WASHINGTON -- Religion has often unintentionally enabled scientific skepticism. The faithful will issue a challenge to science: Ha, you can't explain the development of life, or the moral sense, or the nearly universal persistence of religion. To which the materialist responds: Can too. It is all biology and chemistry, thus disproving your God hypothesis.

To this musty debate, Andrew Newberg, perhaps America's leading expert on the neurological basis of religion, brings a fresh perspective. His new book, "How God Changes Your Brain," co-authored with Mark Robert Waldman, summarizes several years of groundbreaking research on the biological basis of religious experience. And it offers plenty to challenge skeptics and believers alike.

Based on brain imaging studies of Franciscan nuns and Buddhist practitioners, Sikhs and Sufis -- along with everyday people new to meditation -- Newberg asserts that traditional spiritual practices such as prayer and breath control can alter the neural connections of the brain, leading to "long-lasting states of unity, peacefulness and love." He assures the mystically challenged (such as myself) that these neural networks begin to develop quickly -- a matter of weeks in meditation, not decades on a Tibetan mountaintop. And though meditation does not require a belief in God, strong religious belief amplifies its effect on the brain and enhances "social awareness and empathy while subduing destructive feelings and emotions."

Newberg argues that religious belief is often personally and socially advantageous, allowing men and women to "imagine a better future." And he does not contend, as philosophically lazy scientists sometimes do, that a biological propensity toward belief automatically disproves the existence of an object of such belief. "Neuroscience cannot tell you if God does or doesn't exist," Newberg states with appropriate humility. Neurobiology helps explain religion; it does not explain it away.

But Newberg's research offers warnings for the religious as well. Contemplating a loving God strengthens portions of our brain -- particularly the frontal lobes and the anterior cingulate -- where empathy and reason reside. Contemplating a wrathful God empowers the limbic system, which is "filled with aggression and fear." It is a sobering concept: The God we choose to love changes us into his image, whether he exists or not.

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.