Memory Trace Research Articles

Rectified activity-dependent population plasticity implicates cortical adaptation for memory and cognitive functions.

Cortical network undergoes rewiring everyday due to learning and memory events. To investigate the trends of population adaptation in neocortex overtime, we record cellular activity of large-scale cortical populations in response to neutral environments and conditioned contexts and identify a general intrinsic cortical adaptation mechanism, naming rectified activity-dependent population plasticity (RAPP). Comparing each adjacent day, the previously activated neurons reduce activity, but remain with residual potentiation, and increase population variability in proportion to their activity during previous recall trials. RAPP predicts both the decay of context-induced activity patterns and the emergence of sparse memory traces. Simulation analysis reveal that the local inhibitory connections might account for the residual potentiation in RAPP. Intriguingly, introducing the RAPP phenomenon in the artificial neural network show promising improvement in small sample size pattern recognition tasks. Thus, RAPP represents a phenomenon of cortical adaptation, contributing to the emergence of long-lasting memory and high cognitive functions.

Linking new information to a short-lasting memory trace induces consolidation in the hippocampus.

Linking new information to a short-lasting memory trace induces consolidation in the hippocampus.

Dendritic spines of layer 5 pyramidal neurons of the aging somatosensory cortex exhibit reduced volumetric remodeling.

Impairments in synaptic dynamics and stability are observed both in neurodegenerative disorders and in the healthy aging cortex, which exhibits elevated dendritic spine turnover and decreased long-term stability of excitatory connections at baseline, as well as an altered response to plasticity induction. In addition to the discrete gain and loss of synapses, spines also change in size and strength both during learning and in the absence of neural activity, and synaptic volume has been associated with stability and incorporation into memory traces. Furthermore, intrinsic dynamics, an apparently stochastic component of spine volume changes, may serve as a homeostatic mechanism to prevent stabilization of superfluous connections. However, the effects of age on modulation of synaptic weights remain unknown. Using two-photon excitation (2PE) microscopy of spines during chemical plasticity induction in vitro and analyzing longitudinal in vivo 2PE images after a plasticity-inducing manipulation, we characterize the effects of age on volumetric changes of spines of the apical tuft of layer 5 pyramidal neurons of mouse primary somatosensory cortex. Aged mice exhibit decreased volumetric volatility and delayed rearrangement of synaptic weights of persistent connections, as well as greater susceptibility to spine shrinkage in response to chemical long-term depression. These results suggest a deficit in the aging brain's ability to fine-tune synaptic weights to properly incorporate and retain novel memories. This research provides the first evidence of alterations in spine volumetric dynamics in healthy aging and may support a model of impaired processing and learning in the aged somatosensory system.Significance Statement Aging is known to impact cognitive functions and sensory processing, yet the underlying mechanisms at the synaptic level remain unclear. This study investigates dendritic spine dynamics of layer 5 pyramidal neurons in the aging somatosensory cortex. By employing two-photon excitation microscopy and analyzing spine volume changes during plasticity induction, we reveal that aged mice exhibit decreased volumetric volatility and delayed synaptic weight rearrangement. These alterations may impair the brain's ability to fine-tune synaptic weights, which is crucial for incorporating and retaining new memories. This research provides the first evidence of altered spine volumetric dynamics in healthy aging, suggesting a potential mechanism for impaired processing and learning in the aged cortex. Understanding these changes could aid in mitigation of age-related cognitive decline.

Visual short-term memory for crossed and uncrossed binocular disparities.

