Retrieval flexibility and reinstatement in the developing hippocampus

Memories of structured input become increasingly distorted across development

Trajectories of cognitive and neural development suggest that, despite early emergence, the ability to extract environmental patterns changes across childhood. Here, 5- to 9-year-olds and adults (N = 211, 110 females, in a large Canadian city) completed a memory test assessing what they remembered after watching a stream of shape triplets: the particular sequence in which the shapes occurred and/or their group-level structure. After accounting for developmental improvements in overall memory, all ages remembered specific transitions, while memory for group membership was only observed in older children and adults (age by test-type interaction η2  = .05). Thus, while young children form memories for specifics of structured experience, memory for derived associations is refined later-underscoring that adults and young children form different memories despite identical experience.

Task‐related functional neuroimaging contribution to sex/gender differences in cognition and emotion during development

Recent research has shown that sex/gender (s/g) influences on cognitive functions and related brain anatomy, functional responses, and connectivity are less clear than previously assumed, and most studies investigated adult population. In this mini-review, we summarize research progress in the study of s/g differences in the human brain function as investigated by neuroimaging methods adopting a developmental perspective. In particular, we review original studies published from 2000 to 2021 investigating s/g differences in task-related brain functional activation and connectivity in healthy children and adolescents. We summarize results about studies in the domains of language, visuospatial ability, social cognition, and executive functions. Overall, a clear relation between cognition and brain activation or connectivity pattern is far from being established and the few coherent results should be considered exploratory, despite in some cases, brain function seems to present specific patterns in comparison with what reported in adults. Moreover, future studies should address methodological limitations, such as fragmentation of tasks, lack of control for confounding variables, and lack of longitudinal designs to study developmental trajectories.

Developmental differences in memory reactivation relate to encoding and inference in the human brain

Despite the fact that children can draw on their memories to make novel inferences, it is unknown whether they do so through the same neural mechanisms as adults. We measured memory reinstatement as participants aged 7-30 years learned new, related information. While adults brought memories to mind throughout learning, adolescents did so only transiently, and children not at all. Analysis of trial-wise variability in reactivation showed that discrepant neural mechanisms-and in particular, what we interpret as suppression of interfering memories during learning in early adolescence-are nevertheless beneficial for later inference at each developmental stage. These results suggest that while adults build integrated memories well-suited to informing inference directly, children and adolescents instead must rely on separate memories to be individually referenced at the time of inference decisions.

Contextual features in the developing hippocampus: A representational similarity analysis

Functional divisions of labor in support of memory have been reported along the anterior-posterior axis of the hippocampus. However, little is known about how the developing hippocampus represents associative memories along this axis. The present research employed representational similarity analysis to ask whether developmental differences exist in the extent to which the anterior versus the posterior hippocampus represent features of the context and associative memories. Functional magnetic resonance imaging data were collected during the retrieval phase of an associative recognition task from 8-year-olds, 10-year-olds, and adults (N = 58). Participants were asked to retrieve pairs of items, which were presented either in the same location as during encoding or in a flipped location. In the anterior hippocampus and only for adults, pattern similarity between the two studied pair conditions was greater than pattern similarity between studied pairs presented in the same location and novel pairs. In contrast, this difference was not significant in the posterior hippocampus. Older, but not younger, children showed a similar, albeit attenuated, similarity pattern to that of adults, but measures of patterns similarity predicted associative recognition across ages. In addition, exploratory analyses showed that similarity patterns in the adult posterior, but not anterior, hippocampus tracked the order of the runs. Overall, the results suggest functional and developmental dissociations in processing different contextual features, with the anterior hippocampus responding to salient and rapid-changing features and the posterior hippocampus responding to slower-changing features of the context.

Age-Related Increases in Posterior Hippocampal Granularity Are Associated with Remote Detailed Episodic Memory in Development

