Infant memory development: Implications for childhood amnesia

Event as the central construal of psychological time in humans

Time is a fundamental dimension of our perception and mental construction of reality. It enables resolving changes in our environment without a direct sensory representation of elapsed time. Therefore, the concept of time is inferential by nature, but the units of subjective time that provide meaningful segmentation of the influx of sensory input remain to be determined. In this review, we posit that events are the construal instances of time perception as they provide a reproducible and consistent segmentation of the content. In that light, we discuss the implications of this proposal by looking at "events" and their role in subjective time experience from cultural anthropological and ontogenetic perspectives, as well as their relevance for episodic memory. Furthermore, we discuss the significance of "events" for the two critical aspects of subjective time-duration and order. Because segmentation involves parsing event streams according to causal sequences, we also consider the role of causality in developing the concept of directionality of mental timelines. We offer a fresh perspective on representing past and future events before age 5 by an egocentric bi-directional timeline model before acquiring the allocentric concept of absolute time. Finally, we illustrate how the relationship between events and durations can resolve contradictory experimental results. Although "time" warrants a comprehensive interdisciplinary approach, we focus this review on "time perception", the experience of time, without attempting to provide an all encompassing overview of the rich philosophical, physical, psychological, cognitive, linguistic, and neurophysiological context.

The self-memory system: Exploring developmental links between self and memory across early to late childhood

This study tests whether developments in self-knowledge and autobiographical memory across early to late childhood are related. Self-descriptions and autobiographical memory reports were collected from 379 three- to eleven-year-old predominantly white Scottish children, Mage = 90.3 months, SD = 31.1, 54% female. Episodic memory was measured in an enactment task involving recall and source monitoring of performed and witnessed actions. The volume and complexity of self-knowledge and autobiographical memory reports increased with age, as did source monitoring ability and recall bias for own actions. Regression analyses and structural equation modeling confirmed a close association between these developments. These results inform our theoretical understanding of the development of the self-memory system in childhood, which may contribute to the gradual offset of childhood amnesia.

Mental causation: an evolutionary perspective

The relationship between consciousness and individual agency is examined from a bottom-up evolutionary perspective, an approach somewhat different from other ways of dealing with the issue, but one relevant to the question of animal consciousness. Two ways are identified that would decouple the two, allowing consciousness of a limited kind to exist without agency: (1) reflex pathways that incorporate conscious sensations as an intrinsic component (InCs), and (2) reflexes that are consciously conditioned and dependent on synaptic plasticity but not memory (CCRs). Whether InCs and CCRs exist as more than hypothetical constructs is not clear, and InCs are in any case limited to theories where consciousness depends directly on EM field-based effects. Consciousness with agency, as we experience it, then belongs in a third category that allows for deliberate choice of alternative actions (DCs), where the key difference between this and CCR-level pathways is that DCs require access to explicit memory systems whereas CCRs do not. CCRs are nevertheless useful from a heuristic standpoint as a conceptual model for how conscious inputs could act to refine routine behaviors while allowing evolution to optimize phenomenal experience (i.e., qualia) in the absence of individual agency, a somewhat counterintuitive result. However, so long as CCRs are not a required precondition for the evolution of memory-dependent DC-level processes, the later could have evolved first. If so, the adaptive benefit of consciousness when it first evolved may be linked as much to the role it plays in encoding memories as to any other function. The possibility that CCRs are more than a theoretical construct, and have played a role in the evolution of consciousness, argues against theories of consciousness focussed exclusively on higher-order functions as the appropriate way to deal with consciousness as it first evolved, as it develops in the early postnatal period of life, or with the conscious experiences of animals other than ourselves. An evolutionary perspective also resolves the problem of free will, that it is best treated as a property of a species rather than the individuals belonging to that species whereas, in contrast, agency is an attribute of individuals.

Protracted neuronal recruitment in the temporal lobes of young children

The temporal lobe of the human brain contains the entorhinal cortex (EC). This region of the brain is a highly interconnected integrative hub for sensory and spatial information; it also has a key role in episodic memory formation and is the main source of cortical hippocampal inputs1-4. The human EC continues to develop during childhood5, but neurogenesis and neuronal migration to the EC are widely considered to be complete by birth. Here we show that the human temporal lobe contains many young neurons migrating into the postnatal EC and adjacent regions, with a large tangential stream persisting until the age of around one year and radial dispersal continuing until around two to three years of age. By contrast, we found no equivalent postnatal migration in rhesus macaques (Macaca mulatta). Immunostaining and single-nucleus RNA sequencing of ganglionic eminence germinal zones, the EC stream and the postnatal EC revealed that most migrating cells in the EC stream are derived from the caudal ganglionic eminence and become LAMP5+RELN+ inhibitory interneurons. These late-arriving interneurons could continue to shape the processing of sensory and spatial information well into postnatal life, when children are actively interacting with their environment. The EC is one of the first regions of the brain to be affected in Alzheimer's disease, and previous work has linked cognitive decline to the loss of LAMP5+RELN+ cells6,7. Our investigation reveals that many of these cells arrive in the EC through a major postnatal migratory stream in early childhood.

On the retrieval of earliest memories

Earliest memories were examined with respect to recollection type (i.e., remember-know), retrieval type (i.e., direct-generative), retrieval speed, and memory fluency (i.e., phonemic, semantic, and autobiographical). A total of 137 young adults (94 females; Mage = 20.47, SDage = 1.57) reported their earliest memories and specified their recollection and retrieval types for reported memories. They further dated their recollections by reporting the age at event, rated event characteristics and completed the phonemic, semantic, and autobiographical memory fluency tasks. Remembered and known earliest memories were similar in retrieval speed, but remembered memories were more prevalent. For retrieval type, direct and generative retrieval were similar in prevalence, but direct retrieval was faster in recalling the earliest memories. Directly retrieved memories were dated earlier than generated ones, but no such pattern in dating was observed for remember-know distinction. In terms of memory fluency, none of the three fluency tasks predicted the retrieval speed, recollection and retrieval type. For event characteristics, significant differences were observed only for vividness and rehearsal for both retrieval and recollection type. The present study is the first to explore recollection and retrieval type, retrieval speed, memory fluency together with dating and event characteristics in the context of earliest memories.

