The end state of yoga nidra is psychic sleep or sleep in the state of inner awareness. It is a state on the borderline between sleep and wakefulness that allows contact with the subconscious and unconscious mind where we have stored all our past memories. Those experiences that were particularly painful have been pushed deep into the unconscious, beyond remembrance. However, they are still alive and are the source of our fears and obsessions. Also in the unconscious are our instinctive desires, constantly competing for expression and satisfaction through the conscious mind. We can look at tension as the accumulation of repressed energy that powers those drives and desires which are denied conscious satisfaction. During yoga nidra these frustrations and thwarted desires are given expression so that tension is reduced and the energy behind them is freed for use in other directions. This process also takes place during normal sleep when we dream.
In their search for the memory banks in the brain, neurologists have failed to pin down any one area that is the storehouse of our memories. However, the Canadian neurosurgeon Wilfred Penfield found that when some secretions of the temporal cortex were stimulated, the patient recalled apparently full blown memory sequences- an evening at a concert, a childhood experience and so forth. Repeated stimulation of the same spot would evoke the same recollections each time. It is now thought that particular sets of brain circuits and firing patterns form the relevant code for memory, but any single memory is not localized in a single network. Rather, it will be duplicated in both hemispheres and many times over.
Once the brain has chanced upon a particular circuit, perhaps as a result of spontaneous, random firing as in dreaming, then a particular memory sequence and its ensuing emotional state will follow almost of necessity. The brain flips into particular states which will then run their course, unrolling otherwise suppressed memory sequences as they proceed. The specific instruction must be to fire particular circuits from which the rest will follow. This is exactly what happens in yoga nidra. Yoga nidra brings us to a state of self induced dreaming- with a difference. Regular dreams are composed simply of a random selection of impulses. During yoga nidra we create our own dream by visualizing a wide variety of symbols that have powerful and universal significance.
"A number of different things will be named and you should try to develop a vision of these things on all levels- feeling, awareness, emotion, imagination...
Shiva lingam, standing Christ, flickering candle, weeping willow tree, dead body, coloured clouds gathering, starlit night, full moon, setting sun, golden spider web, cross over a church, cold winter's day, temple bell ringing, monk with shaven head, Buddha in repose, a yogi sitting deep in meditation."
More importantly, experience has shown that just like Penfield's electrodes, these 'rapid images' also spark totally unrelated memory sequences. The temporal cortex where these memories are encoded has links with the hypothalamus, which governs the emotions, so that every memory comes with an emotional charge. Some recollections may seem trivial. Others have emotional impact that would be overwhelming if recalled under normal circumstances, but which becomes manageable in the deeply relaxed state of yoga nidra. In this way many kinds of tension are released and the mind is cleaned of disturbing material. Sometimes these are very positive memories, but either way, these recollections have a very powerful effect that can change one's whole life. When we regularly review the contents of the unconscious in this way, we greatly reduce anxiety and bring our inner being into greater harmony.
Yoga nidra is not just a matter of emotional hygiene- it is also a spiritual practice. It is a method of pratyahara or sense withdrawal which reduces our awareness of the outside work! and our physical existence. Paradoxically, this is accomplished mainly by heightening awareness of the body during the rotation of consciousness through the different limbs and organs. A possible explanation for why this is so may be made in terms of brain mechanisms.
When a nerve receives information, an electrical impulse is discharged. The time taken for an impulse to pass the full length of the neurone varies, but the time taken to pass any particular point on the cell membrane is about one millisecond. However, for an equal period after the impulse has passed, the cell is incapable of sending a second signal. By intensifying our awareness of a particular part of the body, we can induce a sensation that causes the cells in that part of the body to fire an impulse to the brain. Immediately after, there is a split second in which the cell cannot send more information. The brain's connection with the outside world via that cell is then cut off- there is an instant of numbness, withdrawal, pratyahara.
Of course, the connection is soon restored, but by this time one's awareness has jumped to another part of the body. That cell is effectively switched off for the duration of the practice, for the connection is not fully reopened; the brain's selective tuning mechanism screens out any later messages. You can personally experience this selective tuning in operation in a crowded room where several people are talking at the same time. Close your eyes and listen to just one person speaking, then tune him out and listen to another person. Although we are not aware of it, we are tuning ourselves in this way all the time. Understanding this mechanism in action adds an extra dimension to Swami Satyananda Saraswati's definition of yoga nidra as "relaxation by creating one pointedness of mind".
