British neurophysiologists conducted a study which established that during the learning process, certain information is selectively tagged for subsequent memory consolidation, which occurs during the sleep phase. This mechanism was found to be controlled by theta rhythm.
In this experiment, published in PLoS Biology, scientists recorded electroencephalograms (EEG) from thirty-one subjects. Recordings were made both during the learning period and during the participants' sleep. Afterward, all participants underwent special tests designed to check their memory.