The whats and whens of sleep-dependent memory consolidation

Sleep Medicine Reviews
Copyright © 2008 Elsevier Ltd All rights reserved.
Physiological review

The whats and whens of sleep-dependent memory consolidation

Susanne Diekelmann1, a, Ines Wilhelm1, a and Jan BornCorresponding Author Contact Information, a, E-mail The Corresponding Author

aUniversity of Lübeck, Department of Neuroendocrinology, Haus 23a, Ratzeburger Allee 160, 23538 Lübeck, Germany

Summary

Sleep benefits memory consolidation. The reviewed studies indicate that this consolidating effect is not revealed under all circumstances but is linked to specific psychological conditions. Specifically, we discuss to what extent memory consolidation during sleep depends on the type of learning materials, type of learning and retrieval test, different features of sleep and the subject population. Post-learning sleep enhances consolidation of declarative, procedural and emotional memories. The enhancement is greater for weakly than strongly encoded associations and more consistent for explicitly than implicitly encoded memories. Memories associated with expected reward gain preferentially access to sleep-dependent consolidation. For declarative memories, sleep benefits are more consistently revealed with recall than recognition procedures at retrieval testing. Slow wave sleep (SWS) particularly enhances declarative memories whereas REM sleep preferentially supports procedural and emotional memory aspects. Declarative memory profits already from rather short sleep periods (1–2 h). Procedural memory profits seem more dose-dependent on the amount of sleep following the day after learning. Children's sleep with high amounts of SWS distinctly enhances declarative memories whereas elderly and psychiatric patients with disturbed sleep show impaired sleep-associated consolidation often of declarative memories. Based on the constellation of psychological conditions identified we hypothesize that access to sleep-dependent consolidation requires memories to be encoded under control of prefrontal-hippocampal circuitry, with the same circuitry controlling subsequent consolidation during sleep.

Keywords: Memory consolidation; Declarative memory; Procedural memory; Learning; Sleep; SWS; REM sleep; Humans

Nomenclature

NREM
non-REM sleep
SWS
slow wave sleep
REMD
REM sleep deprivation
fMRI
functional magnetic resonance imaging
mPFC
medial prefrontal cortex
SRTT
serial reaction time task

Article Outline

Nomenclature
Introduction
Type of learning material

Declarative and procedural memory
Emotional versus neutral material
Memory strength, depth of encoding and task difficulty
Temporal order

Type of learning

Explicit versus implicit learning
Motivational factors

Type of retrieval test
Type of sleep

Timing of sleep

Timing of sleep in the circadian rhythm
Time between learning and sleep

Amount of sleep
Sleep stages

Type of subject population

Infants and children
Elderly
Psychiatric patients

Conclusion
Acknowledgements
References

Corresponding Author Contact InformationCorresponding author.
1 These authors contributed equally to this work.