Studies comparing experienced meditators compared to controls or short-term meditators have demonstrated physiological changes during meditation suggestive of a wakeful hypometabolic state that is characterised by decreased sympathetic nervous activity, important for fight and flight mechanisms, and increased parasympathetic activity, important for relaxation and rest. This wakeful hypometabolic state with parasympathetic dominance has been shown to be qualitatively and quantitatively different from simple rest or sleep.
Sahaja Yoga meditation, for example, a technique that evokes thoughtless awareness on a daily basis, presumably via activation of parasympathetic-limbic pathways, has been shown to reduce autonomic activity in short and long-term practitioners compared to controls.
A series of studies conducted by Prof Rai from the Department of Physiology of the University of Delhi have shown that Sahaja Yoga meditation when compared to a sham meditation elicits a reduction in stress-related physiological parameters than indicate an increase of the parasympathetic nervous system, important for rest and relaxation. This included a reduction in heart, respiratory and pulse rates, of systolic blood pressure, and oxygen metabolism, and of urinary vanilly-mandelic acid (VMA) and increases o skin resistance.
These physiological alterations are indicators of deep parasympathetic activation and therefore physiological relaxation that have been related to stress relief and may have a role in the prevention of stress-related illness, such as respiratory, hypertensive of cardiovascular disease.
In fact, the same physiological effects achieved with Sahaja Yoga meditation in healthy individuals, could also be achieved in patients with epilepsy and with asthma and hypertension after 4 weeks of meditation training, which furthermore were related to the significant reduction of asthma/epilepsy attacks.
A study conducted in Australia by Dr Manocha and colleagues showed that long-term meditators compared to a group of subjects who practiced simple Relaxation showed a reduction in the temperature of their hands during the meditation. This correlates with the subjective feelings of coolness in the hands and on top of the brain that is experienced by SY meditators and has been related to an activation of the parasympathetic-limbic pathway.
Rai, U.C., Seti, S., Singh, S.H., 1988. Some effects of Sahaja Yoga and its role in the prevention of stress disorders. Journal of International Medical Sciences, 19-23.