With a brain scanner, a University of Pennsylvania scientist eavesdrops on the mind of a meditating Buddhist monk, sifting through the activity of neurons for evidence of spiritual grace.

Using skin sensors, a University of California, San Diego, researcher measures the power of holy words by testing how synapses respond to religious texts.A neuropsychiatrist at New York University assesses the effects of prayer. Another scientist measures brain function among those who report feelings of a union with God and the cosmos.

Marshaling high-speed medical imaging devices, radioactive tracers and new theories of mental activity, these researchers are probing the neurobiology of religious experience in search of a scientific perspective on the divine.

Where in the scientific cosmology of the mind does spiritual activity - the intangible essence of faith and moral sensibility - fit?

Is there a biochemistry of belief?

"Does religion require a soul? Does science allow one?" asked UC San Diego theologian Michael J. McClymond, who recently organized a symposium to bring together neuroscientists and religious thinkers.

Such questions - long the province of theologians and philosophers - arise anew from a remarkable flowering in the study of the biology of behavior.

They reflect an upsurge of scientific interest in spirituality at a time when the largest percentage of Americans in a decade say they never doubt the existence of God, say they value daily prayer and believe in divine miracles.

But such experiments also pose an unusual challenge to conventional religious thinking.

"If we recognize the brain does all the things that we (traditionally) attributed to the soul, then God must have some way of interacting with human brains," said Nancey Murphy, a philosopher of science and religion at the Fuller Seminary in Pasadena, Calif.

Consequently, Murphy said, this new wave of research can be seen as an attempt to give "an account of divine action - one of the most difficult and pressing theological questions now - how God acts in the brain."

Many leading brain researchers are confident that science will be able to explain everything about the higher functions of the human brain, including its capacity for spirituality and, by extension, religious belief.

To many researchers, spirituality is just one of several powerful mental states generated by this unique network of interlaced neurons, synapses and glial cells.

"Mind has properties - self-consciousness, wonder, emotion and reason - that make it seem more than merely material," said Arbib at USC.

"Yet I argue that all of this can be explained eventually by the physical properties of the brain. In 20 years, we will understand what happens in the brain when people have religious experiences."