Stuttering is seriously under-researched. There's a few good people working on it but we simply don't have enough attention for people to care. I personally believe, [based on a very impressive presentation on stuttering by William D. Perry](https://www.youtube.com/watch?v=AcNibr3ulVg), that stuttering for the majority of us is caused by problems relating to an overreactive amygdala, and by association, the Valsalva response. Our ability to speak is being hindered and frozen by the Valsalva response because our amygdala has gone completely off the rails and is associating our ability to speak with what it perceives to be potential danger. Our amygdala isn't conscious. It doesn't know what it's doing and it'll simply continue to reinforce it's behavior regardless of how we feel, and that's why an overreactive amygdala, especially an overreactive amygdala that's initiating a freeze response incorrectly, can be so debilitating. This is an involuntary and automatic response similar to what we see in people with Tourette's syndrome. This is not anxiety. If this theory is correct, then we are quite literally being silenced by our brain. I don't think all stuttering is caused by this, but for most of us, I think this is the answer.