Investigating dreams by strategically presenting sounds during REM sleep to reactivate waking experiences

Dreams may partially reflect the memory reorganizing that occurs nightly, improving the usefulness of what we learn each day. However, solid evidence has yet to link dreaming with adaptive overnight memory reorganization. Establishing this link faces several challenges, including the difficulty of experimentally controlling dream content and the susceptibility of dream reports to distortion and forgetting upon awakening. Fortunately, memory consolidation can be systematically manipulated using Targeted Memory Reactivation (TMR), whereby sensory stimulation during sleep can influence previously acquired memories, often reducing forgetting. Stimuli presented during sleep can also be incorporated into dreams, but the extent to which reactivating memories with TMR can influence dream content is still unclear. In the present study, we enlisted TMR to strategically influence dreams. In the evening, participants performed two distinct tasks designed to be readily incorporated into dreams, each associated with a unique sound. The associations between the two tasks and the two (counterbalanced) sounds were further reinforced in a conditioning phase just prior to sleep. The experimenter then presented one of the two sounds when participants were in REM sleep. Dream reports revealed more incorporation of task elements from the cued task than from the uncued task, though incorporation was high for both tasks. Furthermore, dreaming of a task was linked with decreased negative valence and increased creativity. We conclude that this approach to dream curation provides a promising way to investigate the influence of dreaming on memory storage and other cognitive functions.