Working memory deficits can be overcome: Impacts of training and medication on working memory in children with ADHD

This study evaluated the impact of two interventions—a training program and stimulant medication—on working memory (WM) function in children with attention deficit hyperactivity disorder (ADHD). Twenty‐five children aged between 8 and 11 years participated in training that taxed WM skills to the limit for a minimum of 20 days, and completed other assessments of WM and IQ before and after training, and with and without prescribed drug treatment. While medication significantly improved visuo‐spatial memory performance, training led to substantial gains in all components of WM across untrained tasks. Training gains associated with the central executive persisted over a 6‐month period. IQ scores were unaffected by either intervention. These findings indicate that the WM impairments in children with ADHD can be differentially ameliorated by training and by stimulant medication. Copyright © 2009 John Wiley & Sons, Ltd.     

Developmental fractionation of working memory and response inhibition during childhood

The lateral prefrontal cortex (LPFC) plays a major role in both working memory (WM) and response inhibition (RI), which are fundamental for various cognitive abilities. We explored the relationship between these LPFC functions during childhood development by examining the performance of two groups of children in visuospatial and auditory WM tasks and a go/no-go RI task. In the younger children (59 5- and 6-year-olds), performance on the visuospatial WM task correlated significantly with that in the auditory WM task. Furthermore, accuracy in these tasks correlated significantly with performance on the RI task, particularly in the no-go trials. In contrast, there were no significant correlations among those tasks in older children (92 8- and 9-year-olds). These results suggest that functional neural systems for visuospatial WM, auditory WM, and RI, especially those in the LPFC, become fractionated during childhood, thereby enabling more efficient processing of these critical cognitive functions.     

A novel working memory task for preschoolers: sensitivity to age differences from 3-5 years

Working memory (WM) plays an important role in children’s learning and is linked to later academic and occupational success. Understanding the early development of WM can provide critical clues regarding the underlying structure of executive functions and how they change over the life span. The main objectives of the present study were to (1) investigate age differences in the development of three components of WM (retrieval, substitution, transformation) on a novel preschool WM measure and (2) explore whether findings are consistent with the hierarchical model of WM development by examining perseverative and non-perseverative WM errors. Perseverative errors were hypothesized to be more strongly associated with problems substituting and transforming a representation held in mind, whereas non-perseverative errors were hypothesized to be associated with problems maintaining a representation in mind. Participants were 64 children ranging in age from 3.0 to 5.6 years. The results provide evidence for the sensitivity of the WM task to age differences from 3 to 5 years and support for the hierarchical model of WM development.     

Intellectual growth in children as a function of domain specific and domain general working memory subgroups

This study examined whether children's growth on measures of fluid (Raven Colored Progressive Matrices) and crystallized (reading and math achievement) intelligence was attributable to domain-specific or domain-general functions of working memory (WM). A sample of 290 elementary school children was tested on measures of intelligence across three testing waves. Two methods, a hierarchical factor model predicting latent growth and a double dissociation design comparing children divided into high and low performers, tested whether general and/or specific components accounted for performance on intelligence measures. A general domain model for the total sample provided the best fit for latent growth on all measures. Further, the lack of a significant WM subgroup × domain interaction suggested that a general WM system underlies the individual differences on measures of fluid and crystallized intelligence. Overall, the findings support a domain-general view of WM capacity on intelligence measures in children, but also suggest that domain specific storage systems may come into play on isolated measures.     

Binding and strategic selection in working memory: a lifespan dissociation

Working memory (WM) shows a gradual increase during childhood, followed by accelerating decline from adulthood to old age. To examine these lifespan differences more closely, we asked 34 children (10-12 years), 40 younger adults (20-25 years), and 39 older adults (70-75 years) to perform a color change detection task. Load levels and encoding durations were varied for displays including targets only (Experiment 1) or targets plus distracters (Experiment 2, investigating a subsample of Experiment 1). WM performance was lower in older adults and children than in younger adults. Longer presentation times were associated with better performance in all age groups, presumably reflecting increasing effects of strategic selection mechanisms on WM performance. Children outperformed older adults when encoding times were short, and distracter effects were larger in children and older adults than in younger adults. We conclude that strategic selection in WM develops more slowly during childhood than basic binding operations, presumably reflecting the delay in maturation of frontal versus medio-temporal brain networks. In old age, both sets of mechanisms decline, reflecting senescent change in both networks. We discuss similarities to episodic memory development and address open questions for future research.     

