The Effect of Sleep Restriction on Executive Function and Emotion Regulation in Early Childhood

Sleep loss is experienced universally, and significantly impacts cognition and emotion in adults. However, little to no research has investigated this relationship in the preschoolaged years. This is an essential time period in which executive function and emotion regulation undergo extensive development. As sleep patterns also mature in children during this time, pronounced effects of sleep on developmental domains may be apparent. We experimentally manipulated sleep restriction in 4-6 year-old children, to test its effects on executive function and emotion regulation, aspects of cognition and emotion, respectively. We conducted a 10-day study, where executive function and emotion regulation were assessed twice in children, following a strict sleep schedule for five days prior. Children received either a sufficient amount of sleep or a restricted amount of sleep (3 hour sleep loss) the night prior to assessments. Sleep restriction impaired children’s overall performance on tasks and affected physiological responses to affective stimuli, but did not seem to specifically affect executive function or emotion regulation. This study has implications for future work on the development of executive functions, emotion regulation, and on the potential mediational nature of executive function between sleep and emotion regulation. SLEEP RESTRICTION, EXECUTIVE FUNCTION, & EMOTION REGULATION 3 INTRODUCTION Early childhood is characterized by dramatic shifts in development, particularly in sleep. By ages 4-5, children have reduced their sleep duration from infancy by 4-6 hours, by eliminating daytime naps and sleeping primarily only at night (Crosby, LeBourgeois, & Harsh, 2005; Weissbluth, 1995). These sleep pattern alterations may arise naturally, atypically through sleep problems or disorders, or externally through lack of opportunities to sleep (Crosby, et al., 2005). If these maturational changes in sleep do not arise naturally, children may or may not be obtaining adequate amounts of sleep. This could prove consequential because sleep loss significantly impacts cognition and emotion in adults (Durmer, & Dinges, 2005; Nilsson et al., 2005; Killgore, 2010; Gujar, Yoo, Hu, & Walker, 2011; Franzen, Buysse, Dahl, Thompson, & Siegle, 2009), and may in children as well. Children develop both cognitively and emotionally across childhood. Cognitively, children begin to think flexibly, overcome perseverative habits, and demonstrate selfdirected control in difficult situations (Munakata, Synder, & Chatham, 2012). Similarly, they are increasingly able to understand, process, express emotion, and control emotion expression through regulation (Ashiabi, 2000). For example, children can understand happiness and express it in socially acceptable situations. However, they also learn to regulate their expression of happiness in socially unacceptable situations, such as at a funeral. While cognition and emotion are markedly developing in children, little is known about the effects of sleep on these domains in children (Sadeh, 2007). To our knowledge, only one experimental study has investigated the relationship between sleep and emotion regulation in toddlers. Following a nap-deprivation paradigm, children displayed more negative emotions (e.g. shame, frustration) to negative stimuli, SLEEP RESTRICTION, EXECUTIVE FUNCTION, & EMOTION REGULATION 4 and fewer positive emotions (e.g. joy, pride) to positive stimuli (Berger, Miller, Seifer, Cares, & LeBourgeois, 2012), indicating that sleep restriction negatively impacted toddler’s emotional processing and expression. In adults, insufficient sleep negatively impacts executive function and emotion regulation, aspects of cognition and emotion. Executive functions refer to a set of cognitive processes that guide and control attention and behavior to appropriately respond to and interact with the environment. This includes, but is not limited to, flexibly shifting between information, inhibiting irrelevant responses, and actively maintaining and updating information in working memory (Miyake, Friedman, Emerson, Witzki, Howerter, & Wager, 2000). Following sleep impairment, individuals demonstrate impaired executive functioning relative to when a sufficient amount of sleep has been obtained (Durmer, & Dinges, 2005; Nilsson et al., 2005). Namely, individuals demonstrate reduced response inhibition performance (Killgore, 2010), impaired accuracy and reaction times on working memory tasks, and increased perseveration on tasks by reverting to ineffective solutions to achieve a goal (Durmer, & Dinges, 2005). Likewise, insufficient sleep in adults results in substantial differences in emotion expression and regulation when compared to sufficient sleep. Adults who have been sleep deprived demonstrate exaggerated responses to affective stimuli. Responses to negative and positive stimuli are amplified, as ratings of mood decrease substantially (Pilcher, & Huffcutt, 