Testing a Hypothesis of Non-REM Sleep Reinforcement and REM Sleep Refinement for the Benefits of Post-Learning Sleep on Memory Retrieval

Abstract

It is well established that post-learning sleep benefits later memory retrieval, but there is still much to learn about the processes involved and the nature of these benefits. Sleep is composed of stages of non-REM (NREM) and REM sleep: NREM sleep, especially slow wave activity of NREM sleep, and REM sleep have been implicated in memory performance benefits, but the specific contributions of each state remain unclear. This thesis presents a hypothesis proposing that post-learning NREM sleep supports memory accessibility, benefitting the likelihood of successful memory retrieval, and that post-learning REM sleep supports memory fidelity, allowing for more accurate retrieval when retrieval is successful. This hypothesis was tested over studies examining the effects of an afternoon nap (Chapter 2), targeted memory reactivation during NREM slow wave sleep (Chapter 3), and both targeted memory reactivation during NREM slow wave sleep and selective deprivation of REM sleep (Chapter 4) on measures of memory accessibility and memory fidelity in visuospatial memory tasks. In each study, measures of sleep architecture and electroencephalographic power in sleep were examined as predictors of memory performance. Several identified associations and interactions further inform an understanding of how NREM sleep and REM sleep may benefit memory performance. Most notably, these studies consistently found greater slow wave activity of NREM sleep to be specifically associated with better maintenance of memory accessibility. These studies did not identify a clear effect of REM sleep. It is hoped that the hypothesis and findings presented stimulate additional inquires that will further our understanding of the individual and combined contributions of NREM and REM sleep.