Developmental changes in the engagement of episodic retrieval processes and their relationship with working memory during the period of middle childhood

We examined the development of children's engagement of the episodic retrieval processes of recollection and familiarity and their relationship with working memory (WM). Ninety‐six children (24 in four groups aged 8, 9, 10, and 11 years) and 24 adults performed an episodic memory (EM) task involving old/new, remember/know (R/K), and source memory judgements and numerous WM tasks that assessed verbal and spatial components of WM and delayed short‐term memory (STM). Developmental changes were observed in EM with younger children (8‐, 9‐, 10‐year‐olds) making fewer remember responses than 11‐year‐olds and adults while 11‐year‐olds did not differ from adults. Only children aged 10 years plus showed a relationship between EM and WM. EM was related to verbal executive WM in 10‐ and 11‐year‐old children suggesting that children at this stage use verbal strategies to aid EM. In contrast, EM was related to spatial executive WM in adults. The engagement of episodic retrieval processes appears to be selectively related to executive components of verbal and spatial WM, the pattern of which differs in children and adults.     

Does cross‐frequency phase coupling of oscillatory brain activity contribute to a better understanding of visual working memory?

Nesting of fast rhythmical brain activity (gamma) into slower brain waves (theta) has frequently been suggested as a core mechanism of multi‐item working memory (WM) retention. It provides a better understanding of WM capacity limitations, and, as we discuss in this review article, it can lead to applications for modulating memory capacity. However, could cross‐frequency coupling of brain oscillations also constructively contribute to a better understanding of the neuronal signatures of working memory compatible with theoretical approaches that assume flexible capacity limits? Could a theta‐gamma code also be considered as a neural mechanism of flexible sharing of cognitive resources between memory representations in multi‐item WM? Here, we propose potential variants of theta‐gamma coupling that could explain WM retention beyond a fixed memory capacity limit of a few visual items. Moreover, we suggest how to empirically test these predictions in the future.     

Mental Set Shifting in Childhood: The Role of Working Memory and Inhibitory Control

The role of working memory (WM) and inhibition in mental set shifting was examined from an individual difference perspective in children aged 5–14 years (N = 117). Using the Hearts and Flowers task the rationale of the present study was to directly test the theoretical assumption that mental set shifiting in childhood primarily builds on WM and inhibitory processes. Theoretical predictions about WM and inhibitory demands in the congruent and incongruent conditions of the Hearts and Flowers task were also considered because these blocks underlie relevant measures of set shifting. The findings show that both WM and inhibition (extracted as factors in confirmatory factor analysis) are important for set shifting but that this general association is driven by the link between these executive functions (EFs) and the goal‐representation aspect (i.e. global switch costs) of shifting, rather than to the actual switch‐implementation process (i.e. local switch costs). In addition, our findings are novel in showing that, despite a substantial correlation between the two EF components, it was the variance specific to WM and inhibition that was important for mental set shifting. Copyright © 2014 John Wiley & Sons, Ltd.     

Selective attention,filtering, and the development of working memory

Selective attention is fundamental for learning across many situations, yet it exhibits protracted development, with young children often failing to filter out distractors. In this research, we examine links between selective attention and working memory (WM) capacity across development. One possibility is that WM is resource‐limited, with development resulting in an increase in the amount of resources available for processing information. However, it is also possible that development results in greater efficiency of using available resources. In the current research, we explore the latter possibility by examining the developmental trajectory of selectivity and filtering in relation to WM capacity. We report that filtering efficiency of adults (N = 30), 7‐year‐olds (N = 29), and 4‐year‐olds (N = 28) was uniquely predictive of WM capacity. We also report that filtering efficiency continues to develop after 7 years of age, whereas WM capacity may reach an asymptote around 7 years of age. The latter finding suggests that selective attention plays a critical role in developmental and individual differences in visual working memory capacity.     

Children's working memory: Its structure and relationship to fluid intelligence

Working memory (WM) has been predominantly studied in adults. The insights provided by these studies have led to the development of competing theories on the structure of WM and conflicting conclusions on how strongly WM components are related to higher order thinking skills such as fluid intelligence. However, it remains unclear whether and to what extent the theories and findings derived from adult data generalize to children. The purpose of the present study is therefore to investigate children's WM (N = 161), who attended classes at the end of kindergarten in Luxembourg. Specifically, we examine different structural models of WM and how its components, as defined in these models, are related to fluid intelligence. Our results indicate that short-term storage capacity primarily explains the relationship between WM and fluid intelligence. Based on these observations we discuss the theoretical and methodological issues that arise when children's WM is investigated.     

