I think that playing the piano would be good to stimulate the brain, it keeps it active. I think they should study the effects of piano playing on dementia patients. Maybe they already have, but I haven't studied it. I should because my mother in law has it and is living with us.
As far a talking while playing, it happens. At church, people are always talking to me. Sometimes, I just quit and listen to them. Sometimes, I try to ignore them. Sometimes, I answer. If I make a mistake playing the piano, they never know because they are talking to me. It does take some practice though. Maybe women do this better than men, we can multi-task. We have to be able to deal with kids, piano, phone, TV, visitors, answering the door, etc. etc. We have to be able to talk and play, maybe not at concert level.