scholarly journals Human hippocampal CA3 damage disrupts both recent and remote episodic memories

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Thomas D Miller ◽  
Trevor T-J Chong ◽  
Anne M Aimola Davies ◽  
Michael R Johnson ◽  
Sarosh R Irani ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Memory Performance ◽  
Functional Integration ◽  
Resting State Fmri ◽  
Model Organisms ◽  
Default Network ◽  
Episodic Retrieval ◽  
Graph Theoretic ◽  
Episodic Memories

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

scholarly journals Age-Related Compensatory Reconfiguration of PFC Connections during Episodic Memory Retrieval

2020 ◽  
Author(s):  
Lifu Deng ◽  
Mathew L Stanley ◽  
Zachary A Monge ◽  
Erik A Wing ◽  
Benjamin R Geib ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Memory Retrieval ◽  
Medial Temporal Lobe ◽  
Memory Performance ◽  
Functional Integration ◽  
Brain Network ◽  
Age Related ◽  
Connectivity Patterns ◽  
The Brain ◽  
Related Increase

Abstract During demanding cognitive tasks, older adults (OAs) frequently show greater prefrontal cortex (PFC) activity than younger adults (YAs). This age-related increase in PFC activity is often associated with enhanced cognitive performance, suggesting functional compensation. However, the brain is a complex network of interconnected regions, and it is unclear how network connectivity of PFC regions differs for OAs versus YAs. To investigate this, we examined the age-related difference on the functional brain networks mediating episodic memory retrieval. YAs and OAs participants encoded and recalled visual scenes, and age-related differences in network topology during memory retrieval were investigated as a function of memory performance. We measured both changes in functional integration and reconfiguration in connectivity patterns. The study yielded three main findings. First, PFC regions were more functionally integrated with the rest of the brain network in OAs. Critically, this age-related increase in PFC integration was associated with better retrieval performance. Second, PFC regions showed stronger performance-related reconfiguration of connectivity patterns in OAs. Finally, the PFC reconfiguration increases in OAs tracked reconfiguration reductions in the medial temporal lobe (MTL)—a core episodic memory region, suggesting that PFC connectivity in OAs may be compensating for MTL deficits.

scholarly journals Bi-Temporal Anodal Transcranial Direct Current Stimulation during Slow-Wave Sleep Boosts Slow-Wave Density but Not Memory Consolidation

2021 ◽  
Vol 11 (4) ◽  
pp. 410
Author(s):  
Simon Ruch ◽  
Kristoffer Fehér ◽  
Stephanie Homan ◽  
Yosuke Morishima ◽  
Sarah Maria Mueller ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Slow Wave ◽  
Direct Current ◽  
Memory Consolidation ◽  
Transcranial Direct Current Stimulation ◽  
Slow Wave Sleep ◽  
Memory Performance ◽  
Direct Current Stimulation ◽  
Sleep Parameters ◽  
Episodic Memories

Slow-wave sleep (SWS) has been shown to promote long-term consolidation of episodic memories in hippocampo–neocortical networks. Previous research has aimed to modulate cortical sleep slow-waves and spindles to facilitate episodic memory consolidation. Here, we instead aimed to modulate hippocampal activity during slow-wave sleep using transcranial direct current stimulation in 18 healthy humans. A pair-associate episodic memory task was used to evaluate sleep-dependent memory consolidation with face–occupation stimuli. Pre- and post-nap retrieval was assessed as a measure of memory performance. Anodal stimulation with 2 mA was applied bilaterally over the lateral temporal cortex, motivated by its particularly extensive connections to the hippocampus. The participants slept in a magnetic resonance (MR)-simulator during the recordings to test the feasibility for a future MR-study. We used a sham-controlled, double-blind, counterbalanced randomized, within-subject crossover design. We show that stimulation vs. sham significantly increased slow-wave density and the temporal coupling of fast spindles and slow-waves. While retention of episodic memories across sleep was not affected across the entire sample of participants, it was impaired in participants with below-average pre-sleep memory performance. Hence, bi-temporal anodal direct current stimulation applied during sleep enhanced sleep parameters that are typically involved in memory consolidation, but it failed to improve memory consolidation and even tended to impair consolidation in poor learners. These findings suggest that artificially enhancing memory-related sleep parameters to improve memory consolidation can actually backfire in those participants who are in most need of memory improvement.

