Memory consolidation

Cocaine diminishes consolidation of cued fear memory in female rats through interactions with ventral hippocampal D2 receptors

In addition to cocaine's addictive properties, cocaine use may lead to heightened risk-taking behavior. The disruptive effects of cocaine on aversive memory formation may underlie this behavior. The present study investigated the effects of cocaine on fear memory using a cued fear conditioning paradigm in female Sprague Dawley rats, and further determined the role of D2 receptors in modulating the effect of cocaine on cued fear expression. Animals received six evenly spaced shocks preceded by a tone. The following day, rats were returned to the fear chamber where tones, but no shocks, were delivered. In Experiment 1, separate or concurrent administrations of cocaine (15 mg/kg; i.p.) and the D2 receptor antagonist eticlopride (0.1 mg/kg; i.p.) were given immediately after conditioning trials. It was determined that cocaine administration during the consolidation period diminished the expression of cued fear during the subsequent test day. Concurrent eticlopride administration attenuated this effect, indicating the involvement of D2 receptors in the deleterious effects of cocaine on fear memory consolidation. In Experiment 2, eticlopride (0.05 μg) was infused directly into the ventral hippocampus (VH) after fear conditioning and before cocaine administration. Cocaine continued to disrupt consolidation of cued and contextual fear memory, and concurrent intra-VH eticlopride blocked this effect, thereby demonstrating that VH D2 receptors mediate cocaine-induced impairment of fear memory consolidation. Overall, the present study provides evidence that acute cocaine administration impairs aversive memory formation and establishes a potential circuit through which cocaine induces its detrimental effects on fear memory consolidation.

Memory Consolidation and Sleep in Children With Epilepsy: A Systematic Review

BACKGROUND

Sleep is essential in the process of memory consolidation. Children and adolescents with epilepsy hold a significantly higher risk for memory impairment. Understanding the relationship between sleep and memory impairment in adolescents with epilepsy will help us to develop effective support services for this patient population. The present study provides a summary of the current research on the influence of epilepsy-related altered sleep patterns on memory consolidation in children and adolescents with epilepsy. The aim of this systematic review is to investigate the influence of epilepsy-related altered sleep conditions in children and adolescents and their impact on memory performance.

MATERIALS

A systematic review was conducted according to the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses using the search terms "memory," "sleep," "epilepsy," "children," and "adolescents." A total of 4 studies met the inclusion criteria. The review focused on the association of sleep disorders and memory performance in children and adolescents aged up to 21 years without psychiatric comorbidities.

RESULTS

The reviewed studies highlight a higher risk of sleep disturbance and lower sleep quality in children with epilepsy in comparison to control groups. Group differences in memory consolidation were found before, but not after one night of sleep. Three studies reported a significant association between sleep and memory performance. Two studies demonstrated an association between nocturnal interictal epileptiform discharges and memory performance in adolescents.

CONCLUSION

Children and adolescents with epilepsy have a higher risk of sleep and memory disorders. Nocturnal interictal epileptiform discharges have been shown to interfere with memory consolidation. Conclusions on underlying mechanisms remain unclear. Further case-control studies addressing sleep and its influence on memory problems in pediatric epilepsy patients are needed.

Using recognition testing to support semantic learning in developmental amnesia

ABSTRACTPatients with developmental amnesia (DA) have suffered hippocampal damage in infancy and subsequently shown poor episodic memory, but good semantic memory. It is not clear how patients with DA learn semantic information in the presence of episodic amnesia. However, patients with DA show good recognition memory and it is possible that semantic learning may be supported by recognition. Building on previous work, we compared two methods for supporting semantic learning in DA; recognition-learning and recall-learning. In each condition, a patient with DA (aged 8 years) was presented with semantic information in animated videos. After each presentation of a video, learning was supported by an immediate memory test. Two videos were paired with a cued recall test. Another two videos were paired with a multiple-choice test to enable recognition-based learning. The outcome measure was semantic recall performance after a short delay of 30 min and a long delay of one week. Results showed a benefit of recognition-learning compared to recall-learning on cued recall in the patient with DA (76% vs. 35%). This finding indicates that young people with severe hippocampal damage can utilize recognition to support semantic learning. This has implications for the support of school-aged children with episodic memory difficulties.

Autoimmune hypothesis of Alzheimer's disease: unanswered question

Alzheimer's disease (AD) was described more than a century ago. However, there are still no effective approaches to its treatment, which may suggest that the search for the cure is not being conducted in the most productive direction. AD begins as selective impairments of declarative memory with no deficits in other cognitive functions. Therefore, understanding of the AD pathogenesis has to include the understanding of this selectivity. Currently, the main efforts aimed at prevention and treatment of AD are based on the dominating hypothesis for the AD pathogenesis: the amyloid hypothesis. But this hypothesis does not explain selective memory impairments since β-amyloid accumulates extracellularly and should be toxic to all types of cerebral neurons, not only to "memory engram neurons." To explain selective memory impairment, I propose the autoimmune hypothesis of AD, based on the analysis of risk factors for AD and molecular mechanisms of memory formation. Memory formation is associated with epigenetic modifications of chromatin in memory engram neurons and, therefore, might be accompanied by the expression of memory-specific proteins recognized by the adaptive immune system as "non-self" antigens. Normally, the brain is protected by the blood-brain barrier (BBB). All risk factors for AD provoke BBB disruptions, possibly leading to an autoimmune reaction against memory engram neurons. This reaction would make them selectively sensitive to tauopathy. If this hypothesis is confirmed, the strategies for AD prevention and treatment would be radically changed.

Memory traces of duration and location in the right intraparietal sulcus

Time and space form an integral part of every human experience, and for the neuronal representation of these perceptual dimensions, previous studies point to the involvement of the right-hemispheric intraparietal sulcus and structures in the medial temporal lobe. Here we used multi-voxel pattern analysis (MVPA) to investigate long-term memory traces for temporal and spatial stimulus features in those areas. Participants were trained on four images associated with short versus long durations and with left versus right locations. Our results demonstrate stable representations of both temporal and spatial information in the right posterior intraparietal sulcus. Building upon previous findings of stable neuronal codes for directly perceived durations and locations, these results show that the reactivation of long-term memory traces for temporal and spatial features can be decoded from neuronal activation patterns in the right parietal cortex.

An immersive virtual reality-based object-location memory task reveals spatial long-term memory alterations in Long-COVID

Object-location memory (OLM) is a type of declarative memory for spatial information and consists of the individual's ability to establish accurate associations between objects and their spatial locations. Long-COVID describes the long-term effects of the COVID-19 disease. Long-COVID patients show medial temporal lobe dysfunction and neuropsychological alterations affecting memory. This study aimed to assess OLM in a group of Long-COVID patients, n=66, and a Control group of healthy individuals with similar age and sex composition, n=21, using an immersive virtual reality (iVR)-based OLM task. We also explored associations between the performance in the iVR-based OLM task and general cognitive function (MoCA), and both verbal (VSTM) and visuospatial (SSTM) span. The Long-COVID group showed fewer correct responses, made more task attempts, and invested more time in the iVR-based OLM task than the Control group. Delayed memory was more severely altered than immediate memory in Long-COVID participants. Better MoCA scores of the Long-COVID group were strongly associated with shorter times to complete the immediate recall of the iVR-based OLM task. Besides, the months elapsed since the COVID-19 infection were slightly associated with fewer correct responses in the immediate and 24-hour recalls. These results corroborate previous findings of memory alterations in the Long-COVID syndrome using an iVR-based OLM task, adding new evidence on spatial memory and long-term memory in this population. Implementing spatial iVR tasks to clinical research may improve our understanding of neuropsychological disorders.

