The effects of mnemonic variability and spacing on memory over multiple timescales.

The memory benefit that arises from distributing learning over time rather than in consecutive sessions is one of the most robust effects in cognitive psychology. While prior work has mainly focused on repeated exposures to the same information, in the real world, mnemonic content is dynamic, with some pieces of information staying stable while others vary. Thus, open questions remain about the efficacy of the spacing effect in the face of variability in the mnemonic content. Here, in two experiments, we investigated the contributions of mnemonic variability and the timescale of spacing intervals, ranging from seconds to days, to long-term memory. For item memory, both mnemonic variability and spacing intervals were beneficial for memory; however, mnemonic variability was greater at shorter spacing intervals. In contrast, for associative memory, repetition rather than mnemonic variability was beneficial for memory, and spacing benefits only emerged in the absence of mnemonic variability. These results highlight a critical role for mnemonic variability and the timescale of spacing intervals in the spacing effect, bringing this classic memory paradigm into more ecologically valid contexts.

Goal Shifts Structure Memories and Prioritize Event-defining Information in Memory.

Every day, we encounter far more information than we could possibly remember. Thus, our memory systems must organize and prioritize the details from an experience that can adaptively guide the storage and retrieval of specific episodic events. Prior work has shown that shifts in internal goal states can function as event boundaries, chunking experiences into distinct and memorable episodes. In addition, at short delays, memory for contextual information at boundaries has been shown to be enhanced compared with items within each event. However, it remains unclear if these memory enhancements are limited to features that signal a meaningful transition between events. To determine how changes in dynamic goal states influence the organization and content of long-term memory, we designed a 2-day experiment in which participants viewed a series of black-and-white objects surrounded by a color border on a two-by-two grid. The location of the object on the grid determined which of two tasks participants performed on a given trial. To examine if distinct types of goal shifts modulate the effects of event segmentation, we changed the border color, the task, or both after every four items in a sequence. We found that goal shifts influenced the temporal memory in a manner consistent with the formation of distinct events. However, for subjective memory representations in particular, these effects differed by the type of event boundary. Furthermore, to examine if goal shifts lead to the prioritization of goal-relevant features in longer lasting memories, we tested the source memory for each object's color and grid location both immediately and after a 24-hr delay. On the immediate test, boundaries enhanced the memory for all concurrent source features compared with nonboundary items, but only if those boundaries involved a goal shift. In contrast, after a delay, the source memory was selectively enhanced for the feature relevant to the goal shift. These findings suggest that goals can adaptively structure memories by prioritizing contextual features that define a unique episode in memory.

Understanding spatiotemporal effects of food supplementation on host-parasite interactions using community-based science.

Supplemental feeding can increase the overall health of animals but also can have variable effects on how animals defend themselves against parasites. However, the spatiotemporal effects of food supplementation on host-parasite interactions remain poorly understood, likely because large-scale, coordinated efforts to investigate them are difficult. Here, we introduce the Nest Parasite Community Science Project, which is a community-based science project that coordinates studies with bird nest box 'stewards' from the public and scientific community. This project was established to understand broad ecological patterns between hosts and their parasites. The goal of this study was to determine the effect of food supplementation on eastern bluebirds (Sialia sialis) and their nest parasite community across the geographic range of the bluebirds from 2018 to 2021. We received 674 nests from 69 stewards in 26 states in the eastern United States. Nest box stewards reported whether or not they provided mealworms or suet near nesting bluebirds, then they followed the nesting success of the birds (number of eggs laid and hatched, proportion that hatched, number and proportion of nestlings that successfully fledged). We then identified and quantified parasites in the nests. Overall, we found that food supplementation increased fledging success. The most common nest parasite taxon was the parasitic blow fly (Protocalliphora sialia), but a few nests contained fleas (Ceratophyllus idius, C. gallinae and Orchopeas leucopus) and mites (Dermanyssus spp. and Ornithonyssus spp.). Blow flies were primarily found at northern latitudes, where food supplementation affected blow fly prevalence. However, the direction of this effect varied substantially in direction and magnitude across years. More stewards fed bluebirds at southern latitudes than at northern latitudes, which contradicts the findings of other community-based science projects. Overall, food supplementation of birds was associated with increased host fitness but did not appear to play a consistent role in defence against these parasites across all years. Our study demonstrates the importance of coordinated studies across years and locations to understand the effects of environmental heterogeneity, including human-based food supplementation, on host-parasite dynamics.

Awake Hippocampal-Cortical Co-reactivation Is Associated with Forgetting.