Working memory recall precision is a more sensitive index than span

Delayed adjustment tasks have recently been developed to examine working memory (WM) precision, that is, the resolution with which items maintained in memory are recalled. However, despite their emerging use in experimental studies of healthy people, evaluation of patient populations is sparse. We first investigated the validity of adjustment tasks, comparing precision with classical span measures of memory across the lifespan in 114 people. Second, we asked whether precision measures can potentially provide a more sensitive measure of WM than traditional span measures. Specifically, we tested this hypothesis examining WM in a group with early, untreated Parkinson's disease (PD) and its modulation by subsequent treatment on dopaminergic medication. Span measures correlated with precision across the lifespan: in children, young, and elderly participants. However, they failed to detect changes in WM in PD patients, either pre‐ or post‐treatment initiation. By contrast, recall precision was sensitive enough to pick up such changes. PD patients pre‐medication were significantly impaired compared to controls, but improved significantly after 3 months of being established on dopaminergic medication. These findings suggest that precision methods might provide a sensitive means to investigate WM and its modulation by interventions in clinical populations.     

Cognitive processes in children's reading and attention: The role of working memory,divided attention,and response inhibition

Children experiencing attention difficulties have documented cognitive deficits in working memory (WM), response inhibition and dual tasks. Recent evidence suggests however that these same cognitive processes are also closely associated with reading acquisition. This paper therefore explores whether these variables predicted attention difficulties or reading among 123 children with and without significant attention problems sampled from the school population. Children were screened using current WM and attention task measures. Three factors explained variance in WM and attention tasks. Response inhibition tasks loaded mainly with central executive measures, but a dual processing task loaded with the visual‐spatial WM measures. Phonological loop measures loaded independently of attention measures. After controls for age, IQ and attention‐group membership, phonological loop and ‘central processing’ measures both predicted reading ability. A ‘visual memory/dual‐task’ factor predicted attention group membership after controls for age, IQ and reading ability. Results thus suggest that some of the processes previously assumed to be predictive of attention problems may reflect processes involved in reading acquisition. Visual memory and dual‐task functioning are, however, purer indices of cognitive difficulty in children experiencing attention problems.     

The structure of working memory and how it relates to intelligence in children

This study explored the structure of working memory, and its relationship with intelligence in 176 typically-developing children in the 4th and 5th grades at school. Different measures of working memory (WM), and intelligence (g) were administered. Confirmatory factor analyses showed that WM involves an attentional control system and storage aspects that rely on domain-specific verbal (STM-V) and visuospatial (STM-VS) resources. The structural equation models showed that WM predicts a large portion (66%) of the variance in g, confirming that the two constructs are separable but closely related in young children. Findings also showed that only WM and STM-VS are significantly related to g, while the contribution of STM-V is moderate. Theoretical implications for the relationship between WM and g are discussed.     

Socioeconomic gradients predict individual differences in neurocognitive abilities

Socioeconomic status (SES) is associated with childhood cognitive achievement. In previous research we found that this association shows neural specificity; specifically we found that groups of low and middle SES children differed disproportionately in perisylvian/language and prefrontal/executive abilities relative to other neurocognitive abilities. Here we address several new questions: To what extent does this disparity between groups reflect a gradient of SES‐related individual differences in neurocognitive development, as opposed to a more categorical difference? What other neurocognitive systems differ across individuals as a function of SES? Does linguistic ability mediate SES differences in other systems? And how do specific prefrontal/executive subsystems vary with SES? One hundred and fifty healthy, socioeconomically diverse first‐graders were administered tasks tapping language, visuospatial skills, memory, working memory, cognitive control, and reward processing. SES explained over 30% of the variance in language, and a smaller but highly significant portion of the variance in most other systems. Statistically mediating factors and possible interventional approaches are discussed.     

Executive functions after age 5: Changes and correlates

Research and theorizing on executive function (EF) in childhood has been disproportionately focused on preschool age children. This review paper outlines the importance of examining EF throughout childhood, and even across the lifespan. First, examining EF in older children can address the question of whether EF is a unitary construct. The relations among the EF components, particularly as they are recruited for complex tasks, appear to change over the course of development. Second, much of the development of EF, especially working memory, shifting, and planning, occurs after age 5. Third, important applications of EF research concern the role of school-age children’s EF in various aspects of school performance, as well as social functioning and emotional control. Future research needs to examine a more complete developmental span, from early childhood through late adulthood, in order to address developmental issues adequately.     

