Human memory development and its dysfunction after early hippocampal injury

Neural Marker of Habituation at 5 Months of Age Associated with Deferred Imitation Performance at 12 Months: A Longitudinal Study in the UK and The Gambia

Across cultures, imitation provides a crucial route to learning during infancy. However, neural predictors which would enable early identification of infants at risk of suboptimal developmental outcomes are still rare. In this paper, we examine associations between ERP markers of habituation and novelty detection measured at 1 and 5 months of infant age in the UK (n = 61) and rural Gambia (n = 214) and infants' responses on a deferred imitation task at 8 and 12 months. In both cohorts, habituation responses at 5 months significantly predicted deferred imitation responses at 12 months of age in both cohorts. Furthermore, ERP habituation responses explained a unique proportion of variance in deferred imitation scores which could not be accounted for by a neurobehavioural measure (Mullen Scales of Early Learning) conducted at 5 months of age. Our findings highlight the potential for ERP markers of habituation and novelty detection measured before 6 months of age to provide insight into later imitation abilities and memory development across diverse settings.

Neuroinflammation Induced by Transgenic Expression of Lipocalin-2 in Astrocytes

Transgenic mice are a useful tool for exploring various aspects of gene function. A key element of this approach is the targeted overexpression of specific genes in cells or tissues. Herein, we report for the first time, the generation and characterization of conditional transgenic (cTg) mice for lipocalin-2 (LCN2) expression. We generated the R26-LCN2-transgenic (LCN2-cTg) mice that carried a loxP-flanked STOP (neo) cassette, Lcn2 cDNA, and a GFP sequence. When bred with Tg mice expressing Cre recombinase under the control of various tissues or cell-specific promoters, Cre-mediated recombination deletes the STOP cassette and allows the expression of LCN2 and GFP. In this study, we achieved the recombination of loxP-flanked LCN2 in hippocampal astrocytes of cTg mouse brain, using a targeted delivery of adeno-associated virus (AAVs) bearing Cre recombinase under the control of a GFAP promoter (AAVs-GFAP-mCherry-Cre). These mice with localized LCN2 overexpression in astrocytes of the hippocampus developed neuroinflammation with enhanced glial activation and increased mRNA and protein levels of proinflammatory cytokines. Furthermore, mice showed impairment in cognitive functions as a typical symptom of hippocampal inflammation. Taken together, our study demonstrates the usefulness of LCN2-cTg mice in targeting specific cells at various organs for conditional LCN2 expression and for subsequent investigation of the functional role of cell-type-specific LCN2 within these sites. Moreover, the LCN2-cTg mice with targeted expression of LCN2 in hippocampal astrocytes are a new in vivo model of neuroinflammation.

Semantic and episodic memory in adults with temporal lobe epilepsy

The primary aims were to (1) identify the factor structure of tests thought to measure semantic and episodic memory and (2) examine whether patterns of impairment would show a double dissociation between these two memory systems at an individual level in patients with temporal lobe epilepsy (TLE). The secondary aim was to explore the impact of epilepsy-related variables on performance. This retrospective study involved a cohort of 54 adults who had been diagnosed with TLE and had undergone a neuropsychological assessment that included four memory tests traditionally used to measure either semantic memory (picture naming, animal fluency) or episodic memory (story recall, word list recall) at a single epilepsy surgery center in Australia. Principal component analysis revealed two factors albeit with unexpected loadings. Picture naming and story recall loaded on one factor. Animal fluency and word list recall loaded on another factor. There was no evidence of a double dissociation between semantic and episodic memory at an individual level. Left hemisphere seizure focus and early age of seizure onset related to worse performance on word list recall, picture naming and animal fluency, respectively. Our study highlights the importance of caution when interpreting the results of neuropsychological assessments, as not all putative tests of semantic and episodic memory may necessarily be measuring the same construct. Future directions for research are also considered.

Altered hippocampal-prefrontal functional network integrity in adult macaque monkeys with neonatal hippocampal lesions

The dorsolateral prefrontal cortex (DLPFC) and ventral lateral prefrontal cortex (VLPFC) play critical but different roles in working memory (WM) processes. Resting-state functional MRI (rs-fMRI) was employed to investigate the effects of neonatal hippocampal lesions on the functional connectivity (FC) between the hippocampus (H) and the DLPFC and VLPFC and its relation to WM performance in adult monkeys. Adult rhesus monkeys with neonatal H lesions (Neo-H, n = 5) and age- and gender-matched sham-operated monkeys (Neo-C, n = 5) were scanned around 10 years of age. The FC of H-DLPFC and H-VLPFC in Neo-H monkeys was significantly altered as compared to controls, but also switched from being positive in the Neo-C to negative in the Neo-H. In addition, the altered magnitude of FC between right H and bilateral DLPFC was significantly associated with the extent of the hippocampal lesions. In particular, the effects of neonatal hippocampal lesion on FC appeared to be selective to the left hemisphere of the brain (i.e. asymmetric in the two hemispheres). Finally, FC between H and DLPFC correlated with WM task performance on the SU-DNMS and the Obj-SO tasks for the control animals, but only with the H-VLPFC and SU-DNMS task for the Neo-H animals. In conclusion, the present rsfMRI study revealed that the neonatal hippocampal lesions significantly but differently altered the integrity in the functional connectivity of H-DLPFC and H-VLPFC. The similarities between the behavioral, cognitive and neural alterations in Neo-H monkeys and Schizophrenia (SZ) patients provide a strong translational model to develop new therapeutic tools for SZ.

Perinatal Docosahexaenoic Acid Supplementation Improves Cognition and Alters Brain Functional Organization in Piglets

Epidemiologic studies associate maternal docosahexaenoic acid (DHA)/DHA-containing seafood intake with enhanced cognitive development; although, it should be noted that interventional trials show inconsistent findings. We examined perinatal DHA supplementation on cognitive performance, brain anatomical and functional organization, and the brain monoamine neurotransmitter status of offspring using a piglet model. Sows were fed a control (CON) or a diet containing DHA (DHA) from late gestation throughout lactation. Piglets underwent an open field test (OFT), an object recognition test (ORT), and magnetic resonance imaging (MRI) to acquire anatomical, diffusion tensor imaging (DTI), and resting-state functional MRI (rs-fMRI) at weaning. Piglets from DHA-fed sows spent 95% more time sniffing the walls than CON in OFT and exhibited an elevated interest in the novel object in ORT, while CON piglets demonstrated no preference. Maternal DHA supplementation increased fiber length and tended to increase fractional anisotropy in the hippocampus of offspring than CON. DHA piglets exhibited increased functional connectivity in the cerebellar, visual, and default mode network and decreased activity in executive control and sensorimotor network compared to CON. The brain monoamine neurotransmitter levels did not differ in healthy offspring. Perinatal DHA supplementation may increase exploratory behaviors, improve recognition memory, enhance fiber tract integrity, and alter brain functional organization in offspring at weaning.

