Came across a tremendous reference book that those of us who practice qigong and want to understand more from a physiological standpoint will find interesting. Title is "Zen and the Brain" by James Austin.
He is a physician (neurologist) as well as a Zen practitioner. He goes into depth about some of the science behind meditation. Fascinating and seems as applicable to qigong as it does to Zen practices.
Pricey ($75 and 800 pages) but well worth the price and effort to digest. Added a lot ot my understanding.