Die Bedeutung von Schlaf und Schlafstörungen für Lernen und Gedächtnis bei Kindern – ein Überblick
Abstract
Zusammenfassung: Schlafstörungen im Kindesalter sind weit verbreitet. Häufig wirken sich kindliche Schlafprobleme auf die kognitive Leistungsfähigkeit und damit auf die schulischen Leistungen aus. Ziel der vorliegenden Arbeit war es, eine Übersicht über den Zusammenhang zwischen den Schlafparametern Nachtschlaf, Schlafdauer, Schlafeffizienz, Schlafqualität, Schlafprobleme sowie der kognitiven und schulischen Leistungsfähigkeit im Kindesalter (fünf bis 13 Jahre) zu geben. Einige der 25 gefundenen Studien konnten aufzeigen, dass der Nachtschlaf den Kindern das Lernen erleichtert. Dabei konnten Aufgaben, die keine tiefen Verarbeitungsprozesse benötigten, von Kindern mit Schlafeinbußen zumeist kompensiert werden, Aufgaben mit tieferen Verarbeitungsprozessen hingegen häufig nicht. Der Nachtschlaf scheint sich in diesem Alter vor allem auf die deklarative Gedächtnisleistung positiv auszuwirken. Demnach scheint die Gedächtniskonsolidierung während des Schlafs vom Typ des Lernmaterials abzuhängen. Eine zu kurze Schlafdauer, zu geringe Schlafeffizienz und das Vorhandensein von Schlafproblemen hängen überwiegend mit Einbußen bei kognitiven Lernprozessen im Kindesalter zusammen. Hingegen korrelierten subjektive Schlafqualität und Lernen nicht miteinander. Insgesamt existieren noch wenige Studien, die den Zusammenhang zwischen den verschiedenen Schlafparametern und kognitiven Prozessen der Kinder untersuchen. Weitere systematische Studien sind daher sinnvoll und notwendig, die überdies beeinflussende Variablen, wie zum Beispiel elterliche Kontrolle, in die Betrachtung einbeziehen. Da Schlafstörungen bei Kindern eine Gefahr für die kognitive und schulische Entwicklung darstellen, sollten sie frühzeitig diagnostiziert werden. Daher sollten Eltern, Lehrer und alle in der Erziehung tätigen Praktiker über ein ausreichendes Wissen zu den Symptomen und Folgen schlechten Schlafs bei Kindern sowie über geeignete Präventions- und Interventionsmöglichkeiten verfügen. Gezielte Förderprogramme zur Verbesserung der schulischen und kognitiven Leistungen der Kinder könnten eingesetzt werden.
Extended abstract
The Importance of Sleep and Sleep Disorders for Learning and Memory in Children – a Review
Background: Sleep plays a decisive role for learning, memory processing, and cognitive functioning. However, sleep can be disturbed in various ways. Hence sleep disorders in childhood are common. The prevalence rates vary between 20 % and 45 % (Esser & Schmidt, 1987; Hoedlmoser, Kloesch, Wiater & Schabus, 2010; Kahn et al., 1989; Mindell, 1993). Usually, children have difficulties falling asleep or maintaining sleep, show bed-time resistance, complain about poor quality of sleep or daytime sleepiness, or have parasomnia, e. g., nightmares (Hoedlmoser et al., 2010; Jenni, Fuhrer, Iglowstein, Molinari & Largo, 2005; Mindell & Barrett, 2002). Furthermore, sleep disorders in childhood often even persist (Schlarb, Velten-Schurian, Poets & Hautzinger, 2011) until adulthood (Johnson, Roth, Schultz & Breslau, 2006). Various variables (e. g., physiological maturing, temperament, behavior, individual circadian differences, physical factors, mental retardation, and stress) influence the development, maintenance, degree, and chronicity of sleep disorders in childhood (Jenni et al., 2005; Kraenz et al., 2004). In addition, parenting style, parental educational background, family stress as well as quality and quantity of parental sleep may affect the sleep behavior of children (Meltzer & Mindel, 2007; Schlarb et al., 2011). Hence, consequences of sleep problems in childhood are broad, and comprise cognitive, motivational, social, neurological, and cardiovascular restraints. Almost a fifth of children with sleep disorders report daytime sleepiness or limited attention and motivation (Blunden, Lushington, Lorenzen, Martin & Kennedy, 2005; Dahl, 1996; Kahn et al., 1989; Smedje, Broman & Hetta, 2001). Moreover, behavioral problems, e. g., social conflicts or aggressive behavior, are related to shortened sleep duration (Aronen, Paavonen, Fjällberg, Soininen & Törrönen, 2000; Gregory & O’Connor, 2002; Hoedlmoser et al., 2010; Paavonen, Porkka-Heiskanen & Lahikainen, 2009; Velten-Schurian, Hautzinger, Poets & Schlarb, 2010). Untreated persisting sleep problems can lead to serious and harmful consequences, e. g., neurological dysfunction (Jan et al., 2010), and impairment of the cardiovascular or immune system (Mullington, Haack, Toth, Serrador & Meier-Ewert, 2009). Shortened sleep duration and poor sleep quality may also lead to reduced cognitive abilities (Sadeh, Gruber & Raviv, 2002). Thus, children’s sleep difficulties are frequently associated with lower cognitive capabilities and lower school performance. There are diverse theories explaining the effect of inadequate sleep on cognitive functioning and behavior. First, sleep plays a major role in the maturation of the brain, information processing, memory consolidation, and learning (e. g., Born & Wilhelm, 2011; Wilhelm, Prehn-Kristensen & Born, 2012). Thus, inadequate sleep may affect all these processes and lead to problems with consolidation at night and retrieval of knowledge (Dewald, Meijer, Oort, Kerkhof & Bogels, 2010). Second, sleep serves as a regeneration process. Therefore, inadequate sleep may lead to daytime sleepiness and reduced attention. Moreover, cognitive functioning and regulation of behavior could be impaired due to restricted functionality of specific brain areas (Sadeh, 2007).
