Asynchronous development of memory integration and differentiation influences temporal memory organization.

Adults remember items with shared contexts as occurring closer in time to one another than those associated with different contexts, even when their objective temporal distance is fixed. Such temporal memory biases are thought to reflect within-event integration and between-event differentiation processes that organize events according to their contextual similarities and differences, respectively. Within-event integration and between-event differentiation are hypothesized to differentially rely on binding and control processes, which may develop at different ages. To test this hypothesis, 5- to 12-year-olds and adults (N = 134) studied quartets of image pairs that contained either the same scene (same-context) or different scenes (different-context). Participants remembered same-context items as occurring closer in time by older childhood (7-9 years), whereas different-context items were remembered as occurring farther apart by early adolescence (10-12 years). The differential emergence of these temporal memory biases suggests within-event integration and between-event differentiation emerge at different ages. RESEARCH HIGHLIGHTS: Children are less likely than adults to use contextual information (e.g., location) to organize their continuous experience in memory, as indicated by temporal memory biases. Biases reflecting within-event integration (i.e., remembering elements with a shared context as occurring closer together in time) emerged in late childhood. Biases reflecting between-event differentiation (i.e., remembering elements from different contexts as occurring farther apart in time) emerged in early adolescence. The differential emergence of biases reflecting within-event integration and between-event differentiation suggests they are distinct, yet complementary, processes that support developmental improvements in event memory organization.

Self-derivation of new knowledge through memory integration varies as a function of prior knowledge.

ABSTRACTThe current research was an investigation of the effects of prior, domain-relevant knowledge on self-derivation of new, integrated knowledge. Adults were presented with novel "stem" facts and tested for self-derivation of new knowledge through integration of the facts in memory. To examine the effects of prior knowledge on memory integration, we tested participants under three within-subject conditions, in which in advance of stem encoding, they were provided with either: (1) no domain relevant information (No Knowledge control), (2) generally relevant information about the domain (General), or (3) generally relevant information about the domain along with a stem fact that was directly necessary for self-derivation (General + Stem). Prior exposure to both General and General + Stem knowledge facilitated memory for the novel, explicitly-taught stem facts. Moreover, for both prior knowledge conditions, the amount of domain-relevant knowledge retained in memory was associated with trial-by-trial self-derivation success. Importantly, the type of prior knowledge modulated memory integration in different ways. Whereas General + Stem knowledge enhanced selective retrieval and integration of the stem facts, General knowledge supported learning of the individual stem facts, but not their integration with one another. Together, the findings indicate how malleable, domain-specific experience shapes encoding, integration, and flexible extension of new, related information.

Delta-modulated cortical alpha oscillations support new knowledge generation through memory integration.

The ability to generate new knowledge depends on integration of separate information. For example, in one episode an individual may learn that apple seeds are called pips. In a separate episode, the individual may then learn that pips contain cyanide. Integration of the related facts in memory may then support derivation of the new knowledge that apple seeds contain cyanide. Past studies show that adults form relational memories that represent the commonalities among discrete events, and that such integrated representation supports the ability to infer new knowledge. Although these integrated representations are thought to result from linking separate memories to the same neuronal ensemble, the neural mechanisms that underlie formation of such linkages are not well understood. Here we examined whether self-derivation of new, integrated knowledge was supported by oscillatory coherence, a means of linking discrete neuronal ensembles. Cortical alpha coherence was greater when adults encoded new facts that could be integrated with existing knowledge, relative to encoding unrelated facts, particularly in participants who showed better performance on the subsequent test of knowledge generation via fact integration. In high performers, posterior alpha amplitude was also modulated by delta phase, a form of cross-frequency coupling previously implicated in coordinating information stored widely throughout the cortex. Examination of the timing and topography of these respective signatures suggested that these oscillatory dynamics work in concert to encode and represent new knowledge with respect to prior knowledge that is reactivated, thus revealing fundamental mechanisms through which related memories are linked into integrated knowledge structures.

Using Event-related Potentials to Inform the Neurocognitive Processes Underlying Knowledge Extension through Memory Integration.

