The way I understand it you receive the Holy-spirit when you get born-again. Being baptized in the Holy-spirit is an extra level. The bible says that when you speak in tongues, then your spirit speaks, not your mind. I saw something about that on Wikipedia - I'll see if I can find it and post it here.

In 2006, at the University of Pennsylvania, researchers, under the direction of Andrew Newberg, MD, completed the worlds first brain-scan study of a group of individuals while they were speaking in tongues. The study concluded that while parti nts were exercising glossolalia, activity in the language centers of the brain actually decreased, while activity in the emotional centers of the brain increased. During this study, researchers observed significant cerebral blood flow changes among individuals while exercising glossolalia, concluding that the observed changes were consistent with some of the described aspects of glossolalia. Further, the researchers observed no changes in any language areas, suggesting that glossolalia is not associated with usual language function. One of the researchers is a practitioner of glossolalia and a self-described born-again Christian.[30]

New York Times wrote about the study, and it has been published in Psychiatry Research: Neuroimaging, Volume 148, Issue 1, 22 November 2006, Pages 67-71.