Offline memory consolidation during waking rest

People spend approximately half of their waking hours in a so-called offline state — daydreaming, mind wandering or otherwise inattentive to their surroundings. These activities are often viewed as a waste of time, perhaps as moments of lost productivity. However, periods of offline waking rest can facilitate the consolidation of newly formed memories. Even a few minutes of rest with closed eyes can improve memory, perhaps to the same degree as a full night of sleep. These findings have profound implications for understanding the memory consolidation process, its time course and its underlying mechanisms. In this Review, I describe evidence that offline waking rest retroactively facilitates memory. Similar to the beneficial effect of sleep, the effect of rest might be driven by neural-level reactivation of newly formed memory traces. As both rest and sleep seem to support consolidation, I next consider whether these two states support the same or dissociable stages of consolidation. Then I review evidence that seconds-long bouts of offline rest occur throughout the day and that even these ultrashort offline periods might benefit memory. Finally, I conclude by describing future directions for research into the underlying processes of sleep and wake states.