How special is sleep for human memory consolidation?

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Background:A plethora of evidence suggests that sleep plays an important, perhaps critical role in the consolidation of memories. However, despite the seemingly overwhelming evidence, the sleep-memory hypothesis has faced a steady stream of critical commentaries and contradictory evidence. For example, many of the plasticity mechanisms thought to mediate synaptic memory consolidation (e.g., reactivation and neuronal replay, slow oscillations) also operate during wakefulness, albeit at a lower rate. In particular, the state of quiet waking (QW) appears to share similarities with sleep in terms of the activation of consolidation mechanisms. However, almost all empirical studies use active waking (AW) as a comparison condition for sleep, which may amplify the apparent differences between sleep and waking in terms of memory consolidation. ***The proposed experiments perform a systematic analysis of the role of sleep and different types of waking, focusing on the potential differences between AW and QW in their effectiveness to promote memory consolidation in humans. Four objectives (O) are proposed: ***O1: Establish and explicitly contrast the role of napping, AW, and QW in explicit and implicit memory consolidation. ***O2: Compare the effectiveness of sensory cue-elicited memory reactivation during napping, AW, and QW. Note that sensory (e.g., auditory) cues present during learning and subsequent sleep enhance the memory consolidation, presumably by triggering reactivation of learning-related neuronal activity. ***O3: Identify electroencephalographic (EEG) and sleep-stage correlates of memory consolidation napping, AW, and QW.***O4: Assess the effectiveness of auditory-entrainment and biofeedback to influence EEG activity and enhance memory consolidation. Guided by the results of O3, acoustic stimuli or biofeedback procedures are used to enhance activity in the EEG frequency bands linked to effective consolidation. ***Significance: A direct comparison of consolidation between AW, QW, and sleep provides a powerful test of the hypothesis that sleep plays a specialized or critical role in memory consolidation, as opposed to sleep merely falling along a continuum of behavioral states that vary in the effectiveness to permit effective consolidation in the human brain. Thus, the proposed work will provide new and important insights into the functions of different behavioural states to allow the effective storage and long-term memories in the human nervous system. Importantly, the experimental and analytic work involved in the proposed research provides a rich training environment for HQP at all levels (undergraduate to Ph.D. students), who will play critical roles in the process of determining experimental designs and hypotheses, the collection, analysis, and interpretation of data, as well as the communication of experimental findings in the form of seminars, conference presentations, and peer-reviewed journal publications. **