Serious life events and associated PTSD in Gambian girls exposed to female genital cutting

Introduction

Poor mental health, such as post-traumatic stress disorder (PTSD), has been reported after female genital cutting (FGC). However, data documenting adverse consequences of FGC have insufficiently considered confounding factors, such as other traumatising events. Here, we examined the extent to which FGC versus other serious life events disturbed Gambian girls subjected to FGC. We additionally assessed the prevalence of PTSD and the extent to which it was attributed to FGC versus other serious life events.

Methods

We conducted a cross-sectional study with a community-based sample of 12 years-old Gambian girls who had been subjected to FGC (N = 125). Using structured interviews, we assessed serious life events and probable PTSD related to the event that the girls cited as bothering them the most.

Results

Most of the girls reported several serious life events in addition to FGC, such as witnessing violence, experiencing violence or assaults, death of a close relative, and being exposed to natural disasters or serious accidents, for an average 4.5 events per girl. Around one-sixth of the girls (16.8%) stated that FGC was the event that currently bothered them the most, whereas the majority (75.2%) emphasised other experiences. The girls who said they were most troubled by other events reported more impaired daily functioning than those most bothered by FGC. Overall, we found a prevalence of probable PTSD of 19.2%. Of 24 PTSD cases, one was attributed to the experience of FGC, and the remaining 23 were attributed to other events.

Conclusion

Our findings indicate that FGC is less important than other serious life events in explaining high rates of PTSD in Gambian girls. Associations established in the field between FGC and adverse mental health must be interpreted with caution because girls who have undergone FGC may be severely exposed to other traumatising events.

Dynamic developmental changes in neurotransmitters supporting infant attachment learning

Infant survival relies on rapid identification, remembering and behavioral responsiveness to caregivers' sensory cues. While neural circuits supporting infant attachment learning have largely remained elusive in children, use of invasive techniques has uncovered some of its features in rodents. During a 10-day sensitive period from birth, newborn rodents associate maternal odors with maternal pleasant or noxious thermo-tactile stimulation, which gives rise to a preference and approach behavior towards these odors, and blockade of avoidance learning. Here we review the neural circuitry supporting this neonatal odor learning, unique compared to adults, focusing specifically on the early roles of neurotransmitters such as glutamate, GABA (Gamma-AminoButyric Acid), serotonin, dopamine and norepinephrine, in the olfactory bulb, the anterior piriform cortex and amygdala. The review highlights the importance of deepening our knowledge of age-specific infant brain neurotransmitters and behavioral functioning that can be translated to improve the well-being of children during typical development and aid in treatment during atypical development in childhood clinical practice, and the care during rearing of domestic animals.

The Development of Flexible Problem Solving: An Integrative Approach

Flexible problem solving, the ability to deal with currently goal-irrelevant information that may have been goal-relevant in previous, similar situations, plays a prominent role in cognitive development and has been repeatedly investigated in developmental research. However, this research, spanning from infancy to the school years, lacks a unifying framework, obscuring the developmental timing of flexible problem solving. Therefore, in this review paper, previous findings are gathered, organized, and integrated under a common framework to unveil how and when flexible problem solving develops. It is showed that the development of flexible problem solving coincides with increases in executive functions, that is, inhibition, working memory and task switching. The analysis of previous findings shows that dealing with goal-irrelevant, non-salient information received far more attention than generalizing in the presence of goal-irrelevant, salient information. The developmental timing of the latter can only be inferred from few transfer studies, as well as executive functions, planning and theory of mind research, to highlight gaps in knowledge and sketch out future research directions. Understanding how transfer in the presence of seemingly relevant but truly irrelevant information develops has implications for well-balanced participation in information societies, early and lifespan education, and investigating the evolutionary trajectory of flexible problem solving.

6-, 10-, and 12-month-olds remember complex dynamic events across 2 weeks

Whereas infants' ability to remember simple static material (e.g., pictures) has been documented extensively, we know surprisingly little about infants' memory of dynamic events (i.e., events unfolding in time) in the first year after birth. Although there is evidence to suggest that infants show some kind of sensitivity toward complex dynamic events (i.e., events involving agents and a storyline) as indicated by visual engagement in the first year after birth, 16- to 18-month-olds are hitherto the youngest infants documented to remember such material. Using a visual paired-comparison (VPC) task, in Experiment 1 we examined 6-, 10-, and 12-month-olds' (N = 108) ability to encode and remember cartoons involving complex dynamic events across 2 weeks. Results showed that all age groups remembered these cartoons. To investigate further the role of a complex storyline, in Experiment 2 we assessed the memory of 107 infants of the same age groups for similar cartoons but without coherent storyline information by scrambling the temporal presentation of the information in the cartoons. The results showed that the two youngest age groups did not remember this version. To our knowledge, this is the first experiment to document memory for such complex material in young infants using VPC.

Hippocampal parvalbumin interneurons play a critical role in memory development

Episodic memories formed in early childhood rapidly decay, but their latent traces remain stored long term. These memories require the dorsal hippocampus (dHPC) and seem to undergo a developmental critical period. It remains to be determined whether the maturation of parvalbumin interneurons (PVIs), a major mechanism of critical periods, contributes to memory development. Here, we show that episodic infantile learning significantly increases the levels of parvalbumin in the dHPC 48 h after training. Chemogenetic inhibition of PVIs before learning indicated that these neurons are required for infantile memory formation. A bilateral dHPC injection of the γ-aminobutyric acid type A receptor agonist diazepam after training elicited long-term memory expression in infant rats, although direct PVI chemogenetic activation had no effect. Finally, PVI activity was required for brain-derived neurotrophic factor (BDNF)-dependent maturation of memory competence, i.e., adult-like long-term memory expression. Thus, dHPC PVIs are critical for the formation of infantile memories and for memory development.

Adults who are more anxious and were anxiously attached as children report later first memories

Here, we examined retrospective reports of adults' earliest autobiographical memory, the age of this report and whether the reported age was associated with exposure to early life adversity, current anxiety and childhood attachment. Across four studies, we found that reporting a later 'earliest' memory was associated with higher self-reported anxiety in both American (Studies 1, 2 and 4) and Australian (Study 3) samples. Furthermore, in Studies 2-4, we found that reporting a later earliest memory uniquely predicted anxiety when controlling for number of adverse childhood events (a risk factor for the development of anxiety). In Study 4, we established that this relation is partially mediated by childhood anxious attachment. Although we consistently demonstrated that later earliest memories were associated with current anxiety, we found little evidence for a relation between reported age at the time of earliest memory and childhood adversity. We also found no evidence of gender differences in the associations of interest. These results suggest that poorer memory of early childhood is associated with greater childhood anxious attachment and anxiety in adulthood. The implications of this work are discussed in terms of the adaptive nature of autobiographical memory and the development of a coherent life narrative.

