Negative emotion reduces the temporal compression of events in episodic memory

Recent studies have revealed that the continuous flow of information that characterises naturalistic events is temporally compressed in episodic memory, so that remembering an event generally takes less time than the duration of the past episode. However, the specific characteristics of an event that influence its temporal compression in memory remain poorly understood. In the present study, we examined the extent to which the negative valence of events impacts their rate of compression in memory representations. We conducted two experiments in which participants were instructed to mentally replay a series of videos depicting negative or neutral events. The results showed that the time taken to mentally replay a video, relative to the actual video duration, was significantly longer for negative than for neutral videos. These results suggest that negative emotion increases the sampling rate of units of experience that represent the course of events, leading to a lower compression of events in memory representations.

Fast-timescale hippocampal processes bridge between slowly unfurling neocortical states during memory search

Prior behavioral work showed that event structure plays a key role in our ability to mentally search through memories of continuous naturalistic experience. We hypothesized that, neurally, this memory search process involves a division of labor between slowly unfurling neocortical states representing event knowledge and fast hippocampal-neocortical communication that supports retrieval of new information at transitions between events. To test this, we tracked slow neural state-patterns in a sample of ten patients undergoing intracranial electroencephalography as they viewed a movie and then searched their memories in a structured naturalistic interview. As patients answered questions ("after X, when does Y happen next?"), state-patterns from movie-viewing were reinstated in neocortex; during memory-search, states unfurled in a forward direction. Moments of state-transition were marked by low-frequency power decreases in cortex and preceded by power decreases in hippocampus that correlated with reinstatement. Connectivity-analysis revealed information-flow from hippocampus to cortex underpinning state-transitions. Together, these results support our hypothesis that fast hippocampal processes bridge between slow neocortical states during memory search.

Mindfulness and time perception: A systematic integrative review

Several recent studies have explored the relationships between mindfulness and time perception, an area of research that has become increasingly popular in the last 10-15 years. In this article, we present a systematic integrative review of the evidence on this subject. We also integrate the field's findings into a conceptual framework which considers the multifaceted nature of both mindfulness, and time perception research. To identify the relevant literature, we searched the following databases using relevant keywords: PsycINFO; Medline; EBSCO Host Psychology and Behavioral Sciences Collection; and Web of Science. These searches were last performed on the 4th of May 2022, and additional hand searches were also conducted. To be included, articles had to be in English and contain original data about the potential relationship(s) between mindfulness and time perception. Articles which did not present usable data about the relationship(s) between the variables of interest were excluded. In total, 47 research articles were included in the review (combined sample size of ∼5800 participants). Risks of bias in the selected studies were evaluated using two separate assessment tools designed for this purpose. Through an integrative narrative synthesis, this article reviews how mindfulness may relate to time perception for various reference frames, and for various time perception measures and methods. It also provides new insights by exploring how a wide range of findings can be integrated into a coherent whole, in light of some relevant time perception models and mindfulness theories. Altogether, the reviewed data suggest the existence of complex and multifaceted relationships between mindfulness and time perception, highlighting the importance of considering many factors when planning research or interpreting data in this field. Limitations of the current review include the scarceness of data for certain categories of findings, and the relatively low prevalence of studies with a randomized controlled design in the source literature. This research was partly funded by a grant from the Natural Science and Engineering Research Council of Canada.

Working memory capacity for continuous events: The root of temporal compression in episodic memory?

Remembering the unfolding of past episodes usually takes less time than their actual duration. In this study, we evaluated whether such temporal compression emerges when continuous events are too long to be fully held in working memory. To do so, we asked 90 young adults to watch and mentally replay video clips showing people performing a continuous action (e.g., turning a car jack) that lasted 3, 6, 9, 12, or 15 s. For each clip, participants had to carefully watch the event and then to mentally replay it as accurately and precisely as possible. Results showed that mental replay durations increased with event duration but in a non-linear manner: they were close to the actual event duration for short videos (3-9 s), but significantly smaller for longer videos (12 and 15 s). These results suggest that working memory is temporally limited in its capacity to represent continuous events, which could in part explain why the unfolding of events is temporally compressed in episodic memory.

