Glossolalia, sometimes called "speaking in tongues," is a phenomenon in which a person vocalizes in an unknown and unintelligible language. Glossolalia often occurs as part of a religious practice. In some Christian traditions, the phenomenon is believed to signify a person's being "filled with the Holy Spirit."
There is some disagreement as to what exactly glossolalia is. Glossolalia is sometimes thought to be a language that the speaker does not know, but many recorded cases are not intelligible as any known language. Alternatively, some interpret glossolalia as an unknown, spiritual language, while others think it is only gibberish. Technically, spontaneous speech in a language unknown to the speaker, but recognized as a real world language, is termed xenoglossia. Xenoglossia, which can also be called "speaking in tongues," is at times associated with channeling spirits or with demonic possession rather than with a spiritually heightened state.
Participants in a religious practice including glossolalia may be able not only to produce glossolalia, but also to understand the glossolalia of others. In the most well known biblical account of glossolalia, the story of the Pentecost in the book of Acts, the glossolalia of the Apostles is understood by many witnesses as if it were speech in each of their own varied native tongues. Today, the Pentecostal and Charismatic Christian denominations are best known for their use of glossolalia. It is a part of private prayer rather than public worship for many practitioners, who say it brings a feeling of peace.
Glossolalia is a controversial issue in the Christian Church, with strong opinions on both sides of the issue. The practice is not limited to Christianity, however, but appears in religions around the world. In ancient times, it was notably practiced by the Greek Oracle at Delphi and by Roman Gnostics.
Psychologists and neurologists have conducted a few studies of glossolalia over the years, with varying conclusions. Around the turn of the century, psychologists Emil Kraepelin and G. B. Cutten linked the phenomenon to schizophrenia, though modern psychologists acknowledge no such link. Nicholas Spanos and others believe that the ability to speak in tongues is acquired. The practice has recently been linked to lowered stress levels, and a 2006 University of Pennsylvania study found that the brain has less activity in language areas and more activity in emotional areas during glossolalia.