Enhancing the Suppression of Unwanted Memories During NREM Sleep.

Memory suppression, the ability to exclude unwanted memories from awareness, plays a critical role in maintaining mental well-being. Whereas the mechanisms of memory suppression during wakefulness have been extensively studied, the effects of sleep on this process and its associated neural mechanisms remain understudied. Targeted memory reactivation, an experimental approach for investigating the relationship between sleep and memory processing, provides a unique opportunity to further explore this relationship. Here, we combined the Think/No-Think paradigm with targeted memory reactivation to investigate whether and how reactivating suppression processes during sleep engages its associated neural mechanisms and influences later memory performance. Participants first learned cue-associate word pairs. They were then presented with trials, each exposing a cue word, preceded by an auditory instruction requiring the participant to either retrieve or suppress the corresponding target word. Subsequently, during NREM sleep, we unobtrusively re-presented the auditory tone signaling the instruction to suppress retrieval. We found that cueing people to suppress in this manner significantly enhanced suppression-induced forgetting on a later post-sleep test, compared to pairs that were not cued during sleep. Electroencephalogram analyses revealed that reactivation of suppression instructions increased theta power and reduced the coupling strength between spindles and the slow oscillation (SO) up-states. Importantly, only reduced SO up-state-spindle coupling predicted poorer later memory retrieval for suppressed pairs. The present results suggest that the disruption of neural synchrony between SO up-state and spindles during sleep plays a critical role in enhancing subsequent suppression-induced forgetting.