As I understand it, infirmities that fall under the general heading of schizophrenia cause erroneous neural inputs that convince the mind that reality is not what it appears and that the sufferer becomes, understandably, convinced that “only he understands the situation correctly.” Both a ‘normal’ subject and a sufferer will experience the same stimuli, but the sufferer will find himself interpreting the stimuli in an abnormal and irrational manner and thus arriving at irrational conclusions.
So it is with glossolalia, there are two discrete events – the production of noise that conforms roughly to speech patterns and the irrational mind running a script, often by way of an image or “feelings” in the native tongue or at least in an “apparently comprehensible” manner.
To the outside observer, (and later, when played a recording, to the actor), the noises are incomprehensible. However, this does not prevent the actor from asserting the clear impression that he received at the time, i.e. he was speaking a language comprehensible (or at least expressing meaning) both to himself and to whomsoever he was speaking.
In the mind there is often an image of the imaginary listener whose facial features an other gesture often respond appropriately to the imagined meaning. The imaginary listener may then respond in a like manner and the person speaking in tongues will receive a mental image of the intentions and a “feeling” of the meanings of the imaginary person he was addressing.
It seems to be similar to going “Dum-diddly-dum-di-dee, etc” to a song you know but whose words you do not. The essential difference is that when presented with several sets of lyrics, the normal person will be able to recognise the correct set, whereas the person “speaking in tongues” would have no idea what was said. He would explain this by giving an irrational excuse.
A problem with glossalalia is that it is an easy habit to get into and a difficult one for the mind to break. I would suspect, without evidence, that there are learned neural pathways that have been developed or that the autonomic nervous system is malfunctioning and sending inappropriate (amounts of) neurotransmitter to the brain (See http://www.sciencedaily.com/releases/2013/04/130418124641.htm
) or both.