My mother suffers from dementia. It's not Alzheimer's, and she's not incapacitated, but she struggles with what was once instinctive. The cause is mostly attributed to age and her neurologist stated that most everyone will eventually suffer with dementia is some form or another.
What does this mean? Gentle love and patience that you didn't know you had. That, and the acceptance you'll have your heart broken now and then when you watch how hard the sufferer struggles and the fear they can never completely hide.
It sucks, in my opinion. I miss the long involved conversations about politics and life in general. Since there's nothing I can do to change this, I can only watch and hope it never progresses to the point she's completely unaware of her condition.
So, go give your parents a hug. If they're far away, give them a call and spend some time visiting. You may never get this chance again.