Belief is not as invisible as we might think. Neuroscientist Andrew Newberg has scanned the brains of nuns, monks, and fundamentalist Christians during prayer and other transcendent religious moments. He's invited Pentocostal preachers into his lab to speak in tongues (which is when he found out that his lab assistant also possessed the power of glossalalia). Whether God exists or not, the human brain certainly seems to be "wired" to engage in mystical relationships with the cosmos.
Even Daniel Dennett, known alongside Sam Harris, Richard Dawkins, and the late Christopher Hitchens as one of the "Four Horsemen of Atheism" has his spiritual moments -- but only in the blandest sense of the word. The secular benefits of spiritual practice are clear. "Of course we can change our brains through meditation," he says. He speculates that it's similar to sleep in that it can restore balance, get rid of tension and calm the system so that it can confront the world anew.