Can you teach me not to be angry? Relations between temperament and the emotion regulation strategy distraction in 2-year-olds

Little is known about toddlers' acquisition of specific emotion regulation (ER) strategies, and how early ER is shaped by temperament. This study investigated if 24-month-old German toddlers, predominantly from families with high levels of parental education (N = 96, n = 49 male), learned the ER strategy distraction through observational learning, and its interaction with temperament. Increased use of distraction correlated with reduced negative affect. Use of distraction increased through observational learning. Highly active toddlers tended to use active playing activities to distract themselves in a frustrating situation, whereas toddlers with a less active temperament used calmer activities. Toddlers' learning to apply distraction through observational learning was independent of a match between their own temperament and the model's actions.

Predicting explicit memory for meaningful cartoons from visual paired comparison in infants and toddlers

We tested the memory of 18-, 33-, and 39-month-olds (N = 120) for dynamic stimulus material (simple cartoons) after 6 months in a visual paired comparison (VPC) task. We also tested the explicit recognition memory (ERM) for the same material. Only the oldest age group (39-month-olds) showed a significant visual (familiarity) preference at the test. Similarly, only the oldest group reliably chose the correct cartoon in the ERM test. Data from the VPC and ERM tasks did not correlate in any age group. However, we suggested a novel score (coined ΔVPC) measuring how much visual preference changes during the test phase in the VPC task. We found that this ΔVPC score (and vocabulary) predicted children's performance in the ERM task, whereas other potential predictors such as age and conventional novelty preference did not. We discuss the impact of these findings in relation to the development of implicit and explicit memory. Furthermore, we propose that VPC measures are associated with explicit memory only when the participants processed the stimuli conceptually. In such cases, we suggest that the ΔVPC score is an approximation of how demanding it is to construct the mental representation of the familiar stimulus during the test phase.

Prior sleep timing and visual recognition of emotional faces in 6-month-old infants

Face recognition is an important mnemonic ability for infants when navigating the social world. While age-related changes in face processing abilities are relatively well documented, less is known about short-term intra-individual fluctuations in this ability. Given that sleep deprivation in adults leads to impairments in information processing, we assessed the role of prior sleep on 6-month-old infants' (N = 17) visual recognition of faces showing three emotional expressions (neutral, sad, angry). Visual recognition was inferred by assessing novelty preferences for unfamiliar relative to familiarized faces in a visual recognition memory paradigm. In a within-subject design, infants participated once after they had recently woken up from a nap (nap condition) and once after they had been awake for an extended period of time (awake condition). Infants failed to show visual recognition for the neutral faces in either condition. Infants showed recognition for the sad and angry faces when tested in the awake condition, but not in the nap condition. This suggests that timing of prior sleep shapes how effectively infants process emotionally relevant information in their environment.

A Multivariate Assessment of Age-Related Cognitive Impairment in Octodon degus

Aging is a progressive functional decline characterized by a gradual deterioration in physiological function and behavior. The most important age-related change in cognitive function is decline in cognitive performance (i.e., the processing or transformation of information to make decisions that includes speed of processing, working memory, and learning). The purpose of this study is to outline the changes in age-related cognitive performance (i.e., short-term recognition memory and long-term learning and memory) in long-lived Octodon degus. The strong similarity between degus and humans in social, metabolic, biochemical, and cognitive aspects makes it a unique animal model for exploring the mechanisms underlying the behavioral and cognitive deficits related to natural aging. In this study, we examined young adult female degus (12- and 24-months-old) and aged female degus (38-, 56-, and 75-months-old) that were exposed to a battery of cognitive-behavioral tests. Multivariate analyses of data from the Social Interaction test or Novel Object/Local Recognition (to measure short-term recognition memory), and the Barnes maze test (to measure long-term learning and memory) revealed a consistent pattern. Young animals formed a separate group of aged degus for both short- and long-term memories. The association between the first component of the principal component analysis (PCA) from short-term memory with the first component of the PCA from long-term memory showed a significant negative correlation. This suggests age-dependent differences in both memories, with the aged degus having higher values of long-term memory ability but poor short-term recognition memory, whereas in the young degus an opposite pattern was found. Approximately 5% of the young and 80% of the aged degus showed an impaired short-term recognition memory; whereas for long-term memory about 32% of the young degus and 57% of the aged degus showed decreased performance on the Barnes maze test. Throughout this study, we outlined age-dependent cognitive performance decline during natural aging in degus. Moreover, we also demonstrated that the use of a multivariate approach let us explore and visualize complex behavioral variables, and identified specific behavioral patterns that allowed us to make powerful conclusions that will facilitate further the study on the biology of aging. In addition, this study could help predict the onset of the aging process based on behavioral performance.

Recovery of memory from infantile amnesia is developmentally constrained

Episodic memories formed during infancy are rapidly forgotten, a phenomenon associated with infantile amnesia, the inability of adults to recall early-life memories. In both rats and mice, infantile memories, although not expressed, are actually stored long term in a latent form. These latent memories can be reinstated later in life by certain behavioral reminders or by artificial reactivations of neuronal ensembles activated at training. Whether the recovery of infantile memories is limited by developmental age, maternal presence, or contingency of stimuli presentation remains to be determined. Here, we show that the return of inhibitory avoidance memory in rats following a behavioral reactivation consisting of an exposure to the context (conditioned stimuli [CS]) and footshock (unconditioned stimuli [US]) given in a temporally unpaired fashion, is evident immediately after US and is limited by the developmental age at which the reactivations are presented; however, it is not influenced by maternal presence or the time interval between training and reactivation. We conclude that one limiting factor for infantile memory reinstatement is developmental age, suggesting that a brain maturation process is necessary to allow the recovery of a “lost” infantile memory.

