To update or to create? The influence of novelty and prior knowledge on memory networks.

Schemas are foundational mental structures shaped by experience. They influence behaviour, guide the encoding of new memories and are shaped by associated information. The adaptability of memory schemas facilitates the integration of new information that aligns with existing knowledge structures. First, we discuss how novel information consistent with an existing schema can be swiftly assimilated when presented. This cognitive updating is facilitated by the interaction between the hippocampus and the prefrontal cortex. Second, when novel information is inconsistent with the schema, it likely engages the hippocampus to encode the information as part of an episodic memory trace. Third, novelty may enhance hippocampal dopamine through either the locus coeruleus or ventral tegmental area pathways, with the pathway involved potentially depending on the type of novelty encountered. We propose a gradient theory of schema and novelty to elucidate the neural processes by which schema updating or novel memory traces are formed. It is likely that experiences vary along a familiarity-novelty continuum, and the degree to which new experiences are increasingly novel will guide whether memory for a new experience either integrates into an existing schema or prompts the creation of a new cognitive framework. This article is part of the theme issue 'Long-term potentiation: 50 years on'.

Emotional responses and psychological health among young people amid climate change, Fukushima's radioactive water release, and wars in Ukraine and the Middle East, and the mediating roles of media exposure and nature connectedness: a cross-national analysis.

BACKGROUND: New global crises are emerging, while existing global crises remain unabated. Coping with climate change, the radioactive water released into the Pacific Ocean subsequent to the Fukushima nuclear accident in Japan, and the wars in Ukraine and the Middle East (hereafter referred to as the wars) as individual crises can negatively affect the psychological health of young people, but little is known about the compounded impact of multiple crises. We aimed to examine: (1) the emotional responses of young people towards each individual crisis, (2) how aggregate levels of emotional engagement in global crises might pose different potential trajectories in psychological health, and (3) the protective or exacerbating role of media exposure and nature connectedness as mediators on psychological health outcomes of young people. METHODS: We conducted a cross-national online survey among young people (aged 18-29 years) from China, Portugal, South Africa, the USA, and the UK. We adopted stratified purposive sampling and distributed the survey using online platforms (www.wenjuan.com and www.prolific.com). Individuals were eligible for inclusion in our analysis if they were literate in Chinese or English and had no mental disorders diagnosed within the past 12 months. Participants were asked questions on their demographic characteristics and time spent on social media, including proportion of time exposed to media pertaining to global crises of interest, and they completed surveys based on validated scales that measure depression, anxiety, stress, and wellbeing, as well as emotional responses to each global crisis and nature relatedness. We assessed the survey results using descriptive statistics, ANOVA tests, cluster analysis for individual emotional responses, and structural equation modelling for the aggregate measure of emotional engagement towards individual global crises. FINDINGS: Between Oct 20 and Nov 3, 2023, 2579 individuals participated in the survey, of whom 400 participants from each country (200 male and 200 female participants) were included in our analysis (mean age 24·36 years [SD 2·86]). The mean emotional engagement varied between the global crises of interest (on a scale from 0 to 68, where 0 indicates no emotional response and 68 indicates strong emotional responses across 17 different emotions; wars: 32·42 [SD 14·57]; climate change: 28·79 [14·17]; radioactive water: 21·26 [16·08]), and emotional engagement also varied by country; for instance, for respondents from China, mean emotional engagement in radioactive water was relatively high (39·15 [10·72]) compared with the other countries, and for respondents from the USA, engagement with the wars was relatively low (29·45 [15·78]). We found significant variations in the level of emotional engagement between different crises, with distinct emotional profiles observed among individual countries. To assess the role of media exposure and nature connectedness on psychological outcomes, using structural equation modelling, we constructed a multi-country model comprising Portugal, South Africa, the USA, and the UK, and a standalone model for China. These models elucidated associations between emotional engagement and psychological distress and wellbeing, explaining substantial portions of the variance in both. Notably, while greater emotional engagement in the ecological crises (ie, climate change and radioactive water) generally predicted worse psychological health outcomes, we found the direction of effect for war crises to have positive outcomes for mental health in the standalone China model. Additionally, we found that media exposure mediated the negative effect of wars on psychological distress in the multi-country model, and positive psychological wellbeing in the standalone China model. Moreover, nature connectedness emerged as a potent mediator, effectively mitigating the adverse mental health effects of emotional engagement with some crises, such as radioactive water and climate change. INTERPRETATION: Our findings offer valuable insights into the nuanced dynamics of emotional engagement in global crises and its implications for mental health outcomes among young people across diverse global contexts. Further research is needed to understand the contribution of ongoing and new global crises towards a compounded negative future outlook on young people's mental health to identify effective communication and intervention strategies that can mitigate the effect of this global challenge. FUNDING: Research Grants Council of Hong Kong, China.