Aberrant glutamatergic systems underlying impulsive behaviors: Insights from clinical and preclinical research

Impulsivity is a broad construct that often refers to one of several distinct behaviors and can be measured with self-report questionnaires and behavioral paradigms. Several psychiatric conditions are characterized by one or more forms of impulsive behavior, most notably the impulsive/hyperactive subtype of attention-deficit/hyperactivity disorder (ADHD), mood disorders, and substance use disorders. Monoaminergic neurotransmitters are known to mediate impulsive behaviors and are implicated in various psychiatric conditions. However, growing evidence suggests that glutamate, the major excitatory neurotransmitter of the mammalian brain, regulates important functions that become dysregulated in conditions like ADHD. The purpose of the current review is to discuss clinical and preclinical evidence linking glutamate to separate aspects of impulsivity, specifically motor impulsivity, impulsive choice, and affective impulsivity. Hyperactive glutamatergic activity in the corticostriatal and the cerebro-cerebellar pathways are major determinants of motor impulsivity. Conversely, hypoactive glutamatergic activity in frontal cortical areas and hippocampus and hyperactive glutamatergic activity in anterior cingulate cortex and nucleus accumbens mediate impulsive choice. Affective impulsivity is controlled by similar glutamatergic dysfunction observed for motor impulsivity, except a hyperactive limbic system is also involved. Loss of glutamate homeostasis in prefrontal and nucleus accumbens may contribute to motor impulsivity/affective impulsivity and impulsive choice, respectively. These results are important as they can lead to novel treatments for those with a condition characterized by increased impulsivity that are resistant to conventional treatments.

Enhancing and advancing the understanding and study of dreaming and memory consolidation: Reflections, challenges, theoretical clarity, and methodological considerations

Empirical investigations that search for a link between dreaming and sleep-dependent memory consolidation have focused on testing for an association between dreaming of what was learned, and improved memory performance for learned material. Empirical support for this is mixed, perhaps owing to the inherent challenges presented by the nature of dreams, and methodological inconsistencies. The purpose of this paper is to address critically prevalent assumptions and practices, with the aim of clarifying and enhancing research on this topic, chiefly by providing a theoretical synthesis of existing models and evidence. Also, it recommends the method of Targeted Memory Reactivation (TMR) as a means for investigating if dream content can be linked to specific cued activations. Other recommendations to enhance research practice and enquiry on this subject are also provided, focusing on the HOW and WHY we search for memory sources in dreams, and what purpose (if any) they might serve.

Physical Activity and Children's Episodic Memory: A Meta-Analysis

PURPOSE

The purpose of this review was to evaluate the effects of physical activity on children's free recall, cued recall, and recognition episodic memory and to explore potential moderating factors.

METHODS

The following databases were searched: PubMed, ERIC, APA Psych Info, CINHAL, SPORTDiscus, and Google Scholar. Studies were included if: (1) participants were aged 4-18 years, (2) participants were typically developed, (3) participants were randomized to groups, (4) interventions employed gross movements, (5) sedentary group was used for control, (6) memory tests were quantitative, and (7) employed acute or chronic intervention.

RESULTS

14 studies met inclusion criteria resulting in the analysis of data from 7 free recall, 7 cued recall, and 8 recognition memory tests. Physical activity was found to have a positive influence on tests free (g = 0.56), cued recall (g = 0.67), and no influence on tests of recognition (g = 0.06). While some moderator analyses were significant, the authors do not consider these results to be meaningful in application.

CONCLUSIONS

The effects of acute and chronic physical activity enhance specific aspects of long-term episodic memory. These findings suggest physical activity interventions developed for children may be expected to benefit some, but not all, types of memory processing.

Harnessing the frontal aslant tract's structure to assess its involvement in cognitive functions: new insights from 7-T diffusion imaging

The first therapeutical goal followed by neurooncological surgeons dealing with prefrontal gliomas is attempting supramarginal tumor resection preserving relevant neurological function. Therefore, advanced knowledge of the frontal aslant tract (FAT) functional neuroanatomy in high-order cognitive domains beyond language and speech processing would help refine neurosurgeries, predicting possible relevant cognitive adverse events and maximizing the surgical efficacy. To this aim we performed the recently developed correlational tractography analyses to evaluate the possible relationship between FAT's microstructural properties and cognitive functions in 27 healthy subjects having ultra-high-field (7-Tesla) diffusion MRI. We independently assessed FAT segments innervating the dorsolateral prefrontal cortices (dlPFC-FAT) and the supplementary motor area (SMA-FAT). FAT microstructural robustness, measured by the tract's quantitative anisotropy (QA), was associated with a better performance in episodic memory, visuospatial orientation, cognitive processing speed and fluid intelligence but not sustained selective attention tests. Overall, the percentual tract volume showing an association between QA-index and improved cognitive scores (pQACV) was higher in the SMA-FAT compared to the dlPFC-FAT segment. This effect was right-lateralized for verbal episodic memory and fluid intelligence and bilateralized for visuospatial orientation and cognitive processing speed. Our results provide novel evidence for a functional specialization of the FAT beyond the known in language and speech processing, particularly its involvement in several higher-order cognitive domains. In light of these findings, further research should be encouraged to focus on neurocognitive deficits and their impact on patient outcomes after FAT damage, especially in the context of glioma surgery.

Synaptic weight dynamics underlying memory consolidation: implications for learning rules, circuit organization, and circuit function

Systems consolidation is a common feature of learning and memory systems, in which a long-term memory initially stored in one brain region becomes persistently stored in another region. We studied the dynamics of systems consolidation in simple circuit architectures with two sites of plasticity, one in an early-learning and one in a late-learning brain area. We show that the synaptic dynamics of the circuit during consolidation of an analog memory can be understood as a temporal integration process, by which transient changes in activity driven by plasticity in the early-learning area are accumulated into persistent synaptic changes at the late-learning site. This simple principle naturally leads to a speed-accuracy tradeoff in systems consolidation and provides insight into how the circuit mitigates the stability-plasticity dilemma of storing new memories while preserving core features of older ones. Furthermore, it imposes two constraints on the circuit. First, the plasticity rule at the late-learning site must stably support a continuum of possible outputs for a given input. We show that this is readily achieved by heterosynaptic but not standard Hebbian rules. Second, to turn off the consolidation process and prevent erroneous changes at the late-learning site, neural activity in the early-learning area must be reset to its baseline activity. We propose two biologically plausible implementations for this reset that suggest novel roles for core elements of the cerebellar circuit.

Significance Statement

How are memories transformed over time? We propose a simple organizing principle for how long term memories are moved from an initial to a final site of storage. We show that successful transfer occurs when the late site of memory storage is endowed with synaptic plasticity rules that stably accumulate changes in activity occurring at the early site of memory storage. We instantiate this principle in a simple computational model that is representative of brain circuits underlying a variety of behaviors. The model suggests how a neural circuit can store new memories while preserving core features of older ones, and suggests novel roles for core elements of the cerebellar circuit.

