My dad had it too. I noticed he remembered the music from his youth. When I played the 50s channel in the car, he knew all the songs, and seemed to come alive for a bit. Got him some CDs to listen to. It sucked.
My mom has to remind herself of the same thing. Which has at times been hard due to some of the things he has put her through, which I won't go into other than to say if he wasn't in the condition he is in he would surely have been prosecuted for it. I have safeguards in place now and I spend no less than 3 days a week up there helping her and helping him. We also recently got him on hospice so now he gets a nurse and a nurses aid twice a week who perform various duties, some medical, some practical. And my mom gets 3 hours 3 times a week to go do things she needs or wants to do with someone staying with my dad. And that doesn't include the 3 or so hours every Thursday night when I stay with him for her bowling night. I think it's important that she has free time. She's 82 and we could all see her paying a heavy toll being his caregiver. So my sister and I stepped in and got her some help for the times when I can't be there.