NMDARs Containing NR2B Subunit Do Not Contribute to the LTP Form of Hippocampal Plasticity: In Vivo Pharmacological Evidence in Rats

Synaptic plasticity is the key to synaptic health, and aberrant synaptic plasticity, which in turn impairs the functioning of large-scale brain networks, has been associated with neurodegenerative and psychiatric disorders. The best known and most studied form of activity-dependent synaptic plasticity remains long-term potentiation (LTP), which is controlled by glutamatergic N-methyl-d-aspartate) receptors (NMDAR) and considered to be a mechanism crucial for cellular learning and memory. Over the past two decades, discrepancies have arisen in the literature regarding the contribution of NMDAR subunit assemblies in the direction of NMDAR-dependent synaptic plasticity. Here, the nonspecific NMDAR antagonist ketamine (5 and 10 mg/kg), and the selective NR2B antagonists CP-101606 and Ro 25-6981 (6 and 10 mg/kg), were administered intraperitoneally in Sprague Dawley rats to disentangle the contribution of NR2B subunit in the LTP induced at the Schaffer Collateral-CA1 synapse using the theta burst stimulation protocol (TBS). Ketamine reduced, while CP-101606 and Ro 25-6981 did not alter the LTP response. The administration of CP-101606 before TBS did not influence the effects of ketamine when administered half an hour after tetanization, suggesting a limited contribution of the NR2B subunit in the action of ketamine. This work confirms the role of NMDAR in the LTP form of synaptic plasticity, whereas specific blockade of the NR2B subunit was not sufficient to modify hippocampal LTP. Pharmacokinetics at the doses used may have contributed to the lack of effects with specific antagonists. The findings refute the role of the NR2B subunit in the plasticity mechanism of ketamine in the model.

The effect of napping and nighttime sleep on memory in infants

During the first year of life, infants devote the majority of their time to sleep. Research in adults has shown that sleep supports a variety of memory processes. Surprisingly, sleep's function for infant memory has only started to receive attention in research. In this chapter, we will describe age-related changes in sleep and in memory processing over the first years of life, as well as methods to capture both sleep and memory. Then, we will review current findings on the effects of sleep on memory processing in infants. Lastly, we will also point out gaps in current knowledge and describe potential avenues for future research. Overall, the results of recent experimental studies provide evidence that timely, extended napping is involved in how memories are encoded and stored in the long-term and contribute to the formation of knowledge networks in infants.

The association between physical complications following female genital cutting and the mental health of 12-year-old Gambian girls: A community-based cross-sectional study

BACKGROUND

Female genital cutting (FGC) involve an acute physical trauma that hold a potential risk for immediate and long-term complications and mental health problems. The aim of this study was to examine the prediction of depressive symptoms and psychological distress by the immediate and current physical complications following FGC. Further, to examine whether the age at which 12-year-old Gambian girls had undergone the procedure affected mental health outcomes.

METHOD

This cross-sectional study recruited 134 12-year-old girls from 23 public primary schools in The Gambia. We used a structured clinical interview to assess mental health and life satisfaction, including the Short Mood and Feeling Questionnaire (SMFQ), the Symptom check list (SCL-5) and Cantril's Ladder of Life Satisfaction. Each interview included questions about the cutting procedure, immediate- and current physical complications and the kind of help and care girls received following FGC.

RESULTS

Depressive symptoms were associated with immediate physical health complications in a multivariate regression model [RR = 1.08 (1.03, 1.12), p = .001], and with present urogenital problems [RR = 1.19 (1.09, 1.31), p < .001]. The girls that received medical help following immediate complications had a lower risk for depressive symptoms [RR = .73 (.55, .98), p = .04]. Psychological distress was only associated with immediate complications [RR = 1.04 (1.01, 1.07), p = .004]. No significant differences in mental health outcomes were found between girls who underwent FGC before the age of four in comparison to girls who underwent FGC after the age of four.

CONCLUSION

Our findings indicate that the immediate and long-term complications following FGC have implications for psychological health. Only a minimal number of girls received medical care when needed, and the dissemination of health education seems crucial in order to prevent adverse long-term physical and psychological health consequences.

Metabolomic profiling reveals a differential role for hippocampal glutathione reductase in infantile memory formation

The metabolic mechanisms underlying the formation of early-life episodic memories remain poorly characterized. Here, we assessed the metabolomic profile of the rat hippocampus at different developmental ages both at baseline and following episodic learning. We report that the hippocampal metabolome significantly changes over developmental ages and that learning regulates differential arrays of metabolites according to age. The infant hippocampus had the largest number of significant changes following learning, with downregulation of 54 metabolites. Of those, a large proportion was associated with the glutathione-mediated cellular defenses against oxidative stress. Further biochemical, molecular, and behavioral assessments revealed that infantile learning evokes a rapid and persistent increase in the activity of neuronal glutathione reductase, the enzyme that regenerates reduced glutathione from its oxidized form. Inhibition of glutathione reductase selectively impaired long-term memory formation in infant but not in juvenile and adult rats, confirming its age-specific role. Thus, metabolomic profiling revealed that the hippocampal glutathione-mediated antioxidant pathway is differentially required for the formation of infantile memory.

Childhood maltreatment and poor functional outcomes at the transition to adulthood: a comparison of prospective informant- and retrospective self-reports of maltreatment

PURPOSE

Growing evidence suggests that prospective informant-reports and retrospective self-reports of childhood maltreatment may be differentially associated with adult psychopathology. However, it remains unknown how associations for these two maltreatment reporting types compare when considering functional outcomes. The present study compared associations between childhood maltreatment and functional outcomes at age 18 years using these two methods.

METHODS

We used data from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative birth cohort of 2232 children born in England and Wales in 1994-1995. Maltreatment prior to age 12 years was assessed prospectively (during multiple home visits between birth and age of 12 years based on interviews with caregivers, researcher observations, and information from practitioners where child protection referrals were made) and retrospectively (at age 18 via self-report on the Childhood Trauma Questionnaire). Nine functional outcomes were measured at age 18, forming two variables capturing: (i) psychosocial and (ii) vocational disadvantage.

RESULTS

Among the 2054 participants with available data, childhood maltreatment was associated with poorer functional outcomes regardless of whether this was reported only prospectively, only retrospectively, or both. Stronger associations with psychosocial disadvantage arose in the context of retrospective recall by participants (OR = 8.25, 95% CI 4.93-13.82) than prospective reports by informants (OR = 2.03, 95% CI 1.36-3.04) of maltreatment. Conversely, associations with vocational disadvantage were comparable for both prospective informant-reports (OR = 2.19, 95% CI 1.42-3.38) and retrospective self-reports (OR = 1.93, 95% CI 1.33-2.81) of maltreatment.

