No, it wouldn't show on a brain MRI (rarely it can, but it's very atypical). They test for it with an EMG and clinical examination.
I don't THINK that *** can mimic the mechanism behind hiccups. I have never heard of it being a symptom. Sneezing and yawning CAN be symptoms (bulbar disinhibition), but never once have I read hiccuping (I actually wondered the same thing when I started hiccuping a lot which has pretty much stopped now).
Anxiety is far more likely to cause muscular twitching and can cause hiccups. Surely you've heard of people hiccuping when they become anxious; it's pretty cliche'.
Don't learn about ***. Continue to avoid it like the plague. It isn't going to happen to you.
Nervous excitement is a process both benign (anxiety) and malignant (***). The processes can have similar symptoms, but one is much more sinister in what it does on a cellular level and typically a more severe form of excitation, however anxiety can be as bad as to reach a parallel intensity -- without the sinister involvement of nervous destruction course. See JER's post about brisk reflexes and pseudo-weakness. This is why *** fear is so popular and insidious (as with MS).