Here's two email messages that I got from a woman who practices Kriya Yoga and has had some pretty amazing yogic experiences. Yet she considers that the experiences are entirely based on the body/brain.
The book referred to in the first message is Yogananda's "Autobiography of a Yogi." Way back when (early 70's probably) I read the book and marveled at the far-out descriptions of mystical goings-on.
Yes, unfortunately, a lot of people believed what Yogananda experienced was true. This is what helped build the organization he founded in California... The Self Realization Fellowship which later was incorporated as a church for tax purposes. I read part of the book when I was in my 20"s; now I'm 52 (an old gal). Back then I believed what was written.
About a year and a half ago I picked up the book and starting reading some of it and had to close the book realizing how it resembled a fantasy story (Lord of The Rings came to mind for some reason). Oh yes, I believe he did experience visions as this is what the practice of kriya yoga meditation will do. However, I think his religious fanaticism and devotion to a being called God, which does not exist, set the stage for these far out experiences.
My experiences with kriya yoga had me seeing golden light, wheels of light in red, yellow, orange, blue and violet (Oh yeah, gotta love this one, my guru says these are the chakras coming into view, keep placing OM at each chakra with the upward breath as we need to cleanse the chakras).
Then later on in the practice I kept seeing a full white moon, after that came the bursting forth of many suns while practicing yoni mudra. Which after a while my guru told me it was showing me how creation forms, a bursting forth of energy and light.
Anyway, with this practice I have found no god entity, no existence of heaven or hell and certainly no soul or spirit residing in the human body. Only matter, energy, and consciousness in other words, body, and brain.
Paramahansa Yogananda proclaimed to have come to the West to spread the teachings of an ancient yogic science called Kriya Yoga. In Chapter 26 of his book "Autobiography Of A Yogi" entitled "The Science Of Kriya Yoga" 3rd paragraph it is written:
Kriya Yoga is a simple psychophysiological method whereby, the blood is decarbonated and recharged with oxygen. Atoms of this extra oxygen are transmitted into life current to rejuvenate the brain and spinal centers. By stopping the accumulation of venous blood the yogi is able to lessen or prevent the decay of tissues. The advanced yogi transmutes his cells into energy. He then goes on to state Elijah, Jesus, Kabir, and other prophets used kriya or some similar method to cause their bodies to materialize and dematerialize at will.
Sound far fetched? You bet!
I am initiated into kriya yoga and have been practicing this tantric meditation technique for a while now. With this method one is instructed on where and how to locate the 7 chakras which in reality are the lumbar points in the spine. The 7th chakra is not part of the spine as it is the crown/ top of the head. The kriyaban is instructed in various mudras and in pranayama. Many of which come from the Hatha Yoga Pradipika. Such as the correct asana for practicing kriya meditation, kechari, the mahamudra, shambhavi mudra.
The practice of kriya yoga pranayam, whereby one draws the breath upwards mentally touching each of the chakras (spinal centers) then resting in the kumbhaka state produced visions of wheels of light in red, yellow, orange, blue, and violet. These I was told by my guru are the chakras coming into view. Keep placing OM at each chakra as we need to cleanse the karmic seeds from our chakra database. (Okaaay,)
Then suddenly, one day my entire head was flooded with a golden light and the internal sounds of Omkar resounded within. Such peace, joy and bliss. I was sure I had found the god within! Turns out it was all brought about by the practice of pranayama. Breath and mind are linked!
Next came all the sensations of energy (prana) moving up and down the spine. The body would gently sway like the motion of a pendulum on a clock. The spine felt like it was tingling and vibrating. I saw a pure white orb like the full moon on several occasions. Wow! such a great spiritual vision, so I thought. Then came the bursting forth of many suns while practicing yoni mudra.
According to my guru, this mudra was showing me creation, the bursting forth of energy and light even though this mudra is manipulated by the one practicing it. One takes a deep inhalation, retains it, thumbs close the ears, index fingers cover closed eyelids, middle fingers close the nostrils while the ring fingers and pinkies are placed at the corners of the mouth.
To sum up everything, all the visions are just a product of practicing pranayama (breathing technique). The energy flows of prana are also produced by practicing pranayama. Breath and mind are definitely linked. Nothing mystical.
The sense that all is one or everything is one also arises from doing this practice. However, the feeling of being one with everything is impermanent.