88 research outputs found
Brief targeted memory reactivation during the awake state enhances memory stability and benefits the weakest memories.
Reactivation of representations corresponding to recent experience is thought to be a critical mechanism supporting long-term memory stabilization. Targeted memory reactivation, or the re-exposure of recently learned cues, seeks to induce reactivation and has been shown to benefit later memory when it takes place during sleep. However, despite recent evidence for endogenous reactivation during post-encoding awake periods, less work has addressed whether awake targeted memory reactivation modulates memory. Here, we found that brief (50 ms) visual stimulus re-exposure during a repetitive foil task enhanced the stability of cued versus uncued associations in memory. The extent of external or task-oriented attention prior to re-exposure was inversely related to cueing benefits, suggesting that an internally-orientated state may be most permissible to reactivation. Critically, cueing-related memory benefits were greatest in participants without explicit recognition of cued items and remained reliable when only considering associations not recognized as cued, suggesting that explicit cue-triggered retrieval processes did not drive cueing benefits. Cueing benefits were strongest for associations and participants with the poorest initial learning. These findings expand our knowledge of the conditions under which targeted memory reactivation can benefit memory, and in doing so, support the notion that reactivation during awake time periods improves memory stabilization
Similarity Breeds Proximity: Pattern Similarity within and across Contexts Is Related to Later Mnemonic Judgments of Temporal Proximity
SummaryExperiences unfold over time, but little is known about the mechanisms that support the formation of coherent episodic memories for temporally extended events. Recent work in animals has provided evidence for signals in hippocampus that could link events across temporal gaps; however, it is unknown whether and how such signals might be related to later memory for temporal information in humans. We measured patterns of fMRI BOLD activity as people encoded items that were separated in time and manipulated the presence of shared or distinct context across items. We found that hippocampal pattern similarity in the BOLD response across trials predicted later temporal memory decisions when context changed. By contrast, pattern similarity in lateral occipital cortex was related to memory only when context remained stable. These data provide evidence in humans that representational stability in hippocampus across time may be a mechanism for temporal memory organization
Distortion and Signal Loss in Medial Temporal Lobe
Background: The medial temporal lobe (MTL) contains subregions that are subject to severe distortion and signal loss in functional MRI. Air/tissue and bone/tissue interfaces in the vicinity of the MTL distort the local magnetic field due to differences in magnetic susceptibility. Fast image acquisition and thin slices can reduce the amount of distortion and signal loss, but at the cost of image signal-to-noise ratio (SNR). Methodology/Principal Findings: In this paper, we quantify the severity of distortion and signal loss in MTL subregions for three different echo planar imaging (EPI) acquisitions at 3 Tesla: a conventional moderate-resolution EPI (36363 mm), a conventional high-resolution EPI (1.561.562 mm), and a zoomed high-resolution EPI. We also demonstrate the advantage of reversing the phase encode direction to control the direction of distortion and to maximize efficacy of distortion compensation during data post-processing. With the high-resolution zoomed acquisition, distortion is not significant and signal loss is present only in the most anterior regions of the parahippocampal gyrus. Furthermore, we find that the severity of signal loss is variable across subjects, with some subjects showing negligible loss and others showing more dramatic loss. Conclusions/Significance: Although both distortion and signal loss are minimized in a zoomed field of view acquisition with thin slices, this improvement in accuracy comes at the cost of reduced SNR. We quantify this trade-off between distortion and SNR in order to provide a decision tree for design of high-resolution experiments investigating the functio
Hippocampus guides adaptive learning during dynamic social interactions
How do we evaluate whether someone will make a good friend or collaborative peer? A hallmark of human cognition is the ability to make adaptive decisions based on information garnered from limited prior experiences. Using an interactive social task measuring adaptive choice (deciding who to reengage or avoid) in male and female participants, we find the hippocampus supports value-based social choices following single-shot learning. These adaptive choices elicited a suppression signal in the hippocampus, revealing sensitivity for the subjective perception of a person and how well they treat you during choice. The extent to which the hippocampus was suppressed was associated with flexibly interacting with prior generous individuals and avoiding selfish individuals. Further, we found that hippocampal signals during decision-making were related to subsequent memory for a person and the offer they made before. Consistent with the hippocampus leveraging previously executed choices to solidify a reliable neural signature for future adaptive behavior, we also observed a later hippocampal enhancement. These findings highlight the hippocampus playing a multifaceted role in socially adaptive learning
They saw a movie: Long-term memory for an extended audiovisual narrative.
