Developmental differences in medial temporal lobe function during memory encoding

Neuroanatomical correlates of behavioral rating versus performance measures of working memory in typically developing children and adolescents

OBJECTIVE

The frequent lack of correspondence between performance and observational measures of executive functioning, including working memory, has raised questions about the validity of the observational measures. This study was conducted to investigate sources of this discrepancy through correlation of volumetric and cortical thickness (CT) neuroimaging values with performance and questionnaire measures of working memory (WM).

METHODS

Using longitudinal data from the NIH MRI Study of Normal Brain Development (Volumes, N= 347, 54.3% female; CT, N= 350, 54.6% female; age range: 6 to 16.9 years), scores on the Behavioral Rating Inventory of Executive Function (BRIEF) WM, Emotional Control (EC) and Inhibition (INH) scales; Wechsler Scale of Intelligence for Children-III Digit Span; and Cambridge Neuropsychological Test Battery Spatial Working Memory (CANTAB SWM) were correlated with each other and with morphometric measurements using mixed effects linear regression models.

RESULTS

BRIEF WM was correlated with CANTAB SWM (p < .001). With whole brain correction, BRIEF WM and EC were both correlated with CT of the posterior parahippocampal gyrus (PHG), EC on the right side only. Performance measures of WM were unrelated to lobar volumes or CT, but were associated with volumes of hippocampus and amygdala.

CONCLUSIONS

The known role of PHG in contextual learning suggests that the BRIEF WM assesses contextualized learning/memory, potentially explaining its loose correspondence to the decontextualized performance measures. Observational measures can be useful and valid functional metrics, complementing performance measures. Labels used to characterize scales should be interpreted with caution, however.

Regional hippocampal volumes and development predict learning and memory

The hippocampus is an anatomically and functionally heterogeneous structure, but longitudinal studies of its regional development are scarce and it is not known whether protracted maturation of the hippocampus in adolescence is related to memory development. First, we investigated hippocampal subfield development using 170 longitudinally acquired brain magnetic resonance imaging scans from 85 participants aged 8-21 years. Hippocampal subfield volumes were estimated by the use of automated segmentation of 7 subfields, including the cornu ammonis (CA) sectors and the dentate gyrus (DG), while longitudinal subfield volumetric change was quantified using a nonlinear registration procedure. Second, associations between subfield volumes and change and verbal learning/memory across multiple retention intervals (5 min, 30 min and 1 week) were tested. It was hypothesized that short and intermediate memory would be more closely related to CA2-3/CA4-DG and extended, remote memory to CA1. Change rates were significantly different across hippocampal subfields, but nearly all subfields showed significant volume decreases over time throughout adolescence. Several subfield volumes were larger in the right hemisphere and in males, while for change rates there were no hemisphere or sex differences. Partly in support of the hypotheses, greater volume of CA1 and CA2-3 was related to recall and retention after an extended delay, while longitudinal reduction of CA2-3 and CA4-DG was related to learning. This suggests continued regional development of the hippocampus across adolescence and that volume and volume change in specific subfields differentially predict verbal learning and memory over different retention intervals, but future high-resolution studies are called for.

The Contribution of Executive Function to Source Memory Development in Early Childhood

Age-related differences in episodic memory judgments assessing recall of fact information and the source of this information were examined. The role of executive function in supporting early episodic memory ability was also explored. Four- and 6-year-old children were taught 10 novel facts from two different sources (experimenter or puppet) and memory for both fact and source information was later tested. Measures of working memory, inhibitory control, and set-shifting were obtained to produce an indicator of children's executive function. Six-year-olds recalled more fact and source information than 4-year-olds. Regression analyses revealed that age, language ability, and executive function accounted for unique variance in children's fact recall and source recall performance. These findings suggest a link between episodic memory and executive function, and we propose that developmental investigations should further explore this association.

Volume of hippocampal subfields and episodic memory in childhood and adolescence

Episodic memory critically depends on the hippocampus to bind the features of an experience into memory. Episodic memory develops in childhood and adolescence, and hippocampal changes during this period may contribute to this development. Little is known, however, about how the hippocampus contributes to episodic memory development. The hippocampus is comprised of several cytoarchitectural subfields with functional significance for episodic memory. However, hippocampal subfields have not been assessed in vivo during child development, nor has their relation with episodic memory been assessed during this period. In the present study, high-resolution T2-weighted images of the hippocampus were acquired in 39 children and adolescents aged 8 to 14 years (M=11.30, SD=2.38), and hippocampal subfields were segmented using a protocol previously validated in adult populations. We first validated the method in children and adolescents and examined age-related differences in hippocampal subfields and correlations between subfield volumes and episodic memory. Significant age-related increases in the subfield volume were observed into early adolescence in the right CA3/DG and CA1. The right CA3/DG subfield volumes were positively correlated with accurate episodic memory for item-color relations, and the right CA3/DG and subiculum were negatively correlated with item false alarm rates. Subfield development appears to follow a protracted developmental trajectory, and likely plays a pivotal role in episodic memory development.

