The role of dreaming in REM and NREM sleep-dependent memory functions

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Strong evidence now shows that REM and NREM sleep contribute differentially to offline improvements in memory, e.g., REM sleep to emotional memory and NREM sleep to declarative memory. And although a recent surge of studies suggests that dreaming about a learning task predicts later improvement on this task, no studies have yet determined if REM and NREM dreaming are implicated in different memory systems. This, despite ample evidence of parallels between REM/NREM dreaming features and different memory types, i.e., REM dreaming is more emotionally rich than NREM dreaming, while the latter is more thoughtlike in nature. The emotional nature of REM dreaming is of particular interest because the mere presentation of emotional stimuli prior to, during, or following a learning task (when awake) improves later memory for that task--regardless of whether the emotional stimuli are positive or negative or conceptually unrelated to the task. In a similar manner, REM dream emotions may facilitate memory for new information that is reactivated in close temporal proximity. The proposed research aims to: 1) determine if dreaming about a learning task is correlated with offline improvement on that task, 2) assess if REM and NREM dreaming are differentially associated with emotional and declarative memory tasks respectively, and 3) test whether the experimental intensification of REM dream emotions will enhance memory for a non-emotional task. Healthy subjects will participate in a series of studies that use protocols known to induce REM and NREM sleep-dependent memory effects, and that are modified to include standardized assessments of REM and NREM dreaming. Learning tasks given before sleep will be retested the next day while the intervening night of sleep is monitored and quantified in the laboratory. Dream ratings of emotional intensity and conceptual content are expected to be associated with overnight improvements in learning, even when correlations between REM/NREM sleep and improvement are statistically removed. Findings will help uncover the functions of dreaming and the mechanisms of memory more generally and may provide insights into strategies for memory improvement.