We measured long-term memory for a narrative film. During the study session, participants watched a 27-min movie episode, without instructions to remember it. During the test session, administered at a delay ranging from 3 h to 9 mo after the study session, long-term memory for the movie was probed using a computerized questionnaire that assessed cued recall, recognition, and metamemory of movie events sampled ∼20 sec apart. The performance of each group of participants was measured at a single time point only. The participants remembered many events in the movie even months after watching it. Analysis of performance, using multiple measures, indicates differences between recent (weeks) and remote (months) memory. While high-confidence recognition performance was a reliable index of memory throughout the measured time span, cued recall accuracy was higher for relatively recent information. Analysis of different content elements in the movie revealed differential memory performance profiles according to time since encoding. We also used the data to propose lower limits on the capacity of long-term memory. This experimental paradigm is useful not only for the analysis of behavioral performance that results from encoding episodes in a continuous real-life-like situation, but is also suitable for studying brain substrates and processes of real-life memory using functional brain imaging. Experimental protocols that probe brain correlates of episodic memory formation commonly use paradigms in which memoranda are presented as individual items devoid of continuous context outside of the laboratory setting Movies are capable of simulating aspects of real-life experiences by fusing multimodal perception with emotional and cognitive overtones Here, we describe the use of a 27-min narrative movie to investigate long-term cued recall and recognition as well as metamemory judgments. We measured memory performance of several groups of participants, each at a different delay ranging from 3 h to 9 mo after watching the movie, by probing memory for events occurring in the movie ∼20 sec apart. Participants remembered many events in the movie that they had seen only once without prior instructions to remember it, even months after watching it. We have dissected multiple facets of memory and metamemory as a function of time and type of occurrence in the movie. Our analysis also suggests lower limits on the capacity of long-term memory for a real-life-like situation. Results Memory of the movie persists for months The first set of experimental groups watched the movie and answered the questionnaire ( Heuristic subdivisions in long-term memory Pairwise comparisons among all groups, corrected for multiple comparisons, reveal superior performance of the 3-h, 1-wk, and 3-wk groups compared with the 3-mo and 9-mo groups ( Recall attempts over time Participants made fewer attempts at recall as more time passed between study and test sessions ( Memory confidence over time The proportions of all answers made at different levels of confidence were compared across time-interval groups, revealing a surprisingly stable proportion of high-confidence recognition (HCR) answers over time, and a significant decrease in the use of recall over time. In contrast, the proportion of low-confidence recognition (LCR) and guess answers significantly increased over time ( One might expect a smaller proportion of correct answers as confidence declines with the passage of time. To test this assumption, the proportion of correct answers was calculated from all answers made in each level of confidence Furthermore, the main group effect suggests that distribution of correct answers between the four possible levels of confidence is uneven among time-interval groups. The interaction between these two main effects, time and confidence-level, was further explored by performing pairwise contrasts, revealing performance differences that further support differentiation of ST and LT groups. As can be seen in The findings described above indicate that confidence measures of memory are time-sensitive: more high-confidence answers (using recall and HCR) are used after short time durations, while more lower-confidence answers (LCR and guessing) are used after longer time durations. We further sought to characterize the temporal dynamics of metamemory measures using analysis of answers by confidence level. We find that on the one hand, proportion of overall use of recall declines over time Memory density The availability of memory performance scores that sample events every 20 sec in a 27-min episode renders it tempting to attempt tapping into long-term memory capacity per unit time, or density (Dudai 1997). Any such attempt is bound to yield only rough estimates. First, formal units that might be used for quantifying the stored memory, such as bits Using the algorithm specified in the Materials and Methods, we estimate that 56% of information in the movie is remembered after 3 h, while 53%, 39%, 25%, and 19% are remembered after 1 wk, 3 wk, 3 mo, and 9 mo, respectively. Equating for the sake of calculation a memory unit as a questionnaire item to be answered correctly and assuming independence among items, Long-term memory of a movie Learning & Memory 459 www.learnmem.org Cold Spring Harbor Laboratory Press on December 7, 2007 -Published by www.learnmem.org Downloaded from hence, 77 items that could be potentially encoded over 27 min, this implies retrievability ranging from 1.6 items per minute movie after 3 h to 1.4 and 1.0 items per 2 min after 3 and 9 mo, respectively. The robustness of the assumptions involved and the relevance to