Temporal gamma tACS and auditory stimulation affect verbal memory in healthy adults

Research suggests a potential of gamma oscillation entrainment for enhancing memory in Alzheimer's disease and healthy subjects. Gamma entrainment can be accomplished with oscillatory electrical, but also sensory stimulation. However, comparative studies between sensory stimulation and transcranial alternating current stimulation (tACS) effects on memory processes are lacking. This study examined the effects of rhythmic gamma auditory stimulation (rAS) and temporal gamma-tACS on verbal long-term memory (LTM) and working memory (WM) in 74 healthy individuals. Participants were assigned to two groups according to the stimulation techniques (rAS or tACS). Memory was assessed in three experimental blocks, in which each participant was administered with control, 40, and 60 Hz stimulation in counterbalanced order. All interventions were well-tolerated, and participants reported mostly comparable side effects between real stimulation (40 and 60 Hz) and the control condition. LTM immediate and delayed recall remained unaffected by stimulations, while immediate recall intrusions decreased during 60 Hz stimulation. Notably, 40 Hz interventions improved WM compared to control stimulations. These results highlight the potential of 60 and 40 Hz temporal cortex stimulation for reducing immediate LTM recall intrusions and improving WM performance, respectively, probably due to the entrainment of specific gamma oscillations in the auditory cortex. The results also shed light on the comparative effects of these neuromodulation tools on memory functions, and their potential applications for cognitive enhancement and in clinical trials.

Distributional Learning and Overnight Consolidation of Nonnative Tonal Contrasts by Tonal Language Speakers

PURPOSE

Previous studies have reported the success of distributional learning for adult speakers across segmental and suprasegmental categories immediately after training. On the other hand, second language (L2) perception models posit that the ease with which learners perceive a nonnative speech contrast depends on the perceptual mapping between the contrast and learners' first language (L1) categories. This study examined whether a difference in perceptual mapping patterns for different L2-Mandarin tonal contrasts might result in a difference in distributional learning effectiveness for tonal speakers and whether an interval of sleep enhanced the knowledge through consolidation.

METHOD

Following a pretest-training-posttest design, 66 L1-Cantonese participants with fewer than 9 years of Mandarin training were assigned to either the bimodal or unimodal distribution conditions. The participants of each group were asked to discriminate Mandarin level-falling (T1-T4) and level-rising (T1-T2) tone pairs on novel syllables in a within-subject design. All participants were trained in the evening, tested after training, and returned after 12 hr for overnight consolidation assessment.

RESULTS

A significant distributional learning effect was observed for Mandarin T1-T4, but only after sleep. No significant distributional learning effect was observed for Mandarin T1-T2, either after training or after sleep.

CONCLUSIONS

The findings may imply that distributional learning is contingent on perceptual mapping patterns of the target contrasts and that sleep may play a role in the consolidation of knowledge in an implicit statistical learning paradigm.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.25970008.

The hippocampus supports precise memory for public events regardless of their remoteness

The necessity of the human hippocampus and surrounding medial temporal lobe structures to semantic memory remains contentious. Impaired semantic memory following hippocampal lesions could arise either due to partially intertwined episodic memories and/or retrograde/anterograde effects. In this study, we tested amnesic individuals with lesions in hippocampus and surrounding medial temporal lobe (n = 7) and age-matched controls (n = 14) on their ability to precisely recall the dates of famous public events that occurred either before (i.e., pre-lifetime) or after participants' birth date (lifetime). We show that deficits in dating precision are greatest for recent lifetime events, consistent with the notion that recent event memory may be particularly intertwined with episodic memory. At the same time, individuals with medial temporal lobe lesions showed more subtle impairments in their ability to date pre-birth and remote lifetime events precisely. Together, these findings suggest that the hippocampus and surrounding medial temporal lobe structures are important for representational precision of semantic memories regardless of their remoteness.

Affective music during episodic memory recollection modulates subsequent false emotional memory traces: an fMRI study

Music is a powerful medium that influences our emotions and memories. Neuroscience research has demonstrated music's ability to engage brain regions associated with emotion, reward, motivation, and autobiographical memory. While music's role in modulating emotions has been explored extensively, our study investigates whether music can alter the emotional content of memories. Building on the theory that memories can be updated upon retrieval, we tested whether introducing emotional music during memory recollection might introduce false emotional elements into the original memory trace. We developed a 3-day episodic memory task with separate encoding, recollection, and retrieval phases. Our primary hypothesis was that emotional music played during memory recollection would increase the likelihood of introducing novel emotional components into the original memory. Behavioral findings revealed two key outcomes: 1) participants exposed to music during memory recollection were more likely to incorporate novel emotional components congruent with the paired music valence, and 2) memories retrieved 1 day later exhibited a stronger emotional tone than the original memory, congruent with the valence of the music paired during the previous day's recollection. Furthermore, fMRI results revealed altered neural engagement during story recollection with music, including the amygdala, anterior hippocampus, and inferior parietal lobule. Enhanced connectivity between the amygdala and other brain regions, including the frontal and visual cortex, was observed during recollection with music, potentially contributing to more emotionally charged story reconstructions. These findings illuminate the interplay between music, emotion, and memory, offering insights into the consequences of infusing emotional music into memory recollection processes.

A theory of hippocampal function: New developments

We develop further here the only quantitative theory of the storage of information in the hippocampal episodic memory system and its recall back to the neocortex. The theory is upgraded to account for a revolution in understanding of spatial representations in the primate, including human, hippocampus, that go beyond the place where the individual is located, to the location being viewed in a scene. This is fundamental to much primate episodic memory and navigation: functions supported in humans by pathways that build 'where' spatial view representations by feature combinations in a ventromedial visual cortical stream, separate from those for 'what' object and face information to the inferior temporal visual cortex, and for reward information from the orbitofrontal cortex. Key new computational developments include the capacity of the CA3 attractor network for storing whole charts of space; how the correlations inherent in self-organizing continuous spatial representations impact the storage capacity; how the CA3 network can combine continuous spatial and discrete object and reward representations; the roles of the rewards that reach the hippocampus in the later consolidation into long-term memory in part via cholinergic pathways from the orbitofrontal cortex; and new ways of analysing neocortical information storage using Potts networks.

Potential role of oxytocin in the regulation of memories and treatment of memory disorders

Oxytocin (OXT) is an "affiliative" hormone or neurohormone or neuropeptide consists of nine amino acids, synthesized in magnocellular neurons of paraventricular (PVN) and supraoptic nuclei (SON) of hypothalamus. OXT receptors are widely distributed in various region of brain and OXT has been shown to regulate various social and nonsocial behavior. Hippocampus is the main region which regulates the learning and memory. Hippocampus particularly regulates the acquisition of new memories and retention of acquired memories. OXT has been shown to regulate the synaptic plasticity, neurogenesis, and consolidation of memories. Further, findings from both preclinical and clinical studies have suggested that the OXT treatment improves performance in memory related task. Various trials have suggested the positive impact of intranasal OXT in the dementia patients. However, these studies are limited in number. In the present study authors have highlighted the role of OXT in the formation and retrieval of memories. Further, the study demonstrated the outcome of OXT treatment in various memory and related disorders.

A personalized semi-automatic sleep spindle detection (PSASD) framework

BACKGROUND

Sleep spindles are distinct electroencephalogram (EEG) patterns of brain activity that have been posited to play a critical role in development, learning, and neurological disorders. Manual scoring for sleep spindles is labor-intensive and tedious but could supplement automated algorithms to resolve challenges posed with either approaches alone.

NEW METHODS

A Personalized Semi-Automatic Sleep Spindle Detection (PSASD) framework was developed to combine the strength of automated detection algorithms and visual expertise of human scorers. The underlying model in the PSASD framework assumes a generative model for EEG sleep spindles as oscillatory components, optimized to EEG amplitude, with remaining signals distributed into transient and low-frequency components.

RESULTS

A single graphical user interface (GUI) allows both manual scoring of sleep spindles (model training data) and verification of automatically detected spindles. A grid search approach allows optimization of parameters to balance tradeoffs between precision and recall measures.

