The under-research is indeed a tragedy. I believe directly that the amygdala is hyperactive in stutters. That is in my opinion caused by stuttering itself which makes people so afraid and hyper alert on social cues. Therefore controlling the diaphragm is In my opinion the most logical thing to learn because when people can control their diaphragm stuttering is impossible. And the vasalsa respons for me means just that people block their diaphragm and try to speak when inhaling which causes the vasalva response. So you are very right about that our brain silence us because that's indeed what happening. The brain controls the diaphragm when speaking and it does this automatically in a good way when sining. The brainactivity from singing must be applied to the normal speech. OF this I am very convinced. But that just my opinion. So I don't disagree about your theory of the amygdala perse.