Episodic memory is critical to human functioning. In adults, episodic memory involves a distributed neural circuit in which the hippocampus plays a central role. As episodic memory abilities continue to develop across childhood and into adolescence, studying episodic memory maturation can provide insight into the development and construction of these hippocampal networks, and ultimately clues to their function in adulthood. While past developmental studies have shown that the hippocampus helps to support memory in middle childhood and adolescence, the extent to which ongoing maturation within the hippocampus contributes to developmental change in episodic memory abilities remains unclear. In contrast, slower maturing regions, such as the PFC, have been suggested to be the neurobiological locus of memory improvements into adolescence. However, it is also possible that the methods used to detect hippocampal development during middle childhood and adolescence are not sensitive enough. Here, we examine how temporal covariance (or differentiation) in voxel representations within anterior and posterior hippocampus change with age to support the development of detailed recollection in male and female developing humans. We find age-related increases in the distinctiveness of temporal activation profiles in the posterior, but not anterior, hippocampus. Second, we show that this measure of granularity, when present during postencoding rest periods, correlates with the recall of detailed memories of preceding stimuli several weeks postencoding, suggesting that granularity may promote memory stabilization.SIGNIFICANCE STATEMENT Studying hippocampal maturation can provide insight into episodic memory development, as well as clues to episodic functioning in adulthood. Past work has shown evidence both for and against hippocampal contributions to age-related improvements in memory performance, but has relied heavily on univariate approaches (averaging activity across hippocampal voxels), which may not be sensitive to nuanced developmental change. Here we use a novel approach, examining time signatures in individual hippocampal voxels to reveal regionally specific (anterior vs posterior hippocampus) differences in the distinctiveness (granularity) of temporal activation profiles across development. Importantly, posterior hippocampus granularity during windows of putative memory stabilization was associated with long-term memory specificity. This suggests that the posterior hippocampus gradually builds the capacity to support detailed episodic recall.

Altered structure and functional connectivity of the hippocampus are associated with social and mathematical difficulties in nonverbal learning disability

The hippocampus is known to play a critical role in a variety of complex abilities, including visual-spatial reasoning, social functioning, and math. Nonverbal learning disability (NVLD) is a neurodevelopmental disorder characterized by deficits in visual-spatial reasoning that are accompanied by impairment in social function or mathematics, as well as motor or executive function skills. Despite the overlap between behaviors supported by the hippocampus and impairments in NVLD, the structure and function of the hippocampus in NVLD has not been studied. To address this gap in the literature, we first compared hippocampal volume and resting-state functional connectivity in children with NVLD (n = 24) and typically developing (TD) children (n = 20). We then explored associations between hippocampal structure, connectivity, and performance on measures of spatial, social, and mathematical ability. Relative to TD children, those with NVLD showed significant reductions in left hippocampal volume and greater hippocampal-cerebellar connectivity. In children with NVLD, reduced hippocampal volume associated with worse mathematical problem solving. Although children with NVLD exhibited more social problems (social responsiveness scale [SRS]) and higher hippocampal-cerebellar connectivity relative to TD children, greater connectivity was associated with fewer social problems among children with NVLD but not TD children. Such an effect may suggest a compensatory mechanism. These structural and functional alterations of the hippocampus may disrupt its putative role in organizing conceptual frameworks through cognitive mapping, thus contributing to the cross-domain difficulties that characterize NVLD.

Neural Development of Memory and Metamemory in Childhood and Adolescence: Toward an Integrative Model of the Development of Episodic Recollection

Memory and metamemory processes are essential to retrieve detailed memories and appreciate the phenomenological experience of recollection. Developmental cognitive neuroscience has made strides in revealing the neural changes associated with improvements in memory and metamemory during childhood and adolescence. We argue that hippocampal changes, in concert with surrounding cortical regions, support developmental improvements in the precision, complexity, and flexibility of memory representations. In contrast, changes in frontoparietal regions promote efficient encoding and retrieval strategies. A smaller body of literature on the neural substrates of metamemory development suggests that error monitoring processes implemented in the anterior insula and dorsal anterior cingulate cortex trigger, and perhaps support the development of, metacognitive evaluationsin the prefrontal cortex, while developmental changes in the parietal cortex support changes in the phenomenological experience of episodic retrieval. Our conclusions highlight the necessity of integrating these lines of research into a comprehensive model on the neurocognitive development of episodic recollection.

Functional parcellation of the hippocampus by semi-supervised clustering of resting state fMRI data

Many unsupervised methods are widely used for parcellating the brain. However, unsupervised methods aren’t able to integrate prior information, obtained from such as exiting functional neuroanatomy studies, to parcellate the brain, whereas the prior information guided semi-supervised method can generate more reliable brain parcellation. In this study, we propose a novel semi-supervised clustering method for parcellating the brain into spatially and functionally consistent parcels based on resting state functional magnetic resonance imaging (fMRI) data. Particularly, the prior supervised and spatial information is integrated into spectral clustering to achieve reliable brain parcellation. The proposed method has been validated in the hippocampus parcellation based on resting state fMRI data of 20 healthy adult subjects. The experimental results have demonstrated that the proposed method could successfully parcellate the hippocampus into head, body and tail parcels. The distinctive functional connectivity patterns of these parcels have further demonstrated the validity of the parcellation results. The effects of aging on the three hippocampus parcels’ functional connectivity were also explored across the healthy adult subjects. Compared with state-of-the-art methods, the proposed method had better performance on functional homogeneity. Furthermore, the proposed method had good test–retest reproducibility validated by parcellating the hippocampus based on three repeated resting state fMRI scans from 24 healthy adult subjects.

