Memory Trace Research Articles

The memory trace of an intrusive trauma-analog episode

Intrusive memories are a core symptom of posttraumatic stress disorder. Compared with memories of everyday events, they are characterized by several seemingly contradictory features: intrusive memories contain distinct sensory and emotional details of the traumatic event and can be triggered by various perceptually similar cues, but they are poorly integrated into conceptual memory. Here, we conduct exploratory whole-brain analyses to investigate the neural representations of trauma-analog experiences and how they are reactivated during memory intrusions. We show that trauma-analog movies induce excessive processing and generalized representations in sensory areas but decreased blood-oxygen-level-dependent (BOLD) responses and highly distinct representations in conceptual/semantic areas. Intrusive memories activate generalized representations in sensory areas and reactivate memory traces specific to trauma-analog events in the anterior cingulate cortex. These findings provide the first evidence of how traumatic events could distort memory representations in the human brain, which may form the basis for future confirmatory research on the neural representations of traumatic experiences.

Active forgetting and neuropsychiatric diseases.

Recent and pioneering animal research has revealed the brain utilizes a variety of molecular, cellular, and network-level mechanisms used to forget memories in a process referred to as "active forgetting". Active forgetting increases behavioral flexibility and removes irrelevant information. Individuals with impaired active forgetting mechanisms can experience intrusive memories, distressing thoughts, and unwanted impulses that occur in neuropsychiatric diseases. The current evidence indicates that active forgetting mechanisms degrade, or mask, molecular and cellular memory traces created in synaptic connections of "engram cells" that are specific for a given memory. Combined molecular genetic/behavioral studies using Drosophila have uncovered a complex system of cellular active-forgetting pathways within engram cells that is regulated by dopamine neurons and involves dopamine-nitric oxide co-transmission and reception, endoplasmic reticulum Ca2+ signaling, and cytoskeletal remodeling machinery regulated by small GTPases. Some of these molecular cellular mechanisms have already been found to be conserved in mammals. Interestingly, some pathways independently regulate forgetting of distinct memory types and temporal phases, suggesting a multi-layering organization of forgetting systems. In mammals, active forgetting also involves modulation of memory trace synaptic strength by altering AMPA receptor trafficking. Furthermore, active-forgetting employs network level mechanisms wherein non-engram neurons, newly born-engram neurons, and glial cells regulate engram synapses in a state and experience dependent manner. Remarkably, there is evidence for potential coordination between the network and cellular level forgetting mechanisms. Finally, subjects with several neuropsychiatric diseases have been tested and shown to be impaired in active forgetting. Insights obtained from research on active forgetting in animal models will continue to enrich our understanding of the brain dysfunctions that occur in neuropsychiatric diseases.

Learning leaves a memory trace in motor cortex

How are we able to learn new behaviors without disrupting previously learned ones? To understand how the brain achieves this, we used a brain-computer interface (BCI) learning paradigm, which enables us to detect the presence of a memory of one behavior while performing another. We found that learning to use a new BCI map altered the neural activity that monkeys produced when they returned to using a familiar BCI map in a way that was specific to the learning experience. That is, learning left a "memory trace" in the primary motor cortex. This memory trace coexisted with proficient performance under the familiar map, primarily by altering neural activity in dimensions that did not impact behavior. Forming memory traces might be how the brain is able to provide for the joint learning of multiple behaviors without interference.

Discerning Temporal Difference Learning

Temporal difference learning (TD) is a foundational concept in reinforcement learning (RL), aimed at efficiently assessing a policy's value function. TD(λ), a potent variant, incorporates a memory trace to distribute the prediction error into the historical context. However, this approach often neglects the significance of historical states and the relative importance of propagating the TD error, influenced by challenges such as visitation imbalance or outcome noise. To address this, we propose a novel TD algorithm named discerning TD learning (DTD), which allows flexible emphasis functions—predetermined or adapted during training—to allocate efforts effectively across states. We establish the convergence properties of our method within a specific class of emphasis functions and showcase its promising potential for adaptation to deep RL contexts. Empirical results underscore that employing a judicious emphasis function not only improves value estimation but also expedites learning across diverse scenarios.

The visual familiarity effect on attentional working memory maintenance.