Previous work on visual short-term memory (VSTM) has encompassed various stimulus attributes including spatial frequency, color, and contrast, revealing specific time courses and a dependence on stimulus parameters. This study investigates visual short-term memory for binocular depth, using dynamic random dot stereograms (DRDS) featuring disparity planes in front of or behind the plane of fixation. In a delayed match-to-sample paradigm, we employed four distinct reference disparities (17.5', 28.8' either crossed or uncrossed) at two contrast levels (20%, 80%), spanning interstimulus intervals (ISI) of up to 4 s. Test stimuli represented a range of equally spaced values centered around the reference disparity of the ongoing trial. In addition, the impact of a memory masking stimulus was also tested in a separate experiment. Accuracy and point of subjective equality (PSE) served as performance markers. The performance, indicated by the accuracy of responses, was better for smaller reference disparities (±17.5') compared to larger ones (±28'), but both deteriorated as a function of ISI. The PSE demonstrated a consistent shift with increasing ISIs, irrespective of the magnitude of the initial disparity, converging gradually toward the range of 20-22' and deviating from the reference disparity. Notably, the influence of masking stimuli on the PSE was more marked when the mask disparity diverged from the reference value. The findings from our study indicate that the retention of absolute disparity in memory is imprecise, it deteriorates with retention time or due to perturbation by dissimilar masking stimuli. As a result, the memory trace is gradually replaced by a default depth value. This value could potentially signify an optimal point within low-level perceptual memory, however, our results are better explained by perceptual averaging whereby the visual system computationally derives a statistical summary of the presented disparities over time. The latter mechanism would aid in the computation of relative disparity in a dynamically changing environment.

Pattern separation during encoding and Subsequent Memory Effect

Memory retrieval has been extensively studied in relation to the encoding processes that precede access to stored information. Event related potentials (ERP) research has compared brain potentials elicited during the study phase of successful and unsuccessful retrieval, finding greater activation for the subsequent retrieval information. In this work we were interested in exploring the neural markers associated to subsequent recognition when similar memories are subsequently encoded. We used a Subsequent Memory paradigm in which we manipulated the number of similar items within a category (2 or 6) that participants encoded. Manipulating the number of similar encoded items within a category allowed us to test whether encoding markers of subsequent recognition depend solely on memory trace strength or, on the contrary, successful recognition is influenced by subsequently presented similar memories, and consequently may not be reflected in higher activation in such cases. After a 20-minute period, participants performed a recognition task providing one of a three-option judgement: “old”, “similar” and “new”, which allowed us to test if the amplitude of ERP waveforms varied based on the similarity judgement of the unrecognized encoded item. We did not observe a significant parietal subsequent memory effect, however, old hits and similar false alarms were both significantly different from similar correct rejections and old false alarms in ERP retrieval. These findings suggest that differences in brain responses between conditions are specifically related to the retrieval process and not the encoding process, indicating potential differential effects on memory during retrieval. Moreover, it is also possible that differences in brain responses develop or change over the rest time between phases, influencing how these conditions manifest across different stages of information processing.

Long-term memory in <i>Thrips tabaci</i> (Thysanoptera, Thripidae)

Microinsects are capable of associative learning and memory retention despite significant reduction in the number and size of neurons. Previously, the capabilities of Thrips tabaci (Thysanoptera, Thripidae) for associative learning and the formation of short-term memory have been demonstrated. In this study, an additional training session was added, as well as a time interval between them. Increasing the number of training sessions and spacing these out over time allowed us to demonstrate the persistence of memory traces for up to 24 hours. Thus, for the first time, the presence of consolidated forms of memory in the order Thysanoptera has been revealed.

Tracing Memory, Trauma, and Childhood: The Bangladesh Liberation War in Sorayya Khan’s Noor

This article addresses the representation of childhood memory and trauma in Sorayya Khan’s novel Noor (2003) against the backdrop of the 1971 Bangladesh Liberation War. It discusses how personal recollections of public events contribute to the collective memory of the nation-state. The exploration includes the intergenerational transmission of trauma, employing Marianne Hirsch’s concept of ‘Postmemory,’ which describes how traumatic experiences are passed down, particularly in the context of the Holocaust. This framework has been contextualized within the 1971 Bangladesh Liberation War and its aftermath on children, carrying the memories of war trauma forward, as illustrated in the novel through Noor and Sajida’s experiences. Through a close reading of the novel, this article aims to extricate the underlying patterns of childhood war memory and personal experiences that often get subsided in historical representations and emphasizes the pertinence of reading a representational narrative of the 1971 Bangladesh Liberation War even after half a century.

