For Newberg, this is not a simple critique of religious fundamentalism -- a phenomenon varied in its beliefs and motivations. It is a criticism of any institution that allies ideology or faith with anger and selfishness. "The enemy is not religion," writes Newberg, "the enemy is anger, hostility, intolerance, separatism, extreme idealism, and prejudicial fear -- be it secular, religious, or political."

Newberg employs a vivid image: two packs of neurological wolves, he says, are found in every brain. One pack is old and powerful, oriented toward survival and anger. The other is comprised of pups -- the newer parts of the brain, more creative and compassionate -- "but they are also neurologically vulnerable and slow when compared to the activity in the emotional parts of the brain." So all human beings are left with a question: Which pack do we feed?

"How God Changes Your Brain" has many revelations -- and a few limitations. In a practical, how-to tone, it predicts "an epiphany that can improve the inner quality of your life. For most Americans, that is what spirituality is about." But if this is what spirituality is all about, it isn't about very much. Mature faith sometimes involves self-sacrifice, not self-actualization; anguish, not comfort. If the primary goal of religion is escape or contentment, there are other, even more practical methods to consider. "I didn't go to religion to make me happy," said C.S. Lewis, "I always knew a bottle of port would do that." The same could be said of psychedelic drugs, which can mimic spiritual ecstasy.

Every religious discussion eventually comes down to the question of truth. Can we escape from the wheel of becoming, or hear God's voice in a wandering prophet, or meet a man once dead? Without such beliefs, religion is mere meditation. Newberg's research shows an amplified influence of religious practices on those who "truly believe." But Newberg himself has difficulty sharing such belief. His research on the varieties of religious experience -- and his scientific understanding that the brain is drawn naturally toward artificial certainties -- leave him skeptical about the capacity of the human mind to accurately perceive "universal or ultimate truth."

Yet, he told me, "To this day, I am still seeking and searching." And that is the most honest kind of science.