Attentional refreshing has been described as an attention-based, domain-general maintenance mechanism in working memory. It is thought to operate via focusing executive attention on information held in working memory, protecting it from temporal decay and interference. Although attentional refreshing has attracted a lot of research, its functioning is still debated. At least one conception of refreshing supposes that it relies on semantic long-term memory representations to reconstruct working memory traces. Although investigations in the verbal domain found evidence against this hypothesis, a different pattern could emerge in visuospatial working memory in which absence of refreshing evidence has been observed for stimuli with minimal associated long-term knowledge. In a series of four experiments, the current study investigated the hypothesis of an involvement of semantic long-term representations in the functioning of attentional refreshing in the visuospatial domain. Both cognitive and memory load effects have been proposed as indexes of attentional refreshing. Therefore, we investigated the interaction between the effects of visual familiarity (a long-term memory effect) and cognitive load on recall performance (Experiments 1A and 1B), as well as the interaction between the effects of visual familiarity and memory load on the response times in a concurrent processing task (Experiments 2A and 2B). Results were consistent across experiments and go against the hypothesis of the involvement of semantic long-term memory in the functioning of attentional refreshing in visuospatial working memory. As such, this study corroborates the results found in the verbal domain. Implications for attentional refreshing and working memory are discussed.

Overnight neuronal plasticity and adaptation to emotional distress.

Expressions such as 'sleep on it' refer to the resolution of distressing experiences across a night of sound sleep. Sleep is an active state during which the brain reorganizes thesynaptic connections that form memories. This Perspective proposes a model of how sleep modifies emotional memory traces. Sleep-dependent reorganization occurs through neurophysiological events in neurochemical contexts that determine the fates of synapses to grow, to survive or to be pruned. We discuss how low levels of acetylcholine during non-rapid eye movement sleep and low levels of noradrenaline during rapid eye movement sleep provide a unique window of opportunity for plasticity in neuronal representations of emotional memories that resolves the associated distress. We integrate sleep-facilitated adaptation over three levels: experience and behaviour, neuronal circuits, and synaptic events. The model generates testable hypotheses for how failed sleep-dependent adaptation to emotional distress is key to mental disorders, notably disorders of anxiety, depression and post-traumatic stress with the common aetiology of insomnia.

Emergent dynamics in fractional-order Wilson–Cowan neural network systems

The firing dynamics of excitable systems are critical to understand organized responses in cortical networks. In this paper, we examine a fractional-order Wilson–Cowan (W–C) neural network model composed of excitatory and inhibitory neuron populations, utilizing Caputo’s fractional-order derivative formalism to explore the influence of fractional-order dynamics on firing behavior. The significance of extending to the fractional-order domain lies in the model’s theoretical framework, which inherently retains memory and hereditary characteristics. We investigate memory-dependent response functions and average neuronal characteristics, enabling us to formulate a fractional-order model that incorporates past dynamics into the neuronal populations’ features. This generalized model is capable of producing alternations between spiking and bursting phenomena, including mixed-mode oscillations (MMOs). Using stability and bifurcation analyses, we delineate the parameter space within which variations in firing patterns emerge. One notable impact of the model’s memory property is the potential stabilization of neuronal activity. We demonstrate that our numerical findings are in alignment with the analytical predictions and that the memory trace depends on the fractional-order dynamics.

Amylovis-201 enhances physiological memory formation and rescues memory and hippocampal cell loss in a streptozotocin-induced Alzheimer's disease animal model

Alzheimer's disease is the most common neurodegenerative disease, and its treatment is lacking. In this work, we tested Amylovis-201, a naphthalene-derived compound, as a possible therapeutic candidate for the treatment of AD. For this purpose, we performed three experiments. In the first and third experiment, animals received a bilateral administration of streptozotocin and, starting 24 h after injection, a daily dose of Amylovis-201 (orally), for 17 days or for the whole time of the experiment respectively (28 days), after which learning and memory, as well as the number of hippocampal dentate gyrus cells, were assessed. In the second experiment, healthy animals received a single dose of Amylovis-201, 10 min or 5 h after the learning section to assess whether this substance could promote specific mechanisms involved in memory trace formation. Our data show that, administration of a single dose of Amylovis-201, 10 min after the end of training, but not at 5 h, produces a prolongation in memory duration, probably because it modulates specific mechanisms involved in memory trace consolidation. Furthermore, daily administration of Amylovis-201 to animals with bilateral intracerebroventricular injection of STZ produces a reduction in the loss of the hippocampus dentate gyrus cells and an improvement in spatial memory, probably because Amylovis-201 can interact with some of the protein kinases of the insulin signaling cascade, also involved in neural plasticity, and thereby halt or reverse some of the effects of STZ. Taking to account these results, Amylovis-201 is a good candidate for the therapeutic treatment of AD.

