Manipulating and Classifying Memory Processing during Sleep

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The ability to remember is central to human success. Whereas most memory research focuses on the formation and/or recall of memories, events intervening between the acquisition of new information and its subsequent retrieval may play a central role in shaping memory storage and determining what can be remembered. In particular, recent research suggests that memories are reactivated during sleep. This insight has led researchers to hypothesize that reactivation during sleep may have a profound influence on whether a memory persists or fades away. However, investigating this question in humans has been hindered by difficulties in measuring reactivation. Furthermore, merely measuring reactivation is insufficient for showing that reactivation improves memory. To establish causality, one must directly manipulate reactivation instead of just observing when it happens. An overarching objective of this project is thus to monitor, characterize, and manipulate memory reactivation during sleep. These efforts at the intersection of memory research and sleep research will expand our understanding of how memories are stored in the brain, providing knowledge that can then guide efforts to improve learning and memory in a variety of contexts, including in education, in the legal system, in public service training, for individuals with memory dysfunction due to disease, for older individuals with age-related memory decline, and for a wide variety of on-the-job uses of memory. The research will also highlight the relevance of sleep for effective learning, bolstering societal appreciation of the need for sleep.This project will take the innovative approach of combining auditory stimulation during sleep with extensive analysis of EEG recordings. Through systematic arrangement of learning and testing procedures, auditory stimulation will function as a prompt for memory reactivation in the brain while relevant neural activity is simultaneously monitored. These procedures make it possible to analyze neurocognitive processing during sleep and to relate this processing to later memory performance. By manipulating which memories are cued during sleep, causal inferences about how reactivation affects stored memories will be made. Dr. Paller and his team will focus on established physiological signals (e.g., N400 and sleep spindles) as well as on multivariate analyses. By applying sophisticated pattern classifier analyses to sleep EEG data collected immediately after the auditory cues are played, a time-varying neural measure of how strongly the associated memory is reactivated during sleep will be derived. This neural signature of memory reactivation can be related to features of sleep physiology and also subsequent memory to shed light on exactly which aspects of sleep promote strong memory reactivation and, ultimately, accurate recall. This work thus provides a powerful new set of approaches for investigating the fundamental brain events that enable memory storage to be enduring for the vast amount of information we all need to remember.