Elsevier

Sleep Medicine

Volume 16, Issue 10, October 2015, Pages 1192-1197
Sleep Medicine

Original Article
Association between sleep and working memory in children with ADHD: a cross-sectional study

https://doi.org/10.1016/j.sleep.2015.06.006Get rights and content

Highlights

  • We assessed sleep and working memory in 189 children with attention-deficit/hyperactivity disorder (ADHD) aged 5–13 years.

  • Child-reported sleep problems were associated with poorer working memory.

  • Parent-reported bedtime resistance was associated with poorer working memory.

  • Other parent-reported sleep difficulties were not associated with working memory.

Abstract

Objective/Background

This study aimed to examine the relationship between sleep problems and working memory in children aged 5–13 years with attention-deficit/hyperactivity disorder (ADHD).

Patients/Methods

Children with ADHD were recruited into a randomized controlled trial from 21 paediatric practices in VIC, Australia. Cross-sectional data for intervention and control children were pooled at 6 months post randomization for the current analyses (n = 189). Children who met the Diagnostic Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) criteria for ADHD and had a parent-reported moderate/severe sleep problem that fulfilled diagnostic criteria for a behavioural sleep disorder were recruited into the study. Sleep was assessed by detailed parent (Children's Sleep Habits Questionnaire) and self-reports (Self-Sleep Report). Working memory was measured using the Working Memory Test Battery for Children (low and very low working memory defined as <25th and <10th percentiles, respectively). Analyses were adjusted for child age and gender, internalizing and externalizing comorbidities, and socio-economic status.

Results

Self-reported sleep problem severity was associated with poorer working memory; for each standard deviation increase in self-reported sleep problems, working memory scores decreased by −3.8 points (95% confidence interval (CI): −6.7, −0.8; p = 0.01). There was some evidence that self-reported sleep problems were associated with low (p = 0.06) and very low working memory (p = 0.01). There was minimal evidence that parent-reported sleep problems were associated with poorer working memory with the exception of bedtime resistance problems.

Conclusions

Behavioural sleep problems and working memory are associated in children with ADHD, particularly when sleep is assessed by self-report.

Introduction

Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent neurodevelopmental disorder affecting approximately 5% of children worldwide [1]. Children with ADHD commonly present with comorbidities including externalizing and internalizing comorbidities [2], and they are also at risk of sleep problems [3]. Up to 70% of children with ADHD experience sleep problems including difficulties initiating and maintaining sleep [3], and these sleep problems exacerbate existing impairments [4], [5]. Children with ADHD and sleep problems have poorer quality of life (QoL), poorer daily functioning, and more severe ADHD symptoms, than children with ADHD and no sleep problems [4]. However, the impact of sleep problems on executive functioning, particularly working memory function in children with ADHD, is unclear. This is important given that working memory difficulties are very common in this population. A recent meta-analysis reported large effect-size differences on measures of working memory between children with ADHD and controls [6].

Working memory is defined as the ability to hold and manipulate verbal or visual information simultaneously, and it is a key predictor of academic functioning [7]. A number of studies examining sleep deprivation in adults have demonstrated associations with impaired prefrontal functioning including working memory and executive functioning performance [8]. A growing body of research has also linked sleep difficulties to poorer neurocognitive functioning in typically developing children [9], [10], [11], [12], [13].

A recent meta-analysis reported that reduced sleep duration but not sleep efficiency was associated with poorer executive functioning, including working memory, inhibitory control, and cognitive flexibility, in school-aged children [14]. However, the results for working memory alone were not reported in this meta-analysis. In a large sample of primary school-aged children (n = 508), Calhoun et al. found that parent-reported excessive daytime sleepiness was associated with reductions in processing speed and working memory performance, which in turn predicted learning and hyperactivity difficulties [10]. However, no relationship between sleep duration (measured by one night of polysomnography) and neurocognitive functioning was detected. Sadeh, Gruber, and Raviv reported an association between sleep quality and neurobehavioural functioning in primary school-aged children (n = 135) [12]. Poor sleepers, as defined by at least three awakenings per night and reduced sleep efficiency, had worse working memory performance (measured via digit recall) than good sleepers; however, there was no relationship between actual sleep duration and neurocognitive functioning. Similarly, Steenari et al. reported a relationship between longer sleep-onset latency and poorer sleep efficiency and poorer working memory in school-aged children (n = 60) [13]. Short sleep duration was associated with poorer working memory at the highest load only. In summary, existing studies suggest that there is a relationship between sleep and working memory function for typically developing children. Of note, these studies suggest that sleep quality, more so than sleep duration, is important for working memory functioning.

