Sleep-learning (also known as sleep-teaching, hypnopædia, or hypnopedia) attempts to convey information to a sleeping person, typically by playing a sound recording to them while they sleep.
This technique is supposed to be moderately effective at making people remember direct passages or facts, word for word. Since the electroencephalography studies by Charles W. Simon and William H. Emmons in 1956, learning by sleep has not been taken seriously. The researchers concluded that learning during sleep was "impractical and probably impossible." They reported that stimulus material presented during sleep was not recalled later when the subject awoke unless alpha wave activity occurred at the same time the stimulus material was given. Since alpha activity during sleep indicates the subject is about to awake, the researchers felt that any learning occurred in a waking state.
Research from the Weizmann Institute of Science indicates that classical conditioning can occur during sleep.
Read more about Sleep-learning: In Fiction