> It isn't a monotonic decline with memories disappearing forever.

Last time I visited my grandpa he was really far gone. The day we arrived and subsequent two days he didn't even recognize his daughter, my mom, or even recall he had one. He'd sit in the bedroom and watch the garden, and ask "who's that guy" every 15 minutes or so, as he'd forget about me in the livingroom.

The last day we visited before flying home. I entered first, and this time he sat in the living room, and as he saw me enter the hallway he exclaimed my name. We reminisced for hours in fluent English, his third language and my second language, as I wasn't so good in his and my moms native language. He recalled lots of details, some even I had forgotten but I confirmed later.

He passed away a couple of weeks later.