As these mediums communicate with the dead, found a new study, parts of their brains involved in language and purposeful activity shut down, alongside other patterns of increased and decreased activity.
The findings add to our limited understanding of how the spiritual brain works, though for now, science cannot speak to the existence of the spirit world.
"I don't think this does anything to make (the experience) less real or less profound or to make it less important in the moment," said Andrew Newberg, a neuroscientist at Thomas Jefferson University in Philadelphia.
"At some point, maybe we will design the perfect study that can prove there were not spirits there and this is just a fascinating way that the brain works," he added. "At the moment, all we're really doing is saying that this is what happens in the brain when you do this particular practice."
In an attempt to understand how the human brain experiences spirituality, Newberg and colleagues have studied a range of practices, including yoga, meditation, prayer and speaking in tongues.
This time, he turned to psychography, one of a variety of practices associated with mediums, who lose their own sense of self as they connect with external souls.
Of the ten Brazilian psychographers considered in the study, five were experts who had been practicing for an average of 37 years and conducted an average of 15 sessions per month. The other five were novices who had been practicing for far less time and practiced with much less frequency. All were well adjusted and mentally healthy.
Each medium entered a trance state and began writing. After 10 minutes, the scientists injected them with a radioactive tracer that traveled to the brain, where it essentially got locked in place, reflecting how blood was flowing to various parts of the brain at the moment of injection. When the session was over 15 minutes later, a scanner illuminated that moment for the researchers.
Compared to times when they were simply writing about their thoughts, sessions of psychography induced a number of brain changes in experienced mediums, the researchers report today in the journal PLoS ONE. Specifically, activity decreased in six areas, including the left hippocampus, the left anterior cingulate and the right superior temporal gyrus.
The parts that shut down while the spirits moved their hands are areas normally involved in actively writing, concentrating and processing language, Newburg said. Similar trends showed up in a previous study of people who spoke in tongues. Both groups shared the common belief that spirits moved through them to be heard.
Novices in the new study showed the opposite pattern, with increased activity in the same parts of the brain that shut down in the advanced practitioners, suggesting that training improves the ability of the brain to enter a spirit-channeling state.
To Newburg's surprise, experienced psychographers also consistently produced more complex language on the page when they entered a trance state.
"You would expect this to mean that language areas were more active because they were making more detailed writings," he said. "In fact, it was just the opposite. The less active the brain was and the more expert the person was, the more complex the writing was."
With so few studies done on the brains of people involved in spiritual activities, the new research is a helpful contribution to the field of neurotheology, said Patrick McNamara, a neuropsychologist at Northcentral University in Prescott Valley, Arizona.
More research might eventually reveal reliable patterns of brain activation that occur across spiritual disciplines, eventually offering insight into the roots of religion and why some people are more devout than others.
"Then we can ask the big questions," McNamara said. "Is that activation of the brain state necessary to enter into the spiritual experience? Or is the spiritual experience key to activate those brain areas?
"Some people find it easier to access those brain areas associated with spirituality. Other people have to work harder at their religious lives. We have known that for centuries," he added. "The brain science just allows us to give a more concrete explanation about why that is the case."