The study, published in the Proceedings of the National Academy of Sciences, took an innovative approach by examining two groups of individuals with focal brain lesions resulting from injuries or disorders. One cohort consisted of 106 Vietnam veterans who suffered traumatic brain injuries in combat decades ago. The other included 84 patients from rural Iowa who experienced strokes, surgical complications, or other brain injuries.
I mean, from the abstract it looks like what the study did was localise the specific network of right hemisphere neuronal clusters that, when damaged, predict religious fundamentalism. Since they only studied patients with TBIs, they weren’t testing the claim that brain damage increases the likelihood of fundamentalism. The rate of fundamentalism in the general population could, hypothetically, be higher than among TBI patients (i.e., if brain injuries actually reduce fundamentalism) and this study’s insights would still hold.