Short periods of unoccupied waking rest can facilitate consolidation in a manner similar to that proposed to occur during sleep

Memory Consolidation during Waking Rest. Erin J. Wamsley. Trends in Cognitive Sciences, https://doi.org/10.1016/j.tics.2018.12.007

Abstract: Recent studies show that brief periods of rest after learning facilitate consolidation of new memories. This effect is associated with memory-related brain activity during quiet rest and suggests that in our daily lives, moments of unoccupied rest may serve an essential cognitive function.

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In fact, a growing body of evidence suggests that short periods of unoccupied waking rest can facilitate consolidation in a manner similar to that proposed to occur during sleep [1–3,5,6] (quiet wake conditions, Figure 1). Our group and others have demonstrated that a 15min period of eyes-closed rest following encoding enhances memory for both procedural [5] and declarative [1,2] memory tasks, compared to an equivalent period spent completing a distractor task. Other recent studies have demonstrated that post-learning rest enhances subsequent memory for spatial and temporal information [7] , facilitates insight into a complex problem [3] , and enhances auditory statistical learning [6]. These memory effects can be maintained for a week or more after the rest intervention [2,7]. Together, these observations suggest that even during wakefulness, memory is preferentially consolidated during offline states characterized by reduced attentional demands.

Thus, the fundamental insight yielded by these new studies of waking rest is not so much that consolidation can occur during wakefulness but that consolidation is not uniformly distributed throughout all of wakefulness. Instead, memory is preferentially facilitated during periods of unoccupied time in which attentional and cognitive demands are reduced [1,2,5]. This insight helps us to understand the necessary and sufficient conditions for consolidation to occur. Increasingly, it appears that for many forms of consolidation, sleep-specific neural mechanisms may not be strictly required. Instead, both sleep and other of fl ine states share common neurobiological features essential for consolidation to take place.

Indeed, many of the same neurobiological mechanisms thought to underlie sleep’s effect on memory are shared in common by waking rest. First, cellular-level memory ‘reactivation’ occurs during quiescent waking rest in the hippocampus as well as in other brain regions. During this process, sequences of neuronal fi ring representing recent experience are reiterated of fl ine. Blocking these reactivations impairs learning and memory [8]. In humans, a growing number of neuroimaging studies demonstrate memory-related brain activity during periods of post-training rest that predicts subsequent memory. For example, fMRI has been used to demonstrate that patterns of hippocampal activity characterizing encoding persist into post-learning rest and that this predicts subsequent memory [9]. Our own group has meanwhile reported that low-frequency electroencephalogram oscillations thought to support consolidation during sleep similarly predict memory retention across quiet waking rest [1]. And the neuromodulatory environment during quiet rest is also well own group has meanwhile reported that low-frequency electroencephalogram oscillations thought to support consolidation during sleep similarly predict memory retention across quiet waking rest [1]. And the neuromodulatory environment during quiet rest is also well suited to facilitate consolidation; in both sleep and quiet rest, acetylcholine levels are substantially reduced from active waking levels, thought to promote hippocampal-cortical communication dynamics that benefit consolidation, as opposed to new learning. Thus, converging lines of evidence suggest that like sleep, rest benefits memory by enabling an active process of consolidation, facilitated by the offline reactivation and synaptic plasticity.