Experimental evidence of the existence of a fourth state of unified, transcendental consciousness, which lies in the yoga nidra state at the transition between sensory and sleep consciousness, was first recorded at the Menninger Foundation in Kansas, USA in 1971. Under the direction of Dr. Elmer Green, researchers used an electroencephalograph to record the brainwave activity of an Indian yogi, Swami Rama, while he progressively relaxed his entire physical, mental and emotional structure through the practice of Yoga Nidra.
What they recorded was a revelation to the scientific community. The swami demonstrated the capacity to enter the various states of consciousness at will, as evidenced by remarkable changes in the electrical activity of his brain. Upon relaxing himself in the laboratory, he first entered the yoga nidra state, producing 70% alpha wave discharge for a predetermined 5 minute period, simply by imagining an empty blue sky with occasional drifting clouds.
Next, Swami Rama entered a state of dreaming sleep which was accompanied by slower theta waves for 75% of the subsequent 5 minute test period. This state, which he later described as being 'noisy and unpleasant', was attained by 'stilling the conscious mind and bringing forth the subconscious'. In this state he had the internal experience of desires, ambitions, memories and past images in archetypal form rising sequentially from the subconscious and unconscious with a rush, each archetype occupying his whole awareness.
Finally, the swami entered the state of (unconscious) deep sleep, as verified by the emergence of the characteristic pattern of slow rhythm delta waves. However, he remained perfectly aware throughout the entire experimental period. He later recalled the various events which had occurred in the laboratory during the experiment, including all the questions that one of the scientists had asked him during the period of deep delta wave sleep, while his body lay snoring quietly.
Such remarkable mastery over the fluctuating patterns of consciousness had not previously been demonstrated under strict laboratory conditions. The capacity to remain consciously aware while producing delta waves and experiencing deep sleep is one of the indications of the superconscious state (turiya). This is the ultimate state of yoga nidra in which the conventional barriers between waking, dreaming and deep sleep are lifted, revealing the simultaneous operation of the conscious, subconscious and unconscious mind. The result is a single, enlightened state of consciousness and a perfectly integrated and relaxed personality.
Dr. Kamakhya Kumar in 2006 awarded by Ph. D. degree by Dr. A. P J Abdul Kalam (President of India) for his work "Psycho-physiological Changes as Related to Yoga Nidra". He observed six months effects of yoga nidra on some Physiological, hematological and some Psychological parameters on the practitioners and he found a significant change on above mentioned parameters. One of the research published entitled "A study on the impact on stress and anxiety through Yoga nidra; Indian Journal of Traditional Knowledge, Vol. 7 No 3".(Published through NISCAIR)
Indian clinical psychologist Sachin Kumar Dwivedi (2009) found in his research that Yoga Nidra decreases levels of anxiety. Dwivedi, S., Awasthi, S.& Pandey,B.B.(2011) found in " Yoga Nidra increased the α-eeg on α-eeg biofeedback. That is open scrate [secret?] that Yoga Nidra is a type of deep meditation. Nikhra,M & Dwivedi,S.K.(2010) found in a study "Yoga nidra reduce the level of Stress