The Changing Process of Adolescents' Self-Independence Consciousness: From the Perspective of David Hume's Human Nature Theory and Freud's Psychodynamic Theory

During the mental development of contemporary teenagers, due to the influence of their own growth and the environment, many parts have more or less mental illness, which is obvious and recessive, but it is a part that needs attention in the process of understanding themselves. The emergence of self-consciousness is not a simple transfer of the object and content of consciousness, but a new stage of psychological development, which is the result of human socialization and one of the special forms of higher psychological activities. We do not know enough about other sources of adolescent consciousness, so it is worth considering carefully when the subject we propose produces consciousness rather than memory traces. The ideas that are active during adolescence will be more pronounced, and this situation will be closer to what the superego wants the individual to feel.

Bilingualism Influences How Articulation Enhances Verbal Encoding.

Learning information may benefit from movement: Items that are spoken aloud are more accurately remembered than items that are silently read (the production effect). Candidate mechanisms for this phenomenon suggest that speaking may enrich or improve the feature content of memory traces, yet research suggests that prior language skill also plays a role. Recent work showed a larger production effect in bilinguals for words in their second language (L2) compared to their first language (L1), potentially suggesting that bilinguals engage different or additional linguistic features when speaking L2 compared to L1 words. The current study examined whether the increased L2 production effect reduces for L2 and L1 pseudowords, which may similarly engage mainly phonological features. German (L1)-English (L2) bilinguals first read (out loud or silently) and subsequently recognized German or English words or pseudowords following German or English phonology. The production effect increased for L2 compared to L1 items and for words compared to pseudowords. Modest evidence suggested L2-L1 similarity in production effect scores for pseudowords, but different L2-L1 scores for words. Integrating feature models of memory with models of bilingual language production, we propose that speaking an L2 may engage more extensive and diverse linguistic features than an L1.

Hippocampal ripples coincide with "up-state" and spindles in retrosplenial cortex.

During NREM sleep, hippocampal sharp-wave ripple (SWR) events are thought to stabilize memory traces for long-term storage in downstream neocortical structures. Within the neocortex, a set of distributed networks organized around retrosplenial cortex (RS-network) interact preferentially with the hippocampus purportedly to consolidate those traces. Transient bouts of slow oscillations and sleep spindles in this RS-network are often observed around SWRs, suggesting that these two activities are related and that their interplay possibly contributes to memory consolidation. To investigate how SWRs interact with the RS-network and spindles, we combined cortical wide-field voltage imaging, Electrocorticography, and hippocampal LFP recordings in anesthetized and sleeping mice. Here, we show that, during SWR, "up-states" and spindles reliably co-occur in a cortical subnetwork centered around the retrosplenial cortex. Furthermore, retrosplenial transient activations and spindles predict slow gamma oscillations in CA1 during SWRs. Together, our results suggest that retrosplenial-hippocampal interaction may be a critical pathway of information exchange between the cortex and hippocampus.

Individual features of the temporal dynamics of inhibitory processes in visual short-term memory depending on the content of stimuli and memorization training

Introduction. Age-related changes in cognitive functions are caused by various processes: degrading inhibitory control, decrease in the volume of working memory, or a slowdown in the speed of thought processes. However, there is no unanimous opinion on the dynamics of these processes and their interactions yet. Based on this, our research goal became finding the temporal dynamics and individual relationship of the effects of proactive interference (Retrival-Induced Forgeting (RIF)) and learning to remember (Retrieval-Based Learning (RBL)) depending on the content of the presented stimuli as well as the age-related specifics of memorization when training the short-term visual memory. Materials and methods. Memory training was carried out in a mode independently organized by the study participants using a computerized memorization program in a proactive interference model, including five sessions of visual presentation of stimuli. University students participated in the first part of the study, aimed at clarifying the meaning of the content of two different sets of stimuli, (220 people, 20.4 ± 1.9 years old), whereas second part aimed to determine the age-related characteristics of visual short-term memory training in a group of students, (70 subjects, 21.7±2.5 years) and a group of elderly women (25 subjects, 64.4±6.3 years). Research results. The results of the memory trace retrieval analysis showed that the RIF effect dominates over the RBL effect regardless of the content of the stimuli, but at different rates of its development depending on the set of stimuli used. With significant individual diversity in the combination of memory strategies, the RIF effect dominated at the initial stage of stimulus presentation (67.6% of cases) and gradually replaced by RBL (56.2% in the fifth run of the experiment). Analysis of age-related characteristics of the effectiveness of short-term visual memory training showed that when it is independently organized, maintaining activity is observed in 32% of university students and 50% in the elderly group. Along with this. Only average of ten approaches to complete this task accompanied by a further decrease in the number of training participants. Comparison of the results of the first three training sessions revealed a significant increase in the memory index in both groups compared to the initial value and the presence of a RIF effect with a further more rapid increase in the efficiency of memorization in students. Conclusion. Proactive interference while memorization of visual stimuli repeatedly presented in five sessions, appears regardless of their content, age of the subjects and memorization training. The efficiency of memorization due to training grows faster in the group of students and accompanied by the combination of the RIF and RBL effects that is characterized by individual diversity without a significant effect on the final result of the memory retrieval.