Delayed testing in directed forgetting dissociates active and passive forms of forgetting.

Across two experiments, we assessed the rates of relative forgetting following instructions to remember or forget information in an item-method directed forgetting paradigm across several retention intervals. In addition to the Forget and Remember cues, we also included Thought Substitution (TS) cues in the same design instructing participants to mentally shift to a different context on some study trials. TS cues have been shown to impair memory compared with Remember cues, but not as effectively as cues to Forget in item-method studies (Hubbard & Sahakyan, 2021). The results demonstrated that Forget cues produce accelerated rates of forgetting compared with Remember cues and showed that these differences are independent of initial learning rates, which were deliberately equated in Experiment 2. TS cued items showed faster forgetting than Remember cued items but were less effective than Forget cues and exhibited a more complex pattern likely reflecting individual differences. Thus, delayed testing demonstrated that active forgetting can have long-lasting effects on memory traces beyond initial suppression, in line with cognitive neuroscientific theory suggesting inhibition can produce lasting changes to memory traces. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Discovering Dadu: A Ludemic Enigma from South Asia

Abstract Dadu is a traditional board game exclusively played within the Muslim Dawoodi Bohra community in South Asia. Most households have their own hand-stitched cloth board, together with a set of wood-turned playing pieces and cowrie shells for dice. Though formally a two-player game, it is commonly played in large teams during family gatherings. Non-community members rarely take part and the game remains virtually unknown to outsiders. Descriptions of the game are absent from the scholarly literature and it does not find mention in any of the major game encyclopedias. Surviving boards and communal memory trace the game back to the early 20th century, but the hybrid nature of the game and the origin of the Dawoodi Bohra community in Yemen suggest that it may go back several centuries further. The present article uses ludemic theory to analyze the constituent elements of the game and demonstrate their affinity with elements in other games both inside and outside South Asia. The findings are contextualized within the wider history of the Dawoodi Bohra community, suggesting that Dadu may have resulted from the adaptation of a West Asian Tab game to a South Asian single track race game. A detailed set of rules gathered from interviews with members of the Dawoodi Bohra community is appended to the article.

Variation in Valence Intensity Within Frames: Testing Predictions of Prospect Theory and Fuzzy‐Trace Theory

ABSTRACTRisk and decision‐making are central to human behavior and have been extensively studied across many disciplines. To better understand the factors that influence an individual's risk‐related choices, this paper investigates the influence of frame valence intensity. It does so by comparing predictions from two prominent theories of decision‐making: Prospect theory (PT) and fuzzy‐trace theory (FTT). PT relies on the numerical transformation of subjective value information suggesting that the intensity of the frame should not affect the decision outcome. In contrast, FTT predicts that the level of frame valence should correspond to the intensity of the extracted memory trace and have predictable effects on risky choice. The results demonstrate that risky choice varies across different levels of the frame's valence. For positive frames, increasing valence intensity is associated with decreased risk preference. For negative frames, the relationship is more complex and context‐dependent. These findings extend our understanding of framing effects, suggesting that both the direction and intensity of frame valence influence risk preferences. While broadly aligning with FTT predictions regarding gist extraction, our results also indicate that PT could be extended to account for valence intensity effects, potentially bridging these theoretical perspectives.

Stimulation of an entorhinal-hippocampal extinction circuit facilitates fear extinction in a post-traumatic stress disorder model.