1996), stimuli are perceived as more negative or more positive (Gujar, et al., 2011), and physiological and neurological patterns differ from baseline observations (Franzen, et al., 2009; Gujar, et al., 2011). Pupillary dilation, indicating affective processing and cognitive effort, changes significantly in sleep-deprived individuals; however, whether SLEEP RESTRICTION, EXECUTIVE FUNCTION, & EMOTION REGULATION 5 this exaggeration occurs only in response to negative stimuli or both positive and negative stimuli is unclear as studies have indicated opposing results (Franzen, et al., 2009; Partala, & Surakka, 2003). Sleep deprivation has resulted in amplification and reduction in activation for various brain regions. The amygdala and other mesolimbic brain regions show amplified activity in sleep-deprived individuals, especially in response to negative stimuli (van der Helm, Yao, Dutt, Rao, Saletin, & Walker, 2011; Yoo, Gujar, Hu, Jolesz, & Walker, 2007). In addition, reduced functional connectivity between the amygdala and the prefrontal cortex is observed in sleep-deprived individuals (Gujar et al., 2011). It is hypothesized that, under such circumstances, the prefrontal lobe lacks the ability to inhibit the over-activated amygdala (van der Helm, & Walker, 2009). These brain regions, namely the amygdala and prefrontal cortex, are viewed as supporting emotion regulation and executive function, respectively (Gallagher, & Chiba, 1996; Arons, Robbins, & Poldrack, 2004). Rather than sleep impacting executive function and emotion regulation independently, it may only impact one domain which, in turn, impacts the other. This connection is demonstrated behaviorally as both executive function and emotion regulation rely on one another to accomplish certain goals. For example, controlling emotion involves inhibiting the automatic response to express internal states. Therefore, the development of inhibitory control, a component of executive function, may partially drive the development of a more mature emotion regulation. Although the above findings with adults are relatively conclusive regarding the general detrimental nature of sleep reduction, inconsistencies remain. How individuals react to positive and negative stimuli both behaviorally and physiologically is ambiguous, SLEEP RESTRICTION, EXECUTIVE FUNCTION, & EMOTION REGULATION 6 as is the specific mechanism underlying the effects of sleep on executive function and emotion regulation. The specific pathway by which sleep affects cognition and emotion may be most clearly understood during the development of these two areas as it may be easier to tease them apart before full maturation is achieved. However, the above findings may not necessarily generalize to preschooland elementary-aged children. This population of children is undergoing extensive changes developmentally and neurologically. It is necessary to investigate the effects of sleep and sleep restriction in this population, as they may be placed at increased risk as their brains have not fully developed. However, little research has been done to investigate these risks. To address these issues, we will investigate how sleep affects executive function and emotion regulation in preschooland elementary-aged children. Drawing from adult research, we hypothesize that overall, children will display more impaired executive function and amplified emotion expression, and thus decreased emotion regulation, when sleep restricted. We will investigate physiological responses to affective stimuli by investigating how pupil diameter changes, measured through a sound listening task. We are interested in pupil diameter changes in response to positive, negative, or neutral stimuli. Additionally, we will measure behavioral responses to affective stimuli by investigating whether negative stimuli (e.g. frustration-eliciting tasks) will cause sleep-restricted children to demonstrate heightened negative emotion expression and decreased positive emotion expression as found in the nap-deprivation study with toddlers (Berger, et al., 2012). Finally, drawing from the neurological findings in adults, we propose that the reduced functional connectivity between the prefrontal cortex and the amygdala, and SLEEP RESTRICTION, EXECUTIVE FUNCTION, & EMOTION REGULATION 7 amplified activity in the amygdala following sleep restriction, signifies a mediating relationship between executive function, emotion regulation, and sleep. Specifically, we propose that sleep restriction will detrimentally impact executive function, which in turn will negatively impact emotion regulation. That is, individuals who experience sleep restriction will demonstrate more impaired executive functioning; and as a result of impaired executive function, emotion regulation will be impaired as well. If this connection does in fact exist, it may be most apparent in early childhood, as this is a key period during the development of mature executive functions and emotion regulation. We will utilize an experiment