Two rooms, two representations? Episodic-like memory in toddlers and preschoolers

Episodic memory involves binding together what-where-when associations. In three experiments, we tested the development of memory for such contextual associations in a naturalistic setting. Children searched for toys in two rooms with two different experimenters; each room contained two identical sets of four containers, but arranged differently. A distinct toy was hidden in a distinct container in each room. In Experiment 1, which involved children between 15 and 26 months who were prompted with a very explicit cue (a part of the hidden toy), we found a marked shift in performance with age: while 15- to 20-month-olds concentrated their searches on the two containers that sometimes contained toys, they did not distinguish between them according to context, but 21-26-month-olds did. However, surprisingly, without toy cues, even the youngest children showed a fragile ability to disambiguate the two containers by room context. In Experiment 2, we tested 34- to 40-month-olds and 64- to 72-month-olds without toy cues. The 5-year-olds were nearly perfect, and the 3-year-olds showed a significant preference for the correct container given only the context. In Experiment 3, we filled in the age range, and also investigated the effects of the use of labels (i.e. names of experimenters and rooms) and of familiarization time, in groups of 34- to 40-month-olds, 42- to 48-month-olds, and 50- to 56-month-olds. Neither labels nor familiarization time had an effect. Across experiments, there was regular age-related improvement in context-based memory. Overall, the results suggest that children's episodic memory may undergo an early qualitative change, yet to be precisely characterized, and that continuing increments in the use of contextual cues occur throughout the preschool period. A video abstract of this article can be viewed at https://www.youtube.com/watch?v=DkwEFw0UEz4&list=PLwxXcOKHPC0llAPVcJyW4EtzlA934A2Rz&index=1.

Remembering things without context: development matters

Spatial context supports memory retrieval in adults. To understand the development of these effects, context effects on object recognition were tested in neurotypical children ages 3 years to adulthood (n 3-6 years = 34, n 10-16 years = 32, n college age = 22) and individuals with Down syndrome (DS) ages 10-29 years (n = 21). Participants engaged in an object recognition task; objects were presented in scenes and either remained in that same scene or were removed at test. In some groups (< 4.5 years and with DS) context effects were present even though object recognition was poor. After 4.5 years, children demonstrated memory flexibility, while later in adolescence context effects reemerged, showing nonlinearity in the development of these effects.

Volumetric changes in hippocampal subregions and their relation to memory in pediatric nonlesional localization-related epilepsy

OBJECTIVE

Developmental differences in structure and function have been reported along the hippocampal subregions. The aims of this study were to determine if there were volumetric differences in hippocampal head (HH), body (HB), tail (HT), and total hippocampus (TotH)) in children with nonlesional localization-related epilepsy relative to controls, and the relation between hippocampal subregions with episodic memory and clinical parameters.

METHODS

Forty-eight children with nonlesional localization-related epilepsy, consisting of 29 left-sided and 19 right-sided epilepsy, and 27 healthy controls were recruited. All patients and controls underwent volumetric T1-weighted imaging, and verbal and nonverbal memory testing. The volume of hippocampal subregions was compared between patients and controls. The associations between left hippocampal subregions with verbal memory; right hippocampal subregions with nonverbal memory; and hippocampal subregions with age, age at seizure onset, and seizure frequency were assessed.

RESULTS

Patients with left-sided epilepsy had smaller left HH (p = 0.003) and HB (p = 0.012), right HB (p = 0.021) and HT (p = 0.015), and right TotH (p = 0.020) volumes. Those with right-sided epilepsy had smaller right HT (p = 0.018) volume. There were no statistically significant differences between verbal and nonverbal memory in left-sided and right-sided epilepsy relative to controls (all p > 0.025). In left-sided epilepsy, there was a significant association between left HH volume with verbal memory (β = 0.492, p = 0.001). There was no significant association between left and right hippocampal subregions with verbal and nonverbal memory, respectively, in right-sided epilepsy and controls (all p > 0.002). In left-sided and right-sided epilepsy, there was no significant association between hippocampal subregions with age, age at seizure onset, and seizure frequency (all p > 0.002).

SIGNIFICANCE

We have found hippocampal volume reduction, but did not identify a gradient in the severity of volume reduction along the hippocampal axis in children with localization-related epilepsy. Further study is needed to clarify if there are volumetric changes within the cornu ammonis subfields and dentate gyrus. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Changes to memory structures in children treated for posterior fossa tumors

Children treated for medulloblastoma (MB) exhibit long-term impairments in declarative memory, but the pathophysiology underlying this is unclear. Previous studies report declines in global white matter volume, but have failed to link this to declines in memory performance. We examined the effects of treatment on measures of global brain structure (i.e., total white and gray matter volume) and specific memory structures (i.e., hippocampus and uncinate fasciculus). We used volumetric MRI and diffusion tensor imaging in pediatric survivors of MB and one survivor of astrocytoma treated with cranial-spinal radiation (n = 20), and healthy controls (n = 13). Compared to controls, the survivor group exhibited reduced white matter volume, damage to the uncinate fasciculus, and a smaller right hippocampus. Critically, reduced hippocampal volume was not related to differences in brain volume, suggesting that the hippocampus may be especially vulnerable to treatment effects. A subset of the survivors (n = 10) also underwent memory testing using the Children's Memory Scale (CMS). Performance on the general index of the CMS was significantly correlated with measures of hippocampal volume and uncinate fasciculus. The examination of treatment effects on specific brain regions provides a better understanding of long-term cognitive outcome in children with brain tumors, particularly medulloblastoma.

