Dreams on-demand: A new method to find out why we dream at night

Dreaming is emblematic of our sleeping experiences. Yet, the functions of dreaming remain elusive. Dreams in REM sleep have been hypothesized to help us generalize and forget information1 2, promote brain plasticity 3 4, update our internal model of the world 5, activate genetic influences on brain development 6 7, process emotional memories 8 9, improve motor performance for complex tasks 10, and have no cognitive functions at all 11. Each theory of dream function draws upon confirmatory evidence-- correlations between dream content or features of REM and various outcomes. Yet, a central challenge of dream research makes it nearly impossible to find evidence against any of these hypotheses. That is, we have yet to find a way to experimentally control REM sleep dream content. Here, we propose to develop methods to trigger specific dream content during REM sleep. Participants will associate music cues with two distinct memories ripe for dream incorporation, and the association will be strengthened by a conditioning training immediately prior to a morning REM episode. Sleep will be monitored by an experimenter, and only one of the two music cues will be presented during sleep. Each memory will entail a unique respiratory signature that can be measured during sleep to objectively verify the modified dream.