Hunting for God in our grey matter seems to be a popular topic for neurologists, with past studies comparing religious highs with drug-induced ones, linking spiritual experiences with neurotransmitters such as serotonin, and identifying which parts of the brain (if any) could be responsible for a faith in the supernatural.

Now a new study has now found that those with damage to a section of the brain associated with planning become less open to new ideas, explaining why some people are more likely to become extreme in their religious beliefs.

Led by neurologist Jordan Grafman from Northwestern University in Illinois, the study dug into a tragic yet useful pool of data known as the Vietnam Head Injury Study (VHIS).

In the late 1960s during the Vietnam War, Korean War veteran and neurologist William Caveness developed a registry of approximately 2,000 soldiers who had experienced head trauma during the conflict.

The detailed information collected by medical personnel proved to be invaluable - not just to Caveness, but to other researchers such as Grafman.

As a result of the quick medical treatment many of the wounded received, many soldiers survived their injuries and returned home where researchers continued to follow up on their health and wellbeing.

Decades later, Grafman is still making interesting discoveries on the brain's inner workings by studying it when it's damaged.

Last year, he found parts of the brain in the frontal and temporal regions were responsible for downplaying the significance of mystical experiences.

In this latest research, he and his colleagues took the study a step further by examining the records of 119 Vietnam veterans who had suffered a penetrating head injury and comparing them with the records of 30 veterans with no brain injuries as controls.

Tests conducted on the group during a relatively recent phase of the VHIS included a religious fundamentalism scale - a standardised measure that requires participants to respond to statements such as "To lead the best, most meaningful life, one must belong to the one, true religion."

They also involved a measure of the veteran's overall intelligence and their cognitive flexibility by having them sort cards into different categories according to different sets of rules.

Grafman and his team then used computed tomography (CT) scans to map the position and size of the brain lesions left by the veterans' injuries.

The researchers focussed on those veterans with damage to their dorsolateral prefrontal cortex (dlPFC), which was already known to play a cognitive role in spiritual experiences, as well as playing a role in problem solving, planning, and task management.

They identified a relationship between lesions in these areas, the strength of the veterans' religious convictions, and low cognitive flexibility, suggesting that areas such as the dlPFC play a key role in helping us remain open to diverse ideas inspired by religious experiences.

Similar studies on the ventromedial prefrontal cortex (vmPFC) have found damage to this region makes people more susceptible to misleading advertising, leading other researchers to propose an idea called false tagging theory to explain the role those parts of the brain might play in providing us with a generous serving of scepticism.

Not so, say the researchers.

"Our results also challenge the 'false belief tagging' hypothesis," the team writes in their study, claiming their research shows fundamentalism is less about actively reserving doubt and more about openness to new experience.

It's important to note this doesn't imply a belief in the supernatural is caused by brain damage; epistemology - or the act of forming a belief - involves a rich mix of neurological processes that cannot be limited to any single piece of brain tissue.

Rather, the research suggests damage to certain parts of the brain involved in considering new evidence could make it harder for a person to evaluate their existing religious beliefs against other ideas.  

There are also the usual caveats to consider in single studies such as these; for example, the subjects were all older, American males who had experienced not just physical trauma, but the psychological trauma of war.

But the research fits in with what we know about the role of the prefrontal regions of the brain in setting the stage for framing religious experiences.

"We need to understand how distinct religious beliefs are from moral, legal, political, and economic beliefs in their representations in the brain, the nature of conversion from one belief system to another, the difference between belief and agency, and the nature of the depth of knowledge that individuals use to access and report their beliefs," Grafman told Eric W. Dolan at Psypost.

Extreme religious ideology is a divisive political issue in today's world, and looks to continue to be so in the future.

Research such as this might go some small way to helping us understand the neurological underpinnings on how our brains are wired to sort facts from faith.

This research was published in Neuropsychologia.