Barbara Bradley Hagerty is the author of “Fingerprint of God: The Search for the Science of Spirituality.”

As mystical experiences go, Barbara Bradley Hagerty’s transcendent moment was not the kind that launches a new world religion. Still, it changed her forever.

The day was June 10, 1995. Hagerty, religion reporter for National Public Radio, was interviewing a terminally ill melanoma patient, Kathy, whose sunny outlook and trust in Jesus seemed to have prolonged her life, inexplicably, for years.

Then, as they talked, “I felt the hair on the back of my neck stand on end,” Hagerty writes in her new book, “Fingerprints of God,” a survey of modern scientific investigation into religious experience.

“The air grew warmer and heavier, as if someone had moved into the circle (of lamplight) and was breathing on us. I glanced at Kathy.” She, too, felt something and had “fallen silent in mid-sentence.”

“I felt an unseen caress, engulfed by a presence I could feel but not touch,” Hagerty continues. “I was paralyzed. … After a minute, although it seemed longer, the presence melted away.”

What was it she sensed? Jesus? An angelic being? Or, as one researcher later suggested, had the temporal lobe of her brain been briefly hyperstimulated? This, he told her, likely induced the illusion of an unseen presence.

Whatever it was, it proved the “continental divide in my life,” Hagerty said during a recent interview. “I decided I should investigate, the way we journalists do.”

Her investigation grew into “Fingerprints of God,” a lucid overview of an essential question: Is mystical experience truly a glimpse of the divine, the eternal, the absolute? Or are the seemingly transformative moments known variously as “enlightenment” or “beatific vision” or cosmic bliss merely swells and quells in brain activity, signifying nothing beyond ourselves?

“I knew this had some risks,” said Hagerty, who grew up in a devout Christian Science family but had parted with the faith as an adult.

She would be poking at the very foundation of religion: the phenomenon of transcendent moments, the kind that had transformed Paul, Muhammad, Moses, Buddha, Indian shamans, Hindu sages — perhaps even Jesus — and thence whole civilizations.

“The main thing was, what if God is a sham?” Hagerty worried. “What if religion is all tissue paper?”

Her “radical project” would take her into monasteries, a trailer park, research labs, an Indian peyote ritual (she just watched), and a Canadian brain stimulation exercise that sought to replicate her 1995 experience of an “unseen presence.”

The body of scientific research into religious experience is so diverse that “Fingerprints of God” never lingers for long on any one topic. But it serves as a broad and readable introduction to the growing field of “neurotheology.”

Typical of the many stories in the book is that of the Rev. Scott McDermott, former pastor of Washington Crossing United Methodist Church in Bucks County, Pa.

One day in 1996 McDermott — who has a doctorate in New Testament theology — struck up a conversation with a Pentecostal preacher from Toronto. When the man told McDermott he would pray for him, McDermott suddenly fell on his back with a vision of the ancient Holy Land, and saw himself running “from Jericho to Jerusalem.”

For 90 minutes McDermott lay on the floor, pumping his arms and legs until he saw himself arriving at the Temple. There he found Jesus waiting for him, he said, “his arms outstretched.”

McDermott had been exceptionally prayerful even as a teenager. Still, the intensity and suddenness of his vision — which compelled him to leave Pennsylvania for a pastorate in Toronto — astonished him. What was it that he experienced that day?

At Hagerty’s request, McDermott submitted to a brain scan at the Hospital of the University of Pennsylvania. There, Andrew Newberg, a radiologist now famous for his studies of the brain functions associated with spiritual practices, observed McDermott’s brain activity.

Newberg observed which parts of McDermott’s brain “lit up” while he prayed. But what really surprised him was McDermott’s thalamus, a tiny region in the brain that regulates the processing of sights and sounds and other data.

Newberg, who has scanned thousands of human brains, including meditating monks and nuns both Christian and Buddhist, told Hagerty that he has found asymmetrical thalami to be a kind of “spiritual marker,” often associated with “spiritual virtuosos.”

Those asymmetries are typically in the range of 3 to 5 percent. McDermott’s thalamus was 15 percent asymmetrical, the most pronounced Newberg had ever seen.

Hagerty also visits the workings of dopamine, serotonin, the DRD4 gene, the VMAT2 gene, identical-twin studies, the frontal lobes of the brain, epilepsy, theta waves, and gamma rhythms in religious experience.

Each seems to offer a tantalizing glimpse into the “truth” of such experiences. But on the ultimate question — do human brains simply generate religious sensations, or can some of us perceive realms of being — Hagerty says there is no way of being certain.

“You can have two views of it and they’re both valid,” Hagerty concluded.

She emerged from her quest with a sense that “the instruments of brain science are picking up something beyond this material world.” But she admits that may be, at least in part, because she is not comfortable with the idea of an absurd, meaningless universe.

Intellectually, at least, she discounts the idea of a God who intervenes in human affairs.

“I came to define God by his handiwork,” she writes. “A craftsman who builds the hope of eternity into our genes, a master electrician and chemist who outfits our brains to access another dimension, a guru who rewards our spiritual efforts by allowing us to feel united with all things, an intelligence that pervades every atom and every nanosecond, all time and space, in the throes of death or the ecstasy of life.”