Hair cortisol concentrations are associated with hippocampal subregional volumes in children

The human hippocampus, a brain structure crucial for memory across the lifespan, is highly sensitive to adverse life events. Stress exposures during childhood have been linked to altered hippocampal structure and memory performance in adulthood. Animal studies suggest that these differences are in part driven by aberrant glucocorticoid secretion during development, with strongest effects on the CA3 region and the dentate gyrus (CA3-DG) of the hippocampus, alongside associated memory impairments. However, only few pediatric studies have examined glucocorticoid associations with hippocampal subfield volumes and their functional relevance. In 84 children (age range: 6-7 years), we assessed whether volumes of hippocampal subregions were related to cumulative glucocorticoid levels (hair cortisol), parenting stress, and performance on memory tasks known to engage the hippocampus. We found that higher hair cortisol levels were specifically related to lower CA3-DG volume. Parenting stress did not significantly correlate with hair cortisol, and there was no evidence to suggest that individual differences in hippocampal subregional volumes manifest in memory performance. Our results suggest that the CA3-DG may be the hippocampal region most closely associated with hair cortisol levels in childhood. Establishing causal pathways underlying this association and its relation to environmental stress and memory development necessitates longitudinal studies.

Nonhuman primate models of hippocampal development and dysfunction

Nonhuman primates provide highly valuable animal models that have significantly advanced our understanding of numerous behavioral and biological phenomena in humans. Here, we reviewed a series of developmental neuropsychological studies that informed us on the timing of development of the hippocampus and of hippocampal-dependent cognitive functions in primates. Data indicate that, in primates, the emergence of adult-like proficiency on behavioral tasks sensitive to hippocampal dysfunction is a stepwise process and reflects the gradual maturation of different hippocampal circuits and their connections with other neural structures. Profound and persistent memory loss resulting from insult to the hippocampus in infancy was absent in early infancy but became evident later in childhood and persisted in adulthood, indicating very little sparing or recovery of function. Finally, the early hippocampal insult resulted in both adaptive and maladaptive neuroplasticity: i.e., sparing contextual memory, but affecting working memory processes as well as emotional reactivity and hypothalamic-pituitary-adrenal (HPA) axis functioning. The results provide significant information on the emergence of hippocampal-dependent functions in humans, on the time course of memory impairment in human cases with early hippocampal insult, and on the clinical implication of the hippocampus in developmental neuropsychiatric disorders.

Using hippocampal-dependent eyeblink conditioning to predict individual differences in spatial reorientation strategies in 3- to 6-year-olds

The hippocampus is a subcortical structure in the medial temporal lobe involved in cognitive functions such as spatial navigation and reorientation, episodic memory, and associative learning. While much is understood about the role of hippocampal function in learning and memory in adults, less is known about the relations between the hippocampus and the development of these cognitive skills in young children due to the limitations of using standard methods (e.g., MRI) to examine brain structure and function in developing populations. This study used hippocampal-dependent trace eyeblink conditioning (EBC) as a feasible approach to examine individual differences in hippocampal functioning as they relate to spatial reorientation and episodic memory performance in young children. Three- to six-year-old children (N = 50) completed tasks that measured EBC, spatial reorientation, and episodic memory, as well as non-hippocampal-dependent processing speed abilities. Results revealed that when age was held constant, individual differences in EBC performance were significantly related to individual differences in performance on the spatial reorientation test, but not on the episodic memory or processing speed tests. When the relations between hippocampal-dependent EBC and different reorientation strategies were explored, it was found that individual differences in hippocampal function predicted the use of geometric information for reorienting in space as opposed to a combined strategy that uses both geometric information and salient visual cues. The utilization of eyeblink conditioning to examine hippocampal function in young populations and its implications for understanding the dissociation between spatial reorientation and episodic memory development are discussed.

Impact of Gold Nanoparticles on Amyloid β-Induced Alzheimer's Disease in a Rat Animal Model: Involvement of STIM Proteins

Alzheimer's disease (AD) is the most common type of neurodegenerative amyloid disorder causing progressive cognitive decline and memory loss. A considerable number of therapies for AD rely on inhibition/delay/dissociation of amyloid beta (Aβ) oligomers and fibrils. In this case, nanoparticles (NPs) demonstrated substantial effects on the Aβ fibrillation process; however, their effects on progressive cognitive decline and memory have been poorly investigated in vivo. In this study, acquisition and retention of spatial learning and memory are studied in a rat animal model of AD after intrahippocampal (IH) and intraperitoneal (IP) injections of a model NP, i.e., gold NPs (AuNPs). The outcomes revealed that the AuNPs could improve the acquisition and retention of spatial learning and memory in Aβ treated rats as indicated by decreased time (Aβ: 39.60 ± 3.23 s vs Aβ+AuNPs: 25.78 ± 2.80 s) and distance (Aβ: 917.98 ± 50.81 cm vs Aβ+AuNPs: 589.09 ± 65.96 cm) of finding the hidden platform during training days and by increased time spent in the target quadrant (Aβ: 19.40 ± 0.98 s vs Aβ+AuNPs: 29.36 ± 1.14 s) in the probe test in Morris water maze (MWM). Expression of brain-derived neurotrophic factor, BDNF, cAMP response element binding protein, CREB, and stromal interaction molecules, e.g., STIM1 and STIM2 was also increased, supporting improved neural survival. Our outcomes may pave a way for mechanistic insights toward the role of NPs on retrieval of the deteriorated behavioral functions in brain tissue after AD outbreak.

The long-term effect of perinatal asphyxia on hippocampal volumes

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) in term-born infants can lead to memory problems. The hippocampus is important for long-term episodic memory. The primary aim was to investigate the effect of HIE on hippocampal volumes in 9- to 10-year-old children. The secondary aim was to investigate the association between hippocampal volumes and previously found impaired memory and cognitive functions in the current cohort.