Effective psychotherapy of post-traumatic stress disorder (PTSD) remains challenging due to the fragile nature of fear extinction, for which ventral hippocampal CA1 (vCA1) region is considered as a central hub. However, neither the core pathway nor the cellular mechanisms involved in implementing extinction are known. Here, we unveil a direct pathway, where layer 2a fan cells in the lateral entorhinal cortex (LEC) target parvalbumin-expressing interneurons (PV-INs) in the vCA1 region to propel low gamma-band synchronization of the LEC-vCA1 activity during extinction learning. Bidirectional manipulations of either hippocampal PV-INs or LEC fan cells sufficed fear extinction. Gamma entrainment of vCA1 by deep brain stimulation (DBS) or noninvasive transcranial alternating current stimulation (tACS) of LEC persistently enhanced the PV-IN activity in vCA1, thereby promoting fear extinction. These results demonstrate that the LEC-vCA1 pathway forms a top-down motif to empower low gamma-band oscillations that facilitate fear extinction. Finally, application of low gamma DBS and tACS to a mouse model with persistent PTSD showed potent efficacy, suggesting that the dedicated LEC-vCA1 pathway can be stimulated for therapy to remove traumatic memory trace.

Distinct mechanisms and functions of episodic memory.

The concept of episodic memory (EM) faces significant challenges by two claims: EM might not be a distinct memory system, and EM might be an epiphenomenon of a more general capacity for mental time travel (MTT). Nevertheless, the observations leading to these arguments do not preclude the existence of a mechanically and functionally distinct EM system. First, modular systems, like cognition, can have distinct subsystems that may not be distinguishable in the system's final output. EM could be such a subsystem, even though its effects may be difficult to distinguish from those of other subsystems. Second, EM could have a distinct and consistent low-level function, which is used in diverse high-level functions such as MTT. This article introduces the scenario construction framework, proposing that EM crucially rests on memory traces containing the gist of an episodic experience. During retrieval, EM traces trigger the reconstruction of semantic representations, which were active during the remembered episode, and are further enriched with semantic information, to generate a scenario of the past experience. This conceptualization of EM is consistent with studies on the neural basis of EM and resolves the two challenges while retaining the key properties associated with EM. This article is part of the theme issue 'Elements of episodic memory: lessons from 40 years of research'.

Latent memory traces for prospective items in visual working memory

Latent memory traces for prospective items in visual working memory

Modeling biological memory network by an autonomous and adaptive multi-agent system

At the intersection of computation and cognitive science, graph theory is utilized as a formalized description of complex relationships description of complex relationships and structures, but traditional graph models are static, lack the dynamic and autonomous behaviors of biological neural networks, rely on algorithms with a global view. This study introduces a multi-agent system (MAS) model based on the graph theory, each agent equipped with adaptive learning and decision-making capabilities, thereby facilitating decentralized dynamic information memory, modeling and simulation of the brain’s memory process. This decentralized approach transforms memory storage into the management of MAS paths, with each agent utilizing localized information for the dynamic formation and modification of these paths, different path refers to different memory instance. The model’s unique memory algorithm avoids a global view, instead relying on neighborhood-based interactions to enhance resource utilization. Emulating neuron electrophysiology, each agent’s adaptive learning behavior is represented through a microcircuit centered around a variable resistor. Using principles of Ohm’s and Kirchhoff’s laws, we validated the model’s efficacy in memorizing and retrieving data through computer simulations. This approach offers a plausible neurobiological explanation for memory realization and validates the memory trace theory at a system level.

Spatio-temporal mechanisms of consolidation, recall and reconsolidation in reward-related memory trace.

The formation of memories is a complex, multi-scale phenomenon, especially when it involves integration of information from various brain systems. We have investigated the differences between a novel and consolidated association of spatial cues and amphetamine administration, using an in situ hybridisation method to track the short-term dynamics during the recall testing. We have found that remote recall group involves smaller, but more consolidated groups of neurons, which is consistent with their specialisation. By employing machine learning analysis, we have shown this pattern is especially pronounced in the VTA; furthermore, we also uncovered significant activity patterns in retrosplenial and prefrontal cortices, as well as in the DG and CA3 subfields of the hippocampus. The behavioural propensity towards the associated localisation appears to be driven by the nucleus accumbens, however, further modulated by a trio of the amygdala, VTA and hippocampus, as the trained association is confronted with test experience. Moreover, chemogenetic analysis revealed central amygdala as critical for linking appetitive emotional states with spatial contexts. These results show that memory mechanisms must be modelled considering individual differences in motivation, as well as covering dynamics of the process.

