Abstract
An outstanding question is whether memory consolidation occurs passively or involves active processes that selectively stabilize memories based on future utility. Here, we differentially modulated the expected future relevance of two sets of picture-location associations after learning. Participants first studied two sets of picture-location associations. After a baseline memory test, they were instructed that only one set of associations would be retested after a 14-hour delay. For half of the participants, this test-retest delay contained a night of sleep; for the other half the delay included a normal working day. At retest, participants were re-instructed and against their expectations tested on both sets of associations. Our results show that post-learning instruction about subsequent relevance selectively improves memory retention for specific associative memories. This effect was sleep-dependent; it was present only in the group of subjects for which the test-retest delay contained sleep. Moreover, time spent asleep for participants in this sleep group correlated with retention of relevant but not irrelevant associations; participants who slept longer forgot fewer associations from the relevant category. In contrast, participants that did not sleep forgot more relevant than irrelevant associations across the test-retest delay. In summary, our results indicate that it is possible to modulate the retention of selected memories after learning with simple verbal instructions on their future relevance. The finding that this effect depends on sleep demonstrates this state’s active role in memory consolidation and may have utility for educational settings.
Highlights
Encoded memories are initially unstable but become stabilized over time through a process known as consolidation [1,2,3]
Further support for emotion as a driving force for sleep-dependent memory consolidation came from two recent studies that demonstrated that sleep stabilizes emotional over neutral memories [12,13]
In the WAKE group, retention of relevant associations was worse than retention of irrelevant associations (D = 21.760.6; F = 9.44, p = 0.005)
Summary
Encoded memories are initially unstable but become stabilized over time through a process known as consolidation [1,2,3]. There, the knowledge that recently encoded word pairs would be tested in the future improved memory retention only for the group of participants that slept during the delay between learning and test [17] This effect might have been based on a general facilitation of the consolidation process, rather than a re-activation of a particular memory, since the instructions on the future relevance of the word pairs were given in an all-or-none fashion. The relevance of particular memories might be directly related to the benefits that are expected to be associated with their long-term retention In line with this idea, a recent study has shown that sleep-dependent consolidation of procedural memories can be facilitated by reward expectancy induced after learning [18]. As we predicted that this effect would depend on sleep-related processes, we expected this relevance benefit to be specific to the SLEEP group and absent in the WAKE group
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