Developmental differences in temporal schema acquisition impact reasoning decisions

Schemas capture patterns across multiple experiences, accumulating information about common event structures that guide decision making in new contexts. Schemas are an important principle of leading theories of cognitive development; yet, we know little about how children and adolescents form schemas and use schematic knowledge to guide decisions. Here, we show that the ability to acquire schematic knowledge based on the temporal regularities of events increases during childhood and adolescence. Furthermore, we show that temporally mediated schematic knowledge biases reasoning decisions in an age-dependent manner. Participants with greater temporal schematic knowledge were more likely to infer that temporally related items shared other, non-temporal properties, with adults showing the greatest relationship between schema knowledge and reasoning choices. These data indicate that the mechanisms underlying schema formation and expression are not fully developed until adulthood and may reflect the ongoing maturation of hippocampus and prefrontal cortex through adolescence.

Memory and the developing brain: From description to explanation with innovation in methods

Recent advances in human cognitive neuroscience show great promise in extending our understanding of the neural basis of memory development. We briefly review the current state of knowledge, highlighting that most work has focused on describing the neural correlates of memory in cross-sectional studies. We then delineate three examples of the application of innovative methods in addressing questions that go beyond description, towards a mechanistic understanding of memory development. First, structural brain imaging and the harmonization of measurements across laboratories may uncover ways in which the maturation of the brain constrains the development of specific aspects of memory. Second, longitudinal designs and sophisticated modeling of the data may identify age-driven changes and the factors that determine individual developmental trajectories. Third, recording memory-related activity directly from the developing brain presents an unprecedented opportunity to examine how distinct brain structures support memory in real time. Finally, the growing prevalence of data sharing offers additional means to tackle questions that demand large-scale datasets, ambitious designs, and access to rare samples. We propose that the use of such innovative methods will move our understanding of memory development from a focus on describing trends to explaining the causal factors that shape behavior.

Longitudinal trajectories of hippocampal and prefrontal contributions to episodic retrieval: Effects of age and puberty

The current study investigated longitudinal change in hippocampal and prefrontal contribution to episodic retrieval. Functional neuroimaging data were collected during an item-context association memory task for children between the ages of 8 and 14 with individuals scanned 1-3 times over the course of 0.75-3.7 years (Timepoint 1 N = 90; Timepoint 2 N = 83, Timepoint 3 N = 75). We investigated developmental changes in functional activation associated with episodic retrieval (correct item-context > incorrect item-context contrast) and asked whether pubertal changes contributed to developmental changes in pattern of activation. Non-linear developmental trajectories were observed. In the hippocampus, activation decreased with age during childhood and then increased into early adolescence. In the dorsolateral prefrontal cortex, activation was largely absent initially, but quickly accelerated over time. Independent of age, changes in pubertal status additionally predicted increases in item-context activation in initially older children, and decreases in initially younger children across both regions and two indicators of puberty: the Pubertal Development Scale and salivary testosterone. These findings suggest that changes in both age and pubertal status uniquely contribute to memory-related activation, and the timing of pubertal onset may play an important role in the neural mechanisms supporting memory retrieval.

Differential Effects of Salient Visual Events on Memory-Guided Attention in Adults and Children

Both salient visual events and scene‐based memories can influence attention, but it is unclear how they interact in children and adults. In Experiment 1, children (N = 27; ages 7–12) were faster to discriminate targets when they appeared at the same versus different location as they had previously learned or as a salient visual event. In contrast, adults (N = 30; ages 18–31) responded faster only when cued by visual events. While Experiment 2 confirmed that adults (N = 27) can use memories to orient attention, Experiment 3 showed that, even in the absence of visual events, the effects of memories on attention were larger in children (N = 27) versus adults (N = 28). These findings suggest that memories may be a robust source of influence on children's attention.

Past is prologue: The role of memory retrieval in young children's episodic prospection

Prior research has revealed a strong link between the ability to remember one's past (i.e., episodic memory) and the ability to envision one's future (i.e., episodic prospection). Indeed, the past holds valuable learning experiences that can inform future choices and plans. Although these abilities both emerge during preschool years, there exist few theoretical accounts of how memory processes might support developmental improvements in prospection abilities. We developed a novel paradigm to determine whether young children (3 and 4 years of age) use past knowledge to inform future choices. Experiment 1 revealed that children find it more difficult to retrieve relevant information from their past when they envision the future versus reflect on the past. Experiment 2 facilitated children's access to past event components and, thereby, eased retrieval of relevant components from memory for future event construction. We discuss results in light of recent proposals on the development of episodic prospection.

