Taken a head trip lately? Feel like giving the old brain a buzz? The hippies who coined these graphic expressions were referring to the state of 'bum bum', the drug-induced flight of fancy, the fascinating world of LSD or hemp hallucinations. But a generation before the drug culture, Canadian neurosurgeon Wilder Penfield was mind tripping in a way that is even more bizarre. Working with patients who had neurological disorders that made brain probing necessary, Penfield stimulated different parts of the cerebral cortex with minute electrical impulses. These stimulation studies allowed him to demonstrate the existence of pathways that carry information to the brain from various parts of the nervous system. In particular, Penfield was able to identify the different brain regions associated with certain parts of the body. As he moved electrodes to assorted locations on the brain surface, specific parts of the body would twitch as if in answer to a normal command from the brain. At other times, bodily sensations would be aroused exactly as if that organ had been activated by some sense stimulus from the external environment. When the visual or auditory cortex was stimulated, the patient saw light flashes or heard buzzing or musical tones. In this way Penfield was able to map those areas of the brain directly governing sensations and muscular activity in the various limbs and organs.
This area is known as the sensorimotor cortex and as we move across its surface we come to the areas associated with the face, neck, thumb, index finger, middle finger, ring finger, little finger, and so on, down to the toes.
This is where we make the connection between the latest neurosurgery and the meditational technique of yoga nidra, a yogic practice evolved from the most ancient tantric scriptures. Yoga nidra is a systematic method for inducing complete physical, mental and emotional relaxation. The state of yoga nidra is one of relaxation so deep that we seem to be asleep to the outside world. If you have ever practiced this technique, then you'll recognize the signposts on the sensorimotor cortex as precisely those parts of the body through which your awareness passes during the 'rotation of consciousness'.
"Rotation of awareness by taking a trip through the body... Right hand thumb, second finger, third finger, fourth finger, fifth finger, palm, wrist, elbow, shoulder, armpit, right waist, right thigh, kneecap, calf muscle, ankle, heel, sole, big toe, second toe, third toe, fourth toe, fifth toe..."
Consciousness is no incorporeal phantasm, but a fine mesh that encompasses the body as surely as the gossamer glory of the spider's web is spun from her abdomen. The brain is the physical mediator of consciousness, linking mind, body and emotions into one harmonious unit. The neurosurgeon affects the body by stimulating the brain. The practitioner of yoga nidra begins at the other end of the nerve pathway by heightening awareness of the body. The progressive movement of awareness through the parts of the body not only brings physical relaxation, but also relaxes the sensorimotor cortex of the brain. If we begin at the toes and end with the tongue, we clear all the nerve pathways to the brain, both those governing physical activity and those concerned with incoming information. At the same time we make a total run of the brain surface from inside out. In this way, yoga nidra relaxes the mind by using the mind to relax the body.
In some forms of yoga nidra the rotation of consciousness does begin at the toes, but it is more common to start with the right hand thumb. Just as it is easier to travel along a much used highway than a rarely trodden cart track, so the more often a nerve impulse travels along a particular pathway the easier it is to activate that pathway in the future. Because the connections with the hands are frequently used, during yoga nidra it is relatively easy to develop mental awareness of the hands. The hands are also among the most sensitive of man's organs of action, with a greater number of nerve endings in the palms and fingers to transmit messages to the brain. For these reasons most people find it easier to develop awareness of the hands than most other parts of the body. This is especially true for beginners in yoga nidra. When you refer to the motor homunculus, you will also note the disproportionately large amount of brain space concerned with the hands and fingers. This region is almost as large as for the entire remainder of the body from the wrist to the toes ! Beginning with the hands is not only easier, but also affects a huge area of the brain, giving an initial impetus to the process of relaxation.
Scattered through the periphery of the body are numerous cells which are sensitive not only to normal electrical nerve impulses, but also to mechanical stimulation such as pressure or touch, temperature and so on. Although we do not usually think of them as such, these cells (proprioceptors) are actually tiny sense organs that are continually gathering information from all parts of the body and sending it to specified sites deep in the brain. Neurologists have located these focal points, the most important of which are those concerned with food and water intake, heat and cold, pain and pleasure.
Once again it is impossible to ignore the connection between the discoveries made by today's brain explorers and those made by the seers who long ago evolved the practice of yoga nidra. After relaxation of the sensorimotor surface of the brain, the practice of yoga nidra moves our attention from the separate outlying areas of the body to arousal of feelings that seem to emanate from the core of our organism yet bathe the body as a whole. As we awaken the sensations of heat and cold, pain and pleasure, we stimulate those centres of the brain responsible for maintaining harmony between our inner and outer environments. Each of these centres has its reciprocal for balancing our basic drives, and the pairing of these sensations in yoga nidra helps this balance as well as bringing normally unconscious functions under control.
Characteristically the first of these feelings to be awakened is that of heaviness... "You are feeling so heavy that you are sinking into the floor." Although this sensation of heaviness has not yet been localized in the brain, it is a whole body sensation that is a product of deep muscular relaxation. At the same time, if relaxation is not complete, awakening the feeling of heaviness acts as a command from the brain encouraging the muscles to 'let go', to drop their burden of upholding the body. The weight of the body is then deposited on the floor, giving the impression that we are sinking through the surface on which we are lying.
As the feeling of heaviness intensifies, so it is superseded by a sensation of lightness... "Awaken a sensation of lightness and weightlessness in all parts of the body... Your body feels so light... that it seems to be floating away from the floor."
To induce a sensation of lightness is not an arbitrary choice but a direct outcome of the way the brain functions. When a nerve cell (neurone) fires, that is, when it transmits an impulse, this is registered in the brain. However, if the cell continues to fire for some time, the message is no longer acknowledged by the brain, it becomes a constant feature to the brain's environment as it were. You can verify this particularly with smell. When you first enter a room where incense has been burning, you are very much aware of the perfume. However, after you have been in the room for some time, you no longer notice the incense. Researchers have called this phenomenon habituation. The brain becomes habituated, accustomed to the stimulus, and ceases to register it as important.
It would seem that this is what happens during yoga nidra. While focusing awareness on the sensation of heaviness throughout the body, the nerves fire a volley of impulses to the brain. After some time, however, the brain ignores these impulses, it breaks the connection with the body. The feeling of lightness then arises spontaneously and our awareness floats free of its physical vehicle. Now, rather than physical sensations shaping our consciousness, our consciousness can determine what will be felt by the body.
Stimulation of these homeostatic mechanisms moves us right into the midbrain, and brings greater awareness of the region known as the hypothalamus. This region is the primary regulator of the autonomic (involuntary) nervous system which is intimately bound up with the glands and emotions. Electrical stimulation of certain parts of the hypothalamus gives rise to the emotions of rage, aggression and fear. Most of us find these negative feelings much stronger and harder to control than positive emotions. Nevertheless, in advanced yoga nidra we are asked to submit voluntarily to these threatening emotions, while still maintaining a state of deep relaxation.
This brings into simultaneous operation nerve circuits that, under normal circumstances, never operate at the same time. Thus a new circuit is established incorporating these two apparently irreconcilable states in such a way that relaxation predominates.
In. this way, yoga nidra allows us to experience mental control of our emotions and senses (at least temporarily) and establishes fresh neuronal patterns that we can fall back on to carry this control into our normal waking lives.
The end state of the practice of yoga nidra is 'psychic sleep' or sleep in a state of inner awareness. It is a state on the borderline between sleep and wakefulness that allows contact with the subconscious and unconscious mind. Next month we will discuss this state in terms of its psychological and spiritual implications.