Is there a biological basis for zealotry?

I was wondering if there was any research done, specifically on the brain, that shows or hints at the difference between a zealot and a normal person.

It seems to happen across all religions, so that also made me wonder if it was something that could be turned on/off by something in a person’s environment. (Is it possible to be zealous about something that isn’t related to religion?)

Does it have any similarities to some medical conditions that can be observed or predicted by chemical levels in the brain?