Experience-dependent induction of
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This study characterizes hypnagogic hallucinations reported during a polygraphically-recorded 90-minute daytime nap following or preceding practice of the computer game Tetris. In the experimental group (n=16), participants played Tetris in the morning for two hours during three consecutive days, while in a first control group (n=13, controlling the effect of experience), participants did not play any game and in a second control group (n=14, controlling the effect of anticipation), participants played Tetris after the nap. During afternoon naps, participants were repetitively awakened 15, 45, 75, 120 or 180 seconds after the onset of sleep stage 1 and were asked to report their mental content. Reports content was scored by three judges (inter-rater reliability 85%). In the experimental group, 48 out of 485 (10%) sleep-onset reports were Tetris-related. They mostly consisted of images and sounds with very little emotional content. They exactly reproduced Tetris elements or mixed them with other mnemonic components. By contrast, in the first control group, only 1 report out of 107 was scored as Tetris-related (1%) and in the second control group only 3 reports out of 112 (3%) (between-groups comparison; p=0.006). Hypnagogic hallucinations were more consistently induced by experience than by anticipation (p=0.039) and they were predominantly observed during the transition of wakefulness to sleep. The observed attributes of experience-related hypnagogic hallucinations are consistent with the particular organization of regional brain activity at sleep onset, characterized by high activity in sensory cortices and in the default mode network.