Subjective experience of episodic memory and metacognition: a neurodevelopmental approach

Episodic retrieval is characterized by the subjective experience of remembering. This experience enables the co-ordination of memory retrieval processes and can be acted on metacognitively. In successful retrieval, the feeling of remembering may be accompanied by recall of important contextual information. On the other hand, when people fail (or struggle) to retrieve information, other feelings, thoughts, and information may come to mind. In this review, we examine the subjective and metacognitive basis of episodic memory function from a neurodevelopmental perspective, looking at recollection paradigms (such as source memory, and the report of recollective experience) and metacognitive paradigms such as the feeling of knowing). We start by considering healthy development, and provide a brief review of the development of episodic memory, with a particular focus on the ability of children to report first-person experiences of remembering. We then consider neurodevelopmental disorders (NDDs) such as amnesia acquired in infancy, autism, Williams syndrome, Down syndrome, or 22q11.2 deletion syndrome. This review shows that different episodic processes develop at different rates, and that across a broad set of different NDDs there are various types of episodic memory impairment, each with possibly a different character. This literature is in agreement with the idea that episodic memory is a multifaceted process.

Memory for fearful faces across development: specialization of amygdala nuclei and medial temporal lobe structures

Enhanced memory for emotional faces is a significant component of adaptive social interactions, but little is known on its neural developmental correlates. We explored the role of amygdaloid complex (AC) and medial temporal lobe (MTL) in emotional memory recognition across development, by comparing fMRI activations of successful memory encoding of fearful and neutral faces in children (n = 12; 8-12 years) and adolescents (n = 12; 13-17 years). Memory for fearful faces was enhanced compared with neutral ones in adolescents, as opposed to children. In adolescents, activations associated with successful encoding of fearful faces were centered on baso-lateral AC nuclei, hippocampus, enthorhinal and parahippocampal cortices. In children, successful encoding of fearful faces relied on activations of centro-mesial AC nuclei, which was not accompanied by functional activation of MTL memory structures. Successful encoding of neutral faces depended on activations in anterior MTL region (hippocampal head and body) in adolescents, but more posterior ones (hippocampal tail and parahippocampal cortex) in children. In conclusion, two distinct functional specializations emerge from childhood to adolescence and result in the enhancement of memory for these particular stimuli: the specialization of baso-lateral AC nuclei, which is associated with the expertise in processing emotional facial expression, and which is intimately related to the specialization of MTL memory network. How the interplay between specialization of AC nuclei and of MTL memory structures is fundamental for the edification of social interactions remains to be elucidated.

Age differences in hippocampus-cortex connectivity during true and false memory retrieval

The present functional magnetic resonance imaging (fMRI) study investigated developmental differences in functional connectivity associated with true and false memory retrieval. A sample of 8- to 9-year-olds and adults (N = 31) was assessed with the Deese/Roediger-McDermott (DRM) paradigm, known to induce high levels of false recognition of lures that are semantically associated with studied items. The strength of semantic association among list items was manipulated. Relative to children, adults correctly recognized more studied items and falsely recognized more critical lures. High-association lists resulted in higher recognition of both studied items and critical lures. Functional connectivity analysis revealed that, overall, true recognition was supported by coupling within two hippocampal-temporal and fronto-parietal set of regions; in contrast, coupling among more distributed hippocampal-temporal-parietal-frontal regions was observed during false recognition. Critically, adults, compared to children, exhibited stronger hippocampal/parietal coupling and stronger hippocampal/dorsolateral prefrontal cortex (PFC) coupling for veridical recognition of high-associative strength items. In contrast, children, compared to adults, exhibited stronger hippocampus/ventrolateral PFC coupling and stronger bilateral middle-temporal gyrus/ventrolateral PFC coupling for high-associative strength critical lures. Our results underscored a role for the anterior hippocampus in true and false recognition, showing different functional patterns as a function of age and association strength.

Autobiographical memory in children with temporal lobe epilepsy

Autobiographical memory involves the recall of personal facts (semantic memory) and re-experiencing of specific personal events (episodic memory). Although impairments in autobiographical memory have been found in adults with unilateral temporal lobe epilepsy (TLE) and attributed to compromised hippocampal integrity, it is not yet known whether this occurs in children with TLE. In the current study, 21 children with TLE and 24 healthy controls of comparable age, sex, and socioeconomic status were administered the Children's Autobiographical Interview. Compared to controls, children with TLE recalled fewer episodic details, but only when no retrieval prompts were provided. There was no difference between the groups for semantic autobiographic details. Interestingly, the number of episodic details recalled increased significantly from 6 to 16 years of age in healthy control children, but not in children with TLE. Exploratory analyses revealed that, within the group of children with TLE, epilepsy factors, including presence or absence of structural hippocampal abnormalities, did not relate to the richness of episodic recall. Our results provide first evidence of autobiographical episodic memory deficits in children with TLE.

The influence of prior knowledge on memory: a developmental cognitive neuroscience perspective

Across ontogenetic development, individuals gather manifold experiences during which they detect regularities in their environment and thereby accumulate knowledge. This knowledge is used to guide behavior, make predictions, and acquire further new knowledge. In this review, we discuss the influence of prior knowledge on memory from both the psychology and the emerging cognitive neuroscience literature and provide a developmental perspective on this topic. Recent neuroscience findings point to a prominent role of the medial prefrontal cortex (mPFC) and of the hippocampus (HC) in the emergence of prior knowledge and in its application during the processes of successful memory encoding, consolidation, and retrieval. We take the lateral PFC into consideration as well and discuss changes in both medial and lateral PFC and HC across development and postulate how these may be related to the development of the use of prior knowledge for remembering. For future direction, we argue that, to measure age differential effects of prior knowledge on memory, it is necessary to distinguish the availability of prior knowledge from its accessibility and use.

