SEVERSON: Dr. Newberg argues his experiments with meditators and those who pray doesn't disprove God.

DR. NEWBERG: When I take a brain image of a nun who has the experience of being in the presence of God, what I can tell you is that this is what is going on in their brain when they have that experience. What I can't tell you, just based on imaging studies alone, is whether or not they've actually been able to do that, they've actually been in the presence of God. But I think it raises some very interesting issues and questions for us, as scientists and also as philosophers, to be able to explore where the true reality lies.

SEVERSON: Dr. Michael Baimes is one of Newberg's subjects -- an expert on meditation and stress management.

DR. MICHAEL BAIMES: It's pretty darn interesting to see that when people do this ancient meditation practice, a predictable change in brain function happens.

SEVERSON: Here's how it works. After the subject has meditated, Dr. Newberg injects them with radioactive dye and he takes pictures of their brain. As they get deeper into their meditative state, the colors depicting brain activity change.

DR. NEWBERG: But when the person went into the meditation, what we see is a dramatic decrease over here in this particular orientation area, and this is that particular part that helps us differentiate the self from objects in the world.

SEVERSON: When we meditate and pray, for instance, the part of the brain that helps us orient ourselves and create a sense of self shows less activity, less red -- the brain quiets down.

DR. NEWBERG: What they are perceiving is a sense of being at one with something else, in this case, the idea of being within the presence of God, or finding some way of becoming joined or in union with a sense of God.

SEVERSON: Newberg believes the brain is engineered to allow spiritual experiences. And Professor Persinger in Canada believes that the brain over generations has evolved to what it is today to allow spiritual experiences.

DR. PERSINGER: People are afraid to die. The sense of diminishing, that tremendous terror of losing a sense of self is incapacitating. So I think somewhere in the development of the brain there was a kind of cognitive process that allows people to have minimal anxiety if they just felt that the self, part of brain activity, was tied to a concept that was infinite and lasted forever. If something is infinite and lasts forever, there is no anxiety. And I think that spirituality that comes out of that process has allowed the human being as a group -- as a species -- to survive.

SEVERSON: So is it possible that one day science will be able to prove or disprove God with a certainty? A goal of science perhaps, but for many of the faithful, a waste of time.

PROF. HAUGHT: The conflict is not between science and religion or science and theology, but it's between two belief systems: the belief system that matter is all there is and the belief system that there is something in addition to matter.

DR. NEWBERG: If there is a God, it certainly makes sense that the brain is set up this way, because it would be silly for us to have some fundamental disconnect with the God that created the brain.

SEVERSON: Like other neuroscientists delving into religion, Professor Persinger has taken some heat for his work. He may be more careful now about what he says, but what he says is that science is not threatening religion.

DR. PERSINGER: The fact that we can now understand the brain basis to faith simply tells us that we can understand it more effectively. It doesn't make it go away any more than when you look at the brain and you are seeing a sunset, and it is beautiful. It doesn't take the beauty away, it just allows you to understand more of it.

SEVERSON: So the science continues, and the debate. And the question: "Will the science challenge the faith of the believers or will it simply add to it?"