30/11/2019
The Psycho-Neuro-Physiology of Meditation
Introduction
Eastern religious and secular groups, such as the Buddhists, Taoists, and the Indian Yogis have practiced meditation throughout history in order to achieve certain mental and physical ends; these include muscular relaxation and "clearing" the mind, as well as the more esoteric union with nature or God. For these practitioners, meditation further serves to reduce negative tensions in both conscious and subconscious realms, and facilitates the integration of an individual into her / his physical, social and psychological environment.
Although diverse types of meditation exist, all meditative techniques attempt to focus attention in a non-analytical way without discursive or discriminating thought. By muting the analytical, reasoning functions of the mind one achieves a sort of non-discriminatory or relaxed awareness.
Eastern philosophers have known for centuries that the practice of meditation allows the human mind to transcend thinking processes into a state of thoughtless awareness. Given the complicated structure of the brain, with its multitude of neurons, infinite possibilities of synaptic connections, and numerous chemical mediators, this transcendent state may one day have a physiological explanation. Indeed, increasing scientific and popular interest in the Eastern practices of meditation has accumulated significant empirical evidence about the physiological modifications produced by the practice of meditation; these include metabolic, autonomic, encephalographic, and psychological effects. These scientific studies clearly show that the meditative state of awareness is distinct from a normal everyday awareness bound by logic and reason, and validate the traditional Eastern belief that mental function has a direct implication on physical function.
The Physiology of Meditation
A review of the scientific literature on meditation reveals that it can reduce stress and anxiety, enhance motor reflexes, increase motor control, increase exercise tolerance, sharpen perceptions, increase awareness, improve concentration, maintain health, provide a general positive outlook on life, and foster the development of a sense of personal meaning in the world.
In general, meditation produces a reduction in multiple biological systems, resulting in a state of relaxation. These changes are, in most studies, significantly different between meditating and non-meditating groups. Benson (1975) argues that this physiological response pattern is not unique to meditation per se, but is common to any passive relaxation procedure. Although some studies have found no physiological or overt behavioral differences between meditation and other relaxation techniques, it is significant to note that subjects report meditational experiences as more profound and enjoyable than their comparative control groups. These subjective differences may have critical relevance from a clinical or research perspective.
Scientific studies reveal that meditation produces a specific physiological response pattern that involves various biological systems. The mechanisms most frequently suggested to mediate or produce meditative effects include metabolic, autonomic, endocrine, neurological, and psychological observations. Precisely how these mechanisms are involved in producing the final pattern of responses is yet unclear. The vast complexity of biological organization indicates that the physiological response to meditation probably occurs on a multidimensional, interactive basis.
Meditation and Metabolism
Mental states can markedly alter physiologic function. For example, stressful situations result in a hyper-metabolic state, with increased oxygen consumption, heart rate, and blood pressure. In contrast, the majority of scientific studies show meditation to be a wakeful state accompanied by a decreased metabolism. This generalized decrease in body metabolism manifests with a decreased breathing pattern, decreased heart rate, and decreased blood pressure. There is also a marked decrease in the level of oxygen utilization and carbon dioxide elimination by muscle. These findings have been verified by an impressive number of studies.
Oxygen consumption is generally regarded as a reliable index of physical activity and arousal. For example, exercise requires an increased consumption of oxygen by muscle. During this metabolic process, oxygen is converted to carbon dioxide, which is eliminated by the lungs. If the body is starved of oxygen, reduced oxygen consumption does not lead to a parallel reduction in carbon dioxide elimination because the cells continue to metabolize the remaining oxygen in the blood. Therefore, oxygen starvation causes a decrease in the concentration of oxygen and an increase in the concentration of carbon dioxide in arterial blood. The relative amount of oxygen and carbon dioxide in the blood is called the respiratory quotient. During normal respiratory processes, this quotient remains constant; in abnormal respiratory situations, however, the reduction in available oxygen and increase in carbon dioxide changes the quotient. Wallace et al (1971) found that during the practice of meditation the amount of carbon dioxide elimination drops in proportion to the amount of oxygen consumed; therefore, the respiratory quotient remains constant. In conclusion, the metabolic changes of meditation arise from a natural reduction in metabolic activity at the cellular level, not from a forced reduction of breathing.
Circulation, especially in muscle and brain, is closely related to the metabolic requirements of tissues, and is very sensitive and consistent in its response to behavior. A study by Jevning et al (1996) illustrates an interesting redistribution in the blood flow of meditators. Blood flow to the kidneys and liver declined in practitioners, with a surprising increase in cardiac output. These changes of blood flow imply a marked redistribution of blood flow during meditation. It is hypothesized that most of the distributed circulation must be to the brain, a hypothesis that has been supported by direct estimation of increased relative cerebral blood flow. The redistribution of blood flow with an increase in cardiac output has interesting significance for the pattern of metabolic changes elicited by meditation; although the response to meditation is hypo-metabolic overall, it appears likely that there is a concomitant increase in the metabolism of certain tissues.