To build a general knowledge base, it is imperative that individuals acquire, integrate, and further extend knowledge across experiences. For instance, in one episode an individual may learn that George Washington was the first president. In a separate episode they may then learn that Washington was the commander of the Continental Army. Integration of the information in memory may then support self-derivation of the new knowledge that the leader of the Continental Army was also the first president. Despite a considerable amount of fMRI research aimed at further elucidating the neuroanatomical regions supporting this ability, a consensus has yet to be reached with regards to the precise neurocognitive processes involved. In the present research, we capitalized on the high temporal resolution of event-related potentials (ERPs) to inform the time course of processes elicited during successful integration and further extension of new factual knowledge. Adults read novel, related stem facts and were tested for self-derivation of novel integration facts while ERPs were recorded. Consistent with current theoretical models, memory integration was first triggered by novelty detection within 400 msec of experience of a second, related stem fact. Two additional temporally staged encoding processes were then observed interpreted to reflect (1) explicit meaning comprehension and (2) representation of the integrated relation in memory. During the test for self-derivation, a single ERP was elicited, which presumably reflected retrieval and/or recombination of previously integrated knowledge. Together, the present research provides important insight into the time course of neurocognitive processing associated with the formation of a knowledge base.

Young adults self-derive and retain new factual knowledge through memory integration.

The present research investigated the retention of new factual knowledge derived through integration of information acquired across temporally distributed learning episodes. Young adults were exposed to novel facts as they read long lists of seemingly unrelated information, one sentence at a time. They then were presented open-ended questions, the answers to which could be self-derived through integration of pairs of facts from the list. Experiment 1 was the first test of self-derivation of new factual knowledge through integration in adults using open-ended testing (as opposed to forced-choice testing). Participants successfully self-derived integrated knowledge under these more challenging conditions. Experiment 2 was a test for long-term retention of newly self-derived information. Newly derived knowledge remained accessible after a 1-week delay. Striking individual differences were also observed, which were related to whether individuals spontaneously identified the relational structure of the learning task. Insight into the relation between explicit task knowledge and strategic processing was also revealed through examination of response speed at the time of test. Specifically, knowledge of the task structure was associated with response latencies on unsuccessful (but not successful) trials, such that participants who were aware of the opportunity to integrate spent longer when they were subsequently unsuccessful, presumably reflecting directed search strategies and heightened perseverance when those processes failed. Together, the present findings provide direct evidence for the role of memory integration in the long-term accumulation of a semantic knowledge base and have theoretical implications for our understanding of this fundamental form of learning.

Integrating across episodes: Investigating the long-term accessibility of self-derived knowledge in 4-year-old children.

Semantic memory, defined as our store of knowledge about the world, provides representational support for all of our higher order cognitive functions. As such, it is crucial that the contents of semantic memory remain accessible over time. Although memory for knowledge learned through direct observation has been investigated previously, we know very little about the retention of knowledge derived through integration of information acquired across separate learning episodes. The current research investigated cross-episode integration in 4-year-old children. Participants were presented with novel facts via distinct story episodes and tested for knowledge extension through cross-episode integration as well as for retention of the information over a 1-week delay. In Experiment 1, children retained the self-derived knowledge over the delay, although performance was primarily evidenced in a forced-choice format. In Experiment 2, we sought to facilitate the accessibility and robustness of self-derived knowledge by providing a verbal reminder after the delay. The accessibility of self-derived knowledge increased irrespective of whether participants successfully demonstrated knowledge of the integration facts during the first visit. The results suggest that knowledge extended through integration remains accessible after delays even in a population where this learning process is less robust. The findings also demonstrate the facilitative effect of reminders on the accessibility and further extension of knowledge over extended time periods.

Effects of delays on 6-year-old children's self-generation and retention of knowledge through integration.

The current research was an investigation of the effect of delay on self-generation and retention of knowledge derived through integration by 6-year-old children. Children were presented with novel facts from passages read aloud to them (i.e., "stem" facts) and tested for self-generation of new knowledge through integration of the facts. In Experiment 1, children integrated the stem facts at Session 1 and retained the self-generated memory traces over 1 week. In Experiment 2, 1-week delays were imposed either between the to-be-integrated facts (between-stem delay) or after the stem facts but before the test (before-test delay). Integration performance was diminished in both conditions. Moreover, memory for individual stem facts was lower in Experiment 2 than in Experiment 1, suggesting that self-generation through integration promoted memory for explicitly taught information. The results indicate the importance of tests for promoting self-generation through integration as well as for retaining newly self-generated and explicitly taught information.

