As anybody who looks at cable news is aware, America recently has learned a bit about the physiology of the human brain, particularly regarding the distiction between the cerebral cortex and the more primitive brain stem and thalamus regions. Here is a brief discussion of the physiology of Zen, from the website of the dojo I attend:
The correct attitude of mind comes naturally from a deep concentration during zazen on the posture and the breathing.
During zazen the conscious flow of thought from the cerebral cortex is greatly diminished and the thinking brain becomes calm and cool. Blood flows toward the deeper layers of the brain, the thalamus and the hypo-thalamus, and this body-brain becomes more active and developed. The nervous system becomes relaxed while our deeper brain becomes more active. Receptive and attentive in every cell of the body, you learn to think with the body, unconsciously.
During zazen, thoughts, conscious and subconscious, naturally and continuously rise to the surface of our mind. Don't try to stop these thoughts from arising. But at the same time, don't get involved with the thoughts or let them take you away from concentration on posture and breathing. Just let the thoughts pass, like clouds in the sky, neither opposing them nor attaching to them. Shadows pass and vanish. Images arise from the subconscious, then disappear. The brain becomes deeply calm. One arrives at the deep unconscious, beyond thought, to hishiryo consciousness, true purity.
Hishiryo is the unconscious of Zen - universal mind. In Japanese, shiryo is thinking, fushiryo non-thinking. But hishiryo is absolute thinking, beyond thinking and non-thinking. Beyond categories, opposites, contradictions. Beyond all problems of personal consciousness. Our original nature, Buddha nature, the Cosmic unconscious.
When the mind empties and the intellect is calm, peaceful, at rest, nothing obstructs the deep intuitive and unlimited life force that springs up from the depths of our being, that which precedes all thought, the eternal flow of the activity of the Cosmos. Practicing zazen, sitting concentration, without object or goal, you can experience hishiryo and understand mushotoku, the secret and essence of Zen. But this understanding must be beyond that of common sense or intellectual logic. It is direct perception, here and now.
Mushotoku is the attitude of non-profit, of not wanting to gain anything for yourself. It is essential to true Zen practice. Giving without expecting to receive, abandoning everything without fear of losing, observing oneself.
Zen students develop wisdom if they are vigilant in their Zen practice, in their effort to know themselves, to go beyond themselves, to give of themselves without expecting any personal gain. If you abandon all, you will obtain all.
I don't mean to suggest that Terri Schiavo was in a Zen state of mind for 15 years. Her cerebral cortex evidently was missing, meaning that she could not be at all aware of here, now, or anything else. By acknowledging that thoughts arise during zazen, Zen recognizes that the cerebral cortex cannot be entirely shut down. And nobody would suggest that atrophy of any portion of the brain is a positive development. However, it strikes me as at least a little interesting that a spiritual/philosophical/religious practice would have a basis in brain physiology, particularly when that practice arose 2,500 years or so ago, before anybody had much of an idea about how the brain works.