Systems consolidation theories posit that consolidation occurs primarily through a coordinated communication between hippocampus and neocortex [Moscovitch, M., & Gilboa, A. Systems consolidation, transformation and reorganization: Multiple trace theory, trace transformation theory and their competitors. PsyArXiv, 2021; Kumaran, D., Hassabis, D., & McClelland, J. L. What learning systems do intelligent agents need? Complementary learning systems theory updated. Trends in Cognitive Sciences, 20, 512-534, 2016; McClelland, J. L., & O'Reilly, R. C. Why there are complementary learning systems in the hippocampus and neocortex: Insights from the successes and failures of connectionist models of learning and memory. Psychological Review, 102, 419-457, 1995]. Recent sleep studies in rodents have shown that hippocampus and visual cortex replay the same information at temporal proximity ("co-replay"; Lansink, C. S., Goltstein, P. M., Lankelma, J. V., McNaughton, B. L., & Pennartz, C. M. A. Hippocampus leads ventral striatum in replay of place-reward information. PLoS Biology, 7, e1000173, 2009; Peyrache, A., Khamassi, M., Benchenane, K., Wiener, S. I., & Battaglia, F. P. Replay of rule-learning related neural patterns in the prefrontal cortex during sleep. Nature Neuroscience, 12, 919-926, 2009; Wierzynski, C. M., Lubenov, E. V., Gu, M., & Siapas, A. G. State-dependent spike-timing relationships between hippocampal and prefrontal circuits during sleep. Neuron, 61, 587-596, 2009; Ji, D., & Wilson, M. A. Coordinated memory replay in the visual cortex and hippocampus during sleep. Nature Neuroscience, 10, 100-107, 2007). We developed a novel repetition time (TR)-based co-reactivation analysis method to study hippocampal-cortical co-replays in humans using fMRI. Thirty-six young adults completed an image (face or scene) and location paired associate encoding task in the scanner, which were preceded and followed by resting state scans. We identified post-encoding rest TRs (± 1) that showed neural reactivation of each image-location trials in both hippocampus (HPC) and category-selective cortex (fusiform face area [FFA]). This allowed us to characterize temporally proximal coordinated reactivations ("co-reactivations") between HPC and FFA. Moreover, we found that increased HPC-FFA co-reactivations were associated with incorrectly recognized trials after a 1-week delay (p = .004). Finally, we found that these HPC-FFA co-reactivations were also associated with trials that were initially correctly recognized immediately after encoding but were later forgotten in 1-day (p = .043) and 1-week delay period (p = .031). We discuss these results from a trace transformation perspective [Sekeres, M. J., Winocur, G., & Moscovitch, M. The hippocampus and related neocortical structures in memory transformation. Neuroscience Letters, 680, 39-53, 2018; Winocur, G., & Moscovitch, M. Memory transformation and systems consolidation. Journal of the International Neuropsychological Society, 17, 766-780, 2011] and speculate that HPC-FFA co-reactivations may be integrating related events, at the expense of disrupting event-specific details, hence leading to forgetting.

VTA and Anterior Hippocampus Target Dissociable Neocortical Networks for Post-Novelty Enhancements.

The detection of novelty indicates changes in the environment and the need to update existing representations. In response to novelty, interactions across the VTA-hippocampal circuit support experience-dependent plasticity in the hippocampus. While theories have broadly suggested plasticity-related changes are also instantiated in the cortex, research has also shown evidence for functional heterogeneity in cortical networks. It therefore remains unclear how the hippocampal-VTA circuit engages cortical networks, and whether novelty targets specific cortical regions or diffuse, large-scale cortical networks. To adjudicate the role of the VTA and hippocampus in cortical network plasticity, we used fMRI to compare resting-state functional coupling before and following exposure to novel scene images in human subjects of both sexes. Functional coupling between right anterior hippocampus and VTA was enhanced following novelty exposure. However, we also found evidence for a double dissociation, with anterior hippocampus and VTA showing distinct patterns of post-novelty functional coupling enhancements, targeting task-relevant regions versus large-scale networks, respectively. Further, significant correlations between these networks and the novelty-related plasticity in the anterior hippocampal-VTA functional network suggest that the central hippocampal-VTA network may facilitate the interactions with the cortex. These findings support an extended model of novelty-induced plasticity, in which novelty elicits plasticity-related changes in both local and global cortical networks.SIGNIFICANCE STATEMENT Novelty detection is critical for adaptive behavior, signaling the need to update existing representations. By engaging the bidirectional hippocampal-VTA circuit, novelty has been shown to induce plasticity-related changes in the hippocampus. However, it remains an open question how novelty targets such plasticity-related changes in cortical networks. We show that anterior hippocampus and VTA target cortical networks at different spatial scales, with respective enhancements in post-novelty functional coupling with a task-relevant cortical region and a large-scale memory network. The results presented here support an extended model of novelty-related plasticity, in which engaging the anterior hippocampal-VTA circuit through novelty exposure propagates cortical plasticity through hippocampal and VTA functional pathways at distinct scales, targeting specific or diffuse cortical networks.

