Mason, L, Alexander, C., Travis, F, Marsh, Orme-Johnson, D.W., Gackenbach, J., Mason, D.C., Rainforth, M., & Walton, K.G. (1997). Electrophysiological correlates of higher states of consciousness during sleep in long-term practitioners of the Transcendental Meditation program. Sleep, 20: 102-110.

Abstract
Standard ambulatory night sleep electroencephalograph (EEG) of 11 long-term practitioners of the Transcendental Meditation (TM) program reporting "higher states of consciousness" during sleep (the experimental group) was compared to that of nine short-term practitioners and 11 non-practitioners. EEG tracings during stages 3 and 4 sleep showed the experimental group to have: (1) theta-alpha activity simultaneously with delta activity and (2) decreased chin electromyogram (EMG) during deep sleep compared to short-term practitioners. Spectral analysis fast Fourier transform (FFT) data of the first three cycles showed that: (3) the experimental subjects had significantly greater theta2 (6-8 Hz)-alpha1 (8-10 Hz) relative power during stages 3 and 4 than the combined control groups with no difference in time in delta; (4) there was a graded difference across groups during stages 3 and 4 in theta2-alpha1, with experimentals having greater power than short-term practitioners,who in turn had greater power than the non-practitioners; and (5) experimentals also had increased rapid eye movement (REM) density compared to short-term practitioners. (There was no eye-movement data for the non-practitioners.) Previous studies have found increased theta-alpha EEG during reported periods of "transcendental consciousness" during the TM technique. In the Vedic tradition, as described by Maharishi Mahesh Yogi, transcendental consciousness is the first of a sequence of higher states. The maintenance of transcendental consciousness along with deep sleep is said to be a distinctive criterion of further, stabilized higher states of consciousness. The findings of this study are interpreted as physiological support for this model.