Article

0082 Circadian Influences On Sleep-dependent Consolidation Of Hippocampus-dependent Memory: Preliminary Results From Adolescents Undergoing 28-hour Forced Desynchrony

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Abstract

Introduction Sleep supports processes necessary for hippocampus-dependent memory consolidation. While experimental paradigms for sleep-dependent memory consolidation commonly involve comparing sleep/wake delays at opposing diurnal phases, whether the memory benefit of sleep is influenced by circadian phase is unclear. Using forced desynchrony (FD), this study tested the hypothesis that the sleep benefit upon hippocampus-dependent memory consolidation depends on the circadian phase at which sleep occurs. Methods 12 adolescents (6F, mean 13.6±0.8 years) completed seven cycles of 28-hour FD. Each 28-hour FD cycle included 17.5 hours scheduled wakefulness and 10.5 hours sleep, decoupling sleep timing from circadian phase. Participants trained on the hippocampus-dependent Mnemonic Similarity Task and tested approximately 12-hours later, in four conditions bracketing wake or sleep during either the biological day or night. Thus, both initial learning and delayed consolidation were tested at opposing levels of sleep pressure and circadian phase. Results Repeated-measures ANOVA found no evidence that sleep pressure, circadian phase, or their interaction predicted initial encoding ability (all p’s > 0.05). When assessing within-subject change scores, a trend emerged indicating an interaction of sleep and circadian phase (F(1,11)=3.56; p=.086) affecting consolidation. Thus, when learning occurred in the circadian morning, a delay that included sleep was associated with reduced forgetting compared to a delay without sleep (t(11)=-1.83; p=.045 [one-tailed]). No benefit of sleep was present across the circadian night (t(11)=0.37; p=.72 [one-tailed]). Conclusion These results provide preliminary evidence that circadian processes may influence the sleep benefit for hippocampus-dependent memory consolidation: a sleep benefit occurred only across the circadian day. Memory-regulating oscillatory properties of sleep, such as sleep spindles, are sensitive to circadian influences. Our future analyses will examine sleep EEG during FD as one potential factor mediating these results. While these results are preliminary and from a small sample, they suggest a need for more direct consideration of circadian timing when assessing sleep-dependent memory consolidation. Support (If Any) R01DK101046 (MAC), K01MH109854 (JMS)

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... As a matter of fact, sleep has an important role in consolidation of sequential motor skills from the childhood to adulthood. Hence, many researchers have confirmed the benefit of the sleep in both declarative memory (verbalize knowledge of facts and events, in which information recall is conscious) and procedural memory (skills memory) in adults [2,11,15,20,27,38]. Although motor learning is an especially critical factor during childhood, sleep is essential in children's cognitive, behavioral, emotional, and motor development and important links to memory and cognition [16,41]. ...
... Learning new skills with practice can be accomplished unintentionally, with little to no awareness (implicit knowledge), or intentionally, with an individual's conscious awareness of the regularities of the task to be learned or rules and facts on how to move (explicit knowledge) [2,21,33,37,42]. Lots of evidence exists about the role of awareness in online and offline motor learning of adults [2,11,12,33,34,38]. ...
... However, other researchers showed that sleep, compared to wake in retention test, enhanced the consolidation of implicit motor sequence tasks. These findings were in contrast with the studies which stated that sleep was only beneficial in explicit skill learning [3,11,15]. ...
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Study aim : The purpose of this study was to investigate the role of sleep and awareness on consolidation of general and Sequence-Specific learning in children. Material and methods : Male participants (n = 48, 10 to 12 years old) were assigned to one of four groups based on awareness and sleep. Acquisition phase took place in the morning (wake groups, 8 ± am) or in the evening (sleep groups, 8 ± pm) followed by a 12 hours retention interval and a subsequent delayed retention test (1 week). Children in the explicit groups were informed about the presence of the sequence, while in the implicit groups were not informed about it. For data analysis in consolidation of general sequence learning and Sequence-Specific Consolidation phases, 2 × 2 × 2 and 2 × 2 × 3 ANOVA with repeated measures on block tests were used respectively. Results : The data provides evidence of offline enhancement of general motor learning after 12 hours which was dependent on sleep and awareness. Moreover, the information persistence after 1-week was significant only in sleep groups. The results also indicated that consolidation of sequence-specific learning was only observed after 12 hours in element duration and it was related to sleep and awareness. Conclusions : The results revealed that sleep wasn’t only an essential factor in enhancement of off-line sequence learning task after 12 hours in children, but performance of the children was dependent on awareness and sleep.
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