Cell-type-specific optogenetic stimulation of the locus coeruleus induces slow-onset potentiation and enhances everyday memory in rats.

Memory formation is typically divided into phases associated with encoding, storage, consolidation, and retrieval. The neural determinants of these phases are thought to differ. This study first investigated the impact of the experience of novelty in rats incurred at a different time, before or after, the precise moment of memory encoding. Memory retention was enhanced. Optogenetic activation of the locus coeruleus mimicked this enhancement induced by novelty, both when given before and after the moment of encoding. Optogenetic activation of the locus coeruleus also induced a slow-onset potentiation of field potentials in area CA1 of the hippocampus evoked by CA3 stimulation. Despite the locus coeruleus being considered a primarily noradrenergic area, both effects of such stimulation were blocked by the dopamine D1/D5 receptor antagonist SCH 23390. These findings substantiate and enrich the evidence implicating the locus coeruleus in cellular aspects of memory consolidation in hippocampus.

Neuronal signature of spatial decision-making during navigation by freely moving rats by using calcium imaging.

A challenge in spatial memory is understanding how place cell firing contributes to decision-making in navigation. A spatial recency task was created in which freely moving rats first became familiar with a spatial context over several days and thereafter were required to encode and then selectively recall one of three specific locations within it that was chosen to be rewarded that day. Calcium imaging was used to record from more than 1,000 cells in area CA1 of the hippocampus of five rats during the exploration, sample, and choice phases of the daily task. The key finding was that neural activity in the startbox rose steadily in the short period prior to entry to the arena and that this selective population cell firing was predictive of the daily changing goal on correct trials but not on trials in which the animals made errors. Single-cell and population activity measures converged on the idea that prospective coding of neural activity can be involved in navigational decision-making.

Changes in brain activity and connectivity as memories age.

The role of the hippocampus during memory consolidation is not fully understood, with human and animal experiments producing conflicting conclusions. In particular, human lesion studies tend to indicate that the hippocampus gradually becomes independent from memory over years, whilst animal studies suggest that this can happen over days. Tallman et al. (this issue) used fMRI to investigate activity and functional connectivity in the brain at four different time points following memory encoding. Their findings include a decrease in functional connectivity between the hippocampus and parahippocampal cortex with memory age, which supports the system consolidation theory, but also argues against the reduced involvement of the hippocampus over time. This study sheds new light on the neurobiology of memory.

Brain region networks for the assimilation of new associative memory into a schema.

Alterations in long-range functional connectivity between distinct brain regions are thought to contribute to the encoding of memory. However, little is known about how the activation of an existing network of neocortical and hippocampal regions might support the assimilation of relevant new information into the preexisting knowledge structure or 'schema'. Using functional mapping for expression of plasticity-related immediate early gene products, we sought to identify the long-range functional network of paired-associate memory, and the encoding and assimilation of relevant new paired-associates. Correlational and clustering analyses for expression of immediate early gene products revealed that midline neocortical-hippocampal connectivity is strongly associated with successful memory encoding of new paired-associates against the backdrop of the schema, compared to both (1) unsuccessful memory encoding of new paired-associates that are not relevant to the schema, and (2) the mere retrieval of the previously learned schema. These findings suggest that the certain midline neocortical and hippocampal networks support the assimilation of newly encoded associative memories into a relevant schema.

