An assembly-line model of sleep, dreaming and memory enhancement: investigating the coordinated roles of REM and nonREM sleep in human memory consolidation

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Both rapid eye movement (REM) and nonREM (NREM) sleep actively contribute to memory improvement and certain oscillatory events, such as sleep spindles (bursts of 11-16 Hz EEG activity), are reliable biomarkers of this activity. Evidence is more mixed as to whether dreaming plays a role in memory and, especially, whether dream replays' of new memories also constitute such a biomarker. We recently replicated findings that NREM and REM sleep influence memory in a complementary fashion and, more importantly, showed for the first time that NREM sleep spindles, amount of REM sleep and dreaming length and content are all inter-correlated measures. These correlations were preferentially strong for the third sleep cycle, suggesting that it is a time particularly conducive to memory plasticity, a phenomenon previously shown only for rodents. As new discoveries, these NREM-REM-dreaming correlations need to be replicated, extended to other sleep measures of memory improvement, and evaluated with tools that permit drawing conclusions about cause and effect. The proposed research aims to achieve these objectives by careful replication and by enhancing memory during sleep using a validated, targeted memory reactivation (TMR), method. With TMR, tones are presented during a task and then again during NREM sleep; the sounds presumably reactivate neural circuits that were formed during task learning. We will enhance learning by presenting task-associated tones in NREM sleep and measuring how NREM, REM and dreaming measures are altered. In a typical experiment, our task will be completed in a virtual reality (VR) setting and will involve navigating a maze. We will assess, in NREM sleep, if spindle activity increases; in REM sleep, if eye movements change; and, in dream reports, if VR task replays appear. If sleep cycle 3 is a privileged window for memory processing, then task improvement and sleep/dream changes should be greatest for subjects to whom TMR sounds are played during cycle 3 (vs. during cycles 2 or 4).The research will be of interest to persons studying sleep and memory, dreaming or TMR and should provide insights into how sleep controls memory storage. It will have a particular relevance for showing how timing and stimulating sleep episodes can optimize memory and thus enhance learning with greater precision. Findings may also help explain if and how dreaming is implicated in memory, i.e., by clarifying its relationship to sleep spindles and whether it replays elements of new learning. Thus, the work may lead to a more profound understanding of both memory and sleep and support a growing outreach to Canadians to improve their cognitive functioning by getting more sleep. This type of research may lead to the development of sleep-based methods for enhancing, optimizing and rehabilitating memory and in protecting it in the face of age-related or illness-related decline.