I too believe that stuttering is due to a dysregulated dopaminergic system in the brain. MRI and PET scans show hyperactive dopamine in the stuttering brain compared to a non-stuttering brain. Everyone is different. Some could have too low dopamine (like in ADHD) and some might have overactive dopamine. I believe the trick is to find that perfect balance in neurotransmitters such as dopamine, seratonin, GABA etc.. in order for speech motor circuits to fire in sync and produce fluent speech. This is why certain medications which target dopamine levels in the brain (Ecopipam, Pagoclone etc) tend to improve fluency for some stutterers.