Episodic-like Memory Research Articles

Involvement of a lateral entorhinal cortex engram in episodic-like memory recall

Episodic memory relies on the entorhinal cortex (EC), a crucial hub connecting the hippocampus and sensory processing regions. This study investigates the role of the lateral EC (LEC) in episodic-like memory in mice. Here, we employ the object-place-context-recognition task (OPCRT), a behavioral test used to study episodic-like memory in rodents. Electrophysiology in brain slices reveals that OPCRT specifically induces a shift in the threshold for the induction of synaptic plasticity in LEC superficial layer II. Additionally, a dual viral system is used to express chemogenetic receptors coupled to the c-Fos promoter in neurons recruited during the learning. We demonstrate that the inhibition of LEC neurons impairs the performance of the mice in the memory task, while their stimulation significantly facilitates memory recall. Our findings provide evidence for an episodic-like memory engram in the LEC and emphasize its role in memory processing within the broader network of episodic memory.

Cognitive screening for children: Piloting a new battery of interactive games in 4- to 8-year-old children

Cognitive screening at the preschool age can be helpful in the early detection of possible difficulties before the start of school attendance as problems during schooling can have profound consequences. While interactive tools are still limited for the Czech population, tools used for cognitive screening at a younger age often consist of traditional pen-and-paper methods. Such examinations can be very demanding and time-consuming. This pilot study therefore focuses on the usability testing of a newly developed battery of interactive games used for the screening of selected cognitive functions in children aged four to eight in a less demanding and more attractive way. The battery consists of three interactive games testing (1) attention (selective attention), (2) executive functions (inhibitory control), (3) memory (episodic-like memory). The study sample included 24 participants of preschool or younger school age, ranging from 4 to 8 years old, girls = 12 (50%). The analyses also concentrated on the comparison of the newly designed screening tool with selected traditional test methods. The results suggest that the newly developed battery is feasible, and for children, it is entertaining and attractive. The designed cognitive battery is a promising tool for the screening of cognitive functions in younger school-age children.

Why might animals remember? A functional framework for episodic memory research in comparative psychology.

One of Clayton's major contributions to our understanding of animal minds has been her work on episodic-like memory. A central reason for the success of this work was its focus on ecological validity: rather than looking for episodic memory for arbitrary stimuli in artificial contexts, focussing on contexts in which episodic memory would serve a biological function such as food caching. This review aims to deepen this insight by surveying the numerous functions that have been proposed for episodic memory, articulating a philosophically grounded framework for understanding what exactly functions are, and drawing on these to make suggestions for future directions in the comparative cognitive psychology of episodic memory. Our review suggests four key insights. First, episodic memory may have more than one function and may have different functions in different species. Second, cross-disciplinary work is key to developing a functional account of episodic memory. Third, there is scope for further theoretical elaboration of proposals relating episodic memory to food caching and, in particular, future-oriented cognition. Finally, learning-related functions suggested by AI (artificial intelligence)-based models are a fruitful avenue for future behavioural research.

Neonatal overfeeding promotes anxiety, impairs episodic-like memory, and disrupts transcriptional regulation of hippocampal steroidogenic enzymes

The objective of our study was to investigate the impact of neonatal overfeeding on cognitive functions and neurosteroidogenesis in male rats. Offspring were assigned to either small litters (SL; 4 pups/mother), resulting in increased milk intake and body weight gain, or normal litters (NL; 10 pups/mother). On postnatal day (PND) 21, half of the male rats were euthanized, while the remaining were kept under standard conditions (4 rats/cage) until PND70. At this stage, subjects underwent assessments for locomotor activity, anxiety levels via the elevated plus maze, and episodic-like memory (ELM) tests. By PND90, the rats were euthanized for brain dissection. Utilizing micropunch techniques, dentate gyrus (DG), CA1, and CA3 regions were extracted for analysis of mRNA expression and methylation patterns. At PND21, SL rats exhibited increased body and adipose tissue weights, alongside elevated cholesterol, glucose, and triglyceride levels compared to NL counterparts. By PND90, although metabolic disparities were no longer evident, SL rats demonstrated heightened anxiety-like behavior and diminished performance in ELM tests. Early life changes included a decreased expression of aromatase (P450arom) and 3α-HSD in CA1, with increased levels in CA3 and DG among SL rats. Additionally, PND90 rats from SL exhibited increased P450arom and decreased 5α-reductase 1 (5αR-1) expression in DG. Notably, some of these variations were correlated with changes in methylation patterns of their promoter regions. Our findings reveal that neonatal overfeeding exerts a long-term adverse effect on cognitive abilities and neurosteroidogenic pathways, underscoring the lasting impact of nutritional experiences during critical early postnatal development periods.

