People who are asleep and having a lucid dream—aware that they are dreaming—can perceive questions from an experimenter and answer them in real time using eye movements and facial muscle contractions. In a study of 36 individuals during REM sleep, including frequent lucid dreamers, a novice, and a patient with narcolepsy, participants performed perceptual analysis of new information, held information in working memory, computed simple answers, and gave volitional replies. Correct answers occurred on 29 occasions across 6 individuals, documented by four independent laboratories. This two-way communication channel allows real-time interrogation of dream cognition and characteristics.
Sleep paralysis and false awakenings are intermediate states between REM sleep and wakefulness. In a sleep-laboratory study of five participants, polysomnography recordings captured five sleep-paralysis episodes and two false awakenings. During sleep paralysis, 70.8% of 3-second mini-epochs showed theta brain waves (compared to 89.7% in normal REM sleep and 21.2% in wakefulness), 93.8% had chin-muscle atonia (vs 89.7% in REM and 33.3% in wakefulness), and 6.9% contained rapid eye movements (vs 11.9% in REM and 8.1% in wakefulness). The electroencephalography spectrum during sleep paralysis was intermediate between wakefulness and REM sleep for alpha, theta, and delta frequencies, while beta frequencies matched normal REM sleep.