COMPARISON WITH EXISTING METHODS

PSASD outperformed DETOKS in F1-score by 19% and 4% on the DREAMS and P-DROWS-E datasets, respectively. It also outperformed YASA in F1-score by 25% in the P-DROWS-E dataset. Further benchmarking analysis showed that PSASD outperformed four additional widely used sleep spindle detectors in F1-score in the P-DROWS-E dataset. Titration analysis revealed that four 30-second epochs are sufficient to fine-tune the model parameters of PSASD. Associations of frequency, duration, and amplitude of detected sleep spindles matched those previously reported with automated approaches.

CONCLUSIONS

Overall, PSASD improves detection of sleep spindles in EEG data acquired from both younger healthy and older adult patient populations.

A memory access gate controlled by dynamic contexts

Temporary difficulties in accessing the contents of memories are a common experience in everyday life, for example, when we try to recognize a known person in an unusual context. In addition, recent experiments seem to indicate that retrograde amnesia in the early stages of Alzheimer's disease is due to disorders in accessing memories that were installed normally. These facts suggest the existence of an intermediate step between the stimulus arrival and the associative recognition. In this work, a multimodular neurocomputational model is presented postulating the existence of a neural gate that controls the access of the stimulus with its context to the consolidated memory. If recognition is not achieved, a random search is initiated in a contextual network aroused by the initial context. The search continues until the appropriate context that allows for recognition is found or until the process is turned off because the initial stimulus is no longer maintained in the working memory. The model is based on vector patterns of neural activity and context-dependent matrix memories. Simple Markov chain simulations are presented to exemplify possible search scenarios in the contextual network. Finally, we discuss some of the characteristics of the model and the phenomenon under study.

Shorter sleep duration and lesser sleep efficiency are associated with poorer memory functions among non-demented, middle-aged, and older rural Indians

Introduction

Sleep is known to be involved in cognitive processes, such as memory encoding and consolidation, and poor sleep is a potential risk factor for dementia. This study aims to investigate the effect of sleep quality on memory functions among middle-aged and older adults from a rural Indian population.

Methods

Participants were non-demented, rural Indians (≥45 years) from an ongoing, prospective, aging cohort study, namely Srinivaspura Aging, NeuroSenescence, and COGnition (SANSCOG) study. Cross-sectional (baseline) data on seven sleep dimensions was obtained using the Pittsburgh Sleep Quality Index (PSQI). Memory functions were assessed using immediate recall, delayed recall, name-face association, and semantic association from a culturally validated, computerized, neurocognitive test battery. Linear regression models, unadjusted and adjusted for cognitive status, age, sex, and depression were used to analyze the association between each sleep dimension and the memory tests.

Results

A total of 1195 participants, with a mean age of 57.10 years, were included. Out of the seven sleep dimensions of the PSQI, only two dimensions, namely sleep duration and sleep efficiency, were significantly associated with memory functions. In the fully adjusted model, shorter sleep duration was significantly associated with poorer performance in delayed recall, and lesser sleep efficiency was significantly associated with poorer delayed recall and semantic association performance.

Conclusions

Specific sleep characteristics appear to influence memory functions in aging Indians well before the onset of dementia. In the backdrop of the non-availability of a definitive treatment for dementia, promptly identifying and addressing these problems could be an effective, community-level strategy for preventing dementia.

Using Team-Based Learning to Teach Pharmacology within the Medical Curriculum

The primary goal of pharmacology teaching is to prepare medical students to prescribe medications both safely and efficiently. At the Utrecht University Medical School, pharmacology is integrated into the three-year bachelor's curriculum, primarily through large group sessions with limited interaction. A recent evaluation highlighted students' appreciation for pharmacology teaching, but students admitted to attending these teaching moments unprepared, resulting in passive learning. To address this, team-based learning (TBL) was implemented to facilitate learning through interaction, critical thinking, problem solving and reflection through six steps, from superficial to deeper cognitive learning. This study, conducted over two academic years, assessed students' perception and performance regarding TBL. Analysis of a digital questionnaire using a 5-point Likert scale showed high student satisfaction with TBL as a teaching methodology. However, confidence in pharmacology knowledge following TBL was moderate. TBL attendees outperformed non-attendees in pharmacology-related exam questions, indicating that TBL has a positive impact on student performance. We conclude that TBL is an engaging and effective method for pharmacology education, positively influencing student learning and performance. This method could be broadly applied for teaching pharmacology within the medical curriculum or other biomedical programs.

The importance of covert memory consolidation in schizophrenia: Dysfunctional network profiles of the hippocampus and the dorsolateral prefrontal cortex

Altered brain network profiles in schizophrenia (SCZ) during memory consolidation are typically observed during task-active periods such as encoding or retrieval. However active processes are also sub served by covert periods of memory consolidation. These periods are active in that they allow memories to be recapitulated even in the absence of overt sensorimotor processing. It is plausible that regions central to memory formation like the dlPFC and the hippocampus, exert network signatures during covert periods. Are these signatures altered in patients? The question is clinically relevant because real world learning and memory is facilitated by covert processing, and may be impaired in schizophrenia. Here, we compared network signatures of the dlPFC and the hippocampus during covert periods of a learning and memory task. Because behavioral proficiency increased non-linearly, functional connectivity of the dlPFC and hippocampus [psychophysiological interaction (PPI)] was estimated for each of the Early (linear increases in performance) and Late (asymptotic performance) covert periods. During Early periods, we observed hypo-modulation by the hippocampus but hyper-modulation by dlPFC. Conversely, during Late periods, we observed hypo-modulation by both the dlPFC and the hippocampus. We stitch these results into a conceptual model of network deficits during covert periods of memory consolidation.

Protective role of Eugenol against the destructive effects of lead on conditioned fear memory in male rats with post-traumatic stress disorder-related behavioral traits

Introduction

Post-traumatic stress disorder (PTSD) is a consequence of living in today's stressful society. Patients have difficulty forgetting traumatic events. lead pollution has many effects on the nervous system, one of which is memory and learning disorders. The herbal medicine Eugenol has a beneficial effect on memory.

Aim

This study aims to investigate the protective effect of Eugenol on lead-induced memory impairments in stressed rats.

Methods

In the first experiment, the animals were divided into three groups: SPS+Saline, SPS+Pb, and naïve. The SPS+Saline, SPS+Pb groups received normal saline and lead through gavage for 21 days, while the sham group remained untreated. Rats were subjected to the modified single prolonged stress model. Memory tests were conducted one week later, evaluating freezing levels in three consecutive tests over three days. In the second experiment, rats were divided into a SPS+Pb+Saline and three treatment groups. The SPS+Pb+Saline group received daily saline injections, while the other groups received different doses of Eugenol (25, 50, and 100 mg/kg). Memory tests similar to the first experiment were conducted.

Results

The results showed significantly higher immobility levels in the SPS+Saline and SPS+Pb groups compared to the sham. Additionally, the SPS+Pb group had a significant higher immobility compared to the SPS+Saline group. In the second experiment, the SPS+Pb+EU 25 group showed a significant lower freezing compared to the SPS+Pb+Saline group. Additionally, freezing in the SPS+Pb+EU 50 and SPS+Pb+EU 100 groups was significantly higher than in the SPS+Pb+EU 25 group. The SPS+Pb+EU 50 group showed a significant higher freezing compared to the SPS+Pb+Saline group.

Conclusion

lead acetate exacerbated memory impairments in stressed rats and Eugenol, particularly at a dose of 25 mg/kg, improved these impairments. Therefore, Eugenol has the potential to partially reduce the negative effects of lead on memory in individuals with PTSD.

Early- and Late-Onset Alzheimer's Disease: Two Sides of the Same Coin?