Electrophysiological investigation of source memory in early childhood

Recollection is well-characterized in adults and school-aged children, yet little is known about how this ability develops in early childhood. This study utilized a behavioral source memory paradigm and event-related potentials (ERPs) to examine recollection in early childhood. ERPs were compared between items whose context was remembered and forgotten as well as new items. Activity late in the electrophysiological response showed a "recollection" effect, which differentiated items with correct source judgments from all others. This study is unique in that it is the first to provide information regarding the spatiotemporal dynamics of the neural networks underlying recollection during early childhood.

Developmental trajectories of associative memory from childhood to adulthood: a behavioral and neuroimaging study

Episodic memory refers to the capacity to bind multimodal memories to constitute a unique personal event. Most developmental studies on episodic memory focused on one specific component, i.e., the core factual information. The present study examines the relevance of a novel episodic paradigm to assess its developmental trajectories in a more comprehensive way according to the type of association (item-feature, item-location, and item-sequence associations) with measures of both objective and subjective recollection. We conducted a behavioral study aimed at testing the effects of age in a large sample of 160 children, adolescents, and young adults (6-23 years old). We confronted the behavioral data to the neural correlates in a subgroup of 30 children using voxel-based morphometry. Behavioral data outlined differential developmental trajectories according to the type of association, with a continuous increase of factual associative memory efficiency until 10 years, a linear increase of performance in spatial associative memory that pursues until early adulthood and an abrupt increase in temporal associative memory efficiency between 9 and 10. Regarding recollection, measures showed a more pronounced enhancement from 9 to 10 years. Hence, behavioral data highlight a peculiar period in late childhood (8-10 years old) crucial for the developmental time course of episodic memory. Regarding structural data, we found that the improvement of associative memory efficiency was related to a decrease in gray matter volume in a large cerebral network including the dorsolateral and ventrolateral prefrontal cortex (and superior and anterior temporal regions), and the hippocampus bilaterally. These data suggest that multimodal integration would probably be related to the maturation of temporal regions and modulated by a fronto-parietal network. Besides, our findings emphasize the relevance of the present paradigm to assess episodic memory especially in the clinical setting.

Development of deactivation of the default-mode network during episodic memory formation

Task-induced deactivation of the default-mode network (DMN) has been associated in adults with successful episodic memory formation, possibly as a mechanism to focus allocation of mental resources for successful encoding of external stimuli. We investigated developmental changes of deactivation of the DMN (posterior cingulate, medial prefrontal, and bilateral lateral parietal cortices) during episodic memory formation in children, adolescents, and young adults (ages 8-24), who studied scenes during functional magnetic resonance imaging (fMRI). Recognition memory improved with age. We defined DMN regions of interest from a different sample of participants with the same age range, using resting-state fMRI. In adults, there was greater deactivation of the DMN for scenes that were later remembered than scenes that were later forgotten. In children, deactivation of the default-network did not differ reliably between scenes that were later remembered or forgotten. Adolescents exhibited a pattern of activation intermediate to that of children and adults. The hippocampal region, often considered part of the DMN, showed a functional dissociation with the rest of the DMN by exhibiting increased activation for later remembered than later forgotten scene that was similar across age groups. These findings suggest that development of memory ability from childhood through adulthood may involve increased deactivation of the neocortical DMN during learning.

The development of episodic memory: items, contexts, and relations

Episodic memory involves the formation of relational structures that bind information about the stimuli people experience to the contexts in which they experience them. The ability to form and retain such structures may be at the core of the development of episodic memory. In the first experiment reported here, 4- and 7-year-olds were presented with paired-associate learning tasks requiring memory structures of different complexity. A multinomial-processing tree model was applied to estimate the use of different structures in the two age groups. The use of two-way list-context-to-target structures and three-way structures was found to increase between the ages of 4 and 7. Experiment 2 demonstrated that the ability to form increasingly complex relational memory structures develops between the ages of 4 and 7 years and that this development extends well into adulthood. These results have important implications for theories of memory development.

Pediatric diabetic ketoacidosis, fluid therapy, and cerebral injury: the design of a factorial randomized controlled trial

Treatment protocols for pediatric diabetic ketoacidosis (DKA) vary considerably among centers in the USA and worldwide. The optimal protocol for intravenous (IV) fluid administration is an area of particular controversy, mainly in regard to possible associations between rates of IV fluid infusion and the development of cerebral edema (CE), the most common and the most feared complication of DKA in children. Theoretical concerns about associations between osmotic fluid shifts and CE have prompted recommendations for conservative fluid infusion during DKA. However, recent data suggest that cerebral hypoperfusion may play a role in cerebral injury associated with DKA. Currently, there are no existing data from prospective clinical trials to determine the optimal fluid treatment protocol for pediatric DKA. The Pediatric Emergency Care Applied Research Network FLUID (FLuid therapies Under Investigation in DKA) study is the first prospective randomized trial to evaluate fluid regimens for pediatric DKA. This 13-center nationwide factorial design study will evaluate the effects of rehydration rate and fluid sodium content on neurological status during DKA treatment, the frequency of clinically overt CE and long-term neurocognitive outcomes following DKA.

