The regions of the brain that are underactive and overactive are interesting, but unfortunately don't represent a mechanism that we can intervene in. Perhaps by brain stimulation, but that's to be determined. It would be great if someone could say "hey, use your left inferior frontal gyrus more bro" and fluent speaking would occur, but that's obviously not plausible. Glucose utilization, cerebral blood flow and dopamine dynamics are 3 mechanisms that I think are getting at the underlying mechanisms.