Inhibitory and working memory demands of the day–night task in children

Gerstadt, Hong, and Diamond (1994) investigated the development of inhibitory control in children aged 3½ – 7 years using the day–night task. In two studies we build on Gerstadt et al.'s findings with a measure of inhibitory control that can be used throughout childhood. In Study 1 (twenty‐four 3½‐year‐olds and sixteen 5‐year‐olds) we modified Gerstadt et al.'s day–night task. Using this modified task we obtained further evidence for the development of inhibitory control in children between 3½ and 5‐years‐old. We also obtained data suggestive of more moderate working memory development. In Study 2 we tested 84 children aged between 3½ and 11 years. The aim was to determine how much inhibition and working memory taxed children of different ages. We obtained evidence that inhibitory demands were high and that inhibitory development was non‐linear, with rapid improvements in children between 3½ and 5 years and only modest improvements thereafter. In contrast, working memory demands were low and working memory development was more linear. We interpret these findings as evidence that working memory has relatively little impact on performance in our modified version of the day–night task.     

The influence of working memory on reading growth in subgroups of children with reading disabilities

This 3-year longitudinal study determined whether (a) subgroups of children with reading disabilities (RD) (children with RD only, children with both reading and arithmetic deficits, and low verbal IQ readers) and skilled readers varied in working memory (WM) and short-term memory (STM) growth and (b) whether growth in an executive system and/or a phonological storage system mediated growth in reading performance. A battery of memory and reading measures was administered to 84 children (11-17 years of age) across three testing waves spaced 1 year apart. The results showed that skilled readers yielded higher WM growth estimates than did the RD groups. No significant differentiation among subgroups of children with RD on growth measures emerged. Hierarchical linear modeling showed that WM (controlled attention), rather than STM (phonological loop), was related to growth in reading comprehension and reading fluency. The results support the notion that deficient growth in the executive component of WM underlies RD.     

A comparison of working memory profiles in school-aged children with Specific Language Impairment, Attention Deficit/Hyperactivity Disorder, Comorbid SLI and ADHD and their typically developing peers

The association between specific language impairment (SLI), attention deficit/hyperactivity disorder (ADHD), and working memory (WM) was examined. WM has been implicated in language acquisition and models of ADHD; however, evidence for WM deficits in SLI and ADHD has been inconsistent. The components of Baddeley's WM model were investigated in 18 children with SLI, 16 children with ADHD, 11 children with comorbid SLI+ADHD, and 24 typically developing (TD) children. The presence of SLI resulted in deficits in more components of WM than the presence of ADHD indicating that children with SLI are more vulnerable to WM deficits than those with ADHD.     

A comparison of working memory profiles in school-aged children with Specific Language Impairment,Attention Deficit/Hyperactivity Disorder,Comorbid SLI and ADHD and their typically developing peers

The association between specific language impairment (SLI), attention deficit/hyperactivity disorder (ADHD), and working memory (WM) was examined. WM has been implicated in language acquisition and models of ADHD; however, evidence for WM deficits in SLI and ADHD has been inconsistent. The components of Baddeley's WM model were investigated in 18 children with SLI, 16 children with ADHD, 11 children with comorbid SLI+ADHD, and 24 typically developing (TD) children. The presence of SLI resulted in deficits in more components of WM than the presence of ADHD indicating that children with SLI are more vulnerable to WM deficits than those with ADHD.     

Socioeconomic status and executive function: developmental trajectories and mediation

Childhood socioeconomic status (SES) predicts executive function (EF), but fundamental aspects of this relation remain unknown: the developmental course of the SES disparity, its continued sensitivity to SES changes during that course, and the features of childhood experience responsible for the SES–EF relation. Regarding course, early disparities would be expected to grow during development if caused by accumulating stressors at a given constant level of SES. Alternatively, they would narrow if schooling partly compensates for the effects of earlier deprivation, allowing lower‐SES children to ‘catch up’. The potential for later childhood SES change to affect EF is also unknown. Regarding mediating factors, previous analyses produced mixed answers, possibly due to correlation amongst candidate mediators. We address these issues with measures of SES, working memory and planning, along with multiple candidate mediators, from the NICHD Study of Early Childcare (n = 1009). Early family income‐to‐needs and maternal education predicted planning by first grade, and income‐to‐needs predicted working memory performance at 54 months. Effects of early SES remained consistent through middle childhood, indicating that the relation between early indicators of SES and EF emerges in childhood and persists without narrowing or widening across early and middle childhood. Changes in family income‐to‐needs were associated with significant changes in planning and trend‐level changes in working memory. Mediation analyses supported the role of early childhood home characteristics in explaining the association between SES and EF, while early childhood maternal sensitivity was specifically implicated in the association between maternal education and planning. Early emerging and persistent SES‐related differences in EF, partially explained by characteristics of the home and family environment, are thus a potential source of socioeconomic disparities in achievement and health across development.