For Jordan Grafman, it was just a split-second vision.

"About 15 years ago, my mom died," Grafman told Live Science. "I was walking down the street to catch the bus at about 5 a.m., and I looked down the street and saw who I thought was my mom, although my mom had been dead for a week. I looked back, and whatever was there was gone."

That momentary flicker in perception intrigued Grafman, who is a cognitive neuroscientist and the director of brain injury research at the Rehabilitation Institute of Chicago.

"That, to me, was a mystical experience," Grafman said. "As a scientist who has seen something that, to me, seemed mystical, I'm interested in figuring out what happened to my brain."

Now, Grafman and his colleagues have pinpointed some of the brain processes that lead to such transcendent moments. It turns out, mystical experiences may stem from the brain letting go of inhibitions, opening a "door of perception," the researchers found. [Spooky! The Top 10 Unexplained Phenomena]

Brush with the infinite

During mystical experiences, people feel connected to a higher power and often describe gaining hidden knowledge or having revelatory insights. Although people around the world have reported mystical experiences, ranging from near-death experiences to ecstatic visions to meditative trances, these visions remain shrouded in mystery, with little neuroscience research to explain their underpinnings in the brain.

Previous research suggested two broad camps of theories to explain the brain origins of mystical experiences, called "push" and "pull" theories, respectively.

"Push theories argue that activation of a single 'God spot' causes mystical beliefs, suggesting that injuries to these spots would reduce mysticism," study co-author Joseph Bulbulia, a religious studies researcher at Victoria University of Wellington in New Zealand, said in a statement. "In contrast, pull theories argue that the suppression of our inhibitory functions opens up the brain to mystical experiences. It is a hotly disputed topic, and we set out to clarify the debate."

Now, Grafman and his colleagues have evidence to suggest that pull theories may help to explain mystical experiences.

In their new study, the scientists analyzed 116 Vietnam War veterans who experienced brain damage and had mystical experiences, and compared them with 32 combat veterans without brain injuries or neurological disorders. All of the veterans took psychological tests before and after their conflicts. [Top 10 Controversial Psychiatric Disorders]

"Often, the veterans said they heard the word of God, or had visions of their family," Grafman said. "Those are common mystical experiences."

The researchers also conducted interviews of the patients using the Mysticism Scale, a well-established test for analyzing reports of mystical experiences. The scale asks respondents about feelings of unity and joy, as well as a sense of transcending time and space. The scientists also carried out high-resolution computed tomography (CT) brain scans of all of the Vietnam veterans participating in the study.

The researchers found that damage to the frontal and temporal lobes was linked with greater mystical experiences. Previous research found that the frontal lobes, located near the forehead, are linked to movement, problem solving, memory, language and judgment, among other functions. The temporal lobes, located near the bottom of the brain, are linked to the senses, language and memory.

Further investigation revealed that damage to a specific area of the brain known as the dorsolateral prefrontal cortex was linked to markedly increased mysticism. Previous research found that this brain region, located in the frontal lobes, is key to imposing inhibitions.

"The frontal lobes are the most evolved areas of the human brain, and help control and make sense of the perceptual input we get from the world," Grafman said. "When the frontal lobes' inhibitory functions are suppressed, a door of perception can open, increasing the chances of mystical experiences."

The brain's door of perception

Previous research into mysticism in the brain examined only a few volunteers, or did not analyze participants both before and after brain injuries. The new findings are the first to both analyze subjects' intellectual function before and after combat and to investigate a significant number of such volunteers, the researchers said.

The findings also suggest that activity in the temporal lobes can generate mystical experiences, the researchers said. However, the dorsolateral prefrontal cortex appears to have a critical role in interpreting and modifying these phenomena, the scientists said.

The researchers suggested that when the brain's inhibitory functions are suppressed and then people undergo an experience without a direct explanation, the brain might then settle for supernatural explanations.

"The more we understand the brain, the more we can make fundamental advances and translate findings into clinical settings," Grafman said in a statement.

The scientists detailed their findings in the Jan. 8 issue of the journal Neuropsychologia.

Follow Charles Q. Choi on Twitter @cqchoi. Follow us @livescience, Facebook & Google+. Original article on Live Science.