Meditation and the Autonomic Nervous System
Skin resistance to electrical current provides a measure of autonomic nervous system reactivity. Several groups have reported an increase in the skin resistance of meditators. Increase in skin resistance indicates a decrease in skin conduction and a reduction in its fluctuations. It is well established that skin resistance decreases in states of anxiety or stress, and increases during relaxation. The large increases in skin resistance of meditators found in these studies are impressive.
Galvanic skin response (GSR), was used to measure recovery from stress; a study by Orme-Johnson (1973) showed that meditators recovered from stress more quickly than non-meditators. Specifically, habituation of the GSR to stress was faster for meditators than for controls, and meditators made fewer multiple responses during habituation, indicating greater stability in response to stress. In other experiments, meditators produced fewer spontaneous GSR than their non-meditating controls, both during and while out of meditation. Spontaneous GSR is defined as spontaneous fluctuations in skin resistance and the frequency of spontaneous GSR defines the lability of an individual to stress. For example, the frequency rises with anger, fear, and increased epinephrine and norepinephrine blood levels. Those individuals with lower frequencies of spontaneous GSR exhibit more effective behavior in a number of stressful situations, are less impulsive on motor tasks, and have quicker perceptions. Rapid GSR habituation and low levels of spontaneous GSR are reported in the literature to be correlated with physiological and behavioral characteristics associated with good mental health. Therefore, meditation benefits practitioners by decreasing the frequency of spontaneous GSR. In general, these studies indicate that meditators possess a more adaptive pattern of stress response than controls.
On another level, meditation produces specific neural activation patterns involving decreased limbic arousal in the brain (Schwartz 1975). Since the limbic system contains the hypothalamus, which controls the autonomic nervous system, reduction in limbic arousal may explain how meditation reduces stress and increases autonomic stability to stress. Ultimately, meditation strengthens and enhances the ability to cope with stress.
Meditation and the Endocrine System
Based upon the metabolic characteristics of meditation and the subjective reports of meditators, several studies were initiated in order to ascertain whether the blood levels of stress-related chemicals decreased during this practice. A number of endocrine reactions have been identified in the meditative response pattern, including reduced blood levels of lactate, cortisol and epinephrine. The reductions in these blood chemicals denote a state of decreased tension and anxiety. For example, the infusion of lactate can produce anxiety symptoms in normal subjects; the decrease in lactate concentration during and after meditation may explain the subjective feelings of wakeful relaxation. These studies further reveal that the reduction in stress-related chemicals persists into the post-meditation period. The most likely explanation of these results seems to be that the long-term practice of meditation develops a psycho-physiological response of persistent decreased endocrine activity, thereby reducing sensitivity to stress. It has been recently demonstrated that meditation reduces sympathetic adrenergic receptor sensitivity, producing a decreased response to stressful situations (Mills et al 1990).
Certain studies have also found unique patterns of blood hormone levels and blood flow to a number of organs including the brain. Increased levels of gamma aminobutyric acid (GABA), melatonin, and dehydro-epiandrosterone sulfate (DHEA-S) have been reported. Meditation is associated with changes in the secretion and release of several pituitary hormones. The hormonal changes induced by meditation mimic the effects of the inhibitory neurotransmitter GABA. It is hypothesized that meditation produces its anxiolytic effects by promoting GABA action in specific areas of the brain, via a mechanism similar to the effects of synthetic anxiolytic and tranquilizing agents. Melatonin has been associated with a variety of biologic functions important in maintaining health and preventing disease, and the serum level of the adrenal androgen DHEA-S has also been associated with measures of health and stress. For example, increased levels of DHEA-S have been connected with a reduction in age-related disorders such as cardiovascular diseases and breast cancer. DHEA-S excretion also decreases in times of stress; since meditators have been shown to have an attenuated autonomic response to stressors, the higher DHEA-S levels found in during meditation may provide protection against stressor stimulation of the adrenal gland.
That the physical effects of meditation persist after the meditation period itself has ended is demonstrated by the fact that hypertension can be effectively controlled by meditation alone without the use of anti-hypertensive drugs. Meditation has also been shown to have long-term effects on the endocrine system (Werner et al 1986). Another recent study reveals that meditators have a general increased exercise tolerance and maximal cardiac workload as compared to non-meditators.
Meditation and the Central Nervous System
Interestingly, the practice of meditation decreases muscle reflex time. Significant reductions in reflex time provides possible neurological evidence for the improved motor performance skills reported in other studies on meditation, such as higher performance on perceptual-motor speed tests, static motor performance tests, and physical task tests of balance. Meditation may somehow accelerate neural conduction or augment the release of neurotransmitters, thereby decreasing synaptic time, resulting in a change in muscle firing threshold and pattern. These findings appear consistent with the development of a heightened sensitivity of the human central nervous system and suggest a neural mechanism underlying the motor performance improvements of those who meditate.
