New evidence for the necessity of a silent plastic period during sleep for a memory benefit of targeted memory reactivation

Abstract

The presentation of learning-related cues during sleep, a procedure known as targeted memory reactivation (TMR), is a promising approach to bias sleep-dependent memory consolidation. Recent evidence suggests that for the TMR procedure to be effective, an undisturbed short plastic period is needed after cueing. In this study, we investigated the impact on memory consolidation of verbatim or interfering auditory presentation of previously learned material during wakefulness or non-rapid eye movement (NREM) sleep. Participants learned a list of 40 word pairs (A–B) presented both visually and aurally. During a 90-min consolidation interval spent awake or asleep (diurnal nap), the first word of half of the pairs was aurally presented, then followed by its correct (A–B) or incorrect (A–C) association. Memory for all pairs was then tested. In the Wake conditions, memory was improved after correct (verbatim) cueing but impaired after the presentation of an incorrect (interference) association, in comparison with uncued word pairs. In the Nap conditions, the TMR procedure had no beneficial or detrimental effects on memory consolidation. Time–frequency analyses indicate that the presentation of the first word during NREM sleep is followed by increased spindle-related sigma activity, suggesting that reactivation of the associated memory content was initiated. However, immediate presentation of the second word, either correct or incorrect, annihilated sigma activity. These results bring additional evidence on the necessity for a silent and undisturbed plastic period during sleep after cueing in a TMR procedure to achieve successful reactivation and the ensuing gain in memory consolidation.