METHODS

In total 26 children with mild HIE, 26 with moderate HIE, and 37 controls were included. The intelligence quotient (IQ) and memory were tested. A 3D-volumetric MRI was obtained. Brain segmentation was performed for hippocampal volumes and intracranial volume. The differences in hippocampal volumes, memory, and IQ between the groups were determined. Multivariable linear regression analyses were performed, including hippocampal volume as a percentage of intracranial volume as a dependent variable.

RESULTS

Smaller hippocampal volumes were found in moderate HIE (p < 0.001), with a trend toward smaller volumes in mild HIE, compared to controls. In multivariable linear regression analysis, hippocampal volume as a percentage of intracranial volume was significantly associated with long-term visuospatial memory.

CONCLUSION

Children with moderate HIE had smaller hippocampal volumes than controls, with a trend toward smaller volumes following mild HIE. Reduced hippocampal volumes were associated with poorer long-term visuospatial memory.

The Neuroprotective Effects of 17β-Estradiol Pretreatment in a Model of Neonatal Hippocampal Injury Induced by Trimethyltin

Hippocampal dysfunction plays a central role in neurodevelopmental disorders, resulting in severe impairment of cognitive abilities, including memory and learning. On this basis, developmental studies represent an important tool both to understanding the cellular and molecular phenomena underlying early hippocampal damage and to study possible therapeutic interventions, that may modify the progression of neuronal death. Given the modulatory role played by 17β-estradiol (E2) on hippocampal functions and its neuroprotective properties, the present study investigates the effects of pretreatment with E2 in a model of neonatal hippocampal injury obtained by trimethyltin (TMT) administration, characterized by neuronal loss in CA1 and CA3 subfields and astroglial and microglial activation. At post-natal days (P)5 and P6 animals received E2 administration (0.2 mg/kg/die i.p.) or vehicle. At P7 they received a single dose of TMT (6.5 mg/kg i.p.) and were sacrificed 72 h (P10) or 7 days after TMT treatment (P14). Our findings indicate that pretreatment with E2 exerts a protective effect against hippocampal damage induced by TMT administration early in development, reducing the extent of neuronal death in the CA1 subfield, inducing the activation of genes involved in neuroprotection, lowering the neuroinflammatory response and restoring neuropeptide Y- and parvalbumin- expression, which is impaired in the early phases of TMT-induced damage. Our data support the efficacy of estrogen-based neuroprotective approaches to counteract early occurring hippocampal damage in the developing hippocampus.

The Role of Diffusion Tensor Imaging in Detecting Hippocampal Injury Following Neonatal Hypoxic-Ischemic Encephalopathy

BACKGROUND AND PURPOSE

Neonatal hypoxic-ischemic injury of the brain and resultant encephalopathy (HIE) leads to major developmental impairments by school age. Conventional/anatomical MRI often fails to detect hippocampal injury in mild cases. We hypothesize that diffusion tensor imaging (DTI) has greater sensitivity for identifying subtle hippocampal injury.

METHODS

We retrospectively analyzed DTI data collected from a cohort of neonates with HIE and controls. Conventional MRI sequences were classified qualitatively according to severity using a modified Barkovich scale. Using multivariate linear regression, we compared hippocampal DTI scalars of HIE patients and controls. Spearman correlation was used to test the association of DTI scalars in the hippocampal and thalamic regions. A multiple regression analysis tested the association of the DTI scalars with short-term outcomes.

RESULTS

Fifty-five neonates with HIE (42% males) and 13 controls (54% males) were included. Hippocampal DTI scalars were similar between HIE and control groups, even when restricting the HIE group to those with moderate-to-severe injury (8 subjects). DTI scalars of the thalamus were significantly lower in the moderate-to-severely affected patients compared to controls (right fractional anisotropy [FA] .148 vs. .182, P = .01; left FA .147 vs. .181, P = .03). Hippocampal and thalamic DTI scalars were correlated (P < .001). Hippocampal DTI scalars were not associated with short-term outcomes.

CONCLUSIONS

Quantitative DTI analysis of the hippocampus in neonates following HIE is a feasible technique to examine neuronal injury. Although DTI scalars were useful in identifying thalamic injury in our cohort, hippocampal DTI analysis did not provide additional information regarding hippocampal injury following HIE.

When two are better than one: Bilateral mesial temporal lobe contributions associated with better vocabulary skills in children and adolescents

This study considered the involvement of the mesial temporal lobe (MTL) in language and verbal memory functions in healthy children and adolescents. We investigated 30 healthy, right-handed children and adolescents, aged 7-16, with a fMRI language paradigm and a comprehensive cognitive test battery. We found significant MTL activations during language fMRI in all participants; 63% of them had left lateralized MTL activations, 20% exhibited right MTL lateralization, and 17% showed bilateral MTL involvement during the fMRI language paradigm. Group analyses demonstrated a strong negative correlation between the lateralization of MTL activations and language functions. Specifically, children with less lateralized MTL activation showed significantly better vocabulary skills. These findings suggest that the mesial temporal lobes of both hemispheres play an important role in language functioning, even in right-handers. Our results furthermore show that bilateral mesial temporal lobe involvement is advantageous for vocabulary skills in healthy, right-handed children and adolescents.

Hippocampal Maturation Drives Memory from Generalization to Specificity

During early ontogeny, the rapid and cumulative acquisition of world knowledge contrasts with slower improvements in the ability to lay down detailed and long-lasting episodic memories. This emphasis on generalization at the expense of specificity persists well into middle childhood and possibly into adolescence. During this period, recognizing regularities, forming stable representations of recurring episodes, predicting the structure of future events, and building up semantic knowledge may be prioritized over remembering specific episodes. We highlight recent behavioral and neuroimaging evidence suggesting that maturational differences among subfields within the hippocampus contribute to the developmental lead-lag relation between generalization and specificity, and lay out future research directions.

Determinants of memory development in childhood and adolescence

Research on the development of memory has a long history and constitutes one of the most active research areas in the field of cognitive development. In this article, we first describe major historical developments in the literature on children's memory, focusing on systematic research that began in the late 1960s. We then examine new developments in the field, describing four important lines of inquiry: (a) the development of implicit memory, (b) short- and long-term memory development in infancy, (c) longitudinal research on memory strategies and metamemory, and (d) developmental cognitive neuroscience of memory. Finally, promising lines of future research on memory development are briefly discussed.

