Abstract
It is now widely accepted that re-exposure to memory cues during sleep reactivates memories and can improve later recall. However, the underlying mechanisms are still unknown. As reactivation during wakefulness renders memories sensitive to updating, it remains an intriguing question whether reactivated memories during sleep also become susceptible to incorporating further information after the cue. Here we show that the memory benefits of cueing Dutch vocabulary during sleep are in fact completely blocked when memory cues are directly followed by either correct or conflicting auditory feedback, or a pure tone. In addition, immediate (but not delayed) auditory stimulation abolishes the characteristic increases in oscillatory theta and spindle activity typically associated with successful reactivation during sleep as revealed by high-density electroencephalography. We conclude that plastic processes associated with theta and spindle oscillations occurring during a sensitive period immediately after the cue are necessary for stabilizing reactivated memory traces during sleep.
Highlights
It is widely accepted that re-exposure to memory cues during sleep reactivates memories and can improve later recall
We demonstrated that strengthening of memories by cueing during sleep was associated with a temporary increase in theta as well as spindle activity after re-exposure to verbal memory cues
In sharp contrast, presenting auditory feedback immediately after the Dutch cue completely blocked the beneficial effect of cueing during sleep on later recall, independent of whether the feedback was correct or false
Summary
It is widely accepted that re-exposure to memory cues during sleep reactivates memories and can improve later recall. Cortical slow oscillations (o1 Hz) coordinate these reactivation processes as a time-giving pace maker, and drive repeated reactivations of memory representations in the hippocampus together with sharp wave ripples and thalamo-cortical sleep spindles Formation of these spindle-ripple events is assumed to represent a core mechanism to enable the redistribution of reactivated hippocampal memory information to neocortical long-term stores, leading to a subsequent stabilization and strengthening of the reactivated memory[14]. Various recent studies have established a causal role of reactivation for consolidation processes during sleep by showing that cueing memories during NREM sleep improves later memory recall[17,18,19,20] In these studies, memory cues (that is, olfactory, auditory) are repeatedly presented during sleep to reactivate the associated memory content, leading to a strengthening of the memory tested after sleep. We demonstrated that strengthening of memories by cueing during sleep was associated with a temporary increase in theta as well as spindle activity after re-exposure to verbal memory cues
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