Going Their Separate Ways: Dissociation of Hippocampal and Dorsolateral Prefrontal Activation during Episodic Retrieval and Post-retrieval Processing

2010 ◽  
Vol 22 (3) ◽  
pp. 513-525 ◽  
Author(s):  
Sarah L. Israel ◽  
Tyler M. Seibert ◽  
Michelle L. Black ◽  
James B. Brewer
Keyword(s):  
Episodic Memory ◽  
Memory Retrieval ◽  
Relative Increase ◽  
Network Activity ◽  
Default Network ◽  
Episodic Retrieval ◽  
Retrieval Task ◽  
Paired Associates ◽  
Hippocampal Activity ◽  
Dorsolateral Prefrontal

Hippocampal activity is modulated during episodic memory retrieval. Most consistently, a relative increase in activity during confident retrieval is observed. Dorsolateral prefrontal cortex (DLPFC) is also activated during retrieval, but may be more generally activated during cognitive-control processes. The “default network,” regions activated during rest or internally focused tasks, includes the hippocampus, but not DLPFC. Therefore, DLPFC and the hippocampus should diverge during difficult tasks suppressing the default network. It is unclear, however, whether a difficult episodic memory retrieval task would suppress the default network due to difficulty or activate it due to internally directed attention. We hypothesized that a task requiring episodic retrieval followed by rumination on the retrieved item would increase DLPFC activity, but paradoxically reduce hippocampal activity due to concomitant suppression of the default network. In the present study, blocked and event-related fMRI were used to examine hippocampal activity during episodic memory recollection and postretrieval processing of paired associates. Subjects were asked to make living/nonliving judgments about items visually presented (classify) or items retrieved from memory (recall–classify). Active and passive baselines were used to differentiate task-related activity from default-network activity. During the “recall–classify” task, anterior hippocampal activity was selectively reduced relative to “classify” and baseline tasks, and this activity was inversely correlated with DLPFC. Reaction time was positively correlated with DLPFC activation and default-network/hippocampal suppression. The findings demonstrate that frontal and hippocampal activity are dissociated during difficult episodic retrieval tasks and reveal important considerations for interpreting hippocampal activity associated with successful episodic retrieval.

Hippocampal-related memory network in multiple sclerosis: A structural connectivity analysis

2018 ◽  
Vol 25 (6) ◽  
pp. 801-810 ◽  
Author(s):  
Sara Llufriu ◽  
Maria A Rocca ◽  
Elisabetta Pagani ◽  
Gianna C Riccitelli ◽  
Elisabeth Solana ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Episodic Memory ◽  
Medial Temporal Lobe ◽  
Structural Integrity ◽  
Memory Performance ◽  
Structural Connectivity ◽  
Occipital Cortex ◽  
Network Efficiency ◽  
Edge Graph ◽  
Memory Network

Background: We used graph theoretical analysis to quantify structural connectivity of the hippocampal-related episodic memory network and its association with memory performance in multiple sclerosis (MS) patients. Methods: Brain diffusion and T1-weighted sequences were obtained from 71 MS patients and 50 healthy controls (HCs). A total of 30 gray matter regions (selected a priori) were used as seeds to perform probabilistic tractography and create connectivity matrices. Global, nodal, and edge graph theoretical properties were calculated. In patients, verbal and visuospatial memory was assessed. Results: MS patients showed decreased network strength, assortativity, transitivity, global efficiency, and increased average path length. Several nodes had decreased strength and communicability in patients, whereas insula and left temporo-occipital cortex increased communicability. Patients had widespread decreased streamline count (SC) and communicability of edges, although a few ones increased their connectivity. Worse memory performance was associated with reduced network efficiency, decreased right hippocampus strength, and reduced SC and communicability of edges related to medial temporal lobe, thalamus, insula, and occipital cortex. Conclusion: Impaired structural connectivity occurs in the hippocampal-related memory network, decreasing the efficiency of information transmission. Network connectivity measures correlate with episodic memory, supporting the relevance of structural integrity in preserving memory processes in MS.

scholarly journals Egocentric Navigation Abilities Predict Episodic Memory Performance