Effect of an interactive educational activity using handheld ultraviolet radiation dosimeters on sun protection knowledge among Australian primary school students.

Ultraviolet radiation (UV) is the main cause of skin cancer, and children are a priority group for reducing UV exposure. We evaluated whether an interactive educational activity using handheld dosimeters improved UV-related knowledge among primary (elementary) school students. We conducted an uncontrolled before-after study among 427 students in grades 3-6 (ages 8-12 years) at five schools in the Greater Sydney region, Australia. Students used UV dosimeters to measure UV exposure, using the UV index scale, at different locations on their school grounds with and without different forms of sun protection, followed by an indoor classroom presentation and discussion. A 10-point anonymous questionnaire was completed by each student before and after the entire session (60-90 min). Before-after responses were compared using a generalised linear mixed model, adjusted for school, grade and gender. Overall, the mean raw scores increased from 6.3 (out of 10) before the intervention to 8.9 after the intervention, and the adjusted difference in scores was 2.6 points (95% confidence interval 2.4-2.8; p < 0.0001). Knowledge improved for all questions, with the greatest improvement for questions related to the UV Index (p < 0.05). The effect of the intervention was similar across different school, grade and gender groups. School and grade had no significant effect on mean survey scores, but girls scored an average 0.2 points higher than boys (95% confidence interval 0.1-0.4; p = 0.01). In conclusion, Australian primary school students had moderate knowledge about UV and sun protection, and knowledge improved significantly after a short interactive educational activity using handheld UV dosimeters.

A Behavioral Task Modeling 'Everyday Memory' in an Event Arena to Foster Allocentric Representations for Rodents.

The event arena provides an optimal platform to investigate learning and memory. The appetitive everyday memory task described in this paper provides a robust protocol for the investigation of episodic and spatial memory in rodents, which specifically fosters allocentric memory representation. Rats are trained to find and dig for food during the encoding phase and, after a time delay, rats are given a choice to find the reward food pellet in the correct location. There are two key elements that promote the use of an allocentric strategy in this protocol: 1) rats start from different start locations within and between sessions, 2) a stable home-base is deployed where rats have to carry their food to eat. By means of these modifications, we effectively encourage the rodents to use allocentric spatial representations to perform the task. In addition, the task provides a good paradigm for within-subject experimental design and allows experimenters to manipulate different conditions to reduce variability. Used in conjunction with behavioral and physiological techniques, the resulting rodent model provides an effective test-bed for future research into memory formation and retention.

Naïve to expert: Considering the role of previous knowledge in memory.

In humans, most of our new memories are in some way or another related to what we have already experienced. However, in memory research, especially in non-human animal research, subjects are often mostly naïve to the world. But we know that previous knowledge will change how memories are processed and which brain areas are critical at which time point. Each process from encoding, consolidation, to memory retrieval will be affected. Here, we summarise previous knowledge effects on the neurobiology of memory in both humans and non-human animals, with a special focus on schemas - associative network structures. Furthermore, we propose a new theory on how there may be a continuous gradient from naïve to expert, which would modulate the importance and role of brain areas, such as the hippocampus and prefrontal cortex.

A stable home-base promotes allocentric memory representations of episodic-like everyday spatial memory.