Remembering an abandoned city: tracing memories and urban narratives of refugees from famagusta

Sullo sfondo del quadro teorico ricostruito nell'articolo precedente, questo contributo presenta i risultati dello studio empirico sulla città abbandonata di Varosha, nella città di Famagosta (Cipro), osservata attraverso lo sguardo dei rifugiati grecociprioti esiliati durante l'invasione turca del 1974. Utilizzando il metodo delle mappe mentali, attraverso interviste strutturate gli esuli sono stati invitati a disegnare Famagosta ripercorrendo la memoria della loro terra perduta. Le mappe mentali dei rifugiati hanno rivelato profonde intuizioni sulla loro percezione dello spazio e una forte relazione con il luogo. Questo studio arricchisce la nostra comprensione di Famagosta e funge da testimonianza dei legami duraturi tra le comunità esiliate e il loro territorio, sottolineando l'importanza di preservare e comprendere i molteplici strati delle dimensioni spaziali mnemoniche di una città al fine di progettarne un futuro condiviso.

Differing Pattern of Mismatch Negativity Responses in Clinical and Nonclinical Voice Hearers Challenge Predictive Coding Accounts of Psychosis

BackgroundAmong people with schizophrenia (PSZ), reduced mismatch negativity (MMN) is conceptualized as evidence of disrupted prediction error signaling that underlies positive symptoms. However, this conceptualization has been challenged by observations that MMN and positive symptoms are often uncorrelated. In the current study, we tested the hypothesis that reduced MMN is associated with the presence of hallucinations and delusions specifically rather than the presence of a psychiatric illness. A second aim was to determine whether the strength of the association with positive symptoms increases for indices that reflect predictions at higher levels of abstraction. MethodsFifty-six PSZ, 34 nonclinical voice hearers, and 48 healthy comparison subjects (HCs) completed 2 MMN paradigms: one with a simple duration deviant type, and one with a higher-level, pattern-violation deviant type. We also measured the repetition positivity, which reflects the formation of auditory memory traces. ResultsWe observed that although PSZ exhibited the expected pattern of significantly reduced simple duration deviant type and reduced pattern-violation deviant type at the trend level compared with HCs, nonclinical voice hearers exhibited a pattern of simple duration deviant type and pattern-violation deviant type amplitude that was statistically similar to that of HCs (ps > .64). Similarly, PSZ exhibited a significantly reduced repetition positivity slope compared with HCs in the duration condition and a trend-level reduction compared with HCs in the pattern-violation condition. Nonclinical voice hearers did not differ from either group in repetition positivity slope in either condition. ConclusionsThese results indicate that the MMN as a prediction error signal does not reflect processes relevant for the manifestation of hallucinations and delusions.

Propagation of sharp wave-ripple activity in the mouse hippocampal CA3 subfield in vitro.