Effects of Epilepsy on Language Functions: Scoping Review and Data Mining Findings

PURPOSE

This study involved a scoping review to identify possible gaps in the empirical description of language functioning in epilepsy in adults. With access to social network data, data mining was used to determine if individuals with epilepsy are expressing language-related concerns.

METHOD

For the scoping review, scientific databases were explored to identify pertinent articles. Findings regarding the nature of epilepsy etiologies, patient characteristics, tested language modalities, and language measures were compiled. Data mining focused on social network databases to obtain a set of relevant language-related posts.

RESULTS

The search yielded 66 articles. Epilepsy etiologies except temporal lobe epilepsy and older adults were underrepresented. Most studies utilized aphasia tests and primarily assessed single-word productions; few studies included healthy control groups. Data mining revealed several posts regarding epilepsy-related language problems, including word retrieval, reading, writing, verbal memory difficulties, and negative effects of epilepsy treatment on language.

CONCLUSION

Our findings underscore the need for future specification of the integrity of language in epilepsy, particularly with respect to discourse and high-level language abilities. Increased awareness of epilepsy-related language issues and understanding the patients' perspectives about their language concerns will allow researchers and speech-language pathologists to utilize appropriate assessments and improve quality of care.

Chemo brain: From discerning mechanisms to lifting the brain fog-An aging connection

Mounting evidence indicates that cancer treatments cause numerous deleterious effects, including central nervous system (CNS) toxicity. Chemotherapy-caused CNS side effects encompass changes in cognitive function, memory, and attention, to name a few. Although chemotherapy treatment-induced side effects occur in 16-75% of all patients, the mechanisms of these effects are not well understood. We have recently proposed a new epigenetic theory of chemo brain and, in a pioneer study, determined that cytotoxic chemotherapy agents induce oxidative DNA damage and affect molecular and epigenetic processes in the brain, and may be associated with brain aging processes. In this paper, we discuss the implications of chemo brain epigenetic effects and future perspectives, as well as outline potential links with brain aging and future translational research opportunities.

PTA scale for children aged 4 to 7 years: Selecting developmentally valid and reliable items

The aim of this study was to select developmentally valid and reliable items for inclusion in criterion-referenced (pass > 90%) posttraumatic amnesia (PTA) scale for children aged 4 to 7 years in a prospective cohort study. Fifty-two typically developing children (26 male/26 female) aged 4 to 7 years were administered a set of 10 items (5 orientation, 5 memory) over 3-4 days. The total score obtained on the set of 10 items had poor developmental validity and test-retest reliability. Nevertheless, individual item analysis identified five items (three orientation and two memory items) that were consistently passed by >90% of the children on each day of testing. For these five items the total scores did not differ significantly either between age groups or between days of testing. Test-retest was extremely high (close to 1). The five items had excellent developmental validity and test-retest reliability. This study identified 5 (3 orientation and 2 memory) items that met our selection criterion and form a new PTA scale, the Sydney PTA scale (SYPTAS), for children aged 4 to 7 years.

Long-term cognitive and neuroanatomical stability in patients with anoxic amnesia: A Case Report

BACKGROUND

Anoxia can result in selective hippocampal damage with associated impairments in declarative memory. Whilst memory impairments and brain structures are thought to be stable, there are little data regarding the effects of ageing or change over time in patients with amnesia from anoxic brain injury.

METHODS

To assess change over time, we compared structural magnetic resonance imaging (MRI) with data obtained over ten years previously in two well-characterized patients with amnesia (JRW and RS) who experienced an anoxic brain injury. Six healthy, age-matched control participants were recruited to compare brain volumes with the patients at Time 2. Wechsler adult intelligence scale-revised and Wechsler memory scale-revised scores were compared to scores on the same tests administered 13 and 19 years prior.

RESULTS

Patients with amnesia had significantly smaller hippocampal volumes than controls, but comparable medial temporal lobe and ventricular volumes. Memory, intellectual function and brain volumes were stable over time.

CONCLUSION

Patients with an amnesia due to anoxia have memory impairments and smaller hippocampal volumes compared to controls; however, memory, intelligence and structural volumes remain stable over time. At ages 50 and 57, they do not appear to have early age-associated cognitive decline that is sometimes observed in patients with traumatic brain injury.

Object and spatial memory after neonatal perirhinal lesions in monkeys

The contribution of the perirhinal cortex (PRh) to recognition memory is well characterized in adults, yet the same lesions have limited effect on recognition of spatial locations. Here, we assessed whether the same outcomes will follow when perirhinal lesions are performed in infancy. Monkeys with neonatal perirhinal (Neo-PRh) lesions and control animals were tested in three operant recognition tasks as they reached adulthood: Delayed Nonmatching-to-Sample (DNMS) and Object Memory Span (OMS), measuring object recognition, and Spatial Memory Span (SMS), measuring recognition of spatial locations. Although Neo-PRh lesions did not impact acquisition of the DNMS rule, they did impair performance when the delays were extended from 30s to 600s. In contrast, the same neonatal lesions had no impact on either the object or spatial memory span tasks, suggesting that the lesions impacted the maintenance of information across longer delays and not memory capacity. Finally, the magnitude of recognition memory impairment after the Neo-PRh lesions was similar to that previously observed after adult-onset perirhinal lesions, indicating minimal, or no, functional compensation after the early PRh lesions. Overall, the results indicate that the PRh is a cortical structure that is important for the normal development of mechanisms supporting object recognition memory. Its contribution may be relevant to the memory impairment observed with human cases of temporal lobe epilepsy without hippocampal sclerosis, but not to the memory impairment found in developmental amnesia cases.

Neonatal Magnetic Resonance Imaging Pattern of Brain Injury as a Biomarker of Childhood Outcomes following a Trial of Hypothermia for Neonatal Hypoxic-Ischemic Encephalopathy

OBJECTIVE

To examine the ability of magnetic resonance imaging (MRI) patterns of neonatal brain injury defined by the National Institute of Child Health and Human Development Neonatal Research Network to predict death or IQ at 6-7 years of age following hypothermia for neonatal encephalopathy.

STUDY DESIGN

Out of 208 participants, 124 had MRI and primary outcome (death or IQ <70) data. The relationship between injury pattern and outcome was assessed.