Neuropsychological assessment of memory in preschoolers.

Memory is of fundamental importance for cognitive, social, and educational function, making it a target for neuropsychological assessment. The subject of this review is one particular type of memory, namely, episodic memory of unique events and experiences. Episodic memory allows for rapid, even one-trial learning of new information and retention of it for later retrieval. It depends on a particular neural substrate that undergoes a protracted developmental course. The review features discussion of some of the challenges associated with valid assessment of this specific form of memory in the preschool period, as well as a description and critical evaluation of available standardized measures. It also features description of two new approaches to assessment of episodic memory and their sensitivity to memory-specific deficits in the preschool years and in infancy. The review ends with introduction of the NIH Toolbox Picture Sequence Memory Test, designed as a measure of episodic memory in the preschool years and beyond.

characters and clues: factors affecting children's extension of knowledge through integration of separate episodes.

Children build up knowledge about the world and also remember individual episodes. How individual episodes during which children learn new things become integrated with one another to form general knowledge is only beginning to be explored. Integration between separate episodes is called on in educational contexts and in everyday life as a major means of extending knowledge and organizing information. Bauer and San Souci (2010) provided an initial demonstration that 6-year-olds extend their knowledge by integrating between separate but related episodes; the episodes shared a high level of surface similarity. Experiments 1A and 1B of the current research were tests of integration under low and high levels of surface similarity, respectively. In Experiment 1A, when surface similarity of the episodes was low, 6-year-olds integrated between passages of text, yet their performance was not as robust as observed previously. In Experiment 1B, when surface similarity of the episodes was high, a replication of Bauer and San Souci's results was observed. In Experiment 2, we tested whether a "hint" to consult the information learned in the passages improved performance even when surface level similarity was low. The hint had a strong facilitating effect. Possible mechanisms of integration between separate yet related episodes are discussed.

Interpersonal Family Dynamics Relate to Hippocampal CA Subfield Structure.

Social environments that are extremely enriched or adverse can influence hippocampal volume. Though most individuals experience social environments that fall somewhere in between these extremes, substantially less is known about the influence of normative variation in social environments on hippocampal structure. Here, we examined whether hippocampal volume tracks normative variation in interpersonal family dynamics in 7- to 12-year-olds and adults recruited from the general population. We focused on interpersonal family dynamics as a prominent feature of one's social world. Given evidence that CA1 and CA2 play a key role in tracking social information, we related individual hippocampal subfield volumes to interpersonal family dynamics. More positive perceptions of interpersonal family dynamics were associated with greater CA1 and CA2/3 volume regardless of age and controlling for socioeconomic status. These data suggest that CA subfields are sensitive to normative variation in social environments and identify interpersonal family dynamics as an impactful environmental feature.

Cognitive correlates of memory integration across development: Explaining variability in an educationally relevant phenomenon.

The current research was an investigation of the cognitive correlates of individual differences in participants' capacity to derive new factual knowledge through integration of information acquired across separate yet related learning episodes. In a sample of 117 adults (Experiment 1) and 57 children aged 8 to 10 years (Experiment 2), we investigated the respective roles of verbal comprehension, working memory span, and relational reasoning in self-derivation of new knowledge through memory integration. The findings revealed patterns of consistency and inconsistency in the cognitive profiles underlying this form of learning in adults and children. In both adults and children, verbal knowledge and skills accounted for variability in self-derivation. Variance in adults, but not in children, was further explained by working memory. Given that individual differences in self-derivation have implications for real-world academic outcome, we also investigated the association between self-derivation and academic performance. We found that performance on the experimentally based self-derivation paradigm was related to concurrent and longitudinal academic success in both samples. The present research thus builds on the growing body of behavioral and neuroscientific research to advance our understanding of the cognitive factors associated with behaviors that depend on memory integration in both childhood and adulthood and also provides suggestive evidence of critical ways in which the process may differ in children and adults. Together, the findings provide a theoretically plausible and practically significant framework from which to guide future research aimed at enhancing this educationally relevant learning phenomenon. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Relations between neural structures and children's self-derivation of new knowledge through memory integration.

