Mon221B

Oh, I'm speaking only of when they're possessed. So far, the possessed people we've seen live long enough post-possession to make any indication have indicated that they were there and awake during the demon's exploits. Also, when Sam talks about the people he's saved with his scary no-Latin exorcisms, he implies that he's frequently managed to save the host as well, which would imply that the soul is present to resume control when the demon is gone. And when they exorcise Meg, Bobby tells them to be careful and not hurt her because there's an innocent girl trapped inside there. Bobby's the resident demon expert, so I'm thinking he's a reliable narrator on that score. All in all, it seems to add up to me to the soul remaining in the possessed body, and being aware of what's going on.