Aim: The aim of this paper was to provide an overview of the relationship between children’s sleep and sleep disorders, on the one hand, and learning and cognitive or learning disabilities, on the other hand. We focused on various sleep parameters and cognitive and academic performance. Inclusion criteria were studies (a) of healthy children aged five to 13 years with or without difficulties initiating or maintaining sleep; (b) sleep parameters, i. e., sleep at night, sleep duration, sleep efficiency, sleep quality, sleep problems, assessed by self-report, parents, sleep reports, or objective instruments such as actigraphy; (c) cognitive or academic functioning, which were measured by standardized performance tests, memory tests, or reaction time tests.
Method: A literature research by DIMDI, MEDLINE, PsycINFO, PsycNET, PubMed, and Google Scholar based on the keywords ’sleep’, ’sleep disorder’, ’learning’, ’memory’, ’performance’ and ’children’ was conducted.
Results: Twenty-five studies were included, whose results were grouped by sleep parameters and are represented below: (a) Sleep at night seems to be an important factor for processing declarative knowledge, whereas the results for processing procedural or implicit knowledge in children are diverse. These results differ remarkably from the results of adults. (b) The results about the relationship between sleep duration and cognitive performance in children demonstrate that longer sleep duration appears to improve cognitive performance, while shortened sleep duration seems to restrain cognitive performance, particularly for tasks with a higher cognitive load. This effect is very likely to last for years. On the other hand, some authors found no relation between sleep duration and cognitive performance, particularly for tasks with a lower processing load. Brief sleep restrictions also had no effect on cognitive functioning in this age group. (c) Low sleep efficacy seems to impair cognitive performance in children. However, no connection between sleep efficacy and type or complexity of learning material was found. (d) Only one of the included studies investigated the relationship between subjective sleep quality and learning in childhood; it showed no correlation between sleep quality and the accuracy or speed of concentration capability, as measured by simple tasks involving continuous selective attention. (e) Additionally, studies showed that sleep problems impair the cognitive and academic performance of children, even for years.
Discussion: This overview shows that sleep appears to play a considerable role for cognitive processing and school performance. Sleep at night seems to facilitate declarative memory processing. Thus, memory consolidation during sleep may depend on the type of learning material. These results are in line with the neurocognitive hypothesis, which implies that sleep affects the neuronal processing as demonstrated by fMRI and EEG studies (Hoedlmoser et al., 2008; Schabus et al., 2006; Walker & Stickgold, 2006). Most studies showed a connection between sleep duration, sleep efficiency, sleep problems, and cognitive learning processes. To conclude, further studies addressing the relationship between various sleep parameters and cognitive processes in childhood should be conducted. Additional systematic studies with children should be performed taking into account biasing variables, e. g., parental control (Kopasz et al., 2010; Owens-Stively et al., 1997), and further factors, e. g., odor as a learning association, which may facilitate memory consolidation while sleeping (Rasch, Buchel, Gais & Born, 2007).
Implications: Sleep disorders in childhood endanger cognitive and school development, and should therefore be diagnosed early on. Hence, parents, teachers, and educational practitioners should have sufficient knowledge about the symptoms and consequences of poor sleep in children as well as about adequate prevention and intervention possibilities. Specific supporting programmes could be implemented to improve cognitive and academic functioning in children.
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