A new open database, the DREAM database, combines standardized sleep magneto/electroencephalography (M/EEG) recordings with dream reports from 505 participants across 20 datasets, totaling 2,643 awakenings. Each awakening includes at least 20 seconds of high-resolution sleep EEG (≥100 Hz, ≥2 electrodes) and a classification of the sleeper's reported experience. Analyses showed that reports of conscious experiences during sleep can be predicted from objective EEG features in both REM and NREM sleep. The database aims to overcome limitations of small sample sizes and methodological variability in dream research, enabling larger-scale investigations of the neurocognitive basis of dreaming.
Mental experiences during wakefulness and sleep are not as distinct as commonly thought. Analyzing electroencephalography (EEG) from 92 participants during daytime rest, researchers collected 375 reports of mental content scored on bizarreness, fluidity, spontaneity, and wake perception. Clustering these reports revealed four distinct types of mental states. Crucially, all four types occurred across wakefulness, N1 sleep, and N2 sleep. EEG measures of spectral power, complexity, and connectivity differentiated these mental states independently of whether participants were awake or asleep. The findings indicate that the waking and sleeping brain can produce the same mental state, and that fine-grained brain dynamics shape the content of mental experiences.