What are the links between maternal social status, hippocampal function, and HPA axis function in children?

The association of parental social status with multiple health and achievement indicators in adulthood has driven researchers to attempt to identify mechanisms by which social experience in childhood could shift developmental trajectories. Some accounts for observed linkages between parental social status in childhood and health have hypothesized that early stress exposure could result in chronic disruptions in hypothalamic-pituitary-adrenal (HPA) axis activation, and that this activation could lead to long-term changes. A robust literature in adult animals has demonstrated that chronic HPA axis activation leads to changes in hippocampal structure and function. In the current study, consistent with studies in animals, we observe an association between both maternal self-rated social status and hippocampal activation in children and between maternal self-rated social status and salivary cortisol in children.

Longitudinal investigation of source memory reveals different developmental trajectories for item memory and binding

The present study used a cohort-sequential design to examine developmental changes in children's ability to bind items in memory during early and middle childhood. Three cohorts of children (aged 4, 6, or 8 years) were followed longitudinally for 3 years. Each year, children completed a source memory paradigm assessing memory for items and binding. Results suggest linear increases in memory for individual items (facts or sources) between 4 and 10 years of age but that memory for correct fact/source combinations (indicative of binding) showed accelerated rates of change between 5 and 7 years. Taken together, these results suggest differences exist in developmental trajectories between the development of memory processes underlying successful item memory and processes underlying binding. Implications of these findings are discussed in relation to longitudinal research examining autobiographical memory.

Structural development of the hippocampus and episodic memory: developmental differences along the anterior/posterior axis

The hippocampus is critically involved in episodic memory, yet relatively little is known about how the development of this structure contributes to the development of episodic memory during middle to late childhood. Previous research has inconsistently reported associations between hippocampal volume and episodic memory performance during this period. We argue that this inconsistency may be due to assessing the hippocampus as a whole, and propose to examine associations separately for subregions along the longitudinal axis of the hippocampus. In the present study, we examined age-related differences in volumes of the hippocampal head, body, and tail, and collected episodic memory measures in children ages 8-11 years and young adults (N = 62). We found that adults had a smaller right hippocampal head, larger hippocampal body bilaterally, and smaller right hippocampal tail compared with children. In adults, but not in children, better episodic memory performance was associated with smaller right hippocampal head and larger hippocampal body. In children, but not in adults, better episodic memory was associated with larger left hippocampal tail. Overall, the results suggest that protracted development of hippocampal subregions contribute to age-related differences in episodic memory.

Development of memory for spatial context: hippocampal and cortical contributions

The goal of the present study was to examine age-related differences in hippocampal and cortical contribution to episodic retrieval of spatial context in 3 age groups. Children ages 8-9 and 10-11 years old, and adults ages 18-25 (N=48) encoded black and white line drawings appearing either on the right side or the left side of a screen. Functional magnetic resonance imaging (fMRI) data were acquired while participants attempted to recall where each studied drawing had originally appeared. Correct recall of spatial source indicated successful episodic retrieval of spatial context. Activity in head and body of the hippocampus was associated with episodic retrieval in adults, but not in children. In children, individual differences in hippocampal activation for recognition predicted rates of correct spatial recall. Developmental differences were also found in regions in posterior parietal cortex, anterior prefrontal cortex, and insula. Overall, these results support the view that the development of episodic memory is supported by functional changes in the hippocampus as well as cortical regions.

Developmental changes in memory encoding: insights from event-related potentials

The aim of the present study was to investigate developmental changes in encoding processes between 6-year-old children and adults using event-related potentials (ERPs). Although episodic memory ('EM') effects have been reported in both children and adults at retrieval and subsequent memory effects have been established in adults, no previous ERP studies have examined subsequent memory effects in children. This represents a critical gap in the literature because encoding processes, and changes in neural correlates supporting encoding, partially account for age-related improvements in children's memory performance. Results revealed that subsequent memory effects differed between children and adults temporally, directionally, and topographically. These findings lend support to the hypothesis that encoding processes and their neural correlates are an important source of change in memory development. A video abstract of this article can be viewed at http://youtu.be/sH83_qVimgc.

From perception to memory: changes in memory systems across the lifespan

Human memory is not a unitary entity; rather it is thought to arise out of a complex architecture involving interactions between distinct representational systems that specialize in perceptual, semantic, and episodic representations. Neuropsychological and neuroimaging evidence are combined in support of models of memory systems, however most models only capture a 'mature' state of human memory and there is little attempt to incorporate evidence of the contribution of developmental and senescence changes in various processes involved in memory across the lifespan. Here we review behavioral and neuroimaging evidence for changes in memory functioning across the lifespan and propose specific principles that may be used to extend models of human memory across the lifespan. In contrast to a simplistic reduced version of the adult model, we suggest that the architecture and dynamics of memory systems become gradually differentiated during development and that a dynamic shift toward favoring semantic memory occurs during aging. Characterizing transformations in memory systems across the lifespan can illustrate and inform us about the plasticity of human memory systems.