Early-onset Alzheimer's disease (EOAD), defined as Alzheimer's disease onset before 65 years of age, has been significantly less studied than the "classic" late-onset form (LOAD), although EOAD often presents with a more aggressive disease course, caused by variants in the APP, PSEN1, and PSEN2 genes. EOAD has significant differences from LOAD, including encompassing diverse phenotypic manifestations, increased genetic predisposition, and variations in neuropathological burden and distribution. Phenotypically, EOAD can be manifested with non-amnestic variants, sparing the hippocampi with increased tau burden. The aim of this article is to review the different genetic bases, risk factors, pathological mechanisms, and diagnostic approaches between EOAD and LOAD and to suggest steps to further our understanding. The comprehension of the monogenic form of the disease can provide valuable insights that may serve as a roadmap for understanding the common form of the disease.

Integrating and fragmenting memories under stress and alcohol

Stress can powerfully influence the way we form memories, particularly the extent to which they are integrated or situated within an underlying spatiotemporal and broader knowledge architecture. These different representations in turn have significant consequences for the way we use these memories to guide later behavior. Puzzlingly, although stress has historically been argued to promote fragmentation, leading to disjoint memory representations, more recent work suggests that stress can also facilitate memory binding and integration. Understanding the circumstances under which stress fosters integration will be key to resolving this discrepancy and unpacking the mechanisms by which stress can shape later behavior. Here, we examine memory integration at multiple levels: linking together the content of an individual experience, threading associations between related but distinct events, and binding an experience into a pre-existing schema or sense of causal structure. We discuss neural and cognitive mechanisms underlying each form of integration as well as findings regarding how stress, aversive learning, and negative affect can modulate each. In this analysis, we uncover that stress can indeed promote each level of integration. We also show how memory integration may apply to understanding effects of alcohol, highlighting extant clinical and preclinical findings and opportunities for further investigation. Finally, we consider the implications of integration and fragmentation for later memory-guided behavior, and the importance of understanding which type of memory representation is potentiated in order to design appropriate interventions.

Memory alterations after COVID-19 infection: a systematic review

SARS-CoV-2 infection has a wide range of both acute and long-term symptoms. Memory alterations have been frequently reported in studies that explore cognition. The main objective of the systematic review is to update and further analyze the existing evidence of objective memory impairments in long-COVID-19 considering sample and study design characteristics, as well as to explore associations between memory performance and their epidemiological, clinical, and pathological features. A total of 13 studies were identified by searching in PubMed, Web of Science, and PsycInfo databases up to May 6, 2022. Most studies evaluated verbal component of memory in the short-term and long-term recall up to 30 min and mainly performed a single assessment completed at 4-6 months after the infection. The samples mainly consisted of middle-aged adults that required hospitalization. Samples were not stratified by sex, age, and severity. Poor verbal learning was reported in most cases (6-58%), followed by deficits in long-term (4-58%) and short-term (4-37%) verbal memory. Visuospatial component of memory was studied less than verbal component, showing impairment of long-term retention of visual items (10-49%). COVID-19 severity in the acute stage was not systematically associated with poor memory performance. Verbal memory deficits were associated with anxiety and depression. The existing literature on objective memory assessment in long-COVID suggests further research is warranted to confirm memory dysfunction in association with epidemiological, pathological, and clinical factors, using both verbal and visuospatial tests, and exploring in deep long-term memory deficits.

Synchronous excitation in the superficial and deep layers of the medial entorhinal cortex precedes early sharp waves in the neonatal rat hippocampus

Early Sharp Waves (eSPWs) are the earliest pattern of network activity in the developing hippocampus of neonatal rodents. eSPWs were originally considered to be an immature prototype of adult SPWs, which are spontaneous top-down hippocampal events that are self-generated in the hippocampal circuitry. However, recent studies have shifted this paradigm to a bottom-up model of eSPW genesis, in which eSPWs are primarily driven by the inputs from the layers 2/3 of the medial entorhinal cortex (MEC). A hallmark of the adult SPWs is the relay of information from the CA1 hippocampus to target structures, including deep layers of the EC. Whether and how deep layers of the MEC are activated during eSPWs in the neonates remains elusive. In this study, we investigated activity in layer 5 of the MEC of neonatal rat pups during eSPWs using silicone probe recordings from the MEC and CA1 hippocampus. We found that neurons in deep and superficial layers of the MEC fire synchronously during MEC sharp potentials, and that neuronal firing in both superficial and deep layers of the MEC precedes the activation of CA1 neurons during eSPWs. Thus, the sequence of activation of CA1 hippocampal neurons and deep EC neurons during sharp waves reverses during development, from a lead of deep EC neurons during eSPWs in neonates to a lead of CA1 neurons during adult SPWs. These findings suggest another important difference in the generative mechanisms and possible functional roles of eSPWs compared to adult SPWs.

Neurobiological mechanisms underlying oxytocin-mediated parental behavior in rodents

Parental behavior is essential for mammalian offspring to survive. Because of this significance, elucidating the neurobiological mechanisms that facilitate parental behavior has received strong interest. Decades of studies utilizing pharmacology and molecular biology have revealed that in addition to its facilitatory effects on parturition and lactation, oxytocin (OT) promotes the expression of parental behavior in rodents. Recent studies have also described the modulation of sensory processing by OT and the interaction of the OT system with other brain regions associated with parental behavior. However, the precise neurobiological mechanisms underlying the facilitation of caregiving behaviors by OT remain unclear. In this Review, I summarize the findings from rats and mice with a view toward integrating past and recent progress. I then review recent advances in the understanding of the molecular, cellular, and circuit mechanisms of OT-mediated parental behavior. Based on these observations, I propose a hypothetical model that would explain the mechanisms underlying OT-mediated parental behavior. Finally, I conclude by discussing some major remaining questions and propose potential future research directions.

Dramatic changes to well-known places go unnoticed

How well do we know our city? It turns out, much more poorly than we might imagine. We used declarative memory and eye-tracking techniques to examine people's ability to detect modifications to real-world landmarks and scenes in Toronto locales with which they have had extensive experience. Participants were poor at identifying which scenes contained altered landmarks, whether the modification was to the landmarks' relative size, internal features, or relation to surrounding context. To determine whether an indirect measure would prove more sensitive, we tracked eye movements during viewing. Changes in overall visual exploration, but not to specific regions of change, were related to participants' explicit endorsement of scenes as modified. These results support the contention that very familiar landmarks are represented at a global or gist level, but not local or fine-grained, level. These findings offer a unified view of memory for gist across verbal and spatial domains, and across recent and remote memory, with implications for hippocampal-neocortical interactions.

Beyond hippocampus: Thalamic and prefrontal contributions to an evolving memory

The hippocampus has long been at the center of memory research, and rightfully so. However, with emerging technological capabilities, we can increasingly appreciate memory as a more dynamic and brain-wide process. In this perspective, our goal is to begin developing models to understand the gradual evolution, reorganization, and stabilization of memories across the brain after their initial formation in the hippocampus. By synthesizing studies across the rodent and human literature, we suggest that as memory representations initially form in hippocampus, parallel traces emerge in frontal cortex that cue memory recall, and as they mature, with sustained support initially from limbic then diencephalic then cortical circuits, they become progressively independent of hippocampus and dependent on a mature cortical representation. A key feature of this model is that, as time progresses, memory representations are passed on to distinct circuits with progressively longer time constants, providing the opportunity to filter, forget, update, or reorganize memories in the process of committing to long-term storage.

