How do we become aware of things and events in the outside world, and how does the brain control the muscular system and behavior? This book examines the history of Western attempts to explain how messages might be sent from the sense organs to the brain and from the brain to the muscles. It focuses on a construct called animal spirit, which would permeate philosophy and guide physiology and medicine for over two millennia.

The authors' story opens along the Eastern Mediterranean, where they examine how Pre-Socratic philosophers related the soul to air-wind or pneuma. They then trace what...