Well well well. I’ve pondered this before.
A Christian friend of mine sent me this link earlier today and I commented similar to the comments below about having been in a cult and having left I didn't think it could be damage to the brain. What intrigued me about the article was the idea that doctrine cause the brain to strengthen connections and how this connection could be inoculated against. Just put the serum in with their measles shot in preschool.
There are many very smart people who were fundamentalists at one time. With redirection and research they came to understand they'd been indoctrinated.
Also, I know of two instances where people suffered brain damage from severe head injuries. They were religious before they became unconscious and woke up atheists.
The brain is complex. It can go the other way too.