Once attention has been withdrawn from the body, the consciousness is then rotated through various thoughts and feelings, causing withdrawal from these also. It is interesting to note that the area thus brought into play, the hypothalamus, is immediately adjacent to the pineal and pituitary glands. These are the two most important endocrine glands in the human organism, both of which secrete hormones that affect our state of consciousness. The pineal gland is otherwise known as the 'third eye' and was designated by the philosopher Descartes as the seat of the soul. To yogis it is known to be the physical counterpart of ajna chakra. This is one of our chief psychic centres, acting as a channel for the higher forces which guide our spiritual growth. Its full awakening marks the elevation of our consciousness from the emotional and intellectual planes to the psychic realms. The pituitary is the master gland of the body, linking the nervous and hormonal systems and influencing all metabolic and emotional reactions. In the terms of yoga, this gland is the physical correspondent of sahasrara chakra, the doorway to enlightened consciousness expanding to infinity. The awakening of sahasrara marks the passage from the merely psychic to the truly spiritual- once sahasrara has opened we become fully human.
These two chakras are vortices of psychic energy or prana and, like other meditation practices, yoga nidra is very much concerned with the generation and balancing of pranic energy in order to induce higher states of consciousness. Some yogic scriptures even go so far as to say that prana is consciousness. Although consciousness is beyond mind and mind is beyond the brain, there are links between physical brain processes and pranic flow. The chemical composition of the fluids in and around nerve cells is such that there is an uneven distribution of positively charged sodium and potassium ions across the cell membrane. When the cell fires, there is not only a travelling electrical impulse, but a flow of ions also. This results in a reversal of the cell's electric charge together with a release of energy. Scientists have accumulated a great deal of evidence that ions are the physical vehicle of prana. It would seem that the flow of consciousness in yoga nidra initiates a flow of ions, and hence a flow of pranic energy.
"Awareness of parts of the body... the consciousness should move around the body and keep moving ... as it moves it changes into prana, the vital energy, in the form of a current of energy."
The full significance of this can be appreciated in view of the often stated fact that we use only one tenth of the brain's potential. In opening up the frontiers of the brain, neurologists have found vast, diffuse zones that do not seem to be tied to any single, definable function. Surgical removal of large amounts of brain tissue from these areas has also been carried out without making any apparent difference to the patient's memory or ability to function. One of the main features of the human brain is the existence of many duplicate pathways and circuits, and, except for the speech centre, control centres in one hemisphere have a duplicate in the other. This is why, when some part of the brain is diseased or injured, partial or total replacement of lost functions can occur. It becomes obvious then, that there is a considerable redundancy of function even in those areas which are currently active in most human beings, and an enormous spare capacity as yet untapped.
In this age of parapsychology and Kirlian photography we are just becoming aware of our energy body, pranamaya kosha, and the supernormal capability released in the human brain by the proper direction of psychic energy. It is more than just a vague possibility that much of this dormant potential is connected with the more subtle energy sheaths of the human organism.
In his book 'The Conscious Brain', neurologist Stephen Rose comments:
"Our cranial capacity or cell number may not be so different from the early homo sapiens, but our environments - our forms of society - are very different and hence so too is our consciousness which also means that so too are our brain states. The connectivity, if nothing else, of the brains of twentieth century humans cannot be identical with that which characterized our ancestors."
The systematic passage of awareness through the brain during yoga nidra is inseparable from the flow of both nervous and pranic energy. As well as clearing old pathways, every time one practices yoga nidra this energy flow forges new connections between brain circuits, and lights up the dark, inactive areas of the brain. Yoga nidra is thus a tool for both physical and spiritual evolution, withdrawing our consciousness from its preoccupation with the outer world and bringing many unconscious functions into the light of conscious control. Yogis have long maintained that the process of self realization is one in which the brain is inundated with subtle energy - sahasrara chakra deluged with kundalini shakti. Yoga nidra is one of the most potent means evolved from tantra for the 'rewiring' of the brain that is the prerequisite of this ultimate enlightenment.