CONCLUSION

Results highlight the importance of considering the maltreatment report type used when interpreting the functional consequences of childhood maltreatment.

Making the World Behave: A New Embodied Account on Mobile Paradigm

In this review article, we describe the mobile paradigm, a method used for more than 50 years to assess how infants learn and remember sensorimotor contingencies. The literature on the mobile paradigm demonstrates that infants below 6 months of age can remember the learning environment weeks after when reminded periodically and integrate temporally distributed information across modalities. The latter ability is only possible if events occur within a temporal window of a few days, and the width of this required window changes as a function of age. A major critique of these conclusions is that the majority of this literature has neglected the embodied experience, such that motor behavior was considered an equivalent developmental substitute for verbal behavior. Over recent years, simulation and empirical work have highlighted the sensorimotor aspect and opened up a discussion for possible learning mechanisms and variability in motor preferences of young infants. In line with this recent direction, we present a new embodied account on the mobile paradigm which argues that learning sensorimotor contingencies is a core feature of development forming the basis for active exploration of the world and body. In addition to better explaining recent findings, this new framework aims to replace the dis-embodied approach to the mobile paradigm with a new understanding that focuses on variance and representations grounded in sensorimotor experience. Finally, we discuss a potential role for the dorsal stream which might be responsible for guiding action according to visual information, while infants learn sensorimotor contingencies in the mobile paradigm.

A New 3-Day Standardized Eyeblink Conditioning Protocol to Assess Extinction Learning From Infancy to Adulthood

Associative learning can be observed from the neonatal period onward, providing opportunities to examine changes in basic learning and memory abilities. One method that is suitable to study associative learning is classical eyeblink conditioning (EBC) which is dependent on the cerebellum. Extinction learning can be systematically investigated in this paradigm by varying the context during learning and extinction. Because of methodological difficulties and ethical challenges, no studies have compared extinction learning using EBC across human development. Our goal was to test feasibility of a 3-day delay EBC paradigm that can be used from infancy to adulthood. Acceptance/safety was tested especially for infancy by investigating attrition rates and parental report on infant wellbeing. On a paradigm side, we tested if the paradigm leads to successful acquisition and extinction. An air puff served as unconditional stimulus (US) and a tone as conditional stimulus (CS). On day 1 during acquisition, participants received 36 US–CS pairings in context A. On day 2, participants received 12 acquisition trials in context A to consolidate association learning, followed by 48 extinction trials (tone alone presentations) in context B. Renewal was assessed on day 3 and incorporated 12 CS alone trials presented in both the acquisition context and the extinction context. Eyeblink responses were videotaped and coded offline. The protocol was tested with 12–36-months-old infants (N = 72), adolescents (N = 8), and adults (N = 8). Concerning the acceptance/safety side, attrition ranged from 21 to 58% in infant samples due to the complex preparation of the children for the paradigm. However, attrition is equal to or lower than other infant learning paradigms. Parents of infant samples were very interested in the paradigm and reported low levels of infant stress, exhaustion, and negative feelings during the sessions. Data quality was very high, and no participant had to be excluded because of insufficient data. Concerning the paradigm side, participants showed successful acquisition and extinction as a group. The procedure is ethically sound, feasible, tolerated by many infants, and acceptable among parents. The data show successful acquisition and extinction rates, making the paradigm a valuable tool for investigating developmental changes in extinction learning over the lifespan.

Re-imagining fMRI for awake behaving infants

Thousands of functional magnetic resonance imaging (fMRI) studies have provided important insight into the human brain. However, only a handful of these studies tested infants while they were awake, because of the significant and unique methodological challenges involved. We report our efforts to address these challenges, with the goal of creating methods for awake infant fMRI that can reveal the inner workings of the developing, preverbal mind. We use these methods to collect and analyze two fMRI datasets obtained from infants during cognitive tasks, released publicly with this paper. In these datasets, we explore and evaluate data quantity and quality, task-evoked activity, and preprocessing decisions. We disseminate these methods by sharing two software packages that integrate infant-friendly cognitive tasks and eye-gaze monitoring with fMRI acquisition and analysis. These resources make fMRI a feasible and accessible technique for cognitive neuroscience in awake and behaving human infants.

State-Dependent Memory in Infants

Why do infants remember some things and not others? Human infants frequently cycle through different states such as calm attentiveness, wakeful activity, and crying. Given that cognitive processes do not occur in isolation, such fluctuations in internal state might influence memory processing. In the present experiment, declarative memory in 9-month-old infants (N = 96) was heavily state dependent. Infants exhibited excellent retention of a deferred imitation task after a 15-min delay if their state at encoding was identical to their state at retrieval (e.g., calm). Infants failed to exhibit retention if their state at encoding was different from their state at retrieval (e.g., calm vs. animated). Infant memory processing depends on internal cues.

The impact of trauma characteristics on post-traumatic stress disorder and substance use disorder outcomes across integrated and substance use treatments

Proponents of complex post-traumatic stress disorder (PTSD) constructs suggest that specific trauma characteristics, such as earlier age of first trauma (trauma age) and higher number of traumas (trauma count), may obstruct PTSD symptom reduction in treatment. PTSD and substance use disorders (SUD) commonly co-occur, but the impact of trauma age and count on PTSD treatment responses in a comorbid PTSD and SUD sample is unclear. Further, no studies have examined the impact of trauma characteristics on SUD treatment outcomes or whether their impact on either PTSD or SUD outcomes varies if PTSD is directly addressed. A secondary analysis of a randomized controlled trial was conducted to examine: (1) whether trauma age and count influence comorbid PTSD and SUD (PTSD+SUD) responses during and following treatment; and (2) whether these effects differed across an exposure-based, integrated PTSD+SUD treatment (Concurrent Treatment of PTSD and Substance Use Disorders using Prolonged Exposure; COPE) and a SUD-only focused treatment (Relapse Prevention Therapy; RPT). Individuals with PTSD+SUD randomized to COPE (n = 39) or RPT (n = 43) provided weekly measurements of PTSD and SUD. Across COPE and RPT, earlier trauma age predicted reduced SUD improvement (B = -0.01, standard error = 0.00). Trauma count did not predict changes in PTSD or SUD during or following treatment. These findings suggest that excluding individuals from exposure-based, integrated treatments on the basis of trauma characteristics is not empirically supported. However, individuals with earlier trauma ages may require additional or unique clinical attention to improve their SUD outcomes.