Tracking the acquisition and retention of novel word representations: an ERP study

ABSTRACT The event-related N400 provides a measure of lexical-semantic processing, indexing the encoding strength of newly learned words. We examined N400 modulations following associative learning of novel written words paired with novel object pictures from early to later stages of acquisition. During the initial learning session, novel picture-word pairs accompanied by semantic attributes were presented as stimuli for learning at multiple timepoints. Following learning at each of these timepoints, we examined behavioural and neural effects for recognition of familiar and novel words, as well as at a follow-up session several days later. Rapid behavioural learning was accompanied by N400 congruity effects for novel words, displaying a similar neurophysiological profile to familiar words. These behavioural and neural effects were largely sustained several days later in the follow-up session. Our findings indicate that explicit learning of novel object-word associations leads to the rapid formation and longer-term retention of new word memory traces.

Mechanistic insights of COVID-19 dynamics by considering the influence of neurodegeneration and memory trace

COVID-19 has been declared a global pandemic as it disturbs education, society, agriculture, the economy, poverty, death rate, social development, mental psychology, and many more. Neurodegenerative disease is a brain disorder associated with several pathological factors along with mental psychology. This paper introduces a mathematical model to inspect mechanistic insights into COVID-19 dynamics by considering the influence of neurodegeneration and memory trace. The analysis of the proposed model and the existence and uniqueness of the model are derived using the fixed-point criteria. A numerical experiment is presented to validate the theoretical results and examine the impact of various biological parameters, the influence of neurodegeneration, and memory trace on the transmission dynamics of COVID-19.

TDCS of right-hemispheric Wernicke’s area homologue affects contextual learning of novel lexicon

Numerous studies have shown robust evidence of the right hemisphere’s involvement in the language function, for instance in the processing of intonation, grammar, word meanings, metaphors, etc. However, its role in lexicon acquisition remains obscure. We applied transcranial direct current stimulation (tDCS) over the right-hemispheric homologue of Wernicke’s area to assess its putative involvement in the processing of different types of novel semantics. After receiving 15 min of anodal, cathodal, or sham (placebo) tDCS, three groups of healthy participants learnt novel concrete and abstract words in the context of short stories. Learning outcomes were assessed using a battery of tests immediately after this contextual learning session and 24 h later. As a result, an inhibitory effect of cathodal tDCS and a facilitatory effect of anodal tDCS were found for abstract word acquisition only. We also found a significant drop in task performance on the second day of the assessment for both word types in all the stimulation groups, suggesting no significant influence of tDCS on the post-learning consolidation of new memory traces. The results suggest an involvement of Wernicke’s right-hemispheric counterpart in initial encoding (but not consolidation) of abstract semantics, which may be explained either by the right hemispheres direct role in processing lexical semantics or by an indirect impact of tDCS on contralateral (left-hemispheric) cortical areas through cross-callosal connections.

Distinct engrams control fear and extinction memory.

Memories are stored in engram cells, which are necessary and sufficient for memory recall. Recalling a memory might undergo reconsolidation or extinction. It has been suggested that the original memory engram is reactivated during reconsolidation so that memory can be updated. Conversely, during extinction training, a new memory is formed that suppresses the original engram. Nonetheless, it is unknown whether extinction creates a new engram or modifies the original fear engram. In this study, we utilized the Daun02 procedure, which uses c-Fos-lacZ rats to induce apoptosis of strongly activated neurons and examine whether a new memory trace emerges as a result of a short or long reactivation, or if these processes rely on modifications within the original engram located in the basolateral amygdala (BLA) and infralimbic (IL) cortex. By eliminating neurons activated during consolidation and reactivation, we observed significant impacts on fear memory, highlighting the importance of the BLA engram in these processes. Although we were unable to show any impact when removing the neurons activated after the test of a previously extinguished memory in the BLA, disrupting the IL extinction engram reactivated the aversive memory that was suppressed by the extinction memory. Thus, we demonstrated that the IL cortex plays a crucial role in the network involved in extinction, and disrupting this specific node alone is sufficient to impair extinction behavior. Additionally, our findings indicate that extinction memories rely on the formation of a new memory, supporting the theory that extinction memories rely on the formation of a new memory, whereas the reconsolidation process reactivates the same original memory trace.

