The hypothesis made sense, but I'm guessing that the Valsalva lock-up in the throat and stomach is the effect, not the cause, of a lock-up in the brain. Having to relax the throat, the stomach, etc. when you're experiencing a block mid-speech amid high nerves is a bit unpractical to carry out. I've tried his daily exercises for many years, and while they can help a severe stutterer get his/her words out, the speech oftentimes feel mechanical and forced, and sometimes blocks and holds would still occur.