The effects of emotion on retrospective duration memory using virtual reality

Our memories for temporal duration may be colored by the emotions we experience during an event. While emotion generally enhances some aspects of memory, temporal duration has been shown to be particularly susceptible to emotion-induced distortions. However, prior work has faced difficulty when studying this phenomenon, having to make some trade-offs on ecological validity or experimental control. Here, we sought to bridge this gap by studying the effects of emotion on temporal duration memory using virtual reality. In the present study, a final sample of 69 participants experienced a series of negative-emotional and neutral worlds within virtual reality. Following this, participants provided ratings of emotionality (arousal, valence, pleasantness) and retrospective duration estimates (i.e., remembered time). We hypothesized that negative events would be recalled as having a greater duration than neutral events (H1). We additionally hypothesized that negative, but not neutral, events would be recalled as being longer than the true duration (H2). The results supported H1 while failing to provide evidence in support of H2. Together, the results bolster the importance of emotion, especially negative emotion, in shaping how we remember the temporal unfolding of the past.

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.

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.

Experience and memory of time and emotions two years after the start of the COVID-19 pandemic

In this French longitudinal study, we assessed judgment of the passage of time in current life and the predictors of this judgment 2 years after the onset of the COVID-19 pandemic, i.e., at a time when there was no lockdown and no protective measures. We then compared these measures with the same participants' passage-of-time judgments assessed during each of the past three French lockdowns. We also assessed their memory representations of the passage of time in the past, i.e., for the various lockdowns. The results showed the persistence of the feeling of time slowing down outside of lockdown. However, this was no longer linked to external factors (lack of activity, disruption of everyday routines) as found in the previous studies conducted during the lockdowns, but to an individual internal factor, namely a high level of depression in the general population. Moreover, the results revealed that the experience of the passage of time for the past lockdowns was compressed in memory, being judged to be faster than it actually was. This time compression tended to be greater in depressed people. It was also associated with a positive bias for all the other examined factors (e.g., sleep quality, life routine, boredom, happiness). We assumed that this time compression would be related to processes involved in the recall of unfolding events, with certain moments being omitted or forgotten during recall, as well as to the process of reconstruction in autobiographical memory. Our study therefore shows the long-lasting effect of lockdowns on mental health of the general population, which was expressed by the persistent feeling of a slowing down of time. It is therefore necessary to take care of this psychologically fragile population and to avoid further lockdowns in response to a new health crisis, that they cannot cope with.

Intrinsic hippocampal connectivity is associated with individual differences in retrospective duration processing

The estimation of incidentally encoded durations of time intervals (retrospective duration processing) is thought to rely on the retrieval of contextual information associated with a sequence of events, automatically encoded in medial temporal lobe regions. "Time cells" have been described in the hippocampus (HC), encoding the temporal progression of events and their duration. However, whether the HC supports explicit retrospective duration judgments in humans, and which neural dynamics are involved, is still poorly understood. Here we used resting-state fMRI to test the relation between variations in intrinsic connectivity patterns of the HC, and individual differences in retrospective duration processing, assessed using a novel task involving the presentation of ecological stimuli. Results showed that retrospective duration discrimination performance predicted variations in the intrinsic connectivity of the bilateral HC with the right precentral gyrus; follow-up exploratory analyses suggested a role of the CA1 and CA4/DG subfields in driving the observed pattern. Findings provide insights on neural networks associated with implicit processing of durations in the second range.

