Recent research found that damage to specific brain networks, primarily in the right hemisphere, is linked to higher levels of religious fundamentalism. These brain regions are involved in cognitive functions like reasoning, belief formation, and moral decision-making.
Someone should also examine the effects of age-related cognitive decline on fundamentalist beliefs. Anecdotally, people turning to fundamentalist religion and/or authoritarian conservatism does seem to correlate with their cognitive capabilities deteriorating to the point of maintaining a nuanced view of the world becoming increasingly challenging.