2020 ◽  
Vol 14 ◽  
Author(s):  
Giorgia Committeri ◽  
Agustina Fragueiro ◽  
Maria Maddalena Campanile ◽  
Marco Lagatta ◽  
Ford Burles ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Semantic Memory ◽  
Path Integration ◽  
Medial Temporal Lobe ◽  
Declarative Memory ◽  
Memory Performance ◽  
Memory Task ◽  
Recognition Task ◽  
Future Research ◽  
Egocentric Navigation

The medial temporal lobe supports both navigation and declarative memory. On this basis, a theory of phylogenetic continuity has been proposed according to which episodic and semantic memories have evolved from egocentric (e.g., path integration) and allocentric (e.g., map-based) navigation in the physical world, respectively. Here, we explored the behavioral significance of this neurophysiological model by investigating the relationship between the performance of healthy individuals on a path integration and an episodic memory task. We investigated the path integration performance through a proprioceptive Triangle Completion Task and assessed episodic memory through a picture recognition task. We evaluated the specificity of the association between performance in these two tasks by including in the study design a verbal semantic memory task. We also controlled for the effect of attention and working memory and tested the robustness of the results by including alternative versions of the path integration and semantic memory tasks. We found a significant positive correlation between the performance on the path integration the episodic, but not semantic, memory tasks. This pattern of correlation was not explained by general cognitive abilities and persisted also when considering a visual path integration task and a non-verbal semantic memory task. Importantly, a cross-validation analysis showed that participants' egocentric navigation abilities reliably predicted episodic memory performance. Altogether, our findings support the hypothesis of a phylogenetic continuity between egocentric navigation and episodic memory and pave the way for future research on the potential causal role of egocentric navigation on multiple forms of episodic memory.

scholarly journals The Encoding/Retrieval Flip: Interactions between Memory Performance and Memory Stage and Relationship to Intrinsic Cortical Networks

2013 ◽  
Vol 25 (7) ◽  
pp. 1163-1179 ◽  
Author(s):  
Willem Huijbers ◽  
Aaron P. Schultz ◽  
Patrizia Vannini ◽  
Donald G. McLaren ◽  
Sarah E. Wigman ◽  
...  
Keyword(s):  
Large Scale ◽  
Posterior Parietal Cortex ◽  
Memory Performance ◽  
Resting State Fmri ◽  
Brain Regions ◽  
Default Network ◽  
Cortical Networks ◽  
Age Related ◽  
Retrieval Processes ◽  
Memory Stage

fMRI studies have linked the posteromedial cortex to episodic learning (encoding) and remembering (retrieval) processes. The posteromedial cortex is considered part of the default network and tends to deactivate during encoding but activate during retrieval, a pattern known as the encoding/retrieval flip. Yet, the exact relationship between the neural correlates of memory performance (hit/miss) and memory stage (encoding/retrieval) and the extent of overlap with intrinsic cortical networks remains to be elucidated. Using task-based fMRI, we isolated the pattern of activity associated with memory performance, memory stage, and the interaction between both. Using resting-state fMRI, we identified which intrinsic large-scale functional networks overlapped with regions showing task-induced effects. Our results demonstrated an effect of successful memory performance in regions associated with the control network and an effect of unsuccessful memory performance in the ventral attention network. We found an effect of memory retrieval in brain regions that span the default and control networks. Finally, we found an interaction between memory performance and memory stage in brain regions associated with the default network, including the posteromedial cortex, posterior parietal cortex, and parahippocampal cortex. We discuss these findings in relation to the encoding/retrieval flip. In general, the findings demonstrate that task-induced effects cut across intrinsic cortical networks. Furthermore, regions within the default network display functional dissociations, and this may have implications for the neural underpinnings of age-related memory disorders.

Lateralization of Prefrontal Activity during Episodic Memory Retrieval: Evidence for the Production-Monitoring Hypothesis

2003 ◽  
Vol 15 (2) ◽  
pp. 249-259 ◽  
Author(s):  
Roberto Cabeza ◽  
Jill K. Locantore ◽  
Nicole D. Anderson
Keyword(s):  
Episodic Memory ◽  
Memory Retrieval ◽  
Medial Temporal Lobe ◽  
Item Recognition ◽  
Cued Recall ◽  
Anterior Cingulate ◽  
Episodic Retrieval ◽  
Context Recognition ◽  
Production Monitoring ◽  
The Right