Collective Healing: A Framework for Building Transformative Collaborations in Public Health.

The capacity of cross-sector collaboration to create meaningful change across social-ecological levels has long been understood in public health. But the ability of cross-sector collaboration to achieve systemic change around the structural determinants of health remains complicated. In 2021, now more than ever, we understand the imperative of strengthening the capacity of collaborative efforts to address the myriad structural health crises facing our communities, from police violence and mass incarceration to Jim Crow laws and redlining, to urban renewal and environmental injustice. Our proposed collective healing framework brings together the collective impact model and radical healing framework to offer a blueprint for cross-sector collaboration that understands the practices of healing to be at the center of public health collaborations and public health practice at large. In this framework, public health practitioners and our collaborators are asked to prioritize relationship building, engage in critical self-reflection, to move beyond compromise, to address differences, to interrogate traditional metrics and approaches, to remake the collective table, and to build shared understanding through action.

Time-dependent transformations of memory representations differ along the long axis of the hippocampus.

Research has shown that sleep is beneficial for the long-term retention of memories. According to theories of memory consolidation, memories are gradually reorganized, becoming supported by widespread, distributed cortical networks, particularly during postencoding periods of sleep. However, the effects of sleep on the organization of memories in the hippocampus itself remains less clear. In a 3-d study, participants encoded separate lists of word-image pairs differing in their opportunity for sleep-dependent consolidation. Pairs were initially studied either before or after an overnight sleep period, and were then restudied in a functional magnetic resonance imaging (fMRI) scan session. We used multivariate pattern similarity analyses to examine fine-grained effects of consolidation on memory representations in the hippocampus. We provide evidence for a dissociation along the long axis of the hippocampus that emerges with consolidation, such that representational patterns for object-word memories initially formed prior to sleep become differentiated in anterior hippocampus and more similar, or overlapping, in posterior hippocampus. Differentiation in anterior hippocampal representations correlated with subsequent behavioral performance. Furthermore, representational overlap in posterior hippocampus correlated with the duration of intervening slow wave sleep. Together, these results demonstrate that sleep-dependent consolidation promotes the reorganization of memory traces along the long axis of the hippocampus.

Sleep Spindles Promote the Restructuring of Memory Representations in Ventromedial Prefrontal Cortex through Enhanced Hippocampal-Cortical Functional Connectivity.

Memory consolidation is hypothesized to involve the distribution and restructuring of memory representations across hippocampal and cortical regions. Theories suggest that, through extended hippocampal-cortical interactions, cortical ensembles come to represent more integrated, or overlapping, memory traces that prioritize commonalities across related memories. Sleep processes, particularly fast sleep spindles, are thought to support consolidation, but evidence for this relationship has been mostly limited to memory retention benefits. Whether fast spindles provide a mechanism for neural changes hypothesized to support consolidation, including the strengthening of hippocampal-cortical networks and integration across memory representations, remains unclear, as does the specificity of regions involved. Using functional connectivity analyses of human fMRI data (both sexes), we show that fast spindle density during overnight sleep is related to enhanced hippocampal-cortical functional connectivity the next day, when restudying information learned before sleep. Spindle density modulated connectivity in distinct hippocampal-cortical networks depending on the category of the consolidated stimuli. Specifically, spindle density correlated with functional connectivity between anterior hippocampus and ventromedial prefrontal cortex (vmPFC) for object-word pairs, and posterior hippocampus and posteromedial cortex for scene-word pairs. Using multivariate pattern analyses, we also show that fast spindle density during postlearning sleep is associated with greater pattern similarity, or representational overlap, across individual object-word memories in vmPFC the next day. Further, the relationship between fast spindle density and representational overlap in vmPFC was mediated by the degree of anterior hippocampal-vmPFC functional connectivity. Together, these results suggest that fast spindles support the network distribution of memory traces, potentially restructuring memory representations in vmPFC.SIGNIFICANCE STATEMENT How new experiences are transformed into long-term memories remains a fundamental question for neuroscience research. Theories suggest that memories are stabilized as they are reorganized in the brain, a process thought to be supported by sleep oscillations, particularly sleep spindles. Although sleep spindles have been associated with benefits in memory retention, it is not well understood how spindles modify neural memory traces. This study found that spindles during overnight sleep correlate with changes in neural memory traces, including enhanced functional connectivity in distinct hippocampal-cortical networks and increased pattern similarity among memories in the cortex. The results provide critical evidence that spindles during overnight sleep may act as a physiological mechanism for the restructuring of neural memory traces.

