Get Into Research. There has been some research into what happens to the brain during mystical experiences. The modalities of study can include functional mri, pet, evoked potentials, & quantitative eeg just to name a few. The web-page, clinicaltrials. Gov contains all of the current research protocols. You may find a trial to participate in.
Get a pet brain ct. If one is really curious about what happens to the brain when speaking in tongues, one may do a brain pet ct to see what areas light up when speaking in tongue. However as this would be considered experimental, it would not be covered by insurance. Pet brain cts are done at university hospitals. There may even be ongoing trials at present.