Not the Root of the Problem-Hair Cortisol and Cortisone Do Not Mediate the Effect of Child Maltreatment on Body Mass Index

BACKGROUND

Experiencing maltreatment during childhood exerts substantial stress on the child and increases the risk for overweight and obesity later in life. The current study tests whether hair cortisol-a measure of chronic stress-and its metabolite cortisone mediate the relation between abuse and neglect on the one hand, and body mass index (BMI) on the other.

METHOD

The sample consisted of 249 participants aged 8 to 87 years (M = 36.13, SD = 19.33). We collected data on child abuse and neglect using questionnaires, measured cortisol and cortisone concentrations in hair, and BMI. In a structural model, the effects of abuse and neglect on hair cortisol, hair cortisone, and BMI were tested, as well as the covariance between hair cortisol and BMI, and hair cortisone and BMI.

RESULTS

Within the sample, 23% were overweight but not obese and 14% were obese. Higher levels of experienced abuse were related to higher cortisone concentrations in hair (β = 0.24, p < .001) and higher BMI (β = 0.17, p =.04). Neglect was not related to hair cortisol, hair cortisone, or BMI. Hair cortisol and cortisone did not mediate the association between maltreatment, and BMI. Sensitivity analyses demonstrate the same pattern of results in a subsample of adult participants currently not living with their parents. However, in younger participants who were still living with their parents, the associations between abuse and cortisone (β = 0.14, p =.35) and abuse and BMI (β = 0.02, p =.92) were no longer significant.

CONCLUSION

These findings confirm that experiencing abuse is related to higher BMI but suggest that hair cortisol and cortisone are not the mechanism underlying the association between child maltreatment and BMI. This is the first study to show abuse may be associated to elevated concentrations of hair cortisone-evidence of long-term alterations in chronic stress levels. Future research may benefit from exploring the effects of maltreatment on weight gain in longitudinal designs, including measures of other potential mediators such as eating as a coping mechanism, and more direct indicators of metabolic health.

Noting a difference: change in social context prompts spontaneous recall in 46-month-olds, but not in 35-month-olds

An experimental paradigm has shown that it is possible to activate spontaneous memories in children by having them re-visit the setting in which they were introduced to a memorable event. Nevertheless, the most important cues for spontaneous recall remain undetermined. In response, we investigated the importance of the experimenter by introducing 35-month-olds (n = 62) and 46-month-olds (n = 62) to the same or a new person after one week. We expected that altering the experimenter would result in fewer recollections through reducing the overlap of cues between encoding and testing. In contrast, the manipulation affected the two age groups differently: no effect of condition was seen in the 35-month-olds, whereas the 46-month-olds performed better, when the experimenter had changed, suggesting a sensitivity to change and an ability to update their knowledge of the event. We replicated previous findings demonstrating that both age groups exhibited spontaneous recollections.

Early life experiences selectively mature learning and memory abilities

The mechanisms underlying the maturation of learning and memory abilities are poorly understood. Here we show that episodic learning produces unique biological changes in the hippocampus of infant rats and mice compared to juveniles and adults. These changes include persistent neuronal activation, BDNF-dependent increase in the excitatory synapse markers synaptophysin and PSD-95, and significant maturation of AMPA receptor synaptic responses. Inhibition of PSD-95 induction following learning impairs both AMPA receptor response maturation and infantile memory, indicating that the synapse formation/maturation is necessary for creating infantile memories. Conversely, capturing the learning-induced changes by presenting a subsequent learning experience or by chemogenetic activation of the neural ensembles tagged by learning matures memory functional competence. This memory competence is selective for the type of experience encountered, as it transfers within similar hippocampus-dependent learning domains but not to other hippocampus-dependent types of learning. Thus, experiences in early life produce selective maturation of memory abilities.

Sociocultural memory development research drives new directions in gadgetry science

Sociocultural developmental psychology can drive new directions in gadgetry science. We use autobiographical memory, a compound capacity incorporating episodic memory, as a case study. Autobiographical memory emerges late in development, supported by interactions with parents. Intervention research highlights the causal influence of these interactions, whereas cross-cultural research demonstrates culturally determined diversity. Different patterns of inheritance are discussed.

New perspectives on childhood memory: introduction to the special issue

This special issue brings together the scholarship that contributes diverse new perspectives on childhood amnesia - the scarcity of memories for very early life events. The topics of the studies reported in the special issue range from memories of infants and young children for recent and distant life events, to mother-child conversations about memories for extended lifetime periods, and to retrospective recollections of early childhood in adolescents and adults. The methodological approaches are diverse and theoretical insights rich. The findings together show that childhood amnesia is a complex and malleable phenomenon and that the waning of childhood amnesia and the development of autobiographical memory are shaped by a variety of interactive social and cognitive factors. This collective body of work will facilitate discussion and deepen our understanding of the dynamics that influence the accessibility, content, accuracy, and phenomenological qualities of memories from early childhood.

Actions speak louder than words: Differences in memory flexibility between monolingual and bilingual 18-month-olds

Bilingual infants from 6- to 24-months of age are more likely to generalize, flexibly reproducing actions on novel objects significantly more often than age-matched monolingual infants are. In the current study, we examine whether the addition of novel verbal labels enhances memory generalization in a perceptually complex imitation task. We hypothesized that labels would provide an additional retrieval cue and aid memory generalization for bilingual infants. Specifically, we hypothesized that bilinguals might be more likely than monolinguals to map multiple perceptual features onto a novel label and therefore show enhanced generalization. Eighty-seven 18-month-old monolingual and bilingual infants were randomly assigned to one of two experimental conditions or a baseline control condition. In the experimental conditions, either no label or a novel label was added during demonstration and again at the beginning of the test session. After a 24-hr delay, infants were tested with the same stimulus set to test cued recall and with a perceptually different but functionally equivalent stimulus set to test memory generalization. Bilinguals performed significantly above baseline on both cued recall and memory generalization in both experimental conditions, whereas monolinguals performed significantly above baseline only on cued recall in both experimental conditions. These findings show a difference between monolinguals and bilinguals in memory generalization and suggest that generalization differences between groups may arise from visual perceptual processing rather than linguistic processing. A video abstract of this article can be viewed at https://youtu.be/yXB4pM3fF2k.

