of voluntary & involuntary episodic memories, future thoughts, and counterfactual thoughts

Voluntary and involuntary mental time travel can take the form of episodic memory, episodic future thinking, and episodic counterfactual thinking. This study uses an individual-differences approach to understand why people engage in these forms of mental time travel. The individual-differences variables include trait-level personality, boredom proneness, depression, anxiety, stress, emotion regulation, mindfulness, mind-wandering, positive and negative affect, rumination, optimism, thinking styles, and time perspective. Across two studies, our results indicate that individual differences underlie these forms of mental time travel. The most unique, episodic counterfactual thinking, was alone positively correlated with negative emotionality and negatively correlated with optimism. We also observe differences as a function of voluntariness and discuss these findings in relation to the cognitively demanding nature of constructing future and counterfactual thoughts. We discuss the importance of distinguishing voluntary from involuntary thinking and assessing episodic counterfactual thinking in relation to episodic memory and episodic future thinking.

Hippocampal morphology in Huntington's disease, implications for plasticity and pathogenesis: The IMAGE-HD study

While striatal changes in Huntington's Disease (HD) are well established, few studies have investigated changes in the hippocampus, a key neuronal hub. Using MRI scans obtained from the IMAGE-HD study, hippocampi were manually traced and then analysed with the Spherical Harmonic Point Distribution Method (SPHARM-PDM) in 36 individuals with presymptomatic-HD, 37 with early symptomatic-HD, and 36 healthy matched controls. There were no significant differences in overall hippocampal volume between groups. Interestingly we found decreased bilateral hippocampal volume in people with symptomatic-HD who took selective serotonin reuptake inhibitors compared to those who did not, despite no significant differences in anxiety, depressive symptoms, or motor incapacity between the two groups. In symptomatic-HD, there was also significant shape deflation in the right hippocampal head, showing the utility of using manual tracing and SPHARM-PDM to characterise subtle shape changes which may be missed by other methods. This study confirms previous findings of the lack of hippocampal volumetric differentiation in presymptomatic-HD and symptomatic-HD compared to controls. We also find novel shape and volume findings in those with symptomatic-HD, especially in relation to decreased hippocampal volume in those treated with SSRIs.

Neurophysiological correlates of altered time awareness in Alzheimer's disease and frontotemporal dementia

BACKGROUND

Alterations in time awareness have been reported in dementia, particularly in Alzheimer's disease (AD) and frontotemporal dementia (FTD). However, the neurophysiological correlates underlying these alterations remain largely unexplored. This study aimed to investigate the neurophysiological correlates of altered time awareness in AD and FTD patients.

METHODS

A total of 150 participants (50 AD patients, 50 FTD patients, and 50 healthy controls [HC]) underwent a standardized neuropsychological assessment, an altered time awareness survey, and transcranial magnetic stimulation (TMS) to assess cholinergic (short latency afferent inhibition-SAI), GABAergic (short interval intracortical inhibition-SICI), and glutamatergic (intracortical facilitation-ICF) circuits.

RESULTS

In AD patients, the most frequent symptom was difficulty in ordering past events (52.0%), while FTD patients primarily struggled with estimating temporal intervals between events (40.0%). Significant differences were observed between HC and both patient groups, as well as between AD and FTD patients in their tendency to re-live past events. Binomial logistic regression analysis revealed that impairments in glutamatergic and cholinergic circuits significantly predicted the likelihood of participants manifesting altered time awareness symptoms.

CONCLUSIONS

This study provides novel insights into the neurophysiological correlates of altered time awareness in AD and FTD patients, highlighting the involvement of specific neurotransmitter circuits, particularly glutamatergic and cholinergic circuits. Further research is needed to explore the potential clinical implications and therapeutic targets arising from these findings.

When the mind's eye prevails: The Internal Dominance over External Attention (IDEA) hypothesis

Throughout the 20th century, the psychological literature has considered attention as being primarily directed at the outside world. More recent theories conceive attention as also operating on internal information, and mounting evidence suggests a single, shared attentional focus between external and internal information. Such sharing implies a cognitive architecture where attention needs to be continuously shifted between prioritizing either external or internal information, but the fundamental principles underlying this attentional balancing act are currently unknown. Here, we propose and evaluate one such principle in the shape of the Internal Dominance over External Attention (IDEA) hypothesis: Contrary to the traditional view of attention as being primarily externally oriented, IDEA asserts that attention is inherently biased toward internal information. We provide a theoretical account for why such an internal attention bias may have evolved and examine findings from a wide range of literatures speaking to the balancing of external versus internal attention, including research on working memory, attention switching, visual search, mind wandering, sustained attention, and meditation. We argue that major findings in these disparate research lines can be coherently understood under IDEA. Finally, we consider tentative neurocognitive mechanisms contributing to IDEA and examine the practical implications of more deliberate control over this bias in the context of psychopathology. It is hoped that this novel hypothesis motivates cross-talk between the reviewed research lines and future empirical studies directly examining the mechanisms that steer attention either inward or outward on a moment-by-moment basis.