Neuroscientist's Behavioral Toolbox for Studying Episodic-Like Memory.

Episodic memory, the ability to recall specific events and experiences, is a cornerstone of human cognition with profound clinical implications. While animal studies have provided valuable insights into the neuronal underpinnings of episodic memory, research has largely relied on a limited subset of tasks that model only some aspects of episodic memory. In this narrative review, we provide an overview of rodent episodic-like memory tasks that expand the methodological repertoire and diversify the approaches used in episodic-like memory research. These tasks assess various aspects of human episodic memory, such as integrated what-where-when or what-where memory, source memory, free recall, temporal binding, and threshold retrieval dynamics. We review each task's general principle and consider whether alternative non-episodic mechanisms can account for the observed behavior. While our list of tasks is not exhaustive, we hope it will guide researchers in selecting models that align with their specific research objectives, leading to novel advancements and a more comprehensive understanding of mechanisms underlying specific aspects of episodic memory.

Mice integrate conspecific and contextual information in forming social episodic-like memories under spontaneous recognition task conditions

The ability to remember unique past events (episodic memory) may be an evolutionarily conserved function, with accumulating evidence of episodic-(like) memory processing in rodents. In humans, it likely contributes to successful complex social networking. Rodents, arguably the most used laboratory models, are also rather social animals. However, many behavioural paradigms are devoid of sociality, and commonly-used social spontaneous recognition tasks (SRTs) are open to non-episodic strategies based upon familiarity. We address this gap by developing new SRT variants. Here, in object-in-context SRTs, we asked if context could be specified by the presence/absence of either a conspecific (experiment 1) or an additional local object (experiment 2). We show that mice readily used the conspecific as contextual information to distinguish unique episodes in memory. In contrast, no coherent behavioural response emerged when an additional object was used as a potential context specifier. Further, in a new social conspecific-in-context SRT (experiment 3) where environment-based change was the context specifier, mice preferably explored a more recently-seen familiar conspecific associated with contextual mismatch, over a less recently-seen familiar conspecific presented in the same context. The results argue that, in incidental SRT conditions, mice readily incorporate conspecific cue information into episodic-like memory. Thus, the tasks offer different ways to assess and further understand the mechanisms at work in social episodic-like memory processing.

Episodic-like memory in wild free-living blue tits and great tits

Episodic-like memory in non-human animals represents the behavioral characteristics of human episodic memory-the ability to mentally travel backward in time to "re-live" past experiences. A focus on traditional model species of episodic-like memory may overlook taxa possessing this cognitive ability and consequently its evolution across species. Experiments conducted in the wild have the potential to broaden the scope of episodic-like memory research under the natural conditions in which they evolved. We combine two distinct yet complementary episodic-like memory tasks (the what-where-when memory and incidental encoding paradigms), each targeting a different aspect of human episodic memory, namely the content (what-where-when) and process (incidental encoding), to comprehensively test the memory abilities of wild, free-living, non-caching blue tits (Cyanistes caeruleus) and great tits (Parus major). Automated feeders with custom-built programs allowed for experimental manipulation of spatiotemporal experiences on an individual-level basis. In the what-where-when memory experiment, after learning individualized temporal feeder rules, the birds demonstrated their ability to recall the "what" (food type), "where" (feeder location), and "when" (time since their initial visit of the day) of previous foraging experiences. In the incidental encoding experiment, the birds showed that they were able to encode and recall incidental spatial information regarding previous foraging experiences ("where" test), and juveniles, but not adults, were also able to recall incidentally encoded visual information ("which" test). Consequently, this study presents multiple lines of converging evidence for episodic-like memory in a wild population of generalist foragers, suggesting that episodic-like memory may be more taxonomically widespread than previously assumed.

