Sociologists of religion, meanwhile, aren’t buying it. They say the researchers’ theory flies in the face of U.S. religious demographics. While it’s true that evangelicals are a minority, they’re a sizable one — 40% of the U.S. population, according to Gallup Polls — and not exactly a stressed-out minority, especially in the South.

For decades, mainline Protestants have been beset by bad news: declining numbers, aging membership, waning cultural influence. A new study from Duke University Medical Center, however, gives these Protestants one reason for cheer: they seem to have larger brains than born-again Christians, Roman Catholics and the religiously unaffiliated.

A study of believer’s brain, based on scans such as this image of a normal brain, found born again Christians had a smaller brain than mainline Protestants, Catholics and those with no religious identity.

The study, which examined the hippocampus region of the brain, found that Protestants who did not have a “born again” experience had significantly more gray matter than either those who reported a life-changing religious experience, Catholics, or unaffiliated older adults.

The study, funded by the National Institutes of Health and the Templeton Foundation, included at least two MRI measurements of the hippocampus region of 268 adults between 1994 and 2005.

It found an association between participants’ professed religious affiliation and the physical structure of their brain. Specifically, those identified as Protestant who did not have a religious conversion or born-again experience — more common among their evangelical brethren — had a bigger hippocampus.

Amy Owen, a psychologist who did a post-doctoral fellowship at Duke and was the main writer for the study, said she hoped others would try to reproduce the study or offer other reasons for the association.

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