Studies of brain physiology during meditation have most frequently employed the electroencephalograph (EEG) for the measurement of brain wave electrical activity. With most meditative practices the EEG patterns exhibit a slowing and synchronization of brain waves, with alpha waves predominating. More advanced practitioners of meditation demonstrate an even greater slowing of their brain waves, with the possible emergence of theta wave patterns. These patterns are consistent with deep relaxation. Alpha rhythm is the classical EEG correlate for a state of relaxed wakefulness, also described as relaxed vigilance. Indeed, emotional tension attenuates or blocks the alpha rhythm. Theta activity is associated with emotional processes and indicates relative maturity of the mechanisms linking the cortex, the thalamus and the hypothalamus; theta rhythm also occurs during a state of maximal awareness. Apparently, an alpha wave pattern is most conducive to creativity and to the assimilation of new concepts, while the theta response seems to be a stage at which the mind is capable of deep insights and intuition. It is significant to note that practiced meditators can continue to exhibit alpha and theta waves after the meditation period has ended.
One study compared different types of breathing during meditation and discovered that diaphragmatic, or deep breathing was associated more with an EEG alpha response than thoracic breathing. Meditative traditions place a great deal of importance on breathing; indeed, breath becomes the object of awareness in most methods.
The cortex of the brain is popularly believed to consist of two halves, the left and right hemispheres. Although simplistic, activities such as speech, logical thinking, analysis, sense of time are thought to function in the left hemisphere, while the ability to recognize faces and comprehend maps is thought to function in the right hemisphere. On the physiological level, it has been demonstrated that the two hemispheres of the cortex are specialized for different modes of information processing; the left hemisphere operates primarily in a verbal, intellectual, sequential mode, while the right hemisphere operates primarily in a spatial oriented mode. The right hemisphere concerns space more than time, and intuition more than logic or language. The right lobe also houses the purported center of motor skills connected with spatial awareness. Most people, under scientific measurement, demonstrate a marked preponderance towards left hemisphere usage.
Several authors hypothesize that systems of meditation alter consciousness by inhibiting cognitive functions associated with the dominant or left cortical hemisphere. Ornstein states that meditation "turns off" the verbal, linear, analytic style of information processing associated with the normal waking state. By inhibiting the left cortical hemisphere, the sense of time and logic no longer dominate consciousness during meditation. In association with this repression of the left hemisphere occurs a hypothesized shift to the right hemispheric manner of experience, described as holistic, receptive, and beyond language or logic. Since it is nonlinear, the right cortical hemisphere devalues the concept of cause and effect. Davidson (1976) argues that meditation leads to the development of right hemisphere associated abilities. This assertion has been verified by several research projects; meditators show faster reaction times on simple visual reaction time tasks, thus demonstrating that meditation facilitates right hemisphere specific abilities. Furthermore, EEG alpha and theta wave coherence is most marked in the right cortical hemisphere during the practice of meditation.
Other analyses suggest the existence of synchronization patterns both between corresponding areas of the two cortical hemispheres and within individual hemispheres. Some tests indicate that the EEG activation patterns in meditators display a greater flexibility in shifting between hemispheres in response to the demands of specific tasks; this represents an integration of the left and right hemispheres of the brain, synchronizing the logical with the intuitive.
Meditation and Psychology
The research literature on meditation suggests that practitioners experience subjective phenomena, such as pronounced feelings of "self-transcendence," "felt meaning in the world," "a heightened sense of connectedness with the world," and "a sense of purpose and meaningfulness". These subjective experiences involve radically revised perceptions of self and the external world. Mood changes include happiness, freedom from anxiety, content with self, and greater vitality. Other articles also suggest that meditators gain enhanced confidence, a sense of self-control, empathy, and self-actualization. Several investigators conclude that the practice of meditation improves cognitive task performance, increases mental concentration, and reduces susceptibility to stress. As described above, many researchers report that meditation reduces the biological components of anxiety. In general, meditation promotes psychological health.
Other psychological consequences of meditation include decreased anger aroused in high-anger situations and an increased concentration for mental as well as physical tasks. Indeed, it has been found that experienced meditators had significantly increased attentional absorption and that attentional absorption increased as the length of meditation experience increased. Long-term meditators appear to possess a more developed ability to voluntarily control attention.
Conclusion
The concept of meditation arose within the philosophical framework of Eastern religious and spiritual disciplines. These traditions practice meditative techniques in order to maintain physical health, induce altered states of consciousness, develop insight, achieve peace, and gain spiritual strength as well as spiritual purification. In these ways, meditation modifies the perception of the world and promotes a more unified conception of self, nature, and humanity. Formal meditation refers to the practice of meditation at specific times, in a specific place and posture. Informal meditation, however, requires no specifications, but can be practiced at any time and place.
Ultimately, the greatest achievement of meditation is simultaneous refinement of mind and body. The special training of consciousness effectively regulates every biological system of the body as well as its technical and mechanical facilities. Cultivation of the mind leads to cultivation of the body, leading to further cultivation of the mind and so on, eventually attaining an exquisite level of cooperation and coordination between the two.
