Abstract
Dream reports are obtained with a high percentage from REM (rapid eye movement) sleep awakening. However, it is not clear when the recalled dream experience actually occurred. To specify sleep states when dream occurs, we controlled sleep duration and examined the relationship between dream reports and sleep variables, using an ultra-short sleep-wake schedule. Eleven healthy males (22.7 ± 1.44 years) participated in the study. Twentymin Polysomnographic recordings (nap trials) were repeated every hour for 78 hour. A structured interview assessed formal aspects of dream (quantity, vividness, comfortableness and uncomfortableness) was performed at the end of each nap. We obtained 172 nap trials including REM sleep (REM trials) and 563 nap trials including only NREM sleep (NREM trials). Dream report was obtained from 51.2% of REM trials, while it was obtained from 17.9% of NREM trials. Scores of dream quantity, vividness and comfortableness in the REM trials were higher than those in the NREM trials. These results suggest that occurrence of dream experiences is higher in REM sleep than in NREM sleep, and confirm that dream experiences can occur in NREM sleep even when effects of the prior REM sleep are experimentally eliminated.
