RE: If you laugh at a joke in your dream, did you laugh at your own joke?
If you think about it, the source is your own brain (just like when you think of funny jokes that you don't speak out loud). However, during dreamstates, you are essentially using most of your faculties to reconstruct visualizations and experiences that are similar to the real world (but not bound by its laws). So if you laugh at a joke in your sleep you are still the source of that joke even if there is a fragmented illusion of another entity speaking it aloud).
So I personally would say that if you can watch someone's brain with an MRI that the same centers that light up when you think of something funny are largely going to be the ones that light up when you are asleep (along with a few centers that are especially active during the Rapid Eye Movement (REM) cycle, of course).
I hear what you're saying. I still believe the answer could be no cause I don't believe every thought in your subconscious is yours. It could have come from someone else, a commercial you saw, an outside source that you were completely unaware of. How many of people's thoughts are actually theirs, how many people actually think for themselves and not just store and regurgitate thoughts from outside sources? So even if it is your brain that stores this thought, it is quite possible that it is not YOUR thought.