When Representation Becomes Reality: Interactive Digital Media and Symbolic Development

One challenge of using an interesting object such as a scale model as a symbol for something else is children's deep interest in the object itself. Attending to the model (the symbol) as a toy, children do not use information about where in the model a tiny dog is hiding to mentally represent where a larger dog is hiding in the full-sized room (the referent). Young children use pictures in this way because they are relatively uninteresting as objects. Today, interactive images on touchscreens function as virtual objects on which to act and which respond to the user's actions. In this chapter, we examine how interactive symbolic media (e.g., touchscreens, video chat, augmented reality) might affect children's symbolic development and the way that psychologists think about representational objects. Young children's learning about and from interactive media may depend upon adults scaffolding children's use of these new cultural tools.

Ontogenesis of learning and memory: Biopsychosocial and dynamical systems perspectives

In this article, we review recent empirical and theoretical work on infant memory development, highlighting future directions for the field. We consider the state of the field since Carolyn Rovee-Collier's call for developmental scientists to "shift the focus from what to why," emphasizing the function of infant behavior and the value of integrating fractionized, highly specialized subfields. We discuss functional approaches of early learning and memory, including ecological models of memory development and relevant empirical work in human and non-human organisms. Ontogenetic changes in learning and memory occur in developing biological systems, which are embedded in broader socio-cultural contexts with shifting ecological demands that are in part determined by the infants themselves. We incorporate biopsychosocial and dynamical systems perspectives as we analyze the state of the field's integration of multiple areas of specialization to provide more holistic understanding of the contributing factors and underlying mechanisms of the development of memory.

Meaningful Memory? Eighteen-Month-Olds Only Remember Cartoons With a Meaningful Storyline

In two studies we investigated the importance of a storyline for remembering cartoons across a delay of 2 weeks in 18-month-old infants by means of the visual paired-comparison (VPC) paradigm. In Study 1 seventy-one 18-month-olds were tested using similar cartoons as in a recent study from our lab while varying the richness of the storyline information. In a VPC task half of the infants watched uncompromised versions of the cartoons used in the recent study (Storyline Condition), whereas the other half watched Pixelized versions of the cartoons (number of pixels reduced by 98% covering up the narrative, but leaving perceptual details, e.g., colors, movements, the same, and Pixelized Condition). Two weeks later they were presented with the familiar cartoon and a novel cartoon from the same version (Storyline or Pixelized) simultaneously, while being eye-tracked. Results showed that only the infants in the Storyline Condition remembered the target cartoon, thus suggesting that the storyline is important for memory. However, an alternative interpretation of the results could be that what made the infants in the Storyline Condition remember the target cartoon was not the storyline, but the static conceptual information of the objects and agents present in the cartoon (which was not visible in the Pixelized version). To test this possibility, a control study was created. In Study 2 thirty-six infants were therefore presented with a version of the cartoon in which we broke down the temporal presentation into 1 s segments and presented these out of order. This was done to preserve the static conceptual information (e.g., objects and agents) while still disturbing the storyline. Results showed that the infants in this condition still did not remember the target cartoon, suggesting that the meaningfulness of the storyline - and not only static conceptual information - is important for later memory.

Retrospective attribution of false beliefs in 3-year-old children

A current debate in psychology and cognitive science concerns the nature of young children's ability to attribute and track others' beliefs. Beliefs can be attributed in at least two different ways: prospectively, during the observation of belief-inducing situations, and in a retrospective manner, based on episodic retrieval of the details of the events that brought about the beliefs. We developed a task in which only retrospective attribution, but not prospective belief tracking, would allow children to correctly infer that someone had a false belief. Eighteen- and 36-month-old children observed a displacement event, which was witnessed by a person wearing sunglasses (Experiment 1). Having later discovered that the sunglasses were opaque, 36-month-olds correctly inferred that the person must have formed a false belief about the location of the objects and used this inference in resolving her referential expressions. They successfully performed retrospective revision in the opposite direction as well, correcting a mistakenly attributed false belief when this was necessary (Experiment 3). Thus, children can compute beliefs retrospectively, based on episodic memories, well before they pass explicit false-belief tasks. Eighteen-month-olds failed in such a task, suggesting that they cannot retrospectively attribute beliefs or revise their initial belief attributions. However, an additional experiment provided evidence for prospective tracking of false beliefs in 18-month-olds (Experiment 2). Beyond identifying two different modes for tracking and updating others' mental states early in development, these results also provide clear evidence of episodic memory retrieval in young children.

Sleep-dependent selective imitation in infants

In adults, sleep selectively consolidates those memories that are relevant for future events. The present study tested whether napping after encoding plays a role in selective memory consolidation in infants. Infants aged 15 and 24 months (n = 48 per age) were randomly assigned to a nap or a no-nap demonstration condition, or a baseline control condition. In the demonstration conditions, infants observed an experimenter perform an irrelevant action followed by a relevant action to achieve a desirable outcome on four different toys. Infant imitation of irrelevant and relevant actions was coded at a test session that occurred after a 24-hr delay. The demonstration and test sessions were scheduled around infants' naturally occurring sleeping patterns. When order of actions was not taken into account, infants in both demonstration conditions exhibited retention of the relevant and irrelevant target actions. Contrary to expectations, infants in the nap condition did not perform the relevant action only more often than infants in the no-nap condition. As expected, only infants in the no-nap condition faithfully reproduced the two actions in the demonstrated order: irrelevant action first, followed by the relevant action. Thus, sleep might help infants to selectively "discard" aspects of a learning experience that they identify as being not useful or relevant in the future.