Psychedelics for alzheimer's disease-related dementia: Unveiling therapeutic possibilities and pathways

Psychedelics have traditionally been used for spiritual and recreational purposes, but recent developments in psychotherapy have highlighted their potential as therapeutic agents. These compounds, which act as potent 5-hydroxytryptamine (5HT) agonists, have been recognized for their ability to enhance neural plasticity through the activation of the serotoninergic and glutamatergic systems. However, the implications of these findings for the treatment of neurodegenerative disorders, particularly dementia, have not been fully explored. In recent years, studies have revealed the modulatory and beneficial effects of psychedelics in the context of dementia, specifically Alzheimer's disease (AD)-related dementia, which lacks a definitive cure. Psychedelics such as N,N-dimethyltryptamine (DMT), lysergic acid diethylamide (LSD), and Psilocybin have shown potential in mitigating the effects of this debilitating disease. These compounds not only target neurotransmitter imbalances but also act at the molecular level to modulate signalling pathways in AD, including the brain-derived neurotrophic factor signalling pathway and the subsequent activation of mammalian target of rapamycin and other autophagy regulators. Therefore, the controlled and dose-dependent administration of psychedelics represents a novel therapeutic intervention worth exploring and considering for the development of drugs for the treatment of AD-related dementia. In this article, we critically examined the literature that sheds light on the therapeutic possibilities and pathways of psychedelics for AD-related dementia. While this emerging field of research holds great promise, further studies are necessary to elucidate the long-term safety, efficacy, and optimal treatment protocols. Ultimately, the integration of psychedelics into the current treatment paradigm may provide a transformative approach for addressing the unmet needs of individuals living with AD-related dementia and their caregivers.

Is there selective retroactive memory enhancement in humans?: a meta-analysis

Memory is an adaptive and flexible system that preferentially stores motivationally relevant information. However, in some cases information that is initially irrelevant can become relevant at a later time. The question arises whether and to what extent the memory system can retroactively boost memories of the initially irrelevant information. Experimental studies in animals and humans have provided evidence for such retroactive memory boosting. Additionally, these studies suggest that retroactive memory enhancement (RME) can be selective to the semantic meaning of the material. Nonetheless, recent experimental work could not replicate these findings, posing the question whether the selective RME effect is reliable. To synthesize the available evidence, we conducted meta-analyses of 14 experiments. Although the classical meta-analytic procedure suggested a small selective RME effect, Cohen's dz = 0.16, when accounting for small-study bias using robust Bayesian meta-analysis the null hypothesis was supported, Cohen's dz = 0.02, BF01 = 3.03. Furthermore strong evidence was found for a bias due to small-study effects, BF10 = 11.39. Together, this calls the reliability of a selective RME effect into question.

Disruption of awake sharp-wave ripples does not affect memorization of locations in repeated-acquisition spatial memory tasks

Storing and accessing memories is required to successfully perform day-to-day tasks, for example for engaging in a meaningful conversation. Previous studies in both rodents and primates have correlated hippocampal cellular activity with behavioral expression of memory. A key role has been attributed to awake hippocampal replay - a sequential reactivation of neurons representing a trajectory through space. However, it is unclear if awake replay impacts immediate future behavior, gradually creates and stabilizes long-term memories over a long period of time (hours and longer), or enables the temporary memorization of relevant events at an intermediate time scale (seconds to minutes). In this study, we aimed to address the uncertainty around the timeframe of impact of awake replay by collecting causal evidence from behaving rats. We detected and disrupted sharp wave ripples (SWRs) - signatures of putative replay events - using electrical stimulation of the ventral hippocampal commissure in rats that were trained on three different spatial memory tasks. In each task, rats were required to memorize a new set of locations in each trial or each daily session. Interestingly, the rats performed equally well with or without SWR disruptions. These data suggest that awake SWRs - and potentially replay - does not affect the immediate behavior nor the temporary memorization of relevant events at a short timescale that are required to successfully perform the spatial tasks. Based on these results, we hypothesize that the impact of awake replay on memory and behavior is long-term and cumulative over time.

Cannabidiol modulates hippocampal genes involved in mitochondrial function, ribosome biogenesis, synapse organization, and chromatin modifications

BACKGROUND

Cannabidiol (CBD) is one of the main cannabinoids present in Cannabis sativa female flowers. Previous investigation has already provided insights into the CBD molecular mechanism; however, there is no transcriptome data for CBD effects on hippocampal subfields. Here, we investigate transcriptomic changes in dorsal and ventral CA1 of adult mice hippocampus after 100 mg/kg of CBD administration (i.p.) for one or seven consecutive days.

METHODS

C57BL/6JUnib mice were treated with either vehicle or CBD for 1 or 7 days. The collected brains were sectioned, and the hippocampal sub-regions were laser microdissected for RNA-Seq analysis.

RESULTS

The transcriptome analysis following 7 days of CBD administration indicates the differential expression of 1559 genes in dCA1 and 2924 genes in vCA1. Furthermore, GO/KEGG analysis identified 88 significantly enriched biological process and 26 significantly enriched pathways for dCBD7, whereas vCBD7 revealed 128 enriched BPs and 24 pathways.

CONCLUSION

This dataset indicates a widespread decrease of electron transport chain and ribosome biogenesis transcripts in CA1, while chromatin modifications and synapse organization transcripts were increased following CBD administration for 7 days.

Context memory formed in medial prefrontal cortex during infancy enhances learning in adulthood

Adult behavior is commonly thought to be shaped by early-life experience, although episodes experienced during infancy appear to be forgotten. Exposing male rats during infancy to discrete spatial experience we show that these rats in adulthood are significantly better at forming a spatial memory than control rats without such infantile experience. We moreover show that the adult rats' improved spatial memory capability is mainly based on memory for context information during the infantile experiences. Infantile spatial experience increased c-Fos activity at memory testing during adulthood in the prelimbic medial prefrontal cortex (mPFC), but not in the hippocampus. Inhibiting prelimbic mPFC at testing during adulthood abolished the enhancing effect of infantile spatial experience on learning. Adult spatial memory capability only benefitted from spatial experience occurring during the sensitive period of infancy, but not when occurring later during childhood, and when sleep followed the infantile experience. In conclusion, the infantile brain, by a sleep-dependent mechanism, favors consolidation of memory for the context in which episodes are experienced. These representations comprise mPFC regions and context-dependently facilitate learning in adulthood.

Remote memory in a Bayesian model of context fear conditioning (BaconREM)

Here, we propose a model of remote memory (BaconREM), which is an extension of a previously published Bayesian model of context fear learning (BACON) that accounts for many aspects of recently learned context fear. BaconREM simulates most known phenomenology of remote context fear as studied in rodents and makes new predictions. In particular, it predicts the well-known observation that fear that was conditioned to a recently encoded context becomes hippocampus-independent and shows much-enhanced generalization ("hyper-generalization") when systems consolidation occurs (i.e., when memory becomes remote). However, the model also predicts that there should be circumstances under which the generalizability of remote fear may not increase or even decrease. It also predicts the established finding that a "reminder" exposure to a feared context can abolish hyper-generalization while at the same time making remote fear again hippocampus-dependent. This observation has in the past been taken to suggest that reminders facilitate access to detail memory that remains permanently in the hippocampus even after systems consolidation is complete. However, the present model simulates this result even though it totally moves all the contextual memory that it retains to the neo-cortex when context fear becomes remote.

Acute Angiotensin II Receptor Blockade Facilitates Parahippocampal Processing During Memory Encoding in High-Trait-Anxious Individuals

Background

Angiotensin II receptor blockers (ARBs) have been associated with preventing posttraumatic stress disorder symptom development and improving memory. However, the underlying neural mechanisms are poorly understood. This study investigated ARB effects on memory encoding and hippocampal functioning that have previously been implicated in posttraumatic stress disorder development.

