Abstract
To investigate how the effects of targeted memory reactivation (TMR) are influenced by memory accuracy prior to sleep and the presence or absence of direct cue-memory associations. 30 participants associated each of 50 pictures with an unrelated word and then with a screen location in two separate tasks. During picture-location training, each picture was also presented with a semantically related sound. The sounds were therefore directly associated with the picture locations but indirectly associated with the words. During a subsequent nap, half of the sounds were replayed in slow wave sleep (SWS). The effect of TMR on memory for the picture locations (direct cue-memory associations) and picture-word pairs (indirect cue-memory associations) was then examined. TMR reduced overall memory decay for recall of picture locations. Further analyses revealed a benefit of TMR for picture locations recalled with a low degree of accuracy prior to sleep, but not those recalled with a high degree of accuracy. The benefit of TMR for low accuracy memories was predicted by time spent in SWS. There was no benefit of TMR for memory of the picture-word pairs, irrespective of memory accuracy prior to sleep. TMR provides the greatest benefit to memories recalled with a low degree of accuracy prior to sleep. The memory benefits of TMR may also be contingent on direct cue-memory associations.
Highlights
Our findings suggest that low accuracy memories are more responsive to targeted memory reactivation (TMR) and that the benefits of TMR for consolidation are contingent on the presence of direct cue-memory associations
Data are shown as mean ± standard error of the mean
Memory Accuracy prior to Sleep Building on prior work,[14,15] our findings demonstrate that the extent to which picture-location memories benefit from TMR is contingent on the accuracy with which those memories are recalled prior to sleep
Summary
There is a wealth of behavioral and physiological evidence in favor of the view that memory consolidation is supported by sleep.[1,2,3] Beyond merely sheltering memories from the interference posed by wakefulness, recent work has indicated that the sleeping brain actively facilitates memory processing and, thereby, instills qualitative changes to representations encoded throughout the preceding day.[4,5] According to the active systems model of consolidation,[4,6] sleep dependent memory processes are underpinned by a covert reactivation of newly formed representations during slow wave sleep (SWS), as indexed by spontaneous neural activity in the brain regions employed at learning, such as the hippocampus and neocortex. Driven by the electroencephalography (EEG) slow oscillations (< 1 Hz) and sleep spindles (~12–15 Hz) that characterize SWS, these memory reactivations are thought to mediate the processes of stabilisation and integration that underpin long-term memory storage. The development of a technique known as targeted memory reactivation (TMR) in recent years has provided a method for cuing the reactivation of specific memories in SWS.[13,14,15] In a typical TMR experiment, participants form a number of new memories (e.g., for the screen locations of different pictures) that are each associated with a semantically related sound (e.g. a picture of a cat and a “meow” sound) before a period of sleep in which a subset of the sounds are replayed during SWS. Earlier work has revealed similar benefits of re-exposing individuals to olfactory memory cues in SWS,[16,17,18,19] but the current study focuses on acoustic cues
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