No, there were no scientific experiments to prove it. However, in absence of concrete proofs of either theory, both are equally probable to be true. The theory that consciousness arises from brain activity alone is just an assumption based on other research. It has never been properly proven or disproven either.

I'm pretty open minded about this stuff, but I recall reading Robert Monroe (author of several books) tried to prove to himself his OBEs were real by having his wife place an object in a box downstairs without his knowledge and trying to find out what it was.

IIRC he said he invariably got sidetracked between leaving his body and going downstairs, or would be attacked by entities of some kind. He suggested perhaps some kind of subconscious resistance to the experiment.

He listed several times where he claimed to have gained knowledge without trying to while OBE but I wasn't entirely convinced by any of them, so who knows.

The fact he claims to have had hundreds of OBEs and couldn't conclusively prove he could gain knowledge makes me sceptical that he wasn't just in a replica of reality generated by his mind. Anyway, they sound fun/scary/ real to the experiencer.

Well, it is not "brain activity alone", there are always light waves, forces, chemicals, and a lot of other things, acting on the brain from "outside" of the body, through some very strange receptor routs, but the "information" somehow travels. And we know 100% that for a lot of receptors, the firing rates depend on the intensity of the stimulus. So, we can see a direct correlation between, say, an applied force and golgi tendon organ firing. And at the same time, we discovered some types of radiation that we cannot see, and yet they can influence distant objects. I think that is pretty weird. So, we found a lot of direct correlations between brain activity and the outside world. Is there some need for an additional invisible field, not covered in current physics?