Sleep architecture and memory consolidation in children with focal epilepsy

Abstract

BackgroundCognitive impairment is a major comorbidity in children with epilepsy. During the past decade, evidence has emerged that the consolidation of declarative memory (memory for facts and events) is promoted by slow-wave sleep. The aim of this study was to investigate whether sleep architecture is disrupted in children with epilepsy, and whether this disruption impacts on memory consolidation in these children compared with healthy children. MethodsA within-subject comparison of memory retention across similar length intervals overnight (sleep condition) or daytime (wake condition) was performed in 20 children with focal epilepsy (aged 6–16 years) and 19 healthy, age-matched children (controls). For each condition, participants learned a list of semantically related word pairs for cued recall after the interval. Patients participated during admission for video electroencephalogram (EEG) telemetry, whereas controls underwent ambulatory EEG polysomnography across the sleep condition. FindingsChildren with epilepsy had less rapid eye movement sleep (ANCOVA with age as covariate F=8·2, p=0·007) and more stage 2 sleep (F=5·335, p=0·027) than did controls, but a similar amount of slow-wave sleep and stage 1 sleep. Memory retention was greater in the sleep than the wake condition (repeated measures ANOVA F=7·876, p=0·008) and there was no significant interaction effect with group (patients vs controls) or order of conditions. The difference in memory retention scores between the sleep and wake conditions correlated with the proportion of time that the child spent in slow-wave sleep across the total sample (Pearson r=0·461, p=0·003). This association was significant in controls (r=0·546, p=0·051), but did not reach significance in children with epilepsy, and was not altered after controlling for age. InterpretationPatients with focal epilepsy show benefit to memory consolidation with sleep similar to that seen in healthy individuals, despite the underlying disease and effects of treatment. The association with slow-wave sleep, which is preserved at the expense of rapid eye movement sleep, also seems robust. Our findings suggest that the enhancement of slow-wave sleep—by behavioural, pharmacological, or physical means—has the potential to improve cognitive outcome in this patient group. FundingAction Medical Research, Reta Lila Howard Foundation.