This outta make "mainline Protestants" happy...

DURHAM, N.C. — 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.

As a Roman Catholic, you'll have to forgive this pea-brained question: what's a "Mainline Protestant?"