You can search 'William Parry' on youtube and btw his vids are stunning and helping me a lot. I am not an expert at this so here is my paraphrase and maybe not correct: Due to hyperactivities of our amygdalas, our 'Valsalva responses' are therefore hpyeractive and even without threats we can have Valsalva responses which can cause our stuttering. Anyway my translation is stuttering may be just a normal prensentation of our neurological responses to threats but our responses are hyperactive. Here is the vid, hope you can check it: https://www.youtube.com/watch?v=AcNibr3ulVg&t=844s