Memory-related hippocampal activation in the sleeping toddler

Nonhuman research has implicated developmental processes within the hippocampus in the emergence and early development of episodic memory, but methodological challenges have hindered assessments of this possibility in humans. Here, we delivered a previously learned song and a novel song to 2-year-old toddlers during natural nocturnal sleep and, using functional magnetic resonance imaging, found that hippocampal activation was stronger for the learned song compared with the novel song. This was true regardless of whether the song was presented intact or backwards. Toddlers who remembered where and in the presence of which toy character they heard the song exhibited stronger hippocampal activation for the song. The results establish that hippocampal activation in toddlers reflects past experiences, persists despite some alteration of the stimulus, and is associated with behavior. This research sheds light on early hippocampal and memory functioning and offers an approach to interrogate the neural substrates of early memory.

Development of Episodic Prospection: Factors Underlying Improvements in Middle and Late Childhood

Episodic prospection is the mental simulation of a personal future event in rich contextual detail. This study examined age-related differences in episodic prospection in 5- to 11-year-olds and adults (N = 157), as well as factors that may contribute to developmental improvements. Participants' narratives of past, future, and make-believe events were coded for episodic content, and self-concept coherence (i.e., how coherently an individual sees himself or herself) and narrative ability were tested as predictors of episodic prospection. Although all ages provided less episodic content for future event narratives, age-related improvements were observed across childhood, suggesting future event generation is particularly difficult for children. Self-concept coherence and narrative ability each independently predicted the episodic content of 5- and 7-year-olds' future event narratives.

Hippocampal CA3-dentate gyrus volume uniquely linked to improvement in associative memory from childhood to adulthood

Associative memory develops into adulthood and critically depends on the hippocampus. The hippocampus is a complex structure composed of subfields that are functionally-distinct, and anterior-posterior divisions along the length of the hippocampal horizontal axis that may also differ by cognitive correlates. Although each of these aspects has been considered independently, here we evaluate their relative contributions as correlates of age-related improvement in memory. Volumes of hippocampal subfields (subiculum, CA1-2, CA3-dentate gyrus) and anterior-posterior divisions (hippocampal head, body, tail) were manually segmented from high-resolution images in a sample of healthy participants (age 8-25 years). Adults had smaller CA3-dentate gyrus volume as compared to children, which accounted for 67% of the indirect effect of age predicting better associative memory via hippocampal volumes. Whereas hippocampal body volume demonstrated non-linear age differences, larger hippocampal body volume was weakly related to better associative memory only when accounting for the mutual correlation with subfields measured within that region. Thus, typical development of associative memory was largely explained by age-related differences in CA3-dentate gyrus.

Age- and performance-related differences in hippocampal contributions to episodic retrieval

•

Age differences are found in hippocampal activity for source retrieval.

•

Performance differences are found in hippocampal activity for source retrieval.

•

8- to 9-year-olds do not show performance-related differences in activity.

•

In 10- to 11-year-olds, only high performers engaged hippocampus for source retrieval.

•

High performing adults engage the hippocampal head selectively.

The goal of the present study was to investigate whether hippocampal contribution to episodic memory retrieval varies as a function of age (8–9 versus 10–11 versus adults), performance levels (high versus low) and hippocampal sub-region (head, body, tail). We examined fMRI data collected during episodic retrieval from a large sample (N = 126). Participants judged whether a stimulus had been encoded previously, and, if so, which of three scenes it had been paired with (i.e., source judgment). For 8- to 9-years-olds as well as low-performing 10- to 11-year-olds, hippocampal activations did not reliably differentiate between trials on which item-scene associations were correctly recalled (correct source), incorrectly recalled (incorrect source), or trials on which the item was forgotten (miss trials). For high-performing 10–11-year olds and low-performing adults, selective hippocampal activation was observed for correct source relative to incorrect source and miss trials; this effect was observed across the entire hippocampus. For high-performing adults, hippocampal activation also distinguished between correct and incorrect source trialsl, but only in the hippocampal head, suggesting that good performance in adults is associated with more focal hippocampal recruitment. Thus, both age and performance are important factors for understanding the development of memory and hippocampal function.

A Time and Place for Everything: Developmental Differences in the Building Blocks of Episodic Memory

This research investigated whether episodic memory development can be explained by improvements in relational binding processes, involved in forming novel associations between events and the context in which they occurred. Memory for item-space, item-time, and item-item relations was assessed in an ethnically diverse sample of 151 children aged 7-11 years and 28 young adults. Item-space memory reached adult performance by 9½ years, whereas item-time and item-item memory improved into adulthood. In path analysis, item-space, but not item-time best explained item-item memory. Across age groups, relational binding related to source memory and performance on standardized memory assessments. In conclusion, relational binding development depends on relation type, but relational binding overall supports episodic memory development.