Time-mapping and future-oriented behavior in free-ranging wild fruit bats

Episodic memory and mental time travel have been viewed as uniquely human traits.1,2,3 This view began to shift with the development of behavioral criteria to assess what is referred to as "episodic-like memory" in animals.4,5 Key findings have ranged from evidence of what-where-when memory in scrub-jays, rats, and bees; through decision-making that impacts future foraging in frugivorous primates; to evidence of planning based on future needs in scrub-jays and tool use planning in great apes.4,6,7,8,9,10,11,12,13 Field studies of these issues have been rare, though there is field-based evidence for future-oriented behaviors in primates.8,10,14,15 We report evidence that free-ranging wild fruit bats rely on mental temporal maps and exhibit future-oriented behaviors when foraging. We tracked young bats as they navigated and foraged, documenting every tree they visited over many months. We prevented the bats from foraging outside for different time periods and monitored their foraging decisions, revealing that the bats map the spatiotemporal patterns of resources in their environment. Following a long period in captivity, the bats did not visit those trees that were no longer providing fruit. We show that this time-mapping ability requires experience and is lacking in inexperienced bats. Careful analysis of the bats' movement and foraging choices indicated that they plan which tree to visit while still in the colony, thus exhibiting future-oriented behavior and delayed gratification on a nightly basis. Our findings demonstrate how the need for spatiotemporal mental mapping can drive the evolution of high cognitive abilities that were previously considered exclusive to humans.

Photobiomodulation in the aging brain: a systematic review from animal models to humans.

Aging is a multifactorial biological process that may be associated with cognitive decline. Photobiomodulation (PBM) is a non-pharmacological therapy that shows promising results in the treatment or prevention of age-related cognitive impairments. The aim of this review is to compile the preclinical and clinical evidence of the effect of PBM during aging in healthy and pathological conditions, including behavioral analysis and neuropsychological assessment, as well as brain-related modifications. 37 studies were identified by searching in PubMed, Scopus, and PsycInfo databases. Most studies use wavelengths of 800, 810, or 1064nm but intensity and days of application were highly variable. In animal studies, it has been shown improvements in spatial memory, episodic-like memory, social memory, while different results have been found in recognition memory. Locomotor activity improved in Parkinson disease models. In healthy aged humans, it has been outlined improvements in working memory, cognitive inhibition, and lexical/semantic access, while general cognition was mainly enhanced on Alzheimer disease or mild cognitive impairment. Anxiety assessment is scarce and shows mixed results. As for brain activity, results outline promising effects of PBM in reversing metabolic alterations and enhancing mitochondrial function, as evidenced by restored CCO activity and ATP levels. Additionally, PBM demonstrated neuroprotective, anti-inflammatory, immunomodulatory and hemodynamic effects. The findings suggest that PBM holds promise as a non-invasive intervention for enhancing cognitive function, and in the modulation of brain functional reorganization. It is necessary to develop standardized protocols for the correct, beneficial, and homogeneous use of PBM.

Eurasian jays (Garrulus glandarius) show episodic-like memory through the incidental encoding of information.

Episodic memory describes the conscious reimagining of our memories and is often considered to be a uniquely human ability. As these phenomenological components are embedded within its definition, major issues arise when investigating the presence of episodic memory in non-human animals. Importantly, however, when we as humans recall a specific experience, we may remember details from that experience that were inconsequential to our needs, thoughts, or desires at that time. This 'incidental' information is nevertheless encoded automatically as part of the memory and is subsequently recalled within a holistic representation of the event. The incidental encoding and unexpected question paradigm represents this characteristic feature of human episodic memory and can be employed to investigate memory recall in non-human animals. However, without evidence for the associated phenomenology during recall, this type of memory is termed 'episodic-like memory'. Using this approach, we tested seven Eurasian jays (Garrulus glandarius) on their ability to use incidental visual information (associated with observed experimenter made 'caches') to solve an unexpected memory test. The birds performed above chance levels, suggesting that Eurasian jays can encode, retain, recall, and access incidental visual information within a remembered event, which is an ability indicative of episodic memory in humans.