Developmental transitions in amygdala PKC isoforms and AMPA receptor expression associated with threat memory in infant rats

Although infants learn and remember, they rapidly forget, a phenomenon known as infantile amnesia. While myriad mechanisms impact this rapid forgetting, the molecular events supporting memory maintenance have yet to be explored. To explore memory mechanisms across development, we used amygdala-dependent odor-shock conditioning and focused on mechanisms important in adult memory, the AMPA receptor subunits GluA1/2 and upstream protein kinases important for trafficking AMPAR, protein kinase M zeta (PKMζ) and iota/lambda (PKCι/λ). We use odor-shock conditioning in infant rats because it is late-developing (postnatal day, PN10) and can be modulated by corticosterone during a sensitive period in early life. Our results show that memory-related molecules did not change in pups too young to learn threat (PN8) but were activated in pups old enough to learn (PN12), with increased PKMζ-PKCι/λ and GluA2 similar to that observed in adult memory, but with an uncharacteristic decrease in GluA1. This molecular signature and behavioral avoidance of the conditioned odor was recapitulated in PN8 pups injected with CORT before conditioning to precociously induce learning. Blocking learning via CORT inhibition in older pups (PN12) blocked the expression of these molecules. PN16 pups showed a more adult-like molecular cascade of increased PKMζ-PKCι/λ and GluA1–2. Finally, at all ages, zeta inhibitory peptide (ZIP) infusions into the amygdala 24 hr after conditioning blocked memory. Together, these results identify unique features of memory processes across early development: AMPAR subunits GluA1/2 and PKC isoform expression are differentially used, which may contribute to mechanisms of early life forgetting.

Entwicklung des Gedächtnisses bei präverbalen Kindern

Zusammenfassung. Gedächtnis ist eine elementare Fähigkeit, deren Entwicklungsverlauf insbesondere für das präverbale Alter bisher nicht eindeutig beschrieben ist. Zur Erfassung von Gedächtnisleistungen im präverbalen Alter werden verschiedene Verhaltensmaße herangezogen. Früheste Beobachtungen von Leistungen des impliziten Gedächtnisses sind über Präferenzverhalten in Paarvergleichs- und Habituationsaufgaben möglich und basieren auf einem Reizinformationsvergleich. Auch operant konditioniertes Verhalten in der Mobile- und Zug-Aufgabe indiziert eine implizite Gedächtnisleistung und basiert auf dem Lernen aus Konsequenzen. Imitationsverhalten als Leistung des expliziten Gedächtnissystems beruht auf Modelllernen in Aufgaben zur verzögerten Imitation. Sowohl im impliziten als auch im expliziten System sind im Entwicklungsverlauf Zuwächse der Gedächtnisleistungen hinsichtlich Kapazität, Behaltensdauer, Enkodiergeschwindigkeit und Flexibilität im Abruf beobachtbar. Die den Aufgaben zur Erfassung von Gedächtnisleistungen zugrundeliegenden Mechanismen deuten auf eine sukzessive Entwicklung zuerst des impliziten, dann des expliziten Systems hin.

Fictional First Memories

In a large-scale survey, 6,313 respondents provided descriptions of their first memory and their age when they encoded that memory, and they completed various memory judgments and ratings. In good agreement with many other studies, where mean age at encoding of earliest memories is usually found to fall somewhere in the first half of the 4th year of life, the mean age at encoding here was 3.15 years. The established view is that the distribution around mean age at encoding is truncated, with very few or no memories dating to the preverbal period, that is, below about 2 years of age. However, we found that 2,479 first memories (nearly 40% of the entire sample) dated to an age at encoding of 2 years and younger, with 887 (14.1%) dating to 1 year and younger. We discuss how such improbable, fictional first memories could have arisen and contrast them with more probable first memories, those with an age at encoding of 3 years and older.

How self-generated labelling shapes transfer of learning during early childhood: The role of individual differences

Multiple factors influence imitation during toddlerhood, including task complexity, social contingency, and individual differences. We conducted a secondary data analysis of individual differences in self-generated labelling using data collected from a complex puzzle imitation task with 355 2- to 3-year-olds. This analysis indicated that toddlers' ability to label the completed puzzle (fish or boat) was associated with better imitation performance. Labelling occurs during social interactions; therefore, our second analysis tested how labelling differed as a function of the level of social scaffolding in each condition. This analysis revealed that self-generated labelling was lower when the social demonstrator was removed and the task was presented on a touchscreen. This study is one of the first to examine self-generated labelling during a complex imitation task in toddlers and increases our understanding of the complexity of memory processing needed for imitation learning. Statement of contribution What is already known on this subject? Toddlers exhibit a transfer of learning deficit from 2D media, including books, TV, and tablets. Self-generated labelling enhances children's learning, through attentional and cognitive mechanisms. Children are sensitive to reduced social cues in screen media contributing to the transfer deficit. What does this study add? Self-generated labelling is associated with better goal imitation performance. Self-generated labelling occurs more frequently under social conditions.

Mechanisms of critical period in the hippocampus underlie object location learning and memory in infant rats

Episodic memories in early childhood are rapidly forgotten, a phenomenon that is associated with "infantile amnesia," the inability of adults to remember early-life experiences. We recently showed that early aversive contextual memory in infant rats, which is in fact rapidly forgotten, is actually not lost, as reminders presented later in life reinstate a long-lasting and context-specific memory. We also showed that the formation of this infantile memory recruits in the hippocampus mechanisms typical of developmental critical periods. Here, we tested whether similar mechanisms apply to a nonaversive, hippocampal type of learning. We report that novel object location (nOL) learned at postnatal day 17 (PN17) undergoes the typical rapid forgetting of infantile learning. However, a later reminder reinstates memory expression. Furthermore, as for aversive experiences, nOL learning at PN17 engages critical period mechanisms in the dorsal hippocampus: it induces a switch in the GluN2A/2B-NMDA receptor ratio, and brain-derived neurotrophic factor injected bilaterally into the dorsal hippocampus immediately after training results in long-lasting memory expression. We conclude that in infancy the hippocampus plays a necessary role in processing episodic and contextual memories, including nonaversive ones, and matures through a developmental critical period.

Changes in infant visual attention when observing repeated actions

Infants' early visual preferences for faces, and their observational learning abilities, are well-established in the literature. The current study examines how infants' attention changes as they become increasingly familiar with a person and the actions that person is demonstrating. The looking patterns of 12- (n = 61) and 16-month-old infants (n = 29) were tracked while they watched videos of an adult presenting novel actions with four different objects three times. A face-to-action ratio in visual attention was calculated for each repetition and summarized as a mean across all videos. The face-to-action ratio increased with each action repetition, indicating that there was an increase in attention to the face relative to the action each additional time the action was demonstrated. Infant's prior familiarity with the object used was related to face-to-action ratio in 12-month-olds and initial looking behavior was related to face-to-action ratio in the whole sample. Prior familiarity with the presenter, and infant gender and age, were not related to face-to-action ratio. This study has theoretical implications for face preference and action observations in dynamic contexts.