Somatosensation, echolocation, and underwater sniffing: adaptations allow mammals without traditional olfactory capabilities to forage for food underwater.

Animals rely mainly on olfaction to locate and track food sources. However, mammals that have evolved to live partially or fully underwater are unable to use traditional olfaction in the foraging process. These animals have subsequently developed alternative underwater foraging techniques. Cetaceans (e.g. dolphins) live exclusively underwater, and most utilize a highly developed sonar system for navigation and tracking of prey. Pinnipeds (e.g. seals) live on land, but forage underwater. These animals' highly sensitive whiskers allow them to locate food sources. Sirenians (e.g. manatees), the only herbivorous aquatic mammals, also use highly developed whiskers during the grazing process. The semiaquatic mammals Condylura cristata (star-nosed mole) and Sortex palustris (water shrew) have developed the ability to sniff and detect semiochemicals underwater, a discovery that contradicts prior views on the evolutionary relationship between olfaction and aquatic adaptation. The current review details the anatomy of the olfactory systems of these mammals that live and/or forage underwater, and the adaptations they use to follow prey and forage underwater.

Acts of generating and their sources: predicting the effects of imagery encoding on false recognition errors.

In the two experiments reported here the basis of the beneficial effects of generating images on false recognition errors is investigated. Acts of generating (descriptions, images, or both) were manipulated while examining the effects of the source of descriptions guiding imagery generations (participant vs peer). False recognition errors were relatively high across encoding conditions except when imagery generations were based on participants' own descriptions (Experiments 1 and 2). These differences in the acts of generating were not attributable to differences in the cohesiveness of descriptions themselves. Acts of generating led to greater "remember" responses than "know" responses only when participants were not the source of the descriptions used to generate images (Experiment 2). Results highlight the importance of examining the effects of the source of descriptions for guiding imagery (participant or peer) when testing predictions about the effects of imagery encoding on false recognition errors.

Children show adult-like hippocampal pattern similarity for familiar but not novel events.

The ability to detect differences among similar events in our lives is a crucial aspect of successful episodic memory performance, which develops across early childhood. The neural substrate of this ability is supported by operations in the medial temporal lobe (MTL). Here, we used representational similarity analysis (RSA) to measure neural pattern similarity in hippocampus, perirhinal cortex, and parahippocampal cortex for 4- to 10-year-old children and adults during naturalistic viewing of clips from the same compared to different movies. Further, we assessed the role of prior exposure to individual movie clips on pattern similarity in the MTL. In both age groups, neural pattern similarity in hippocampus was lower for clips drawn from the same movies compared to those drawn from different movies, suggesting that related content activates processes focused on keeping representations with shared content distinct. However, children showed this only for movies with which they had prior exposures, whereas adults showed the effect regardless of any prior exposures to the movies. These findings suggest that children require repeated exposure to stimuli to show adult-like MTL functioning in distinguishing among similar events.

Memory consolidation as an adaptive process.

We rely on our long-term memories to guide future behaviors, making it adaptive to prioritize the retention of goal-relevant, salient information in memory. In this review, we discuss findings from rodent and human research to demonstrate that active processes during post-encoding consolidation support the selective stabilization of recent experience into adaptive, long-term memories. Building upon literatures focused on dynamics at the cellular level, we highlight that consolidation also transforms memories at the systems level to support future goal-relevant behavior, resulting in more generalized memory traces in the brain and behavior. We synthesize previous literatures spanning animal research, human cognitive neuroscience, and cognitive psychology to propose an integrative framework for adaptive consolidation by which goal-relevant memoranda are "tagged" for subsequent consolidation, resulting in selective transformations to the structure of memories that support flexible, goal-relevant behaviors.

Collaborative encoding and memory accuracy: examining the effects of interactive components of co-construction processes.

In 2 experiments, the effect of collaborative encoding on memory was examined by testing 2 interactive components of co-construction processes. One component focused on the nature of the interactive exchange between collaborators: As the partners worked together to create descriptions about ways to interact with familiar objects, constraints were imposed on the interactions by requiring them to take turns (Experiment 1) or to interact without constraints (Experiment 2). The nature of the relationship between partners was manipulated as well by including 2 pair types, friends or unfamiliar peers (Experiments 1 and 2). Interactive component effects were found to influence spontaneous activations through content analyses of participants' descriptions, the patterns of false recognition errors, and the relationship between content and errors. The findings highlight the value of examining the content of participants' collaborative efforts when assessing the effects of collaborative encoding on memory and point to mechanisms mediating collaboration's effects. Because the interactions occurred within the context of an imagery generation task, the findings are also intriguing because of their implications for the use of guided imagery techniques that incorporate co-construction processes.