Although studies have demonstrated that children with ADHD are more likely to suffer from both sleep and working memory problems compared with children without ADHD, a limited body of research has examined whether sleep problems in children with ADHD exacerbate working memory deficits. Gruber and Sadeh found no relationship between sleep measured using actigraphy and neurobehavioural functioning (including working memory) in children with ADHD (n = 24) [15]. In terms of broader neurocognitive functioning, Hansen et al. (2014) recently examined the relationship between objectively assessed attention (Attention Network Test) and parent-reported sleep problems using the Children's Sleep Habits Questionnaire (CSHQ) in a sample of 137 children (38 ADHD and no anxiety; 39 anxiety with no ADHD; 25 children with ADHD and anxiety; 35 controls) aged 7–13 years [16]. Greater sleep problem severity, bedtime resistance, and sleep-onset delay were associated with poorer directly assessed attention skills, particularly in the alert network (ie, ability to maintain a high sensitivity to incoming stimuli). Working memory was not examined in this study. Similarly, Moreau and colleagues found that sleep duration (assessed using actigraphy) was associated with poorer directly assessed and parent-reported executive functioning in children with ADHD (n = 43) [17], but in contrast to Hansen et al. [16], no relationship was identified between parent-reported sleep problems and attention and executive functioning [17]. Zambrano-Sánchez and colleagues reported a correlation between digit-span performance and inadequate sleep hygiene in children with ADHD; however, the sample was unusual given that children with ADHD did not have more severe sleep problems relative to controls [18]. Finally, experimental studies have reported an association between sleep restriction (1 h over six nights) and poorer neurobehavioural functioning, assessed using the Conners' Continuous Performance Test, in 7–11-year-old children with and without ADHD (n = 43) [19].

Our recent randomized controlled trial examining the efficacy of a behavioural sleep intervention in children with ADHD and moderate–severe sleep problems (n = 244) found that improving sleep in children with ADHD was associated with improved ADHD symptom severity, behaviour, QoL, and daily functioning [20]. We also found that children in the intervention versus usual care group had better working memory performance (backwards digit recall subtest only) [20]; however, given the absence of a baseline measure of working memory, change in working memory over time was unable to be calculated. The direct relationship between sleep severity and working memory was not examined in our original study, and it is the focus of the current investigation.

In summary, research in typically developing children points to a relationship between sleep and working memory functioning. Findings vary depending on the measure used to assess sleep. Although there is some evidence that sleep problems in children with ADHD may be associated with poorer attentional and broader executive functioning [16], [17], research is yet to comprehensively examine the relationship between sleep problems and working memory in this population. The present study is the first of its kind to examine the relationship between sleep (multi-informant measurement) and working memory (detailed direct assessment) in a large, multisite sample of children with ADHD. If sleep problems do contribute to poorer working memory in children with ADHD, identifying and managing sleep problems may be one way of improving working memory for this group of vulnerable children. This may then have flow on effects to improved academic performance.

Therefore, in a sample of 5–13-year-old children with ADHD, we aimed to examine the relationship between working memory and child- (total sleep problem severity) and parent-reported sleep problems (total sleep problem severity, specific sleep problem domains, and sleep duration).

Section snippets

Design

This study uses cross-sectional data from the Sleeping Sound with ADHD study, a randomized controlled trial examining the efficacy of a behavioural sleep intervention for children with ADHD and sleep problems [21]. Approval was obtained from The Royal Children's Hospital (#30033) and from the Victorian Department of Education and Early Childhood Development (#2010_000573) Human Research Ethics Committees. At six months post randomization, a comprehensive assessment of child sleep and working

Sample characteristics

Paediatricians identified 1349 potentially eligible families between August 2010 and June 2012 of whom 336 were eligible to participate. The reasons for ineligibility included not meeting inclusion criteria (n = 696), declined to participate (n = 188), and uncontactable (n = 129). Of the 336 eligible families, 244 consented to participate (73%). There were no differences in child gender, child age, or neighbourhood socio-economic disadvantage for participating versus nonparticipating families.

Discussion

This study examined the relationship between sleep problems and working memory performance in a large clinically diverse sample of children with ADHD. We found that child-reported sleep problems were associated with poorer working memory. Findings were held when examining working memory scores continuously and also when using cut points to define low and very low working memory. Most parent-reported sleep problem domains were not associated with child working memory performance, with the

Conflict of interest

All authors have completed the Conflict of Interest Disclosure and Attestation of Authorship form, and they declare that (1) no authors have support from any company for the submitted work; (2) no authors have relationships with companies that might have an interest in the submitted work in the previous three years; (3) their spouses, partners, or children have no financial relationships that may be relevant to the submitted work; and (4) no authors have any nonfinancial interests that may be

Acknowledgments and funding sources

This study was funded by the Australian National Health and Medical Research Council (NHRMC; # 607362). The funder was not involved with the manuscript preparation, review, or approval. Dr Sciberras and Dr Mensah's positions are funded by an NHMRC Early Career Fellowships in Population Health (No. 1037159 and No. 1037449). A/Prof. Hiscock's position is funded by an NHMRC Career Development Award (No. 607351). The Murdoch Childrens Research Institute is supported by the Victorian Government‘s

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