"Glossolalia" is a practice that started in American charismatic churches around the turn of the 19th century, but that's not what you know it as -- it's more commonly called "speaking in tongues." In fact, the only reason we know the fancy term for it is that for the first time, scientists have scanned the brains of people while they, er, glossolaliazed:
In the study, the researchers used imaging techniques to track changes in blood flow in each woman's brain in two conditions, once as she sang a gospel song and again while speaking in tongues. By comparing the patterns created by these two emotional, devotional activities, the researchers could pinpoint blood-flow peaks and valleys unique to speaking in tongues. ... The new findings contrasted sharply with images taken of other spiritually inspired mental states like meditation, which is often a highly focused mental exercise, activating the frontal lobes. The scans also showed a dip in the activity of a region called the left caudate. "The findings from the frontal lobes are very clear, and make sense, but the caudate is usually active when you have positive affect, pleasure, positive emotions," said Dr. James A. Coan, a psychologist at the University of Virginia. "So it's not so clear what that finding says" about speaking in tongues. The caudate area is also involved in motor and emotional control, Dr. [Andrew] Newberg, [the lead author of the study,] said, so it may be that practitioners, while mindful of their circumstances, nonetheless cede some control over their bodies and emotions.
In other words, they really are possessed?! We don't think that's exactly what the scientists are getting at, but we'd love to see more studies.