When I was in junior high school, I had a giant of a man for a PE teacher - his name was Mr. Geist and he was married to an English teacher whose name was... Mrs. Geist. He was in his late 50s at the time and he was the gentlest giant you could ever meet. One day, while instructing archery and after calling "bows down", an arrow flew out on the field and impaled his hand as he was walking toward the targets. Looking at us, a little irritated, he pointed at his skewered hand and said clearly and forcefully "Now, THIS is why when I tell you 'bows down", I mean BOWS DOWN!"
There are many other stories to tell, but one of the tidbits he passed on to us stuck with me. I don't remember the context, but in some discussion with students Mr. Geist casually mentioned that a key to relaxation and slowing the heart rate was controlled and prolonged exhalation.
Once when I was in the laboratory in Kyoto,... I observed a curious phenomenon. At the time, I was performing pharmacology exeriments on cats and was monitoring the field potentials of several larger groups of nerve cells throughout the brain. As I looked at all these discharges, I became puzzled. Every few seconds, the firing waxed, then waned. The resulting wave forms were a series of peaks and troughs. Why did they follow a regular rhythm? Why were the rhythmical firings at sites higher in the limbic system synchronous with those of other cell groups down in the brain stem? Further observation provided a simple explanation. Every time the cat breathed in, its nerve cells fired much more. Every time the cat breathed out, these discharges slacked off. Breathing out was quieting the brain. Lesser degrees of this same phenomenon have since been observed in the human amygdala and hippocampus.
...When an awake animal breathes in, many of its amygdala nerve cells discharge. In contrast, when exhaling, only half that number fire. Fewer still fire when the animal enters quiet sleep or REM sleep. Such findings reemphasize in important point cited back in chapter 22. Not only does meditation affect breathing; breathing can go on to influence meditative experience. More specifically, expiration quiets down the firing of the central amygdala.
- Zen and the Brain: Toward an Understanding of Meditation and Consciousness