Clinical reviewSleep and memory in healthy children and adolescents – A critical review
Introduction
Over the past years, an increasing number of scientific articles has indicated the growing interest in the interplay between sleep and memory. There is mounting evidence that sleep promotes memory and the underlying neural plasticity in animals and humans.1, 2, 3, 4 Some reviews cover particular sub-populations, including healthy adults5, 6, 7 and children with sleep disorders or other disorders affecting sleep.8, 9, 10, 11, 12 There are also thorough reviews on the association between sleep and academic performance13 as well as on the impact of sleep and sleep loss on various aspects of neuropsychological functioning and behaviour in children and adolescents.14 However, to our knowledge, a review of studies focusing on sleep and memory in healthy children and adolescents is missing so far. This paper intends to fill this gap by critically reviewing studies investigating the association between sleep and memory in healthy children and adolescents. Additionally, suggestions for the direction of future research are presented.
Section snippets
Memory stages and memory systems
Newly acquired memory traces (encoding) are initially unstable and require a process of strengthening (consolidation) to become resistant to interference and accessible for delayed retrieval. A growing body of data, largely derived from adult human and animal studies, suggests that sleep fosters distinct stages of memory processing, including encoding, consolidation, retrieval, or even further processing such as reconsolidation and integration into existing memory networks.15
In addition to the
Methods
A computerised search of the medical and psychological literature for articles published between 1966 and March 2008 was performed using the databases Medline and PsycINFO. The following terms (keywords) were used: “sleep”, “memory”, “learn”, “child”, “adolescents”, “adolescence” and “teenager”. Search results were limited to original articles and short communications in German and English. The bibliographies of the selected articles were searched manually for any articles not captured by the
Sleep, memory encoding and working memory
In comparison to a plethora of studies on adults,15 relatively few studies have investigated the impact of sleep on memory encoding and working memory in children and adolescents. Most studies support the notion that sleep is critically involved in memory encoding and working memory. Interestingly, these studies hint towards a more complex picture showing that a number of parameters including sleep and memory task characteristics as well as developmental and social aspects critically modulate
Sleep and memory consolidation
Other studies have begun to translate the work on sleep and memory consolidation mostly done in animals and healthy adults58 into research on children and adolescents. Most of the studies support a role for sleep in memory consolidation, although significant differences to adults might exist, e.g., limited or reversed effects of sleep on non-declarative memory consolidation during earlier stages of development.
Dworak et al.47 investigated the impact of excessive television and computer game
Neural correlates
Already back in 1988, Horne60 described that functions related to the prefrontal cortex (PFC) play a crucial role in working memory and exhibit the most pronounced deficits after sleep deprivation. Dahl's developmental model for the development of sleep and arousal regulation also attributes a central role to the PFC.30 As in adults, sleep restriction or sleep loss in children and adolescents seems to preferentially affect those tasks that require effective PFC functioning. This applies
Summary and outlook
Most studies reviewed here support the hypothesis that sleep facilitates memory encoding, working memory and long-term memory consolidation not only in adults but also in children and adolescents. Some studies suggest that sleep might be of particular importance for the completion of more demanding and complex tasks, or that it becomes more important under additional adverse conditions such as lower socioeconomic status. However, compared to a solid body of data derived from studies in animals
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