Bringing order to life events: memory for the temporal order of autobiographical events over an extended period in school-aged children and adults

Remembering temporal information associated with personal past events is critical. Yet little is known about the development of temporal order memory for naturally occurring events. In the current research, 8- to 10-year-old children and adults took photographs daily for 4 weeks. Later, they participated in a primacy/recency task (were shown 2 of their photographs and decided which event occurred first) and an ordering task (ordered 12 photographs taken over the 4-week period). All participants showed above-chance performance in primacy/recency; adults were more accurate than children. For ordering, children and adults showed similar patterns and performance was relatively low. This study has implications for autobiographical memory theories and suggests that ordering accuracy might not be necessary for adult-like autobiographical memory. Practical and legal implications of the findings also are discussed.

Elicited Imitation Performance at 20 Months Predicts Memory Abilities in School-Age Children

Over the first decade of life there are marked improvements in mnemonic abilities. An important question from both a theoretical and applied perspective is the extent of continuity in the nature of memory over this period. The present longitudinal investigation examined declarative memory during the transition from toddlerhood to school-age using both experimental and standardized assessments. Results indicate significant associations between immediate nonverbal recall at 20 months (measured by elicited imitation) and immediate verbal and nonverbal memory (measured by standardized and laboratory-based tasks) at 6 years in typically developing children. Regression models revealed this association was specific, as measures of language abilities and temperament were not predictive of later memory performance. These findings suggest both continuity and specificity within the declarative memory system over the first years of life. Theoretical and applied implications of these findings are discussed.

Tracking the eyes to see what children remember

Relational memory is a canonical form of episodic memory known to rely on the hippocampus. Several lines of evidence suggest that relational memory has a developmental trajectory in which it is fragile, inflexible, and error-prone until around 6 years of age, which seems to mirror maturational changes in the morphology of the hippocampus. However, recent findings from Richmond and Nelson (2009) challenge this idea as they provide evidence suggestive of adult-like relational memory in 9-month-old infants. In this study the authors measured the eye movements of infants and showed that they preferentially gazed at correct, as opposed to incorrect, face-scene pairings at test. The goal of the present study was to evaluate the development of relational memory by assessing 4-year-olds using Richmond and Nelson's task and stimuli, but gathering two dependent measures of relational memory: overt response as well as eye movements. The results show that, overall, preferential looking at correct face-scene pairings was at chance; however, preferential looking was observed when the correct face-scene pair was later explicitly identified. Thus, while eye movements do index explicit memory in 4-year-olds, behavioural data are necessary to obtain a full picture of the development of relational memory in childhood.

Prefrontal cortex contributions to controlled memory judgment: fMRI evidence from adolescents and young adults

Cortical regions supporting cognitive control and memory judgment are structurally immature in adolescents. Here we studied adolescents (13-15 y.o.) and young adults (20-22 y.o.) using a recognition memory paradigm that modulates cognitive control demands through cues that probabilistically forecast memory probe status. Behaviorally, adolescence was associated with quicker responding in the presence of invalid cues compared to young adulthood. fMRI data demonstrated that while both groups increasingly activated posterior dorsolateral prefrontal (dlPFC), midline, and lateral parietal regions for invalidly compared to validly cued trials, this differential invalid cueing response ended sooner in adolescents, consistent with their quicker responding on invalidly cued trials. Critically, dlPFC also demonstrated reversed brain-behavior associations across the groups. Increased mean dlPFC activation during invalid cueing was linked to improved performance in young adults, whereas increases within adolescents were linked to impaired performance. Resting state connectivity analysis revealed greater connectivity between dlPFC and episodic retrieval linked regions in young adults relative to adolescents. These data demonstrate that the functional interpretation of dlPFC activation hinges on its physical maturation and suggest that the pattern of behavioral and neural response in adolescents reflects different functional integration of cognitive control and memory systems.

White matter structural differences in young children with type 1 diabetes: a diffusion tensor imaging study

OBJECTIVE

To detect clinical correlates of cognitive abilities and white matter (WM) microstructural changes using diffusion tensor imaging (DTI) in young children with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Children, ages 3 to <10 years, with type 1 diabetes (n = 22) and age- and sex-matched healthy control subjects (n = 14) completed neurocognitive testing and DTI scans.

RESULTS

Compared with healthy controls, children with type 1 diabetes had lower axial diffusivity (AD) values (P = 0.046) in the temporal and parietal lobe regions. There were no significant differences between groups in fractional anisotropy and radial diffusivity (RD). Within the diabetes group, there was a significant, positive correlation between time-weighted HbA(1c) and RD (P = 0.028). A higher, time-weighted HbA(1c) value was significantly correlated with lower overall intellectual functioning measured by the full-scale intelligence quotient (P = 0.03).

CONCLUSIONS

Children with type 1 diabetes had significantly different WM structure (as measured by AD) when compared with controls. In addition, WM structural differences (as measured by RD) were significantly correlated with their HbA(1c) values. Additional studies are needed to determine if WM microstructural differences in young children with type 1 diabetes predict future neurocognitive outcome.

