An increasing number of people turn to yoga in order to cope with problems related to stress - musculoskeletal tension and pain, insomnia, anxiety, mild mood disorders, and so on - obtaining considerable benefits. Yoga is a complex and articulated practice that acts on the physical, energetic, psychic, and spiritual dimensions of the person. In spite of its millenary tradition, only in recent years scientific studies have been carried out with the aim of understanding and explaining which yoga practices work and how. The aim of this article is to illustrate what the different components of yoga are, on what they act and - supported by recent researches on neuroscience and psychoneuroendocrinoimmunology (PNEI) - to explain which are its mechanisms of action.
Yoga was born in India about 5,000 years ago. We can translate the term yoga with ‘union’ and joining or connecting is actually the purpose of this discipline. To unite body, mind, heart, behaviour, that is to unite the physical dimension with the mental, psychic and emotional dimensions. To unite the innermost and most profound self with the outer self - the one shown in relationships, strongly conditioned by contextual factors. And finally to unite the individual self with the universal Self, as each of us is a piece of a cosmic reality.
When the union between these dimensions is not there, or is lacking, people can manifest discomfort, fatigue, and disorders up to developing conditions of illness of the body, the mind, the psyche or of body, mind and psyche together, as evidenced by recent PNEI studies. Modern western culture spurs productivity and consumption, efficiency and success. With its frenetic rhythms and new means of communication it fills life up with experiences, information, and contacts with multitudes of people. But it suffocates spaces of deep connection with oneself, with other people and the environment, which are fundamental for an authentic well being.
Initially the fatigue, the discomfort, the malaise - resulting from the external demands which exceed the individual energetic resources and from the lack of connection with oneself - are manifested in the form of stress, which can evolve into real pathologies.
Stress is a physiological system activated by an external pressure. To a certain extent it is a fundamental mechanism for ontogenetic and phylogenetic development, but when external pressures are excessive and exceed the personal capacities and resources one has to cope with, the physiological activation instead of being functional becomes pathological (to be precise, it is a distress). In fact, our physiological system of responding to stress has evolved much more slowly compared to the rate of change in the world and it is more adapted to the stimuli and environmental pressures of the primitive world than to that of the modern era. A disproportionate stress activation for long periods of time causes negative effects on the overall health of the organism (as underlined in the Sipnei Conference ‘Knowing the human being in its entirety' - Turin, Italy, 30-31 October 2015). The most evident manifestations of distress concern both the organic level (muscular tension, back pain, cervical pain, gastritis, colitis, headaches, dermatitis, food intolerances, etc.) and the psychic level (difficulty in concentration, insomnia, difficulty in memorizing, anxiety, panic attacks, depressed mood, etc.)
Due to the fact that by choice or circumstances people persist in having unhealthy lifestyles (hectic rhythms of work and life or inactivity through unemployment, a few hours of sleep at night, unhealthy nutrition, excessive exposure to noise, social isolation, etc.) ignoring the signals sent by the body, it can happen that the body and emotions do bypass the mind by directly communicating the discomfort through psychosomatic illnesses, anxiety disorders, mood disorders.
Neuroscience, especially in the last decade, has unveiled that in human organism the stress response is modulated at the cerebral level by the HPA axis (Hypothalamic-Pituitary- Adrenal axis). Faced with continuous stress, HPA responds with a mechanism that leads to increased levels of cortisol (stress and anxiety hormone) and with the production of cytokines (protein molecules which are the main cause of the immune system inflammation). Cortisol and cytokines cause an inflammatory state of the immune system in the body, which gives rise to a series of diseases such as headaches, food intolerances, obesity, depression, and so on, as shown by recent studies on stress and the brain (McEwen, 2012; Sapolsky, 2012; McEven & Morrison, 2013); stress and immune system (Kiecolt-Glaser, 2010); stress, hormones and metabolism (Chorousos, 2012).
Furthermore, if the stress is chronic, the changes also occur at the level of the brain structure: in short the activity and the size of the amygdala increases (the 'fire-raiser' which triggers stress) while the hippocampus and the frontal cortex are reduced (the 'firemen' who defuse the stress responses) thus activating a circular effect. In order to break this vicious circle it is necessary to act holistically and not only on the final symptom or on one of the aspects of the problem.
With specific yoga practices this psychosomatic destructive tendency is efficiantly alleviated thanks to a positive and inverse direction, which is the ‘somatopsychic’ one (Swami Satyananda, 2001).
Many centuries ago the Cartesian dualism stated that res extensa and res cogitans are two ontologically separated substances among which there can be no causal influence. Only in 1948 the western culture has regained a concept of global health, thanks to the constitutional Charter of the World Health Organization (WHO). Since then the concept of global health recognizes the biological, psychological, social dimensions and recently also the spiritual one. However, this holistic conception still struggles to enter into clinical practice.
On the contrary, yoga tradition has always considered the human being as a multidimensional creature formed by five dimensions of existence: physical dimension, energetic dimension, mental dimension, psychic dimension, and spiritual dimension. According to yoga, good health is the result of balanced functionality, connection and interaction among these five different dimensions.
