Sleep after learning aids the consolidation of factual knowledge, but not relearning.

James N Cousins,Michael W L Chee,Kian F Wong,Zhi Yi Tan,Teck Boon Teo

doi:10.1093/sleep/zsaa210

Abstract

Study ObjectivesSleep strengthens and reorganizes declarative memories, but the extent to which these processes benefit subsequent relearning of the same material remains unknown. It is also unclear whether sleep-memory effects translate to educationally realistic learning tasks and improve long-term learning outcomes.MethodsYoung adults learned factual knowledge in two learning sessions that were 12 h apart and separated by either nocturnal sleep (n = 26) or daytime wakefulness (n = 26). Memory before and after the retention interval was compared to assess the effect of sleep on consolidation, while memory before and after the second learning session was compared to assess relearning. A final test 1 week later assessed whether there was any long-term advantage to sleeping between two study sessions.ResultsSleep significantly enhanced consolidation of factual knowledge (p = 0.01, d = 0.72), but groups did not differ in their capacity to relearn the materials (p = 0.72, d = 0.10). After 1 week, a numerical memory advantage remained for the sleep group but was no longer significant (p = 0.21, d = 0.35).ConclusionsReduced forgetting after sleep is a robust finding that extends to our ecologically valid learning task, but we found no evidence that sleep enhances relearning. Our findings can exclude a large effect of sleep on long-term memory after 1 week, but hint at a smaller effect, leaving open the possibility of practical benefits from organizing study sessions around nocturnal sleep. These findings highlight the importance of revisiting key sleep-memory effects to assess their relevance to long-term learning outcomes with naturalistic learning materials.

Highlights

There is a long-standing debate about how declarative knowledge is stored and evolves over time: from the initial processes of encoding, to the active mechanisms involved in offline strengthening and restructuring of memory representations, and to the recapitulation of memories during retrieval
The current study addressed three questions: (1) Does sleep benefit the consolidation of a naturalistic factual knowledge task? (2) Does sleep enhance the relearning of factual knowledge? (3) Does sleep between two study episodes enhance long-term memory 1 week later? We utilized the aforementioned factual knowledge task [24,25,26] suited for generalizing research findings to learning in education
There was a trend for better memory of the sleep group after the sleep period at T2 (t(50) = 1.81, p = 0.08, d = 0.5), but not after relearning at T3 (t(50) = 0.96, p = 0.34, d = 0.27) or after 1 week at T4 (t(50) = 1.16, p = 0.25, d = 0.32)

Summary

Introduction

There is a long-standing debate about how declarative knowledge is stored and evolves over time: from the initial processes of encoding, to the active mechanisms involved in offline strengthening and restructuring of memory representations (consolidation), and to the recapitulation of memories during retrieval. It has been consistently shown that a period of sleep after learning results in better recall than when learning is followed by an equivalent period of wakefulness [1,2,3,4,5,6]. This sleep benefit is thought to occur through at least three different mechanisms. Slow-wave activity (SWA) and sleep spindles during nonrapid eye movement (NREM) sleep have been highlighted as potential electrophysiological markers for these memory processes [5, 10,11,12,13,14]

Methods

Results

Discussion

Conclusion