Figure 2. Interactive dreaming (USA group).

(A) Hypnogram showing that REM sleep began 68 min after sleep onset. The auditory cue to induce lucidity was presented two times (blue arrow), followed by a microarousal and then a longer REM period with lucidity signals (LRLRLR) given six times starting at 69 min.

(B) The left panel shows a 5 s period of wake, corresponding to the gray arrow on the hypnogram. The right panel shows a 30 s REM segment, in which the last two lucidity signals (indicated by red asterisks) were followed by two instances of the spoken stimulus “8 minus 6” (vertical lines, and red arrow in A). Both times, the correct answer was produced with eye signals (2). Upon awakening, the participant reported dreaming about his favorite video game: “I was in a parking lot at night…then suddenly it was daytime and I was in the video game…. I thought, okay this is probably a dream. And then something weird…. I lost control of all my muscles. There was a roaring sound of blood rushing to my ears.” The experimenter asked him whether he remembered hearing any math problems, how many he answered, and what he answered. The subject reported, “I think I heard three [problems]…. I answered ‘2’ for all of them, but I don’t remember what the first one was. I just remember the last one was ‘8 minus 6.”’ (For further details on sleep monitoring and terminology, see Nir and Tononi,¹ Appel et al.,⁶ and Baird et al.⁷)