RESULTS

Death or IQ <70 occurred in 4 of 50 (8%) of children with pattern 0 (normal MRI), 1 of 6 (17%) with 1A (minimal cerebral lesions), 1 of 4 (25%) with 1B (extensive cerebral lesions), 3 of 8 (38%) with 2A (basal ganglia thalamic, anterior or posterior limb of internal capsule, or watershed infarction), 32 of 49 (65%) with 2B (2A with cerebral lesions), and 7 of 7 (100%) with pattern 3 (hemispheric devastation), P < .001; this association was also seen within hypothermia and control subgroups. IQ was 90 ± 13 among the 46 children with a normal MRI and 69 ± 25 among the 50 children with an abnormal MRI. In childhood, for a normal outcome, a normal neonatal MRI had a sensitivity of 61%, specificity of 92%, a positive predictive value of 92%, and a negative predictive value of 59%; for death or IQ <70, the 2B and 3 pattern combined had a sensitivity of 81%, specificity of 78%, positive predictive value of 70%, and a negative predictive value of 87%.

CONCLUSIONS

The Neonatal Research Network MRI pattern of neonatal brain injury is a biomarker of neurodevelopmental outcome at 6-7 years of age.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00005772.

Semantic Processing Impairment in Patients with Temporal Lobe Epilepsy

The impairment in episodic memory system is the best-known cognitive deficit in patients with temporal lobe epilepsy (TLE). Recent studies have shown evidence of semantic disorders, but they have been less studied than episodic memory. The semantic dysfunction in TLE has various cognitive manifestations, such as the presence of language disorders characterized by defects in naming, verbal fluency, or remote semantic information retrieval, which affects the ability of patients to interact with their surroundings. This paper is a review of recent research about the consequences of TLE on semantic processing, considering neuropsychological, electrophysiological, and neuroimaging findings, as well as the functional role of the hippocampus in semantic processing. The evidence from these studies shows disturbance of semantic memory in patients with TLE and supports the theory of declarative memory of the hippocampus. Functional neuroimaging studies show an inefficient compensatory functional reorganization of semantic networks and electrophysiological studies show a lack of N400 effect that could indicate that the deficit in semantic processing in patients with TLE could be due to a failure in the mechanisms of automatic access to lexicon.

Natural sequence of recovery from child post-traumatic amnesia: A retrospective cohort study

The aim of this study was to determine the sequence of skills recovery during post-traumatic amnesia (PTA) in children with moderate to severe traumatic brain injuries (TBIs).

SETTING

Fifty children aged 8 to 15 years consecutively admitted to a children's hospital with TBI and PTA>24 were tested in a retrospective cohort study where the main measure was the Westmead PTA Scale (WPTAS). The group analyses show that orientation to time took longer to recover than orientation to person and place, but not memory, while the individual analyses revealed that when orientation to time was grouped with memory, 94% of children recovered orientation to person and place before orientation to time and memory (examiner and pictures). Correlation coefficients between age and the number of days taken to recover skills were not found to be significant. It was established that, in terms of the natural sequence of skills recovery in children aged 8 to 15 years following moderate to severe TBI, recovery of orientation to time is more closely aligned to memory than to orientation to person and place. It was also established that WPTAS items are developmentally appropriate for children aged 8 to 15 years who have sustained TBI. These findings are clinically important because monitoring recovery from PTA both impacts the rehabilitation offered to individuals during acute care and aids discharge planning.

20 years after “The ontogeny of human memory: A cognitive neuroscience perspective,” where are we?

In 1995, Nelson published a paper describing a model of memory development during the first years of life. The current article seeks to provide an update on the original work published 20 years ago. Specifically, we review our current knowledge on the relation between the emergence of explicit memory functions throughout development and the maturation of associated brain regions. It is now well established that the brain regions subserving explicit memory functions (i.e. the hippocampal formation) are far from mature at birth, and exhibit important and gradual structural changes during childhood and beyond. Accordingly, explicit memory functions develop progressively. While some functions are present shortly after birth (formerly proposed as pre-explicit memory), others exhibit protracted developmental profiles during the first years of life. We examine the link between the emergence of different memory functions and the maturation of specific hippocampal circuits.

Alterations of hippocampal projections in adult macaques with neonatal hippocampal lesions: a Diffusion Tensor Imaging study

Neuropsychological and brain imaging studies have demonstrated persistent deficits in memory functions and structural changes after neonatal neurotoxic hippocampal lesion in monkeys. However, the relevant microstructural changes in the white matter of affected brain regions following this early insult remain unknown. This study assessed white matter integrity in the main hippocampal projections of adult macaque monkeys with neonatal hippocampal lesions, using diffusion tensor imaging (DTI). Data analysis was performed using tract-based spatial statistics (TBSS) and compared with volume of interest statistics. Alterations of fractional anisotropy (FA) and diffusivity indices were observed in fornix, temporal stem, ventromedial prefrontal cortex and optical radiations. To further validate the lesion effects on the prefrontal cortex, probabilistic diffusion tractography was used to examine the integrity of the fiber connections between hippocampus and ventromedial prefrontal cortex, and alterations were found in these connections. In addition, increased radial diffusivity in the left ventromedial prefrontal cortex correlated negatively with the severity of deficits in working memory in the same monkeys. The findings revealed microstructural changes due to neonatal hippocampal lesion, and confirmed that neonatal neurotoxic hippocampal lesions resulted in significant and enduring functional alterations in the hippocampal projection system.

The development of object recognition memory in rhesus macaques with neonatal lesions of the perirhinal cortex

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Assessed recognition memory in infant monkeys with neonatal perirhinal lesions using the visual paired comparison task.

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Performance was assessed at 4 developmental ages.

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Novelty preference deteriorated with age after neonatal perirhinal lesions.

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Presence of functional sparing.

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Memory deficits after perirhinal lesions occurred earlier than after hippocampal lesions.

To investigate the role of the perirhinal cortex on the development of recognition measured by the visual paired-comparison (VPC) task, infant monkeys with neonatal perirhinal lesions and sham-operated controls were tested at 1.5, 6, 18, and 48 months of age on the VPC task with color stimuli and intermixed delays of 10 s, 30 s, 60 s, and 120 s. Monkeys with neonatal perirhinal lesions showed an increase in novelty preference between 1.5 and 6 months of age similar to controls, although at these two ages, performance remained significantly poorer than that of control animals. With age, performance in animals with neonatal perirhinal lesions deteriorated as compared to that of controls. In contrast to the lack of novelty preference in monkeys with perirhinal lesions acquired in adulthood, novelty preference in the neonatally operated animals remained above chance at all delays and all ages. The data suggest that, although incidental recognition memory processes can be supported by the perirhinal cortex in early infancy, other temporal cortical areas may support these processes in the absence of a functional perirhinal cortex early in development. The neural substrates mediating incidental recognition memory processes appear to be more widespread in early infancy than in adulthood.

