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the practice of kumbhaka, the brain can be trained to act according to one's demands. One can stop its functions or accelerate them. This is how many yogis have been able to stop the heart for a number of days and revive it again. The heart is not an independent organ; it is controlled by a higher centre in the hypothalamus of the brain. With control of the brain, one can automatically control the coronary behaviour, body temperature, digestive system, and so on. In the advanced stages of kumbhaka the period of breath retention can be extended for long durations until all the vital functions appear to cease. In this way the breath may be suspended for days at a time. Yogis have been buried underground in this nearhibernation state, known as bhu samadhi, for days at a time.
Kevala kumbhaka Spontaneous retention is called kevala kumbhaka, where the breath suspends without any conscious effort on the part of the practitioner. This form of breath suspension is not aided by exhalation and inhalation and is unconditioned by place, time and number. Kevala kumbhaka can happen to anyone, anywhere, any time, even if one does not practise pranayama. There is no risk involved, because this retention is created by a natural state in the body. When kevala kumbhaka occurs, a point of light arises at the mid-eyebrow centre and spreads throughout the space of consciousness. The whole frontal brain becomes illumined, as though it were daybreak, and one emerges from the darkness that is normally seen behind the closed eyes. It has been said in the Hatha Yoga Pradipika (2:73):
प्राणयामोऽयमित्युक्तः स वै केवलकुंभकः। कुंभके केवले सिद्धे रेचपूरकवर्जिते ॥
Perfection of isolated retention is freedom from inhalation and exhalation. This pranayama spoken of is verily kevala kumbhaka.
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