Accumulation of semantic or factual knowledge is a major task during development. Knowledge builds through direct experience and explicit instruction as well as through productive processes that permit derivation of new understandings. In the present research, we tested the neural bases of the specific productive process of self-derivation of new factual knowledge through integration of separate yet related episodes of new learning. The process serves as an ecologically valid model of semantic knowledge accumulation. We tested structure/behavior relations in 5- to 8-year-old children, a period characterized by both age-related differences and individual variability in self-derivation, as well as in the neural regions implicated in memory integration, namely the hippocampus and prefrontal cortex. After controlling for the variance in task performance explained by age, sex, verbal IQ, and gray-matter volume (medial prefrontal cortex, mPFC, only), we observed relations between right mPFC thickness and memory for information explicitly taught to the children as well as the new information they self-derived; relations with the volume of the right hippocampus approached significance. This research provides the first evidence of the neural substrate that subserves children's accumulation of knowledge via self-derivation through memory integration, an empirically demonstrated, functionally significant learning mechanism.

Cortical dynamics of emotional autobiographical memory retrieval differ between women and men.

Retrieval of autobiographical memories entails periods of search, access, and elaboration. Women's reports of their memories feature more detail and emotional content relative to men's. A key question is how these gender differences relate to unfolding changes in cortical activity during retrieval. We recorded EEG activity from 32 scalp electrodes as women and men were cued to retrieve positive, negative, and neutral autobiographical memories. Alpha (9-12Hz) oscillations were prominent at all EEG channels. Alpha coherence between channels was calculated as a measure of ms-level cortical synchrony. Across participants and memory types, a frontal cluster showed pronounced decreases in coherence with other channels during the first second of autobiographical retrieval. In the following second, a left parietal-centered cluster showed increased coherence with other channels. This effect strengthened and spread in the third second of retrieval, perhaps reflecting trace elaboration and/or evaluation of the memory. Although women and men gave similar subjective ratings of their memories, the second-by-second pattern of alpha coherence during autobiographical retrieval differed by gender and memory type. Specifically, women sustained the increased pattern of left-parietal coherence throughout the trial, whereas for men, alpha coherence in this cluster returned to baseline by second two for neutral memories and by second three for emotional memories. Examination of the temporal dynamics of cortical oscillations provides novel insight into autobiographical memory retrieval processes and to gendered retrieval in particular, suggesting that women may persist with elaboration and/or evaluation to a greater extent than men.

Detection of human hematopoietic stem cell engraftment in the livers of adult immunodeficient mice by an optimized flow cytometric method.

Immunodeficient NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ (NSG) mice are a valuable resource to study human hematopoietic stem cells. Prolonged multilineage hematopoiesis indicates stem cell engraftment and generally is measured by flow cytometry. In this study, we took advantage of the multi-parameter detection afforded by modern flow cytometers to optimize detection of human hematopoiesis in NSG mice. Antigens widely expressed by mouse or human cells were evaluated as markers to distinguish mixtures of these cells to optimize and test the limits of chimerism detection. The bone marrow, spleen, and liver of NSG mice transplanted with human hematopoietic cells were analyzed for evidence of engraftment.Mouse bone marrow cells were best marked for exclusion by staining with a combination of CD45, TER-119, and anti-H-2K(d) monoclonal antibodies, whereas live human cells were most accurately identified by elimination of cell doublets and positive staining for CD59. Human stem cells (CD34(++)CD133(+)CD38(low)) and progenitors were detected in the bone marrow and liver, but not in the spleen. An unusual pattern of myeloid antigen expression was detected in the bone marrow and CD3(+)CD4(+)CD8(+) T-cells were detected in the spleen. We concluded that multicolor flow cytometric analysis that clearly distinguishes mouse and human cells offers accurate detection of human chimerism in NSG mice. Human hematopoiesis can be detected in the bone marrow and liver of NSG mice with T-lymphopoiesis, possibly occurring in the spleen.