In order to promote the balance between the different dimensions, yoga (if it refers to a method of transmission that has remained faithful to tradition and adopts an integral approach, such as Satyananda Yoga) uses an integrated series of practices belonging to the branches of the Indian yogic tradition: hatha yoga, raja yoga, kundalini yoga, and so on. Each traditional branch emphasizes a particular aspect (corporeal, meditative, energetic perspectives) and uses different practices: physical postures or asanas; practices to control/expand breathing (pranayama); practices to disconnect from the senses or pratyahara; practices to develop awareness and concentration or dharana; practices of deep relaxation or yoga nidra; and practices of meditation or dhyana. The balanced integration of such different practices produces a synergetic effect that develops, strengthens and integrates among them the five dimensions of existence.
Physical dimension: It is the most material and tangible aspect of the human being, it consists of skin, bones, muscles, organs, etc. The health of this dimension is reinforced thanks to the practice of physical postures (asanas) that tone up the muscles, improve the elasticity of the joints, and enhance the functionality of the organs and the main glands. A healthy lifestyle (self-control, self-regulation) also contributes to the health of this dimension.
Energetic dimension: It is the vital energy that rules the biological processes of breathing, digestion, blood circulation, and so on. This energy (prana) is essential for carrying out any psycho-physical activity. If this energy is missing, the physical body ceases to function. The health of the energetic dimension is reinforced thanks to the practice of control/ expansion of breathing or pranayama and to the practices of the previous point as well. Both the body and the mind depend on prana and an excess or deficiency can cause physical or psychic illnesses. By acting on prana with pranayama it is possible to restore a balance and consequently obtain good health.
Mental dimension: It is responsible for sensory activity and it controls motor activity. It receives inputs from the five senses. It is a very instinctual dimension that rules human behaviour by employing an action-reaction mechanism guided by the senses. The mental dimension is nourished by ‘stimuli/impressions/ images’ that come (or that we select and choose) from the external environment or from our psyche. For example, watching bloody movies and violent video games increases anger, aggression, irritation and irritability. The health of the mental dimension is reinforced thanks to the practice of sense control or pratyahara and deep relaxation, in addition to the practices of the previous points.
Psychic dimension: It consists of all the higher functions of the mind, including awareness, judgment, and discernment. It is the dimension that allows one to create a connection between the stimuli/demands of the environment and the inner requests which helps not to react on an instinctual level but to discern and make ethical choices. It is the dimension that distinguishes human beings from animals. The health of the psychic dimension is reinforced thanks to the practice of meditation and the practices of the preceding points.
Spiritual dimension: It is the transcendental dimension that allows one to give a higher meaning to human existence. In most cases this dimension is ignored or little considered and looked after.
Through which neurophysiological mechanisms does yoga promote the physical and psychological dimensions of well being? Neurosciences and neuroimaging techniques (EEG, PET, MRI, etc.), developed in recent decades, start giving some answers to this question. There are several systematic reviews and international scientific researches that have demonstrated the relevant clinical, physiological, emotional, and psychological effects of yoga by measuring biological indicators and images of brain functionality and structures.
In this paper we do not deal with the aspects and effects of the practices related to physical positions or asanas as they are more known and have more evident effects. Whereas we take into consideration the three practices on which most recent scientific studies are focused: deep relaxation, breathing control/expansion, and meditation.
Deep relaxation with inner awareness (called yoga nidra in the Satyananda Yoga method) is a practice that relaxes the mind by relaxing the body. Awareness is directed to different parts of the body (awareness rotation) thus obtaining not only physical relaxation but also the cleaning-up of the peripheral and central nervous network, by inducing the brain to produce alpha, delta, and theta waves (Swami Satyananda, 2001). Such cerebral waves respectively correspond to: the state that precedes sleep; deep sleep; REM sleep. Several studies report that biochemical tests during the practice of deep relaxation show an increase in the level of BDNF (brain- derived neurotrophic factor), vagal tone, GABA (gamma-aminobutyric acid, inhibitory neurotransmitter) while HPA axis is deactivated and cortisol decreases (Janakiramaiah et al., 2000; Kamei et al., 2000; Streeter et al., 2007).
The expansion/control of breathing or pranayama includes balancing techniques that, by means of the breath, enable one to bring into equilibrium the activity of the right and left brain hemispheres. It also enables one to restore the correct alternation of activation between the sympathetic nervous system (excitatory-activating) which generates muscular, nervous, psychological tension, and the parasympathetic nervous system (relaxing-calming) which reduces breathing frequency, blood hypertension, and heart rate. The balance produced by this breathing technique favours the production of wellness neurotransmitters: endorphin, serotonin, dopamine, and oxytocin.
Last but not least, meditation is a technique which increases the synchronization among the areas of the brain, which leads to a better state of self-awareness, ability to focus attention, concentration, clarity of thought. In general, it improves the cognitive activities of learning, creativity, and intuition. Meditation helps to restructure the perception of a traumatic event or situation and, above all, the perception of oneself in relation to such event/situation, its neurophysiological effect being the reduction of cytokines which are the main cause of inflammation of the immune system. Furthermore, taking into consideration the central nervous system, meditation influences the regulation of arterial pressure and of water balance and also acts by increasing well being neurotransmitters such as endorphin, serotonin, dopamine, and oxytocin (Jacobs T. et al., 2011).
Yoga is therefore a holistic system that develops and integrates every dimension of human being. In addition to the well- known effects of improving skeletal muscle function and enhancing cardiovascular and respiratory systems, yoga is also able to modulate the activity of the central nervous system and of the immune system, to promote psychological balance, to increase the resistance to stress and last but not least, it allows one to develop greater resistance and resilience to physical and psychic illnesses.