I'm doubtful we can really "prove" true unconsciousness exists (in the sense that subjective awareness completely ceases) until we have a much more advanced understanding of how experience arises in the brain. Right now the most we can say is "X results in an amnesic, non-responsive state". After all, if we rely on self-reporting, how can someone remember being unconscious if they have no memory of it?

Also, the article keeps saying the claustrum, but don't we have one in each hemisphere? Which one did the scientists stimulate, and what would happen if you stimulated the other one?