Heterogenous effect of early adulthood stress on cognitive aging and synaptic function in the dentate gyrus.

Cognitive aging widely varies among individuals due to different stress experiences throughout the lifespan and vulnerability of neurocognitive mechanisms. To understand the heterogeneity of cognitive aging, we investigated the effect of early adulthood stress (EAS) on three different hippocampus-dependent memory tasks: the novel object recognition test (assessing recognition memory: RM), the paired association test (assessing episodic-like memory: EM), and trace fear conditioning (assessing trace memory: TM). Two-month-old rats were exposed to chronic mild stress for 6 weeks and underwent behavioral testing either 2 weeks or 20 months later. The results show that stress and aging impaired different types of memory tasks to varying degrees. RM is affected by combined effect of stress and aging. EM became less precise in EAS animals. TM, especially the contextual memory, showed impairment in aging although EAS attenuated the aging effect, perhaps due to its engagement in emotional memory systems. To further explore the neural underpinnings of these multi-faceted effects, we measured long-term potentiation (LTP), neural density, and synaptic density in the dentate gyrus (DG). Both stress and aging reduced LTP. Additionally, the synaptic density per neuron showed a further reduction in the stress aged group. In summary, EAS modulates different forms of memory functions perhaps due to their substantial or partial dependence on the functional integrity of the hippocampus. The current results suggest that lasting alterations in hippocampal circuits following EAS could potentially generate remote effects on individual variability in cognitive aging, as demonstrated by performance in multiple types of memory.

Oxyresveratrol Improves Cognitive Impairments and Episodic-like Memory through Modulating Neuroinflammation and PI3K-Akt Signaling Pathway in LPS-Induced Mice.

Oxyresveratrol is one of the active ingredients derived from mulberry branch with strong anti-inflammatory bioactivity. In this research, we want to explore if oxyresveratrol can improve cognitive impairments and episodic-like memory and its mechanism. In LPS-induced BV-2 cells, 25 μM OXY can significantly inhibit the expression of NO and alter the M1/M2 polarization by regulating M1/M2 phenotype makers. In vivo, OXY (50, 100 mg/kg) significantly reversed cognitive impairments and alleviated neuronal injuries caused by neuroinflammation. According to network pharmacology analysis, OXY alleviated neuroinflammation via the PI3K-Akt pathway. In general, the research revealed that OXY can improve cognitive impairments and episodic-like memory through alleviating LPS-induced neuroinflammation and regulating the PI3K-Akt signaling pathway.

Research on the relationship between episodic memory and sleep in human

This paper reviews and analyzes the important "memory" aspect of brain science, mainly through reading and summarizing the existing literature to explain the relationship between episodic memory and sleep. A large amount of literature on Google scholar shows that sleep plays an important role in consolidating episodic memories, and gives experiments and evidence to support this idea. The study found that slow-wave sleep is an important period for memory consolidation, and that different stages of sleep also play a part in the memory consolidation process. Various experiments have demonstrated the important link between sleep and episodic memory storage, which means that memory quality is closely related to sleep. This paper also contains two hypotheses for the process of memory Consolidation: the "Active System Consolidation Hypothesis" and the "Synaptic Homeostasis Hypothesis". In the course of research, we haven't seen much literature supporting the existence of episodic memory in animals, but they do have memories that look a lot like episodic memory, which most scientists call "episodic-like memory."

Hippocampal motor memory network reorganization depends on familiarity, not time.

