There was a post this morning from Carol Bradley Bursack about studies that point to a connection between Frontotemporal dementia and the inability to understand sarcasm and lying.
Yes, you can add my Mother to that list. A long time ago, she lost the ability to understand jokes, puns, sarcasm, innuendo, teasing...
I'm not sure about lying, because until I had to use fiblets, I did not lie to her. But, it's interesting, now she does yell at me and accuse me of lying to her.
"You're my mother."
"Don't lie to me!"