There are some research papers suggesting a correlation between dopamine pathways and stuttering. When we're in need of something (whether it's love, acknowledgement, sex, money) it produces dopamine to motivate us to achieve it. Often when this unfulfilled state lasts for too long, it converts into depression. So I am guessing there might be some deeper correlation & causation and therefore a chance emotional trauma or depression could cause stuttering. I've heard one of the drugs against stuttering are actually dopamine antagonists. There is a nice way to test it out - try to go to the gym for a month. Do you still stutter after workouts?