We propose a new hypothesis concerning the lateralization of prefrontal cortex (PFC) activity during verbal episodic memory retrieval. The hypothesis states that the left PFC is differentially more involved in semantically guided information production than is the right PFC, and that the right PFC is differentially more involved in monitoring and verification than is the left PFC. This “production-monitoring hypothesis” differs from the existing “systematic-heuristic hypothesis,” which proposes that the left PFC is primarily involved in systematic retrieval operations, and the right PFC in heuristic retrieval operations. To compare the two hypotheses, we measured PFC activity using positron emission tomography (PET) during the performance of four episodic retrieval tasks: stem cued recall, associative cued recall, context recognition (source memory), and item recognition. Recall tasks emphasized production processes, whereas recognition tasks emphasized monitoring processes. Stem cued recall and context-recognition tasks underscored systematic operations, whereas associative cued recall and item-recognition tasks underscored heuristic operations. Consistent with the production-monitoring hypothesis, the left PFC was more activated for recall than for recognition tasks and the right PFC was more activated for recognition than for recall tasks. Inconsistent with the systematic-heuristic hypothesis, the left PFC was more activated for heuristic than for systematic tasks and the right PFC showed the converse result. Additionally, the study yielded activation differences outside the PFC. In agreement with a previous recall/recognition PET study, anterior cingulate, cerebellar, and striatal regions were more activated for recall than for recognition tasks, and the converse occurred for posterior parietal regions. A right medial temporal lobe region was more activated for stem cued recall and context recognition than for associative cued recall and item recognition, possibly reflecting perceptual integration. In sum, the results provide evidence for the production-monitoring hypothesis and clarify the role of different brain regions typically activated in PET and functional magnetic resonance imaging (fMRI) studies of episodic retrieval.

Why does relational binding improve across early childhood? Testing the effects of interference and sleep-filled delays

2020 ◽  
Author(s):  
Susan L. Benear ◽  
Chi Ngo ◽  
Ingrid R. Olson ◽  
Nora Newcombe
Keyword(s):  
Early Childhood ◽  
Young Children ◽  
Episodic Memory ◽  
Memory Performance ◽  
Age Groups ◽  
Developmental Period ◽  
Older Children ◽  
Spatiotemporal Information ◽  
Episodic Memories ◽  
Over Time

Episodic memory consists of distinctive experiences, with specific spatiotemporal information about what happened maintained over time. These memories typically share overlapping elements in distinctive combinations. In this study, we evaluated: (1) whether overlapping elements pose a differential challenge for younger children; and (2) whether a sleep-filled delay stabilizes or even improves children’s episodic memories, and if so, whether effects vary by age. We compared memory for unique and overlapping pairs of visual stimuli, presented once to 4- and 6-year-old children, tested immediately and after a 24-hour delay. As expected, older children outperformed younger children, and both age groups performed worse on overlapping pairs. However, overlapping elements were not differentially problematic for young children, and a sleep-filled delay in testing resulted in decrements in memory performance, for both age groups on both pair types. Despite overall differences in accuracy, important aspects of episodic memory are similar across this key developmental period.

scholarly journals Metric and chronological time in human episodic memory

2020 ◽  
Author(s):  
Hallvard Røe Evensmoen ◽  
Lars M. Rimol ◽  
Henning Hoel Rise ◽  
Tor Ivar Hansen ◽  
Hamed Nili ◽  
...  
Keyword(s):  
Episodic Memory ◽  
Time Scales ◽  
Entorhinal Cortex ◽  
Medial Temporal Lobe ◽  
Brain Network ◽  
Parahippocampal Cortex ◽  
Temporal Pole ◽  
Episodic Memories ◽  
Short Time ◽  
Chronological Time

The relative contributions of metric and chronological time in the encoding of episodic memories are unknown. One hundred one healthy young adults viewed 48 unique episodes of visual events and were later tested on recall of the order of events (chronological time) and the precise timing of events (metric time). The behavioral results show that metric recall accuracy correlates with chronological accuracy for events within episodes, but does not play a role on larger time-scales across episodes. Functional magnetic resonance imaging during encoding and recall showed that metric time was represented in the posterior medial entorhinal cortex, as well as the temporal pole and the cerebellum, whereas chronological time was represented in a widespread brain network including the anterior lateral entorhinal cortex, hippocampus, parahippocampal cortex and the prefrontal cortex. We conclude that metric time has a role in episodic memory on short time-scales and is mainly subserved by medial temporal lobe structures.

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