Phi: A Voyage from the Brain to the Soul
by Giulio Tononi
Pantheon Books, 2012 ($30)

Tononi, a leading researcher on consciousness and sleep at the University of Wisconsin–Madison, imagines Galileo on a Dantesque journey of exploration to discover the fundamental nature of consciousness. His meditation on the meanderings of Galileo, who is accompanied at times by scientists resembling Francis Crick, Alan Turing and Charles Darwin, serves as a vehicle for explaining his own theory that consciousness can be quantified. The brain, Tononi postulates, consists of billions of neurons: think of them as transistorlike elements that represent bits with a particular value. When tallied, they add up to more than the sum of their parts. That increment above and beyond—Tononi calls it “phi”—represents the degree to which any being, whether human or mule, remains conscious.