Sharp wave-ripple complexes (SPW-Rs) are spontaneous oscillatory events that characterize hippocampal activity during resting periods and slow-wave sleep. SPW-Rs are related to memory consolidation - the process during which newly acquired memories are transformed into long-lasting memory traces. To test the involvement of SPW-Rs in this process, it is crucial to understand how SPW-Rs originate and propagate throughout the hippocampus. SPW-Rs can originate in CA3, and they typically spread from CA3 to CA1, but little is known about their formation within CA3. To investigate the generation and propagation of SPW-Rs in CA3, we recorded from mouse hippocampal slices using multi-electrode arrays and patch-clamp electrodes. We characterized extracellular and intracellular correlates of SPW-Rs and quantified their propagation along the pyramidal cell layer of CA3. We found that a hippocampal slice can be described by a speed and a direction of propagation of SPW-Rs. The preferred propagation direction was from CA3c (the subfield closer to the dentate gyrus) toward CA3a (the subfield at the boundary to CA2). In patch-clamp recordings from CA3 pyramidal neurons, propagation was estimated separately for excitatory and inhibitory currents associated with SPW-Rs. We found that propagation speed and direction of excitatory and inhibitory currents were correlated. The magnitude of the speed of propagation of SPW-Rs within CA3 was consistent with the speed of propagation of action potentials in axons of CA3 principal cells. KEY POINTS: Hippocampal sharp waves are considered important for memory consolidation; therefore, it is of interest to understand the mechanisms of their generation and propagation. Here, we used two different approaches to study the propagation of sharp waves in mouse CA3 in vitro: multi-electrode arrays and multiple single-cell recordings. We find a preferred direction of propagation of sharp waves from CA3c toward CA3a - both in the local field potential and in sharp wave-associated excitatory and inhibitory synaptic activity. The speed of sharp wave propagation is consistent with the speed of action potential propagation along the axons of CA3 pyramidal neurons. These new insights into the dynamics of sharp waves in the CA3 network will inform future experiments and theoretical models of sharp-wave generation mechanisms.

Global Analysis of a Fractional‐Order Hepatitis B Virus Model Under Immune Response in the Presence of Cytokines

AbstractThis research proposes and investigates an epidemiological model to study the dynamic behaviors of the Hepatitis B virus (HBV) under immune response and cytokine influence. The model's stability, positivity, boundedness, and equilibria are analyzed using Lyapunov functional methods and the Routh–Hurwitz criterion under Caputo fractional derivative. The study evaluates nucleoside analogues and interferon treatments, determining critical drug efficiencies. Equilibria, including infection‐free and endemic states, are analyzed using the fundamental reproduction number, , to predict disease elimination. Numerical simulations utilize the fractional Adams method and the L1 scheme, capturing memory traces as the fractional order changes. Results show the L1 scheme effectively captures memory traces, providing empirical support for the theoretical findings. Furthermore, Ulam–Hyers stability is treated according to the equilibrium point, which describes relationships between functions. Notably, the findings of the study yielded profound insights. They revealed that the HBV system remains locally asymptotic stable at disease‐free and the endemic point when . At the same time, the simulations illustrated a correlation between the rate of infection and the rise in infected individuals, indicating the feasibility of eradicating and effectively managing HBV infections through a multifaceted approach and various measures such as vaccination and effective drug administration protocols. The proposed framework can guide medical professionals and decision‐makers in developing effective strategies to limit and eliminate the spread of HBV in the population.

Mapping functional traces of opioid memories in the rat brain.

Addiction to psychoactive substances is a maladaptive learned behaviour. Contexts surrounding drug use integrate this aberrant mnemonic process and hold strong relapse-triggering ability. Here, we asked where context and salience might be concurrently represented in the brain during retrieval of drug-context paired associations. For this, we developed a morphine-conditioned place preference protocol that allows contextual stimuli presentation inside a magnetic resonance imaging scanner and investigated differences in activity and connectivity at context recall. We found context-specific responses to stimulus onset in multiple brain regions, namely, limbic, sensory and striatal. Differences in functional interconnectivity were found among amygdala, lateral habenula, and lateral septum. We also investigated alterations to resting-state functional connectivity and found increased centrality of the lateral septum in a proposed limbic network, as well as increased functional connectivity of the lateral habenula and hippocampal 'cornu ammonis' 1 region, after a protocol of associative drug-context. Finally, we found that pre- conditioned place preference resting-state connectivity of the lateral habenula and amygdala was predictive of inter-individual conditioned place preference score differences. Overall, our findings show that drug and saline-paired contexts establish distinct memory traces in overlapping functional brain microcircuits and that intrinsic connectivity of the habenula, septum, and amygdala likely underlies the individual maladaptive contextual learning to opioid exposure. We have identified functional maps of acquisition and retrieval of drug-related memory that may support the relapse-triggering ability of opioid-associated sensory and contextual cues. These findings may clarify the inter-individual sensitivity and vulnerability seen in addiction to opioids found in humans.