Effects of hypothermia for perinatal asphyxia on childhood outcomes

BACKGROUND

In the Total Body Hypothermia for Neonatal Encephalopathy Trial (TOBY), newborns with asphyxial encephalopathy who received hypothermic therapy had improved neurologic outcomes at 18 months of age, but it is uncertain whether such therapy results in longer-term neurocognitive benefits.

METHODS

We randomly assigned 325 newborns with asphyxial encephalopathy who were born at a gestational age of 36 weeks or more to receive standard care alone (control) or standard care with hypothermia to a rectal temperature of 33 to 34°C for 72 hours within 6 hours after birth. We evaluated the neurocognitive function of these children at 6 to 7 years of age. The primary outcome of this analysis was the frequency of survival with an IQ score of 85 or higher.

RESULTS

A total of 75 of 145 children (52%) in the hypothermia group versus 52 of 132 (39%) in the control group survived with an IQ score of 85 or more (relative risk, 1.31; P=0.04). The proportions of children who died were similar in the hypothermia group and the control group (29% and 30%, respectively). More children in the hypothermia group than in the control group survived without neurologic abnormalities (65 of 145 [45%] vs. 37 of 132 [28%]; relative risk, 1.60; 95% confidence interval, 1.15 to 2.22). Among survivors, children in the hypothermia group, as compared with those in the control group, had significant reductions in the risk of cerebral palsy (21% vs. 36%, P=0.03) and the risk of moderate or severe disability (22% vs. 37%, P=0.03); they also had significantly better motor-function scores. There was no significant between-group difference in parental assessments of children's health status and in results on 10 of 11 psychometric tests.

CONCLUSIONS

Moderate hypothermia after perinatal asphyxia resulted in improved neurocognitive outcomes in middle childhood. (Funded by the United Kingdom Medical Research Council and others; TOBY ClinicalTrials.gov number, NCT01092637.).

Neonatal hypoxia, hippocampal atrophy, and memory impairment: evidence of a causal sequence

Neonates treated for acute respiratory failure experience episodes of hypoxia. The hippocampus, a structure essential for memory, is particularly vulnerable to such insults. Hence, some neonates undergoing treatment for acute respiratory failure might sustain bilateral hippocampal pathology early in life and memory problems later in childhood. We investigated this possibility in a cohort of 40 children who had been treated neonatally for acute respiratory failure but were free of overt neurological impairment. The cohort had mean hippocampal volumes (HVs) significantly below normal control values, memory scores significantly below the standard population means, and memory quotients significantly below those predicted by their full scale IQs. Brain white matter volume also fell below the volume of the controls, but brain gray matter volumes and scores on nonmnemonic neuropsychological tests were within the normal range. Stepwise linear regression models revealed that the cohort's HVs were predictive of degree of memory impairment, and gestational age at treatment was predictive of HVs: the younger the age, the greater the atrophy. We conclude that many neonates treated for acute respiratory failure sustain significant hippocampal atrophy as a result of the associated hypoxia and, consequently, show deficient memory later in life.

Episodic future thinking in children compared to adolescents

Episodic thinking involves the ability to re-create past and to construct future personal events, which contain event-specific (episodic) and general (semantic) details. The richness of episodic thought for past events improves as children move into adolescence. The current study aims to examine changes in episodic future thinking and to establish the cognitive underpinning of these changes. Typically developing children (n = 14) and adolescents (n = 15) were tested using an adapted version of the Child Autobiographical Interview (CAI) that required generation of past and future personally relevant events. Relational memory and executive skills were also examined. Significant developmental gains were found in richness of events recall across temporal directions (past and future) and across different types of details (episodic and semantic). Developmental gains in richness of past events were also shown to correspond to developmental gains in generation of future events. Moreover, developmental changes in relational memory and (to a lesser extent) executive functions were found to relate to increases in the amount of episodic (but not semantic) details provided. Our study highlighted the similarities between past and future episodic thinking in typically developing children and adolescents. It also raises a possibility that children with developmental and neurological disorders with impaired relational memory and/or executive skills may be at risk of difficulties with episodic thinking.

Long-term effects of neonatal hippocampal lesions on novelty preference in monkeys

In a recent longitudinal study to assess the development of incidental recognition memory processes in monkeys, we showed that the effects of neonatal hippocampal lesions did alter incidental recognition memory only when the animals reached the juvenile period (Zeamer et al., ). The current follow-up study tested whether this incidental memory loss was long-lasting, i.e., present in adulthood, or only transitory, due to functional compensation with further brain maturation. The same animals with neonatal hippocampal lesions and their sham-operated controls were re-tested in the visual paired-comparison task when they reached adulthood (48 months). The results demonstrated that, at least for easily discriminable color pictures of objects, the involvement of the hippocampus was only transitory, given that when re-tested as adults, animals with neonatal hippocampal lesions performed as well as sham-operated controls at all delays. Yet, significant recognition memory impairment was re-instated when the discriminability of the stimuli was made more difficult (black/white pictures of similar objects). The data demonstrate profound functional remodeling within the hippocampus and its interactions with different medial temporal lobe structures from the juvenile period to adulthood, which is substantiated by a parallel morphological maturation of hippocampal intrinsic circuits (Lavenex et al., ; Jabès et al., ).

Glucose and memory: the influence of drink, expectancy, and beliefs

RATIONALE

An increasing number of studies suggest that glucose can enhance aspects of memory and the central methodology is the use of the glucose-placebo design. One critical issue therefore is separating the pharmacological effects of glucose from the expectancies created by consuming a drink that might contain glucose.

OBJECTIVE

A modified balanced placebo design examined the role that expectancy and belief about the drink consumed has on the pharmacological changes observed following glucose consumption.

METHOD

Ninety-three participants, allocated according to a drink (glucose, placebo) × message (told glucose, told nothing, told placebo) unrelated design, were administered tasks assessing immediate and delayed verbal free recall, spatial recognition and semantic verification. Each task has some evidence for hippocampus involvement, and variations in task difficulty were used to assess the idea that glucose effects are sensitive to task difficulty.