Representational dynamics of memories for real-life events

The continuous flow of experience that characterizes real-life events is not recorded as such in episodic memory but is condensed as a succession of event segments separated by temporal discontinuities. To unravel the neural basis of this representational structure, we recorded real-life events using wearable camera technology and used fMRI to investigate brain activity during their temporal unfolding in memory. We found that, compared to the representation of static scenes in memory, dynamically unfolding memory representations were associated with greater activation of the posterior medial episodic network. Strikingly, by analyzing the autocorrelation of brain activity patterns at successive time points throughout the retrieval period, we found that this network showed higher temporal dynamics when recalling events that included a higher density of event segments. These results reveal the key role of the posterior medial network in representing the dynamic unfolding of the event segments that constitute real-world memories.

Behavioural and neurophysiological signatures in the retrieval of individual memories of recent and remote real-life routine episodic events

Autobiographical memory (AM) has been largely investigated as the ability to recollect specific events that belong to an individual's past. However, how we retrieve real-life routine episodes and how the retrieval of these episodes changes with the passage of time remain unclear. Here, we asked participants to use a wearable camera that automatically captured pictures to record instances during a week of their routine life and implemented a deep neural network-based algorithm to identify picture sequences that represented episodic events. We then asked each participant to return to the lab to retrieve AMs for single episodes cued by the selected pictures 1 week, 2 weeks and 6-14 months after encoding while scalp electroencephalographic (EEG) activity was recorded. We found that participants were more accurate in recognizing pictured scenes depicting their own past than pictured scenes encoded in the lab, and that memory recollection of personally experienced events rapidly decreased with the passing of time. We also found that the retrieval of real-life picture cues elicited a strong and positive 'ERP old/new effect' over frontal regions and that the magnitude of this ERP effect was similar throughout memory tests over time. However, we observed that recognition memory induced a frontal theta power decrease and that this effect was mostly seen when memories were tested after 1 and 2 weeks but not after 6-14 months from encoding. Altogether, we discuss the implications for neuroscientific accounts of episodic retrieval and the potential benefits of developing individual-based AM exploration strategies at the clinical level.

Slices of the past: how events are temporally compressed in episodic memory

Remembering everyday events typically takes less time than the actual duration of the retrieved episodes, a phenomenon that has been referred to as the temporal compression of events in episodic memory. Here, we review recent studies that have shed light on how this compression mechanism operates. The evidence suggests that the continuous flow of experience is not represented as such in episodic memory. Instead, the unfolding of events is recalled as a succession of moments or slices of past experience that includes temporal discontinuities-portions of past experience are omitted when remembering. Consequently, the rate of event compression is not constant but depends on the density of recalled segments of past experience.

The temporal compression of events during episodic future thinking

While the cognitive and neural mechanisms that underlie episodic future thinking are increasingly well understood, little is known about how the temporal unfolding of events is represented in future simulations. In this study, we leveraged wearable camera technology to examine whether real-world events are structured and compressed in the same way when imagining the future as when remembering the past. We found that future events were simulated at proportionally higher speed than past events and that the density of experience units representing the unfolding of events was lower for future than for past episodes. Despite these differences, the nature of events influenced compression rates in the same way for past and future events. Furthermore, the perceived duration of both types of events depended on the density of represented experience units. These results provide novel insight into the mechanisms that structure the unfolding of events during future simulations.

Sequence Memory in the Hippocampal-Entorhinal Region

Episodic memories are constructed from sequences of events. When recalling such a memory, we not only recall individual events, but we also retrieve information about how the sequence of events unfolded. Here, we focus on the role of the hippocampal-entorhinal region in processing and remembering sequences of events, which are thought to be stored in relational networks. We summarize evidence that temporal relations are a central organizational principle for memories in the hippocampus. Importantly, we incorporate novel insights from recent studies about the role of the adjacent entorhinal cortex in sequence memory. In rodents, the lateral entorhinal subregion carries temporal information during ongoing behavior. The human homologue is recruited during memory recall where its representations reflect the temporal relationships between events encountered in a sequence. We further introduce the idea that the hippocampal-entorhinal region might enable temporal scaling of sequence representations. Flexible changes of sequence progression speed could underlie the traversal of episodic memories and mental simulations at different paces. In conclusion, we describe how the entorhinal cortex and hippocampus contribute to remembering event sequences-a core component of episodic memory.