The development of brain systems associated with successful memory retrieval of scenes

Neuroanatomical and psychological evidence suggests prolonged maturation of declarative memory systems in the human brain from childhood into young adulthood. Here, we examine functional brain development during successful memory retrieval of scenes in children, adolescents, and young adults ages 8-21 via functional magnetic resonance imaging. Recognition memory improved with age, specifically for accurate identification of studied scenes (hits). Successful retrieval (correct old-new decisions for studied vs unstudied scenes) was associated with activations in frontal, parietal, and medial temporal lobe (MTL) regions. Activations associated with successful retrieval increased with age in left parietal cortex (BA7), bilateral prefrontal, and bilateral caudate regions. In contrast, activations associated with successful retrieval did not change with age in the MTL. Psychophysiological interaction analysis revealed that there were, however, age-relate changes in differential connectivity for successful retrieval between MTL and prefrontal regions. These results suggest that neocortical regions related to attentional or strategic control show the greatest developmental changes for memory retrieval of scenes. Furthermore, these results suggest that functional interactions between MTL and prefrontal regions during memory retrieval also develop into young adulthood. The developmental increase of memory-related activations in frontal and parietal regions for retrieval of scenes and the absence of such an increase in MTL regions parallels what has been observed for memory encoding of scenes.

Neural changes underlying the development of episodic memory during middle childhood

Episodic memory is central to the human experience. In typically developing children, episodic memory improves rapidly during middle childhood. While the developmental cognitive neuroscience of episodic memory remains largely uncharted, recent research has begun to provide important insights. It has long been assumed that hippocampus-dependent binding mechanisms are in place by early childhood, and that improvements in episodic memory observed during middle childhood result from the protracted development of the prefrontal cortex. We revisit the notion that binding mechanisms are age-invariant, and propose that changes in the hippocampus and its projections to cortical regions also contribute to the development of episodic memory. We further review the role of developmental changes in lateral prefrontal and parietal cortices in this development. Finally, we discuss changes in white matter tracts connecting brain regions that are critical for episodic memory. Overall, we argue that changes in episodic memory emerge from the concerted effort of a network of relevant brain structures.

Brain development during the preschool years

The preschool years represent a time of expansive mental growth, with the initial expression of many psychological abilities that will continue to be refined into young adulthood. Likewise, brain development during this age is characterized by its "blossoming" nature, showing some of its most dynamic and elaborative anatomical and physiological changes. In this article, we review human brain development during the preschool years, sampling scientific evidence from a variety of sources. First, we cover neurobiological foundations of early postnatal development, explaining some of the primary mechanisms seen at a larger scale within neuroimaging studies. Next, we review evidence from both structural and functional imaging studies, which now accounts for a large portion of our current understanding of typical brain development. Within anatomical imaging, we focus on studies of developing brain morphology and tissue properties, including diffusivity of white matter fiber tracts. We also present new data on changes during the preschool years in cortical area, thickness, and volume. Physiological brain development is then reviewed, touching on influential results from several different functional imaging and recording modalities in the preschool and early school-age years, including positron emission tomography (PET), electroencephalography (EEG) and event-related potentials (ERP), functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG), and near-infrared spectroscopy (NIRS). Here, more space is devoted to explaining some of the key methodological factors that are required for interpretation. We end with a section on multimodal and multidimensional imaging approaches, which we believe will be critical for increasing our understanding of brain development and its relationship to cognitive and behavioral growth in the preschool years and beyond.

Developmental differences in hippocampal and cortical contributions to episodic retrieval

Episodic memory, or the ability to form and retrieve conscious memories about specific past events, improves during childhood. Previous adult neuroimaging results indicate a central role of the hippocampus in episodic retrieval, but it is not clear whether the contribution of the hippocampus changes during development. Traditionally, developmental improvements in episodic retrieval have been thought to depend on strategic processes mediated by the prefrontal cortex (PFC), a region that is considered to have a protracted course of development relative to the hippocampus. The primary goal of the present study was to test the hypothesis that the development of episodic retrieval is also associated with changes in hippocampal function. Children ages 8- to 11-years-old and adults ages 18-25 (N = 41) encoded black and white line drawings surrounded by either a green or red border. Functional magnetic resonance imaging (fMRI) data were acquired while participants attempted to recall which colour was originally paired with each drawing. Correct recall of item-colour pairings indicated successful episodic retrieval. Activity in the anterior hippocampus, but not in the posterior hippocampus, was associated with episodic retrieval in adults, whereas activity in the posterior, but not in the anterior hippocampus, was associated with episodic retrieval in children. Developmental differences were also found in regions in anterior lateral PFC and posterior parietal cortex. Overall, these results support the view that the development of episodic memory is supported by functional changes in the hippocampus as well as in other critical cortical regions.

Developmental differences in the neural correlates of relational encoding and recall in children: an event-related fMRI study

Despite vast knowledge on the behavioral processes mediating the development of episodic memory, little is known about the neural mechanisms underlying these changes. We used event-related fMRI to examine the neural correlates of both encoding and recall processes during an episodic memory task in two different groups of school age children (8-9 and 12-13 years). The memory task was composed of an encoding phase in which children were presented with a series of unrelated pictorial pairs, and a retrieval phase during which one of these items acted as a cue to prompt recall of the paired item. Age-related differences in activations were observed for both encoding and recall. Younger children recruited additional regions in the right dorsolateral prefrontal and right temporal cortex compared to older children during successful encoding of the pairs. During successful recall, older children recruited additional regions in the left ventrolateral prefrontal and left inferior parietal cortex compared to younger children. The results suggest that the prefrontal cortex contributes to not only the formation of memories but also access to them, and this contribution changes with development. The protracted development of the prefrontal cortex has implications for our understanding of the development of episodic memory.

