Here are the Scientific Evidence.
Glossolalia (or “speaking in tongues”) is an unusual mental state that has great personal and religious meaning. Glossolalia is experienced as a normal and expected behavior in religious prayer groups in which the individual appears to be speaking in an incomprehensible language. This is the first functional neuroimaging study to demonstrate changes in cerebral activity during glossolalia. The frontal lobes, parietal lobes, and left caudate were most affected.
Conclusion:
Newberg and colleagues used imaging technology to look at the brains of Pentecostal Christians speaking in tongues - known as glossolalia .Then looked at their brains when they were singing gospel music. They found that those practicing glossolalia showed decreased activity in the brain’s language center compared with the singing group.
The imaging results are suggestive of people’s description that they do not have control of their own speech when speaking in tongues.
This information is more for the unbeliever.
Source:The measurement of regional cerebral blood flow during glossolalia: A preliminary SPECT study Andrew B. Newberga, b, , , Nancy A. Winteringa, b, Donna Morgana and Mark R. Waldmanb aDivision of Nuclear Medicine, Department of Radiology, University of Pennsylvania Medical Center, 110 Donner Building, 3400 Spruce Street, Philadelphia, PA 19104, United StatesbCenter for Spirituality and the Mind, University of Pennsylvania, Philadelphia, PA, United States Received 9 May 2006; revised 20 July 2006; accepted 25 July 2006. Available online 12 October 2006.
Link 1:
http://http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TBW-4M3J0R4-1&_user=10&_coverDate=11%2F22%2F2006&_rdoc=1&_fmt=summary&_orig=browse&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=eb99cea50b73f00b819a4190ce812713#cor1
Link 2: http://http://en.wikipedia.org/wiki/Glossolalia
