Modern day brain PET/fMRI scan research shows stuttering is a dysregulation in the dopaminergic system in the brains speech motor networks, such as the Brocas Area, Striatum, Basal Ganglia etc… compared to a “fluent brain”. This overactive dopaminergic system causes misfires in the timing of the speech motor networks in the brain. It can also be an underactive dopaminergic system, like in ADHD. So, it’s definitely a neurological condition, which manifests physiological symptoms such as elevated adrenaline/cortisol, anxiety, tremors, tics etc… Look up Dr Gerald Maguire on YouTube. He explains the neurology behind it really well. He’s a stutter too, but takes dopamine antagonist (D2 receptor blockers) medication to improve his fluency significantly.