Yes, it exists and is very similar to human dementia. Your dog seems to be showing typical symptoms I'm sad to say. It's no more curable than human dementia. The only good part is that the victims don't really know they have it. Their friends and family are the ones who suffer.
There is dementia, as many have mentioned and it manifests itself in some REALLY out of character behavior, like biting etc. There is also cognitive dysfunction, where the dog simply does weird things, like staring into a corner, laying in the dark at barking for no reason...etc.
