> If it's a well-known song, you're simply repeating words that the other person knows about in a well defined rate of sound. Not necessarily - the other person might not know the song you're singing. You could also just be making up a song on the fly! (For example, by taking a familiar tune and giving it new lyrics) Conversely, you could be reciting a memorized non-musical text that the other person also knows by heart, and still stutter (though memorization does usually make it much easier). I wouldn't say that the lack of blood flow is an obvious symptom because as far as I know that's not how the distribution of blood in the brain works, but I'm no neurologist either so I could certainly be wrong. It's completely possible that these researchers were mistaken in some way, but I'm inclined to trust their interpretation of the findings since for now I have no reason to believe they're wrong. If they think blood flow is a cause of stuttering, that's a theory I'm going to accept until a conflicting theory is backed by better arguments or evidence, preferably from someone who has the appropriate knowledge/training to discern what's a plausible neurology-related claim and what's not. For what it's worth, my own experience also leads me to believe that it probably has a neurological basis. When I was a child, I was completely fluent all the time, except for a few (4 instances that I or anyone else can remember) out-of-the-blue, completely unexplained blocks at random moments. I remember them very clearly because they didn't make sense to me at the time - why was I suddenly unable to push out a word while talking to my grandmother? How weird! But I didn't think much of it, and just kept being fluent for the rest of my childhood. My stutter only really kicked in when I was 15 years old, and has persisted to this day (though I can still have long periods of fluency - I was never the type of PWS who stutters on every word or in every sentence). I think it's likely that there was always something wrong with my brain, hence the few weird blocks even back when I was otherwise not a PWS. There could potentially be a psychological theory which would explain these blocks as well, but if there is, I haven't heard it yet.