Individual Differences in Childhood Sleep Problems Predict Later Cognitive Executive Control

VIRTUALLY ALL METHODS OF EXAMINING THE EFFECTS OF SLEEP PROBLEMS ON COGNITION HAVE LED TO THE CONCLUSION THAT SLEEP PROBLEMS OR sleep loss result in cognitive impairment. Cognitive decrements have been found in studies of sleep loss or sleep fragmentation arising from environmental factors such as job demands1; primary sleep disorders such as insomnia, narcolepsy, and sleep apnea2; sleep quality and duration3; and experimentally manipulated deprivation or restriction.4,5 Pilcher and Huffcutt,4 in their meta-analysis of 19 studies, found that sleep deprived individuals performed, on average, 1.55 standard deviations below non-deprived individuals on cognitive tasks. These cognitive consequences of sleep deprivation are not isolated to extreme cases.5,6 For example, Van Dongen et al.6 found that the effects of sleep loss on cognitive functioning can be cumulative, such that even moderate sleep restriction (e.g., sleep ≤ 6 h/night) over the course of 2 weeks can result in cognitive deficits equivalent to those found with up to 2 nights of total sleep deprivation. The majority of the evidence for cognitive deficits with sleep problems/deprivation comes from studies incorporating only one time point or very close time points. Also of interest is the association of early general sleep problems and their developmental trajectories with later cognitive abilities. There is some reason to hypothesize that such developmental patterns may be important: for example, Gregory and colleagues7,8 found that sleep problems at earlier ages and/or stability of sleep problems predicted behavioral and emotional problems at later ages. Touchette et al.9 found that patterns of persistent short sleep duration or increasing tendency for short sleep duration in early childhood (2.5 to 6 years) predicted externalizing problems as well as performance on neurodevelopmental tests at ages 5 to 6. However, to our knowledge, little to no information exists on the cognitive sequelae of different developmental patterns of general sleep problems through adolescence. In this study, we used longitudinal data on parent-reported sleep problems about children from ages 4 years to 16 years to investigate whether different trajectories of general sleep problems throughout development are related to cognitive functioning in late adolescence (~age 17). The particular cognitive abilities on which we focus are executive functions—general-purpose control mechanisms, often neurologically associated with the frontal lobes, that modulate various cognitive subprocesses and thereby regulate one's thoughts and actions. Several researchers have suggested that executive functions may be particularly sensitive to sleep problems or sleep loss, because of the apparent influence of sleep problems on prefrontal cortex functioning.10–15 Although it is still an open question whether executive functions are more affected by sleep problems than abilities thought to depend less on the frontal lobes, existing research does provide some evidence, albeit inconsistent, for impairments on executive function tasks related to sleep deprivation or sleep problems such as sleep apnea.3,10–12,15 However, the bulk of this evidence relies on results obtained with complex “frontal lobe” tasks or individual executive measures. There are 2 main limitations with the use of single tasks to measure executive control. The first is methodological and involves the “task impurity” problem that is particularly problematic for executive function tasks: Because executive functions by definition operate on other cognitive processes, a large portion of the variance in any one executive task is not necessarily executive. The task impurity problem complicates the interpretation of results based on a single complex task (such as the frequently used Wisconsin Card Sorting Test), because it is unclear to what extent those results reflect this non-executive variance. In the current study, we use latent variables constructed from multiple executive function tasks. These latent variables are statistical extractions of the reliable variance common to multiple tasks that have different non-executive requirements, but all tap the same underlying executive ability; as a result, the latent variable is a purer measure that is free from task impurity and measurement error.16 The second limitation with the use of individual tasks is conceptual: One cannot use them to assess how sleep problems affect different executive functions. Although executive control has historically been considered a unitary function, findings from cognitive research studies have provided compelling evidence that it may consist of a family of related but separable functions.17–20 These findings raise the possibility that separable executive functions may not be similarly affected by sleep problems,21,22 a possibility that has not been tested with theoretically derived executive function latent variables. In this study, we examined 3 executive functions based on a theoretically motivated model that has been investigated in the cognitive and neuropsychological literature: inhibiting prepotent or dominant responses (Inhibiting), updating working memory (Updating), and shifting tasks or mental sets (Shifting). Inhibiting refers to the ability to stop a dominant or automatic response. Updating refers to the ability to continuously update the contents of working memory by adding new relevant information and deleting older irrelevant information. Shifting involves the ability to rapidly shift between 2 tasks. Following previous work,17,23 we assessed these 3 functions with latent variables composed of 3 tasks per executive function. Results from a previous examination of the structure of the executive function data from the current study23 indicated that there was variance common to all 3 of these executive functions, but that they were also dissociable (in that there was also variance unique to particular executive functions), making the 3 functions correlated but separable. The primary goals of the current study were to evaluate (1) whether individual differences in developmental patterns of general sleep problems were associated with the 3 executive function abilities in late adolescence, and (2) whether individual differences in developmental trajectories of sleep problems were associated primarily with variance common to the 3 executive functions, or with variance specific to individual executive functions. We first created a developmental model of parent-reported sleep problems in their children from ages 4 to 16 years, using latent variable growth curve analysis.24 This technique provides an efficient way to model individual differences in longitudinal trajectories, using a latent intercept and a latent slope variable. We then added the executive function latent variables to see if they significantly correlated with these developmental intercept and slope variables.