Lifespan age differences in working memory: a two-component framework

We suggest that working memory (WM) performance can be conceptualized as the interplay of low-level feature binding processes and top-down control, relating to posterior and frontal brain regions and their interaction in a distributed neural network. We propose that due to age-differential trajectories of posterior and frontal brain regions top-down control processes are not fully mature until young adulthood and show marked decline with advancing age, whereas binding processes are relatively mature in children, but show senescent decline in older adults. A review of the literature spanning from middle childhood to old age shows that binding and top-down control processes undergo profound changes across the lifespan. We illustrate commonalities and dissimilarities between children, younger adults, and older adults reflecting the change in the two components' relative contribution to visual WM performance across the lifespan using results from our own lab. We conclude that an integrated account of visual WM lifespan changes combining research from behavioral neuroscience and cognitive psychology of child development as well as aging research opens avenues to advance our understanding of cognition in general.

The development of neural correlates for memory formation

A growing body of literature considers the development of episodic memory systems in the brain; the majority are neuroimaging studies conducted during memory encoding in order to explore developmental trajectories in memory formation. This review considers evidence from behavioral studies of memory development, neural correlates of memory formation in adults, and structural brain development, all of which form the foundation of a developmental cognitive neuroscience approach to memory development. I then aim to integrate the current evidence from developmental functional neuroimaging studies of memory formation with respect to three hypotheses. First, memory development reflects the development in the use of memory strategies, linked to prefrontal cortex. Second, developmental effects within the medial temporal lobes are more complex, and correspond to current notions about the nature in which the MTL support the formation of memory. Third, neurocognitive changes in content representation influence memory. Open issues and current directions are discussed.

The two-component model of memory development, and its potential implications for educational settings

We recently introduced a two-component model of the mechanisms underlying age differences in memory functioning across the lifespan. According to this model, memory performance is based on associative and strategic components. The associative component is relatively mature by middle childhood, whereas the strategic component shows a maturational lag and continues to develop until young adulthood. Focusing on work from our own lab, we review studies from the domains of episodic and working memory informed by this model, and discuss their potential implications for educational settings. The episodic memory studies uncover the latent potential of the associative component in childhood by documenting children's ability to greatly improve their memory performance following mnemonic instruction and training. The studies on working memory also point to an immature strategic component in children whose operation is enhanced under supportive conditions. Educational settings may aim at fostering the interplay between associative and strategic components. We explore possible routes towards this goal by linking our findings to recent trends in research on instructional design.

Electrophysiological evidence of altered memory processing in children experiencing early deprivation

Associations between early deprivation and memory functioning were examined in 9- to 11-year-old children. Children who had experienced prolonged institutional care prior to adoption were compared to children who were adopted early from foster care and children reared in birth families. Measures included the Paired Associates Learning task from the Cambridge Neuropsychological Test and Automated Battery (CANTAB) and a continuous recognition memory task during which ERPs were also recorded. Children who experienced prolonged institutionalization showed deficits in both behavioral memory measures as well as an attenuated P300 parietal memory effect. Results implicate memory function as one of the domains that may be negatively influenced by early deprivation in the form of institutional care.

A frequency band analysis of two-year-olds' memory processes

Research on the functional meaning of EEG frequency bands during memory processing has only examined two developmental periods: infancy and from late childhood to adulthood. The purpose of this study was to examine changes in EEG power for three toddler EEG frequency bands (3-5Hz, 6-9Hz, 10-12Hz) during a verbal recall task. To this end, we asked three questions: (a) Which frequency band(s) discriminate baseline from memory processing?; (b) Which frequency band(s) differentiate between memory encoding and retrieval processes?; (c) Which frequency band(s) distinguish toddlers with high and low verbal recall performance? Analysis of 2-year-olds' (n=79) power values revealed that all three frequency bands differentiated the retrieval and encoding phases from the baseline phase; however, the particular regions that exhibited this dissociation varied. Retrieval-related increases in 3-5Hz (theta) power were widespread. Only the 3-5Hz and 6-9Hz bands distinguished encoding and retrieval processes; retrieval power values were higher than encoding power values. High and low verbal recall performers were discriminated by all frequency bands; high performers had greater power values than low performers. Thus, the 3-5Hz (theta) and 6-9Hz (alpha) bands were most informative about 2-year-olds' memory processes. Theta and alpha rhythms are critical to memory processes during late childhood and adulthood, and our findings provide initial evidence that these rhythms are also intricately linked to memory processing during toddlerhood. These findings are discussed in relation to behavioral changes in memory processes.

Children's episodic memory

Episodic memory develops during childhood and adolescence. This trajectory depends on several underlying processes. In this article, we first discuss the development of the basic binding processes (e.g., the processes by which elements are bound together to form a memory episode) and control processes (e.g., reasoning and metamemory processes) involved in episodic remembering. Then, we discuss the role of these processes in false-memory formation. In the subsequent sections, we examine the neural substrates of the development of episodic memory. Finally, we discuss atypical development of episodic memory. As we proceed through the article, we suggest potential avenues for future research. WIREs Cogni Sci 2011 2 365-373 DOI: 10.1002/wcs.114 For further resources related to this article, please visit the WIREs website.