RESULTS

While the messages biased drink judgements in the expected direction, judgements of drink content were at chance and glucose only enhanced delayed free recall. The subtle effects of the messages did not modify the glucose enhancement. However, believing glucose had been consumed showed an independent improvement in delayed free recall. There was no evidence that task complexity enhanced the glucose effect.

CONCLUSIONS

The findings indicate that expectancy effects are unlikely to be confused with glucose enhancements, but beliefs about consuming glucose can augment performance on delayed free recall. The discussion considers the hippocampus and complexity hypotheses of glucose's mode of action and proposes the routine collection of drink beliefs in future studies.

Memory performance and normalized regional brain volumes in patients with pediatric-onset multiple sclerosis

Studies in adults with multiple sclerosis (MS) have associated regional brain abnormalities with memory impairment. While memory problems in children with MS are often reported, little is known about the neural correlates that may contribute to these difficulties. We measured verbal and nonverbal memory using the Test of Memory and Learning (TOMAL-2) in 32 children and adolescents with MS and 26 age- and sex-matched healthy controls. Memory performance was correlated with volumetric measures of the whole brain, hippocampus, amygdala, and thalamus. Brain volumes were normalized for age and sex using magnetic resonance imaging (MRI) data from the National Institutes of Health MRI Study of Normal Brain development. With the exception of story recall, performance on memory tests was similar to that of the control group. Relative to controls, patient with MS showed reduced volume in the whole brain (p < .001), amygdala (p < .005), and thalamus (p < .001), but not the hippocampus. In the patient group, word-list learning correlated with whole brain volume (r = .53) and hippocampal volume (r = .43), whereas visual recognition memory correlated with thalamic volume (r = .48). Findings are consistent with the well-established role of the hippocampus in learning and consolidation and also highlight the importance of diffuse brain pathology on memory function.

Cognitive dysfunction associated with diabetic ketoacidosis in rats

BACKGROUND

Type 1 diabetes mellitus in children may be associated with neurocognitive deficits of unclear cause. A recent retrospective study in children suggested possible associations between diabetic ketoacidosis (DKA) and decreased memory. The current investigation was undertaken to determine whether cognitive deficits could be detected after a single episode of DKA in an animal model.

METHODS

Streptozotocin was used to induce diabetes in juvenile rats, and rats were then treated with subcutaneous insulin injections. In one group, insulin was subsequently withdrawn to allow development of DKA, which was then treated with insulin and saline. After recovery from DKA, subcutaneous insulin injections were re-started. In the diabetes control group, rats continued to receive subcutaneous insulin and underwent sham procedures identical to the DKA group. One week after recovery, cognitive function was tested using the Morris Water Maze, a procedure that requires rats to locate a hidden platform in a water pool using visual cues. During a 10 day period, mean time to locate the platform (latency) during 4 trials per day was recorded.

RESULTS

Comparison of latency curves demonstrated longer mean latency times on days 7 and 8 in the DKA group indicating delayed learning compared to diabetic controls.

CONCLUSIONS

These data demonstrate that a single DKA episode results in measurable deficits in learning in rats, consistent with findings that DKA may contribute to neurocognitive deficits in children with type 1 diabetes.

Basic Information Processing Abilities at 11 years Account for Deficits in IQ Associated with Preterm Birth

Although it is well established that preterms as a group do poorly relative to their full-term peers on tests of global cognitive functioning, the basis for this relative deficiency is less understood. The present paper examines preterm deficits in core cognitive abilities and determines their role in mediating preterm/full-term differences in IQ. The performance of 11-year-old children born preterm (birth weight <1750g) and their full-term controls were compared on a large battery of 15 tasks, covering four basic cognitive domains -- memory, attention, speed of processing and representational competence. The validity of these four domains was established using latent variables and confirmatory factor analysis (CFA). Preterms showed pervasive deficits within and across domains. Additionally, preterm deficits in IQ were completely mediated by these four cognitive domains in a structural equation model involving a cascade from elementary abilities (attention and speed), to more complex abilities (memory and representational competence), to IQ. The similarity of findings to those obtained with this cohort in infancy and toddlerhood suggest that preterm deficits persist - across time, across task, and from the non-verbal to the verbal period.

Visual recognition memory across contexts

In two experiments, we investigated the development of representational flexibility in visual recognition memory during infancy using the Visual Paired Comparison (VPC) task. In Experiment 1, 6- and 9-month-old infants exhibited recognition when familiarization and test occurred in the same room, but showed no evidence of recognition when familiarization and test occurred in different rooms. In contrast, 12- and 18-month-old infants exhibited recognition irrespective of testing room. Thus, flexibility across a change of room was observed at a younger age than flexibility across a change of background that has previously been seen with the VPC procedure (Robinson & Pascalis, 2004). To determine if limitations in representational flexibility across a change of background could be overcome by experiences during encoding, in Experiment 2, 6-, 9-, 12- and 18-month-old infants were familiarized with a picture on multiple backgrounds. At all ages, infants showed recognition across a change in background at test. These findings indicate that dissociating an item from its context during encoding may be an important factor in understanding the representational flexibility of visual recognition memory in infancy. Developmental changes in representational flexibility are likely driven by changes in the functional maturity of the hippocampal formation, and experience.

Maternal arachidonic acid supplementation improves neurodevelopment in young adult offspring from rat dams with and without diabetes

Maternal diabetes may compromise infant arachidonic acid (AA) status and development. This study tested if maternal AA supplementation improves neurodevelopment in adult offspring. Rat dams were randomized into 6 groups: Saline-Placebo, streptozotocin-induced diabetes with glucose controlled at <13mmol/L, or poorly controlled at 13-20mmol/L using insulin; and fed either a Control or AA (0.5% fat) diet throughout reproduction. Weaned-offspring were fed regular chow to 12 weeks of age. Testing included exploratory behavior, rota rod and water maze (WM). Poorly controlled offspring showed longer (p≤0.018) escape-latency on testing-day 1 WM but not thereafter (p>0.05). Maternal glucose concentration positively correlated with (p=0.006) male offspring testing-day 1 WM latency. The AA-diet offspring performed better in WM and rota rod (p≤0.032) and showed higher exploratory behavior (p=0.008) than Control-diet offspring. These data suggest maternal hyperglycemia has longstanding consequences to initial stages of learning in the offspring. Maternal AA supplementation and training positively influence learning outcomes.

