The essential feature which runs throughout the history and prehistory of the study of consciousness is the polarity in every aspect of man's personality: left and right, good and bad, male and female, right and wrong, positive and negative, demonic and angelic, Introvert and extrovert. This can also be seen on the physical level as the brain contains two parts called the left and right hemispheres which are connected by a type of conducting bridge called the corpus collosum.
The left hemisphere controls the right side of the body (in most cases) and it specialises in analytical, logical thinking, especially in mathematical functions. It processes information sequentially and its mode of operation is primarily linear, in the way that mathematics and language are linear- one thing proceeding from another in a logical sequence.
The right hemisphere controls the left side of the body and seems to specialise in holistic mentation. Its language ability is limited, being primarily responsible for orientation in space, artistic endeavour, crafts, the body image. It processes information more diffusely than the left hemisphere. If the left hemisphere Can be called analytical and sequential in its operation, then the right can be called holistic, relational, and more simultaneous in its mode of operation.
The left hemisphere has been called at various times: lineal, light side of the brain, male, intellectual. The right hemisphere has been called non-lineal, dark aide, female, intuitive. It is for this reason that the right side of the body (governed by the left hemisphere) has been called by many schools of thought, both in the orient and the Occident, the male side, and the left side of the body, the female side; the right side, the light side and the left side, the dark side. It can be observed, if we care to study the classical literature of the world, that the wider the gap between the two poles of an individual's awareness, the greater is his mental and emotional disharmony. Take the split personality, for example, these people cannot reconcile the two seemingly opposite aspects of their personality. In contrast, consider those who achieve this harmonisation, who are able to merge the dark with the light, the positive with the negative, the female with the male aspects of their personalities. These people are emotionally, mentally and psychically stable. Merging or reconciling is important in order to realise that opposites are complementary.
How is this balancing, harmonising and merging to be accomplished? Through swara yoga, the method of attaining union between the different aspects of our consciousness, our personality, through the medium of the breath. You may ask yourself, 'But what has breath got to do with my mind, with my way of thinking and acting or with my state of consciousness?' The answer is that it has a great relevance, possibly much more than you could ever have imagined. It is said that swara, the breath, is the link between the internal world, the mind and the consciousness of man, and the external world of the senses. He who has mastery of the breath, has mastery of the different aspects of his consciousness- his personality, mind, emotions and health.
In yogic physiology, left nostril breathing is associated with the parasympathetic nervous system which is active when one is calm and relaxed. It releases a chemical called acetylcholine which induces a state of well being, pleasure, etc. Activation of the parasympathetic nervous system tends to slow the heart beat and cause blood vessels to dilate and relax (with the exception of the coronary vessels where it causes constriction). It causes the pupils of the eyes to constrict. It causes salivary secretions as well as secretions Of sweat and gastric juices. Most interesting of all, parasympathetic activation is associated with an increased degree of sensitivity to telepathy. Researchers found repeatedly that pranayama, apart from inducing a more healthy feeling in the individual, actually increases telepathic and other higher mental functions. They have also shown that if you practise concentration or meditation you will have greater success if you precede it with pranayama.
The sympathetic nervous system is particularly active when we experience strong emotions or when we are engaged in some physical work. It is the other part of the autonomic nervous system, activated by adrenaline secretions in the body. Its functions are generally opposite but complementary to those of the parasympathetic nervous system. The sympathetic accelerates the heart, causes blood vessels to constrict, the coronary vessels and the pupils to dilate. It inhibits secretions of the salivary glands, sweat glands and gastric juices. It also causes inhibition of the gastrointestinal tract. These functions are precisely those which occur with right nostril breathing. It has also been demonstrated that oxygen ions (02) slow respiration, lower blood pressure, increase mental alertness and feelings of well being, and also increase the action of cilia (hairs) in the respiratory passages. These correspond to activation of the parasympathetic nervous system whereas ions of carbon dioxide (C02) induce activation of the sympathetic nervous system.
In swara yoga, prana or energy is circulated in the body through a system of nadis or pathways, of which the three most important are known as ida, pingala and sushumna. These three flow up the spine, ida and pingala coiling around sushumna at the centre. Ida terminates at the upper opening of the left nostril, pingala at the upper opening of the right nostril, and sushumna at sahasrara chakra at the crown of the head.
In the ancient yogic texts these nadis receive much attention. Different states are said to be experienced when one or the other of them is active, and these states are clearly described. Ida is known as the lunar nadi because its activation produces calmness and a feeling of well being. Traditionally, the colour is blue. Pingala is known as the solar nadi because its qualities are heat and dynamism. Its colour is red. Sushumna is the synthesis or spiritual nadi which becomes active when ida and pingala are balanced. Its colour is gold.
There is a direct correspondence between the states associated with the activation of ida, pingala and sushumna nadis and the parasympathetic, sympathetic and central nervous systems respectively. When we breathe in through the left nostril, ida nadi or the parasympathetic nervous system as well as the right hemisphere of the brain are stimulated. When we breathe in through the right nostril, pingala nadi or the sympathetic nervous system as well as the left hemisphere of the brain are stimulated. When the breath is equalised through both nostrils, the brain and the sympathetic and parasympathetic systems are balanced. Then a state of equilibrium is achieved in the central nervous system and the state of meditation dawns as the sushumna awakens.