previous estimates of long-term memory capacity are discussed below. Recall and recognition as function of memory content Six independent raters were asked to classify the questions into eight predetermined categories (while allowing overlap of categories). Questions were then grouped into nonoverlapping clusters based on 66% agreement among raters. Clusters included plot themes, social interactions, couple relationship, and jokes and minor details (13, 19, 6, 5, and 14 questions, respectively). "Social interactions" is a nonoverlapping broader category than "couple relationship," and did not include questions relating to interactions between the central character and his partner, which were included in the "couple relationship" cluster. Twenty of 77 items in the memory questionnaire were not entered into analysis, as the agreement criterion was not reached. For each content cluster, we examined proportion of recall and recognition attempts We find that narrative elements and social interactions between characters are remembered best ("plot themes" questions elicited close to 100% accuracy in all ST groups). Questions about "jokes" and "details" elicit less recall attempts and answer accuracy declines more rapidly and drastically than for all other question clusters. Better performance of ST groups relative to LT groups is established for all content clusters, while comparison of time-dependent performance decline (i.e., curve slope) between content clusters approached significance only for correct recall performance. Significant main effects of content and time-interval group were found (recall attempts: content F (4,3224) = 62.27, P < 0 . 0 0 0 1 , t i m e -i n t e r v a l g r o u p F (4,44.13) = 4.96, P < 0.002; correct recall: content F (4,874) = 8.02, P < 0.0001; timei n t e r v a l g r o u p F ( 4 , 7 5 . 5 4 ) = 8 . 4 9 , P < 0.0001). The interaction between these effects (difference in performance between content clusters as a function of time-interval group, or comparison of slopes) was insignificant for both analyses, but approached significance for correct recall (recall attempts: F (16,3224) = 1.1, P < 0.35; correct recall: F (16,874) = 1.52, P < 0.09). In order to further explore main effects, pairwise contrasts were performed separately according to time-interval groups It is noteworthy that the division of LTM performance into ST and LT groups, introduced above on the basis of analysis of correct and incorrect answers, is also supported by the analysis of content-based correct recall answers, and is partially supported by analysis of content-based recall attempts. Subjects in the ST groups made significantly more recall attempts and more correct recall answers, per content cluster, than subjects in the LT groups. (Two exceptions are the "couple relationship" question cluster, which elicited a high proportion of correct recall answers throughout the tested span, and proportion of recall attempts of the 3-wk group that did not differ from both LT groups; Tables 1, 3.) While superior performance across content clusters is found Cold Spring Harbor Laboratory Press on December 7, 2007 -Published by www.learnmem.org Downloaded from for the ST groups, different content clusters elicited significantly different performance profiles over time. This is illustrated by observing that the starting point of maximal value for forgetting curves varies between plots of different content clusters We should qualify our finding that memory performance can be differentiated according to content elements, as it seems that time since encoding is also an important factor in rendering this differentiation evident. Further examination of correct recall data, where interaction between content and group effects was found to only approach significance, was performed using post hoc comparisons. When examining content effects within timeinterval groups, significant differences between content clusters were found in all but the 3-h and 1-wk groups Manipulation of movie and questionnaire did not diminish memory We further tested whether certain manipulations of the movie during the study session, or of the questionnaire in the test session, or both, will affect memory performance. A separate set of experimental groups all participated in the test session 3 wk after watching the movie, but were subjected to manipulated study or test material. Manipulations were either in the order of content material (scrambling the order of scenes in the movie or the questions in the test) or in perceptual attributes (eliminating color from the movie). One experimental group performed an interference protocol, in which subjects watched a different episode from the same sitcom at the beginning of the test session, and immediately afterward completed the original computerized questionnaire. No significant differences were found in performance (correct answers, collapsing confidence levels) between manipulation protocols and the original 3-wk group (unaltered movie and test, n = 8, 78.79 ‫ע‬ 2.02% correct; scrambled version of the movie followed by regular test, n = 10, 79.87 ‫ע‬ 2.38% correct; unaltered movie followed by scrambled test, n = 6, 73.81 ‫ע‬ 2.97% correct; scrambled movie followed by scrambled test, n = 7, 73.1 ‫ע‬ 2.76% correct; interference protocol, n = 7, 73.28 ‫ע‬ 2.39% correct; regular movie in black and white and regular test using black and white frames as visual cues, n = 6, 70.35 ‫ע‬ 2.99% correct; F (5,40.25) = 2.24, P < 0.07). It is noteworthy that although some of the manipulations did show a trend for decreased performance, scrambling of the order of the scenes in the movie itself