The Role of Memory Reactivation during Wakefulness and Sleep in Determining Which Memories Endure

TLDR

Consolidation enables daily experiences to be stored durably, and covert reactivation may ultimately decide which memories persist, with wake reactivation strengthening salient memories and sleep reactivation linking related ones. The study tests whether covert reactivation during sleep and wakefulness determines which daily memories are retained versus forgotten. Sixty participants learned 72 object‑location pairs paired with characteristic sounds and reward cues, and the researchers later used those sounds to covertly reactivate selected low‑value memories during wake or sleep. Recall of low‑value associations declined more than high‑value ones after a 90‑min nap or wake interval, but targeted reactivation of the sounds rescued low‑value memories—only the cued ones during wake, and all low‑value ones during sleep—demonstrating that covert reactivation is a major determinant of memory consolidation selectivity.

Abstract

Consolidation makes it possible for memories of our daily experiences to be stored in an enduring way. We propose that memory consolidation depends on the covert reactivation of previously learned material both during sleep and wakefulness. Here we tested whether the operation of covert memory reactivation influences the fundamental selectivity of memory storage—of all the events we experience each day, which will be retained and which forgotten? We systematically manipulated the value of information learned by 60 young subjects; they learned 72 object-location associations while hearing characteristic object sounds, and a number on each object indicated the reward value that could potentially be earned during a future memory test. Recall accuracy declined to a greater extent for low-value than for high-value associations after either a 90 min nap or a 90 min wake interval. Yet, via targeted memory reactivation of half of the low-value associations using the corresponding sounds, these memories were rescued from forgetting. Only cued associations were rescued when sounds were applied during wakefulness, whereas the entire set of low-value associations was rescued from forgetting when the manipulation occurred during sleep. The benefits accrued from presenting corresponding sounds show that covert reactivation is a major factor determining the selectivity of memory consolidation in these circumstances. By extension, covert reactivation may determine the ultimate fate of our memories, though wake and sleep reactivation might play distinct roles in this process, the former helping to strengthen individual, salient memories, and the latter strengthening, while also linking, categorically related memories together.