Long-term sleep disturbances in children: a cause of neuronal loss

Short-term sleep loss is known to cause temporary difficulties in cognition, behaviour and health but the effects of persistent sleep deprivation on brain development have received little or no attention. Yet, severe sleep disorders that last for years are common in children especially when they have neurodevelopmental disabilities. There is increasing evidence that chronic sleep loss can lead to neuronal and cognitive loss in children although this is generally unrecognized by the medical profession and the public. Without the restorative functions of sleep due to total sleep deprivation, death is inevitable within a few weeks. Chronic sleep disturbances at any age deprive children of healthy environmental exposure which is a prerequisite for cognitive growth more so during critical developmental periods. Sleep loss adversely effects pineal melatonin production which causes disturbance of circadian physiology of cells, organs, neurochemicals, neuroprotective and other metabolic functions. Through various mechanisms sleep loss causes widespread deterioration of neuronal functions, memory and learning, gene expression, neurogenesis and numerous other changes which cause decline in cognition, behaviour and health. When these changes are long-standing, excessive cellular stress develops which may result in widespread neuronal loss. In this review, for the first time, recent research advances obtained from various fields of sleep medicine are integrated in order to show that untreated chronic sleep disorders may lead to impaired brain development, neuronal damage and permanent loss of developmental potentials. Further research is urgently needed because these findings have major implications for the treatment of sleep disorders.

Developmental differences in medial temporal lobe function during memory encoding

The ability to recollect details about past events improves during childhood. Most researchers favor the view that this improvement depends largely on the development of the prefrontal cortex, which is thought to have a protracted course of development relative to the medial temporal lobes (MTL). The primary goal of the present study was to test the hypothesis that the development of detail recollection is also associated with changes in MTL function. We collected functional magnetic resonance imaging data during an incidental encoding task in 80 participants, divided equally across four age groups: 8-year-olds, 10- to 11-year-olds, 14-year-olds, and young adults. Developmental differences in MTL activation profiles were observed. Fourteen-year-olds and adults engaged regions of the hippocampus and posterior parahippocampal gyrus selectively for subsequent detail recollection, whereas 8- and 10- to 11-year-olds did not. In 8-year-olds, these regions were recruited indiscriminately for detail recollection and item recognition; in 10- to 11-year-olds, activation in these regions did not consistently predict subsequent memory. These results suggest there are changes in the functional organization of the MTL, such that the hippocampus and posterior parahippocampal gyrus become increasingly specialized for recollection; these changes may be in part responsible for long-term memory improvements during childhood.

Imagining fictitious and future experiences: evidence from developmental amnesia

Patients with bilateral hippocampal damage acquired in adulthood who are amnesic for past events have also been reported to be impaired at imagining fictitious and future experiences. One such patient, P01, however, was found to be unimpaired on these tasks despite dense amnesia and 50% volume loss in both hippocampi. P01 might be an atypical case, and in order to investigate this we identified another patient with a similar neuropsychological profile. Jon is a well-characterised patient with developmental amnesia and 50% volume loss in his hippocampi. Interestingly both Jon and P01 retain some recognition memory ability, and show activation of residual hippocampal tissue during fMRI. Jon's ability to construct fictitious and future scenarios was compared with the adult-acquired cases previously reported on this task and control participants. In contrast to the adult-acquired cases, but similar to P01, Jon was able to richly imagine both fictitious and future experiences in a comparable manner to control participants. Moreover, his constructions were spatially coherent. We speculate that the hippocampal activation during fMRI noted previously in P01 and Jon might indicate some residual hippocampal function which is sufficient to support their preserved ability to imagine fictitious and future scenarios.

Developmental trajectory of object recognition memory in infant rhesus macaques with and without neonatal hippocampal lesions

To examine the developmental trajectory of object recognition memory and its neural substrate, 10-12-d-old monkeys (Macaca mulatta) received sham operations or neurotoxic hippocampal lesions and were tested at the ages of 1.5, 6, and 18 months on the visual paired-comparison task using delays of 10, 30, 60, and 120 s. In sham-operated controls, incidental recognition memory was present at 1.5 months, became more robust at 6 months, and was delay-dependent by 18 months of age, suggesting that the brain structures mediating these early developing recognition abilities may undergo significant modifications after 6 months of age in monkeys. A similar developmental progression was also observed in animals with neonatal hippocampal lesions, although the delay-dependent effect at 18 months was significantly more pronounced after the neonatal hippocampal lesions, suggesting that with maturation animals with neonatal hippocampal lesions grow into a recognition-memory deficit. These findings suggest not only that the medial temporal cortical areas, known to mediate incidental recognition memory processes in adulthood, could support these processes in early infancy even when long delays are used, but also that later in development, after reaching functional maturity, the hippocampus begins to interact with the medial temporal cortical areas to mediate this function.

Consequences of low neonatal iron status due to maternal diabetes mellitus on explicit memory performance in childhood

Diabetic pregnancies are characterized by chronic metabolic insults, including iron deficiency, that place the developing brain at risk for memory impairment later in life. A behavioral recall paradigm coupled with electrophysiological measures was used to assess the longevity of these effects in 40 3(1/2)-year-old children. When memory demands were high, recall was significantly impaired in the at-risk group and correlated with perinatal measures of iron. Electrophysiological results suggested both encoding and retrieval processes were compromised. These findings support the hypothesis that prenatal iron deficiency leads to alterations in neural development that have a lasting impact on memory ability.

Evidence for intact memory-guided attention in school-aged children

Visual scenes contain many statistical regularities such as the likely identity and location of objects that are present; with experience, such regularities can be encoded and can ultimately facilitate the deployment of spatial attention to important locations. Memory-guided attention has been extensively examined in adults with the 'contextual cueing' paradigm and has been linked to specific neural substrates - a medial temporal lobe (MTL)-frontoparietal network. However, it currently remains unknown when this ability comes 'online' during development. Thus, we examined the performance of school-aged children on an age-appropriate version of the contextual cueing paradigm. Children searched for a target fish among distractor fish in new displays and in 'old' displays on a touchscreen computer. Old displays repeated across blocks of trials and thus provided an opportunity for prior experience with the invariant configuration of the stimuli to guide attentional deployment. We found that over time children searched old displays significantly faster than new displays, thus revealing intact memory-guided attention and presumed function of an MTL-frontoparietal network in 5- to 9-year-olds. More generally, our findings suggest that children are remarkably sensitive to the inherent structure of their visual environment and this enables attentional deployment to become more efficient with experience.