Researchers have identified specific brain circuitry that is related to people's sense of spirituality — and it's centered in a brain region linked to pain inhibition, altruism and unconditional love.
The findings add to research seeking to understand the biological basis for human spirituality.
"It is something of a treacherous subject to navigate," said lead researcher Michael Ferguson, a principal investigator at the Center for Brain Circuit Therapeutics at Brigham and Women's Hospital, in Boston.
Spirituality and religiosity, as well as the human brain, are obviously complex, he noted.
But given the central role of religion and spirituality in human experience, Ferguson said, "why wouldn't we want to better understand it?"
Over 80% of the world's population identifies as religious, studies show, and even more say they are "spiritual." That's often defined as a belief in forces that cannot be objectively proven, or a connection to something beyond oneself.
Past studies on the brain's role in spirituality have largely used functional MRI scans — showing that certain brain areas "light up" when people envision a previous spiritual experience, for instance.
But it's not clear whether those brain regions actually help cultivate spirituality, or are simply correlated with such experiences.
"We want to look for more than correlations," Ferguson said. "We're looking for causes."
So his team took a different approach, focusing on patients with brain lesions (areas of tissue damage). If the specific location of a lesion correlates to either increased or decreased feelings of spirituality, that suggests that brain area may play a causal role.
Ferguson and his colleagues started with previously published data on 88 patients who were having surgery to remove brain tumors. Before and after the procedure, the patients completed surveys on aspects of their temperament and character, including their degree of "spiritual acceptance."
It turned out that after surgery, roughly one-third of the patients reported a decrease in spirituality, another third reported an increase, and the final third reported no change, the researchers reported.
Ferguson's team used that information to link patients' brain lesion locations to specific brain circuitry. Those circuits had a common connection point in a region of the brainstem known as the periaqueductal gray (PAG).
Past research has linked the PAG to functions as diverse as fear conditioning, pain relief, altruism and unconditional love.
What's striking, according to Ferguson, is that in terms of evolution, the PAG is among the most conserved structures of the brain.
"It suggests that whatever spirituality and religiosity are doing," he said, "they're doing it at a very deep level."
The researchers confirmed their findings from the surgery patients using a separate dataset — on over 100 combat veterans who'd sustained brain lesions from head trauma.
Overall, the veterans' likelihood of describing themselves as religious or non-religious was linked to the "functional connectivity" between their brain lesions and the PAG hub.
Finally, the researchers used another dataset to see whether brain lesions causing neurological or psychiatric symptoms inters ected with the "spirituality" circuit.
They found that lesions causing Parkinson-like symptoms intersected with "positive" nodes of the circuit — similar to lesions that were linked to decreased spirituality. On the other hand, lesions causing delusions or "alien limb" syndrome intersected with the circuit in a manner similar to lesions tied to increased spirituality.
None of that, Ferguson stressed, implies that spirituality is a delusion, or that people develop Parkinson's because they are not spiritual enough.
Instead, he said, the findings suggest a "shared neuroanatomy" between spirituality and certain symptoms.
His team published the findings recently in the journal Biological Psychiatry.
Dr. Marc Potenza is a professor of psychiatry at Yale University who has studied the brain-spirituality connection.
He called the new findings "very interesting," and said researchers may want to pay more attention to the human PAG going forward. Much of what's known about that brain structure, Potenza said, comes from animal research.
What's the ultimate goal of all this work? There could be therapeutic applications, according to Potenza.
For example, he said, many people recovering from addiction or depression cite spirituality as an important component: So research into spirituality could aid in better understanding, and facilitating, the recovery process.
If that sounds "new age," Ferguson noted that throughout time and across cultures, healing systems and spirituality "were in a relationship with one another."
It's only in recent history, he said, that modern medicine and spirituality have become separated.