There is debate as to whether a time-dependent transformation of the episodic-like memory network is observed for nonepisodic tasks, including procedural motor memory. To determine how motor memory networks reorganize with time and practice, mice performed a motor task in a straight alley maze for 1 d (recent), 20 d of continuous training (continuous), or testing 20 d after the original training (remote), and then regional c-Fos expression was assessed. Elevated hippocampal c-Fos accompanied remote, but not continuous, motor task retrieval after 20 d, suggesting that the hippocampus remains engaged for nonhabitual remote motor memory retrieval.

Cephalopod learning and memory

Cephalopod molluscs are renowned for their unique central nervous system - a donut-shaped brain organised around the oesophagus. This brain supports sophisticated learning and memory abilities. Between the 1950s and 1980s, these cognitive abilities were extensively studied in octopus (Figure 1A) - a now leading model for the study of memory and its neural substrates (approximately 200 papers during this period). The focus on octopus learning and memory was mainly due to their curious nature and the fact that they adapt to laboratory-controlled conditions, making them easy to test and maintain in captivity. Research on cephalopod cognition began to widen in the late 20th century, when scientists started focusing on other coleoid cephalopods (i.e., cuttlefish and squid) (Figure 1B,C), and not just on associative learning and memory per se, but other more complex aspects of cognition such as episodic-like memory (the ability to remember the what, where, and when of a past event), source memory (the retrieval of contextual details from a memory), and self-control (the ability to inhibit an action in the present to gain a more valuable future reward). Attention broadened further over the last two decades to focus on the shelled cephalopods - the nautiloids (Figure 1D). The nautiloids have relatively primitive brains compared to their soft-bodied cousins (octopus, cuttlefish, and squid) but research shows that they are still able to comparatively succeed in some cognitive tasks. In this primer, we will provide a general description of the types of memory studied in cephalopods, and discuss learning and memory experiments that address the main challenges cephalopods face during their daily lives: navigation, timing, and food selection. Determining the type of information cephalopods learn and remember and whether they use such information to overcome ecological challenges will highlight why these invertebrates evolved large and sophisticated brains.

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Okra is known for its neuroprotective and antioxidant properties. We aimed to investigate the potential effects of okra seed powder in alleviating high far diet (HFD) induced cognitive deficit and hypercholesterolemia. We randomly allocated thirty-six C57BL/6J male mice into: (i) control, mice fed with a normal fat level diet; (ii) HFD, mice fed with HFD; (iii) HFD-OS1; (iv) HFD-OS2; (v) HFD-OS3, mice fed with HFD and okra seed powder (200, 400, or 800 mg/kg/day, respectively); (vi) HFD-SIM, mice fed with HFD and simvastatin (20 mg/kg/day). After 10 weeks of treatment period, the mice were tested with an episodic-like memory test (EMT) and Morris water maze (MWM). We found significantly higher total and LDL cholesterol levels in mice fed with HFD. Compared to the HFD group, the control group performed better in the EMT test, and also learned and retrieved spatial reference memory better in the MWM test. The okra seed powder significantly improved spatial learning in four days of acquisition trials and the highest dose of okra profoundly improved spatial reference memory retention during the probe trial. Contrary to the MWM results, the okra-treated animals did not perform significantly better than the HFD-treated animals in EMT. At present, we recommend future studies testing the potential neuroprotective or cognitive enhancing effects of okra to assess different cognitive domains using various disease models to have a better understanding on the potential neuroprotective properties of okra.

Menopause causes metabolic and cognitive impairments in a chronic cerebral hypoperfusion model of vascular contributions to cognitive impairment and dementia