Zooming In and Out on One's Life: Autobiographical Representations at Multiple Time Scales

The ability to decouple from the present environment and explore other times is a central feature of the human mind. Research in cognitive psychology and neuroscience has shown that the personal past and future is represented at multiple timescales and levels of resolution, from broad lifetime periods that span years to short-time slices of experience that span seconds. Here, I review this evidence and propose a theoretical framework for understanding mental time travel as the capacity to flexibly navigate hierarchical layers of autobiographical representations. On this view, past and future thoughts rely on two main systems-event simulation and autobiographical knowledge-that allow us to represent experiential contents that are decoupled from sensory input and to place these on a personal timeline scaffolded from conceptual knowledge of the content and structure of our life. The neural basis of this cognitive architecture is discussed, emphasizing the possible role of the medial pFC in integrating layers of autobiographical representations in the service of mental time travel.

The hippocampus contributes to temporal duration memory in the context of event sequences: A cross-species perspective

Although a large body of research has implicated the hippocampus in the processing of memory for temporal duration, there is an exigent degree of inconsistency across studies that obfuscates the precise contributions of this structure. To shed light on this issue, the present review article surveys both historical and recent cross-species evidence emanating from a wide variety of experimental paradigms, identifying areas of convergence and divergence. We suggest that while factors such as time-scale (e.g. the length of durations involved) and the nature of memory processing (e.g. prospective vs. retrospective memory) are very helpful in the interpretation of existing data, an additional important consideration is the context in which the duration information is experienced and processed, with the hippocampus being preferentially involved in memory for durations that are embedded within a sequence of events. We consider the mechanisms that may underpin temporal duration memory and how the same mechanisms may contribute to memory for other aspects of event sequences such as temporal order.

Temporal features of spatial knowledge: Representing order and duration of topographical information

Environmental navigation entails the constant integration of information across space and time; however, the relation between spatial and temporal features involved in wayfinding has not been fully established yet. Here we investigated how two key spatio-temporal aspects of navigation - namely the processing of information concerning the order of landmarks along a route, and the duration of tracts connecting the same landmarks - relate to different types of navigational learning. Participants encoded a path in a real city in both a route and a survey format, and the acquisition of landmark, route and survey knowledge was tested. Participants' knowledge of landmarks order, and their perception of tracts duration were also assessed. Performance in the survey task, but not in the landmark and route tasks, significantly predicted accuracy in landmark ordering. The influence of tract length on retrospectively estimated tracts duration was also found to be significantly predicted only by accuracy in the survey learning task. These results support recent models of spatial navigation, invoking the dynamic interaction between different representation formats. Furthermore, they are consistent with theoretical views of an integrated account of the role of the hippocampus in navigation and memory.

Event segmentation and the temporal compression of experience in episodic memory

Recent studies suggest that episodic memory represents the continuous flow of information that constitutes daily life events in a temporally compressed form, but the nature and determinants of this compression mechanism remain unclear. In the present study, we used wearable camera technology to investigate whether the temporal compression of experience in episodic memory depends on event segmentation. Participants experienced a series of events during a walk on a university campus and were later asked to mentally replay these events. The temporal compression of events in memory and grain size of event segmentation were estimated based on records of participants' experience taken by the camera. The results showed that the temporal compression of events in memory (i.e., the density of recalled moments of experience per unit of time of the actual event duration) closely corresponded to the grain size of event segmentation. Specifically, grain sizes of event segmentation and temporal compression rates were four to five times lower when remembering events that involved goal-directed actions compared to other kinds of events (e.g., spatial displacements). Furthermore, temporal compression rates in memory were significantly predicted by the grain size of event segmentation and event boundaries were more than five times more likely to be remembered than other parts of events. Together, these results provide new insights into the mechanism of temporal compression of events in episodic memory.