Investigators aim to offer a quantifiable, real-time measure of memory processing during NREM sleep by using memory-related cues to influence which behaviours sleepwalkers will exhibit. Because sleepwalking is characterized by complex behaviors emerging from NREM sleep, it could provide an observable window into mental activity in NREM sleep. While neuronal memory reactivations have largely been demonstrated in sleeping rodents, evidence for the existence of such reactivations in humans is at best indirect. Here, investigators will use targeted memory reactivation (TMR), a tool that allows to control which individual memories are reactivated on a trial by trial basis. TMR consists in associating sensory cues with a specific learning, then re-applying these cues during subsequent sleep to trigger the reactivation of the corresponding learning. Sleepwalkers will be trained on a modified version of the serial reaction time task: sleepwalkers will perform as fast and accurately as possible a sequence of gestures in response to auditory cues. Investigators goals are to: i) show that playing the auditory cues during NREM sleep triggers a behavioral replay of the learned 'choreography' in sleepwalkers, ii) quantify, with a gesture recognition algorithm, how the sleep gestures differ from the wake ones (speed, accuracy, sequence fidelity), and iii) test whether this evoked replay is accompanied by a congruent dream.
Sleep is crucial for global cognitive functioning, but its exact functions and mechanisms are still poorly understood. Cognitive studies of sleep typically rely on linking electrophysiological changes measured during sleep with behavioral and neural changes collected in tasks performed during wakefulness. What concomitantly happens in the mind of sleeping subjects is often ignored, certainly because it is virtually inaccessible. Yet, major advances in the understanding of human behaviors have resulted from an integrated approach that combines both neural and cognitive measures of their ongoing mental processes. The goal of this study is to provide real-time measures of the cognitive processes occurring within sleep.~To prompt real-time access to the sleeping mind, investigators will use auditory stimulation in people with unique sleep peculiarities: sleepwalkers whose overt behaviours may enable to objectively visualize ongoing cognitive processes during non-REM (NREM) sleep.