I understand that garlic is a powerful cleanser. So it is possible that any ill effects, on the brain or anywhere else, might be the result of a cleansing reaction on certain kinds of people, producing temporary hot emotions or behavior or even physical effects. It is a "hot" herb and so should be avoided by people with too much heat or too little yin.
And so it is with all strong foods and herbs. Different strokes for different folks, that's all.