BackgroundThe vast majority of women with dementia are post-menopausal. Despite clinical relevance, menopause is underrepresented in rodent models of dementia. Before menopause, women are less likely than men to experience strokes, obesity, and diabetes—known risk factors for vascular contributions to cognitive impairment and dementia (VCID). During menopause, ovarian estrogen production stops and the risk of developing these dementia risk factors spikes. Here, we aimed to determine if menopause worsens cognitive impairment in VCID. We hypothesized that menopause would cause metabolic dysfunction and increase cognitive impairment in a mouse model of VCID.MethodsWe performed a unilateral common carotid artery occlusion surgery to produce chronic cerebral hypoperfusion and model VCID in mice. We used 4-vinylcyclohexene diepoxide to induce accelerated ovarian failure and model menopause. We evaluated cognitive impairment using behavioral tests including novel object recognition, Barnes maze, and nest building. To assess metabolic changes, we measured weight, adiposity, and glucose tolerance. We explored multiple aspects of brain pathology including cerebral hypoperfusion and white matter changes (commonly observed in VCID) as well as changes to estrogen receptor expression (which may mediate altered sensitivity to VCID pathology post-menopause).ResultsMenopause increased weight gain, glucose intolerance, and visceral adiposity. VCID caused deficits in spatial memory regardless of menopausal status. Post-menopausal VCID specifically led to additional deficits in episodic-like memory and activities of daily living. Menopause did not alter resting cerebral blood flow on the cortical surface (assessed by laser speckle contrast imaging). In the white matter, menopause decreased myelin basic protein gene expression in the corpus callosum but did not lead to overt white matter damage (assessed by Luxol fast blue). Menopause did not significantly alter estrogen receptor expression (ERα, ERβ, or GPER1) in the cortex or hippocampus.ConclusionsOverall, we have found that the accelerated ovarian failure model of menopause caused metabolic impairment and cognitive deficits in a mouse model of VCID. Further studies are needed to identify the underlying mechanism. Importantly, the post-menopausal brain still expressed estrogen receptors at normal (pre-menopausal) levels. This is encouraging for any future studies attempting to reverse the effects of estrogen loss by activating brain estrogen receptors.

Computational models of episodic-like memory in food-caching birds

Birds of the crow family adapt food-caching strategies to anticipated needs at the time of cache recovery and rely on memory of the what, where and when of previous caching events to recover their hidden food. It is unclear if this behavior can be explained by simple associative learning or if it relies on higher cognitive processes like mental time-travel. We present a computational model and propose a neural implementation of food-caching behavior. The model has hunger variables for motivational control, reward-modulated update of retrieval and caching policies and an associative neural network for remembering caching events with a memory consolidation mechanism for flexible decoding of the age of a memory. Our methodology of formalizing experimental protocols is transferable to other domains and facilitates model evaluation and experiment design. Here, we show that memory-augmented, associative reinforcement learning without mental time-travel is sufficient to explain the results of 28 behavioral experiments with food-caching birds.

A shift in the mechanisms controlling hippocampal engram formation during brain maturation

The ability to form precise, episodic memories develops with age, with young children only able to form gist-like memories that lack precision. The cellular and molecular events in the developing hippocampus that underlie the emergence of precise, episodic-like memory are unclear. In mice, the absence of a competitive neuronal engram allocation process in the immature hippocampus precluded the formation of sparse engrams and precise memories until the fourth postnatal week, when inhibitory circuits in the hippocampus mature. This age-dependent shift in precision of episodic-like memories involved the functional maturation of parvalbumin-expressing interneurons in subfield CA1 through assembly of extracellular perineuronal nets, which is necessary and sufficient for the onset of competitive neuronal allocation, sparse engram formation, and memory precision.

Resveratrol improves episodic-like memory and motor coordination through modulating neuroinflammation in old rats

Strategies focus on the use of molecules found in food derived from plants as polyphenols, arouse interest for combating aging. The polyphenol resveratrol, due to its antioxidants and anti-inflammatory properties, is increasingly studied, being still unknown their effects on episodic-like memory and motor coordination. This research evaluated the in vivo effect of chronic resveratrol treatment (20 mg/kg/day, i.p, 28 days) in episodic-like memory and motor coordination in non-pathological old rats, comparing with young and old vehicle-treated rats, using the novel object recognition and the rotarod tests. In combination with the analyses of the effect of resveratrol on the immunoreactivity of the main molecular proteins involved in neuroinflammation (SIRT1, SIRT1-75 kDa fragment, NF-κB acetylation) in the hippocampus of these rats. Results suggest a beneficial effect of resveratrol on episodic-like memory and in motor coordination through modulating neuroinflammation, acting on SIRT1 and NF-κB signaling pathway in the hippocampus of old rats.