A key issue in neurobiological studies of episodic-like memory is the geometric frame of reference in which memory traces of experience are stored. Assumptions are sometimes made that specific protocols favour either allocentric (map-like) or egocentric (body-centred) representations. There are, however, grounds for suspecting substantial ambiguity about coding strategy, including the necessity to use both frames of reference occasionally, but tests of memory representation are not routinely conducted. Using rats trained to find and dig up food in sandwells at a particular place in an event arena (episodic-like 'action-where' encoding), we show that a protocol previously thought to foster allocentric encoding is ambiguous but more predisposed towards egocentric encoding. Two changes in training protocol were examined with a view to promoting preferential allocentric encoding-one in which multiple start locations were used within a session as well as between sessions; and another that deployed a stable home-base to which the animals had to carry food reward. Only the stable home-base protocol led to excellent choice performance which rigorous analyses revealed to be blocked by occluding extra-arena cues when this was done after encoding but before recall. The implications of these findings for studies of episodic-like memory are that the representational framework of memory at the start of a recall trial will likely include a path direction in the egocentric case but path destination in the allocentric protocol. This difference should be observable in single-unit recording or calcium-imaging studies of spatially-tuned cells.

Anterior cingulate cortex in schema assimilation and expression.

In humans and in animals, mental schemas can store information within an associative framework that enables rapid and efficient assimilation of new information. Using a hippocampal-dependent paired-associate task, we now report that the anterior cingulate cortex is part of a neocortical network of schema storage with NMDA receptor-mediated transmission critical for information updating, and AMPA receptor-mediated transmission required for the expression and updating of stored information.

Schema-dependent gene activation and memory encoding in neocortex.

When new learning occurs against the background of established prior knowledge, relevant new information can be assimilated into a schema and thereby expand the knowledge base. An animal model of this important component of memory consolidation reveals that systems memory consolidation can be very fast. In experiments with rats, we found that the hippocampal-dependent learning of new paired associates is associated with a striking up-regulation of immediate early genes in the prelimbic region of the medial prefrontal cortex, and that pharmacological interventions targeted at that area can prevent both new learning and the recall of remotely and even recently consolidated information. These findings challenge the concept of distinct fast (hippocampal) and slow (cortical) learning systems, and shed new light on the neural mechanisms of memory assimilation into schemas.

Dopamine and memory: modulation of the persistence of memory for novel hippocampal NMDA receptor-dependent paired associates.

Three experiments investigated the role in memory processing of dopamine (DA) afferents to the hippocampus (HPC) that arise from the ventral tegmental area. One hypothesis is that D(1)/D(5) receptor activation in HPC is necessary for the encoding of novel, episodic-like information; the other is that DA activation ensures the greater temporal persistence of transient hippocampal memory traces. Rats (n = 35) were trained, in separate experiments using an episodic-like memory task, to learn six paired associates (PAs) in an "event arena" involving a repeated association between specific flavors of food and locations in space. After 6 weeks of training, rats had learned a "schema" such that two new paired associates could be acquired in a single trial in one session (episodic-like memory). We show that encoding of novel PAs is sensitive to intrahippocampal microinfusion of the NMDA antagonist d-AP-5. Experiment 1 established that intrahippocampal infusion of the D(1)/D(5) dopaminergic antagonist SCH23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride] before encoding of new PAs caused impaired memory 24 h later but that SCH23390 had no effect on the later memory of previously established PAs. Experiment 2 established that SCH23390 modulated the persistence of new memories over time (30 min vs 24 h) rather than affecting initial encoding. Experiment 3 revealed that the impact of SCH23390 was not mediated by state dependence nor had an effect on memory retrieval. These findings support the second hypothesis and establish that persistent, long-term memory of rapid, hippocampal-mediated acquisition of new paired associates requires activation of D(1)/D(5) receptors in HPC at or around the time of encoding.

Schemas and memory consolidation.

Memory encoding occurs rapidly, but the consolidation of memory in the neocortex has long been held to be a more gradual process. We now report, however, that systems consolidation can occur extremely quickly if an associative "schema" into which new information is incorporated has previously been created. In experiments using a hippocampal-dependent paired-associate task for rats, the memory of flavor-place associations became persistent over time as a putative neocortical schema gradually developed. New traces, trained for only one trial, then became assimilated and rapidly hippocampal-independent. Schemas also played a causal role in the creation of lasting associative memory representations during one-trial learning. The concept of neocortical schemas may unite psychological accounts of knowledge structures with neurobiological theories of systems memory consolidation.