The expression of parental fear-conditioned memory in the hippocampal neurons of subsequent progeny

This paper researches the concept of parental fear-conditioned memory and its potential transmission to subsequent generations, focusing on examining whether memory traces formed in the hippocampus CA3 region of parents are retained in the hippocampus of their offspring. Through experiments conducted on mice, it is expected that the findings will reveal how fear conditioning in the parental generation impacts the behavioral sensitivity and neuroanatomical changes in the hippocampal neurons of the offspring. The study explores the potential inheritance of transgenerational memory from parents to children and the specific brain sites involved.

Short-term interference in learning ballistic motor tasks: Refining the notion of specificity

Introduction Learning of an isometric ballistic force task (BT) can be impaired if it is followed by the learning of a visuomotor accuracy task (VMT) involving isometric contractions of the same muscles (Lundbye-Jensen et al., 2011). This phenomenon, known as retrograde interference, is thought to occur because the memory trace created after learning the BT is affected by the activation of similar neural circuits involved in the VMT (Lundbye-Jensen et al., 2011). However, it remains unclear how the contraction type involved in the two motor tasks influences potential interference effects. The aim of this study was therefore to compare the influence of a VMT involving dynamic position control or isometric force control on short-term retrograde interference in a previously learned isometric BT involving the same muscles. Methods 45 participants were randomly assigned to one of 3 groups. Participants started by learning an isometric BT involving the wrist flexors of the non-dominant hand. Participants in the first two groups then learned a VMT involving dynamic (VMTDynamic group) or isometric (VMTIsometric group) contractions of the same muscles, while participants in the third group took a break (control group). Finally, participants completed the BT retention test. Each BT training consisted of 35 trials in which participants were asked to achieve the highest rate of force development (RFDmax). The VMT training consisted of 50 trials in which participants were asked to follow a curve with a cursor. Position of the cursor was linked to the wrist flexion/extension angle (VMTDynamic) or the isometric force produced (VMTIsometric). Interference was quantified by comparing RFDmax between the end of the initial training (POST) and the start of the retention test (RET). Results A mixed design ANOVA revealed a significant interaction effect (F(2, 40) = 3.87, p = 0.029). Post hoc corrected paired t-tests showed a significant decrease in RFDmax for the VMTIsometric group between POST (2,524 ± 1,144 N/s) and RET (1,960 ± 921 N/s). In contrast, performance of the other two groups did not change (VMTDynamic group: 2,679 ± 1,321 vs. 2,499 ± 1,278 N/s; control group: 2,489 ± 1,005 vs. 2,334 ± 1,013 N/s). Discussion/Conclusion Interference was only observed in the VMTIsometric group, suggesting that the same type of contraction must be involved in the VMT and BT for short-term retrograde interference to occur. It is known that the neural control of isometric contractions is different from dynamic contractions (Duchateau & Enoka, 2016). It can therefore be speculated that the resulting reduction in neural competition between the motor tasks was sufficient to prevent interference in the VMTDynamic group. In conclusion, for retrograde interference to occur, not only must the same muscles be involved in both motor tasks, but they must also perform the same type of contraction.

Asymmetric neurons are necessary for olfactory learning in the Drosophila brain

Animals have complementary parallel memory systems that process signals from various sensory modalities. In the brain of the fruit fly Drosophila melanogaster, mushroom body (MB) circuitry is the primary associative neuropil, critical for all stages of olfactory memory. Here, our findings suggest that active signaling from specific asymmetric body (AB) neurons is also crucial for this process. These AB neurons respond to odors and electric shock separately and exhibit timing-sensitive neuronal activity in response to paired stimulation while leaving a decreased memory trace during retrieval. Our experiments also show that rutabaga-encoded adenylate cyclase, which mediates coincidence detection, is required for learning and short-term memory in both AB and MB. We observed additive effects when manipulating rutabaga co-expression in both structures. Together, these results implicate the AB in playing a critical role in associative olfactory learning and short-term memory.

Energy-Efficient Ferroelectric-FET-Based Agent With Memory Trace for Enhanced Reinforcement Learning

Energy-Efficient Ferroelectric-FET-Based Agent With Memory Trace for Enhanced Reinforcement Learning