Appearance of frontal mid-line theta rhythm during sleep and its relation to mental activity.

Fm theta occurred not only during mental tests in the waking state but also during nocturnal sleep in which it was most frequent during REM and secondarily most frequent during stage 1 of NREM sleep. As for the inner experience of the subjects, they frequently reported dream and distinct mentations on awakening from REM sleep whether or not it was accompanied by Fm theta. They reported dream and distinct mentations more frequently when awakened from stage 1 of NREM sleep with Fm theta than when awakened from stage 1 of NREM sleep without Fm theta. Relationship of Fm theta to mental activity during sleep was briefly discussed.