Methods

In a double-blind randomized design, 40 high-trait-anxious participants (33 women) received the ARB losartan (50 mg) or placebo. At drug peak level, participants encoded images of animals and landscapes before undergoing functional magnetic resonance imaging, where they viewed the encoded familiar images and unseen novel images to be memorized and classified as animals/landscapes. Memory recognition was assessed 1 hour after functional magnetic resonance imaging. To analyze neural effects, whole-brain analysis, hippocampus region-of-interest analysis, and exploratory multivariate pattern similarity analysis were employed.

Results

ARBs facilitated parahippocampal processing. In the whole-brain analysis, losartan enhanced brain activity for familiar images in the parahippocampal gyrus (PHC), anterior cingulate cortex, and caudate. For novel images, losartan enhanced brain activity in the PHC only. Pattern similarity analysis showed that losartan increased neural stability in the PHC when processing novel and familiar images. However, there were no drug effects on memory recognition or hippocampal activation.

Conclusions

Given that the hippocampus receives major input from the PHC, our findings suggest that ARBs may modulate higher-order visual processing through parahippocampal involvement, potentially preserving intact memory input. Future research needs to directly investigate whether this effect may underlie the preventive effects of ARBs in the development of posttraumatic stress disorder.

New in, old out: Does learning a new language make you forget previously learned foreign languages?

Anecdotal evidence suggests that learning a new foreign language (FL) makes you forget previously learned FLs. To seek empirical evidence for this claim, we tested whether learning words in a previously unknown L3 hampers subsequent retrieval of their L2 translation equivalents. In two experiments, Dutch native speakers with knowledge of English (L2), but not Spanish (L3), first completed an English vocabulary test, based on which 46 participant-specific, known English words were chosen. Half of those were then learned in Spanish. Finally, participants' memory for all 46 English words was probed again in a picture naming task. In Experiment 1, all tests took place within one session. In Experiment 2, we separated the English pre-test from Spanish learning by a day and manipulated the timing of the English post-test (immediately after learning vs. 1 day later). By separating the post-test from Spanish learning, we asked whether consolidation of the new Spanish words would increase their interference strength. We found significant main effects of interference in naming latencies and accuracy: Participants speeded up less and were less accurate to recall words in English for which they had learned Spanish translations, compared with words for which they had not. Consolidation time did not significantly affect these interference effects. Thus, learning a new language indeed comes at the cost of subsequent retrieval ability in other FLs. Such interference effects set in immediately after learning and do not need time to emerge, even when the other FL has been known for a long time.

Memory consolidation drives the enhancement of remote cocaine memory via prefrontal circuit

Remote memory usually decreases over time, whereas remote drug-cue associated memory exhibits enhancement, increasing the risk of relapse during abstinence. Memory system consolidation is a prerequisite for remote memory formation, but neurobiological underpinnings of the role of consolidation in the enhancement of remote drug memory are unclear. Here, we found that remote cocaine-cue associated memory was enhanced in rats that underwent self-administration training, together with a progressive increase in the response of prelimbic cortex (PrL) CaMKII neurons to cues. System consolidation was required for the enhancement of remote cocaine memory through PrL CaMKII neurons during the early period post-training. Furthermore, dendritic spine maturation in the PrL relied on the basolateral amygdala (BLA) input during the early period of consolidation, contributing to remote memory enhancement. These findings indicate that memory consolidation drives the enhancement of remote cocaine memory through a time-dependent increase in activity and maturation of PrL CaMKII neurons receiving a sustained BLA input.

A generative model of memory construction and consolidation

Episodic memories are (re)constructed, share neural substrates with imagination, combine unique features with schema-based predictions and show schema-based distortions that increase with consolidation. Here we present a computational model in which hippocampal replay (from an autoassociative network) trains generative models (variational autoencoders) to (re)create sensory experiences from latent variable representations in entorhinal, medial prefrontal and anterolateral temporal cortices via the hippocampal formation. Simulations show effects of memory age and hippocampal lesions in agreement with previous models, but also provide mechanisms for semantic memory, imagination, episodic future thinking, relational inference and schema-based distortions including boundary extension. The model explains how unique sensory and predictable conceptual elements of memories are stored and reconstructed by efficiently combining both hippocampal and neocortical systems, optimizing the use of limited hippocampal storage for new and unusual information. Overall, we believe hippocampal replay training generative models provides a comprehensive account of memory construction, imagination and consolidation.

The formation of episodic autobiographical memory is predicted by mental imagery, self-reference, and anticipated details

Introduction

Despite the ecological nature of episodic memory (EM) and the importance of consolidation in its functioning, studies tackling both subjects are still scarce. Therefore, the present study aims at establishing predictions of the future of newly encoded information in EM in an ecological paradigm.

Methods

Participants recorded two personal events per day with a SenseCam portable camera, for 10 days, and characterized the events with different subjective scales (emotional valence and intensity, self-concept and self-relevance, perspective and anticipated details at a month, mental images…). They then performed a surprise free recall at 5 days and 1 month after encoding. Machine learning algorithms were used to predict the future of events (episodic or forgotten) in memory at 1 month.

Results

The best algorithm showed an accuracy of 78%, suggesting that such a prediction is reliably possible. Variables that best differentiated between episodic and forgotten memories at 1 month were mental imagery, self-reference, and prospection (anticipated details) at encoding and the first free recall.

Discussion

These results may establish the basis for the development of episodic autobiographical memory during daily experiences.

Highly Superior Autobiographical Memory (HSAM): A Systematic Review

Individuals possessing a Highly Superior Autobiographical Memory (HSAM) demonstrate an exceptional ability to recall their own past, excelling most when dates from their lifetime are used as retrieval cues. Fully understanding how neurocognitive mechanisms support exceptional memory could lead to benefits in areas of healthcare in which memory plays a central role and in legal fields reliant on witnesses' memories. Predominantly due to the rareness of the phenomenon, existing HSAM literature is highly heterogenous in its methodologies used. Therefore, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we performed the first systematic review on this topic, to collate the existing behavioural, neuroanatomical, and functional HSAM data. Results from the 20 experimental selected studies revealed that HSAM is categorised by rapidly retrieved, detailed and accurate autobiographical memories, and appears to avoid the normal aging process. Functional neuroimaging studies showed HSAM retrieval seems characterised by an intense overactivation of the usual autobiographical memory network, including posterior visual areas (e.g., the precuneus). Structural neuroanatomical differences do not appear to characterise HSAM, but altered hippocampal resting-state connectivity was commonly observed. We discuss theories of HSAM in relation to autobiographical encoding, consolidation, and retrieval, and suggest future directions for this research.

Impoverished details with preserved gist in remote and recent spatial memory following hippocampal and fornix lesions

INTRODUCTION

Cognitive Map Theory predicts that the hippocampus (HPC) plays a specialized, time-invariant role in supporting allocentric spatial memory, while Standard Consolidation Theory makes the competing prediction that the HPC plays a time-limited role, with more remote memories gaining independence of HPC function. These theories, however, are largely informed by the results of laboratory-based tests that are unlikely to simulate the demands of representing real-world environments in humans. Validation of these theories is further limited by an overall focus on spatial memory of newly encountered environments and on individuals with extensive lesions to the HPC and to surrounding medial temporal lobe (MTL) regions. The current study incorporates naturalistic tests of spatial memory based on recently and remotely encountered environments navigated by individuals with lesions to the HPC/MTL or that are limited to the HPC's major output, the fornix.

METHODS

Four participants with bilateral HPC/MTL and/or fornix lesions drew sketch maps of recently and remotely experienced neighbourhoods and houses. Tests of the appearance, distances, and routes between landmarks from the same real-world environments were also administered. Performance on the tasks was compared to that of control participants closely matched in terms of exposure to the same neighbourhoods and home environments as well as to actual maps.

