Yes there has been research which show that stutterers have restricted bloodflow to the broca area (the part of the brain responsible for language processing). So one might say that there's an incoordination in that part of the brain for stutterers, and that's why there's a delay between language processing and speech, and hence why people stutters. If that's the case, then how do you explain this: Have you ever pre-formed a sentence in your head (several minutes before you enunciate it) and stuttered while you enunciated it? Where is the delay over there? You already knew exactly what you have to say. And a lot of stutterers have trouble saying their names too. What's the reason behind that? They already know what their names are. PS: One reason why they might have restricted bloodflow to the broca area is because they're not using the language part of the brain as efficiently as people who don't stutter, because the stutter is blocking them from doing that.