"Common" stuttering is not caused by lack of oxygen to one part of the brain. By common I mean the kind in which people start stuttering as kids, the disfluencies persist, then you add a layer of anxiety and coping behaviours to it. People with a diagnosis of Parkinson's disease often stutter as the disease progresses, but it's not because their brain lacks oxygen. If your brain cells lack oxygen they simply die. The disfluencies of people with Parkinson's are also different. When you sing/rap, you use different brain areas from when you talk and your respiratory system works differently (you increase control over your diaphragm, which is one of the techniques used by SLPs). I'll edit my comment later with evidence-based information that might be helpful to you. Edit 1: in the meantime... https://www.nbcnewyork.com/news/health/When_Words_Fail__A_Conversation_with_Stuttering_Expert_Dr__Barry_Guitar.html