had no effect whatsoever. The potential implication of this finding to the encoding of the study material is discussed below. Discussion We describe a memory paradigm in which the study material is a 27-min narrative movie. This paradigm was intended to mimic aspects of "real-life" learning and memory under controlled experimental settings. We tested the memory once, in delays ranging from 3 h to 9 mo after the study session. The test targeted events that occur in the movie every ∼20 sec. We found that details from the movie, which the participants watched only once without prior instruction to remember it, were remembered well over several months. Multiple performance measures indicate that long-term memory after hours-to-weeks is different from memory performance after several months. Recall answers, which we considered as the highest confidence answers, proved to be reliable measures of memory only for shorter durations, while HCR answers were highly reliable throughout the measured time span. Despite manipulation of movie and test materials, meant to disrupt narrative construction during encoding and/or retrieval, memory performance was unaffected. One possible explanation is that subjects were still able to successfully reconstruct the narrative from the scrambled segments. We further demonstrate that information content significantly influences memorability over time (though some time is needed for this effect to become evident). Finally, we use the unique resolution of our memory questionnaire to suggest that memory capacity for real-life information might be higher than previously estimated. In clinical neurology and in cellular neurobiology, memory after 3 h is already long-term memory, and memory after 9 mo could be considered remote memory. Studies of human longterm memory and remote memory are abundant in the literature (for review, se
Understanding perirhinal contributions to perception and memory: Evidence through the lens of selective perirhinal damage
© 2019 Elsevier Ltd Although a memory systems view of the medial temporal lobe (MTL) has been widely influential in understanding how memory processes are implemented, a large body of work across humans and animals has converged on the idea that the MTL can support various other decisions, beyond those involving memory. Specifically, recent work suggests that perception of and memory for visual representations may interact in order to support ongoing cognition. However, given considerations involving lesion profiles in neuropsychological investigations and the correlational nature of fMRI, the precise nature of representations supported by the MTL are not well understood in humans. In the present investigation, three patients with highly specific lesions to MTL were administered a task that taxed perceptual and mnemonic judgments with highly similar face stimuli. A striking double dissociation was observed such that I.R., a patient with a cyst localized to right posterior PRc, displayed a significant impairment in perceptual discriminations, whereas patient A.N., an individual with a lesion in right posterior parahippocampal cortex and the tail of the right hippocampus, and S.D., an individual with bilateral hippocampal damage, did not display impaired performance on the perceptual task. A.N. and S.D. did, however, show impairments in memory performance, whereas patient I.R. did not. These results causally implicate right PRc in successful perceptual oddity judgments, however they suggest that representations supported by PRc are not necessary for correct mnemonic judgments, even in situations of high featural overlap
Neural Mechanisms of Memory
The ability to form and access memories of our experiences involves complex neural mechanisms at both the cellular and systems levels. Animal and human (including lesion and neuroimaging) studies have evidenced a critical role for the hippocampus and connected brain regions in these processes. The current chapter will review the role of the hippocampus in the different stages of long-term memory, namely, encoding, consolidation, and retrieval. Specifically, this chapter will illustrate how the hippocampus, in conjunction with other brain regions, supports these processes, giving rise to our rich experience of remembering
Recommended from our members
Awake Reactivation of Prior Experiences Consolidates Memories and Biases Cognition.
After experiences are encoded into memory, post-encoding reactivation mechanisms have been proposed to mediate long-term memory stabilization and transformation. Spontaneous reactivation of hippocampal representations, together with hippocampal-cortical interactions, are leading candidate mechanisms for promoting systems-level memory strengthening and reorganization. While the replay of spatial representations has been extensively studied in rodents, here we review recent fMRI work that provides evidence for spontaneous reactivation of nonspatial, episodic event representations in the human hippocampus and cortex, as well as for experience-dependent alterations in systems-level hippocampal connectivity. We focus on reactivation during awake post-encoding periods, relationships between reactivation and subsequent behavior, how reactivation is modulated by factors that influence consolidation, and the implications of persistent reactivation for biasing ongoing perception and cognition
Cross-modal facilitation of episodic memory by sequential action execution
Data, materials, and analysis code for Gasser, C. & Davachi, L. (2023). Cross-modal facilitation of episodic memory by sequential action execution. Psychological Science. 34(5), 581-602
- …