RESULTS

The performance of individuals with fornix/MTL lesions was found to be largely comparable to that of controls on objective tests of spatial memory, other than one case who was impaired on remote and recent conditions for several tasks. The nature of deficits in recent and remote spatial memory were further revealed on house floorplan drawings, which contained spatial distortions, room/structure transpositions, and omissions, and on neighbourhood sketch maps, which were intact in terms of overall layout but sparse in details such as landmarks.

CONCLUSION

Lab-based tests of spatial memory of newly learned environments are unlikely to fully capture patterns of spared and impaired representations of real-world environments (e.g., peripheral features, configurations). Naturalistic tasks, including generative drawing tasks, indicate that contrary to Cognitive Map Theory, neither HPC nor MTL are critical for allocentric gross representations of large-scale environments. Conversely, the HPC appears critical for representing detailed spatial information of local naturalistic environments and environmental objects regardless of the age of the memory, contrary to Standard Consolidation Theory.

Waveform-based classification of dentate spikes

Synchronous excitatory discharges from the entorhinal cortex (EC) to the dentate gyrus (DG) generate fast and prominent patterns in the hilar local field potential (LFP), called dentate spikes (DSs). As sharp-wave ripples in CA1, DSs are more likely to occur in quiet behavioral states, when memory consolidation is thought to take place. However, their functions in mnemonic processes are yet to be elucidated. The classification of DSs into types 1 or 2 is determined by their origin in the lateral or medial EC, as revealed by current source density (CSD) analysis, which requires recordings from linear probes with multiple electrodes spanning the DG layers. To allow the investigation of the functional role of each DS type in recordings obtained from single electrodes and tetrodes, which are abundant in the field, we developed an unsupervised method using Gaussian mixture models to classify such events based on their waveforms. Our classification approach achieved high accuracies (> 80%) when validated in 8 mice with DG laminar profiles. The average CSDs, waveforms, rates, and widths of the DS types obtained through our method closely resembled those derived from the CSD-based classification. As an example of application, we used the technique to analyze single-electrode LFPs from apolipoprotein (apo) E3 and apoE4 knock-in mice. We observed that the latter group, which is a model for Alzheimer's disease, exhibited wider DSs of both types from a young age, with a larger effect size for DS type 2, likely reflecting early pathophysiological alterations in the EC-DG network, such as hyperactivity. In addition to the applicability of the method in expanding the study of DS types, our results show that their waveforms carry information about their origins, suggesting different underlying network dynamics and roles in memory processing.

Contextual memory engrams, and the neuromodulatory influence of the locus coeruleus

Here, we review the basis of contextual memory at a conceptual and cellular level. We begin with an overview of the philosophical foundations of traversing space, followed by theories covering the material bases of contextual representations in the hippocampus (engrams), exploring functional characteristics of the cells and subfields within. Next, we explore various methodological approaches for investigating contextual memory engrams, emphasizing plasticity mechanisms. This leads us to discuss the role of neuromodulatory inputs in governing these dynamic changes. We then outline a recent hypothesis involving noradrenergic and dopaminergic projections from the locus coeruleus (LC) to different subregions of the hippocampus, in sculpting contextual representations, giving a brief description of the neuroanatomical and physiological properties of the LC. Finally, we examine how activity in the LC influences contextual memory processes through synaptic plasticity mechanisms to alter hippocampal engrams. Overall, we find that phasic activation of the LC plays an important role in promoting new learning and altering mnemonic processes at the behavioral and cellular level through the neuromodulatory influence of NE/DA in the hippocampus. These findings may provide insight into mechanisms of hippocampal remapping and memory updating, memory processes that are potentially dysregulated in certain psychiatric and neurodegenerative disorders.

How neural representations of newly learnt faces change over time: Event-related brain potential evidence for overnight consolidation

Previous experiments have shown that a brief encounter with a previously unfamiliar person leads to the establishment of new facial representations, which can be activated by completely novel pictures of the newly learnt face. The present study examined how stable such novel neural representations are over time, and, specifically, how they become consolidated within the first 24 h after learning. Using event-related brain potentials (ERPs) in a between-participants design, we demonstrate that clear face familiarity effects in the occipito-temporal N250 are evident immediately after learning. These effects then undergo change, with a nearly complete absence of familiarity-related ERP differences 4 h after the initial encounter. Critically, 24 h after learning, the original familiarity effect re-emerges. These findings suggest that the neural correlates of novel face representations are not stable over time but change during the first day after learning. The resulting pattern of change is consistent with a process of consolidation.

Brain connectivity patterns associated with individual differences in the access to experience-near personal semantics: a resting-state fMRI study

It has been proposed that a continuum of specificity exists between episodic and semantic autobiographical memory. Personal semantics have been theorized to situate intermediately on this continuum, with more "experience-near" personal semantics (enPS) closer to the episodic end. We used individual differences in behavior as a model to investigate brain networks associated with the access to episodic autobiographical (EAM) and enPS information, assessing the relation between performance in the EAM and enPS conditions of the Autobiographical Fluency Task (AFT) and intrinsic brain connectivity. Results of an intrinsic connectivity contrast analysis showed that the global connectivity of two clusters in the left and right posterior cingulate cortex (PCC) was predicted by performance in the enPS conditions. Moreover, enPS scores predicted the connectivity strength of the right PCC with the bilateral anterior hippocampus (aHC), anterior middle temporal gyrus (aMTG) and medial orbitofrontal cortex, and the left aMTG and PCC. enPS scores also predicted the connectivity strength of the left PCC with the bilateral HC and MTG. The network highlighted involves parts of the core and of the dorsal medial subsystems of the Default Mode Network, in line with the proposal that enPS represents an intermediate entity between episodic and semantic memory.

Parallel cognitive maps for multiple knowledge structures in the hippocampal formation

The hippocampal-entorhinal system uses cognitive maps to represent spatial knowledge and other types of relational information. However, objects can often be characterized by different types of relations simultaneously. How does the hippocampal formation handle the embedding of stimuli in multiple relational structures that differ vastly in their mode and timescale of acquisition? Does the hippocampal formation integrate different stimulus dimensions into one conjunctive map or is each dimension represented in a parallel map? Here, we reanalyzed human functional magnetic resonance imaging data from Garvert et al. (2017) that had previously revealed a map in the hippocampal formation coding for a newly learnt transition structure. Using functional magnetic resonance imaging adaptation analysis, we found that the degree of representational similarity in the bilateral hippocampus also decreased as a function of the semantic distance between presented objects. Importantly, while both map-like structures localized to the hippocampal formation, the semantic map was located in more posterior regions of the hippocampal formation than the transition structure and thus anatomically distinct. This finding supports the idea that the hippocampal-entorhinal system forms parallel cognitive maps that reflect the embedding of objects in diverse relational structures.

9-cis beta-carotene-enriched diet significantly improved cognition and decreased Alzheimer's disease neuropathology and neuroinflammation in Alzheimer's disease-like mouse models

A significant progressive decline in beta-carotene (βC) levels in the brain is associated with cognitive impairment and a higher prevalence of Alzheimer's disease (AD). In this study, we investigated whether the administration of 9-cis beta-carotene (9CBC)-rich powder of the alga Dunaliella bardawil, the best-known source of βC in nature, inhibits the development of AD-like neuropathology and cognitive deficits. We demonstrated that in 3 AD mouse models, Tg2576, 5xFAD, and apoE4, 9CBC treatment improved long- and short-term memory, decreased neuroinflammation, and reduced the prevalence of β-amyloid plaques and tau hyperphosphorylation. These findings suggest that 9CBC has the potential to be an effective preventive and symptomatic AD therapy.