I am looking for a single word which would define a person who doesn't know or feel the difference between pain and pleasure.
I have looked around a lot, but I am unable to find the proper word. There are words which revolves around it such hedonism , paradox of hedonism , sadist , masochism. But none make the exact sense. Masochistic, I find is the closest one, but as per it's meaning it means when your pain gives you pleasure, which is not the same sense I am looking for.
Usage of the word would something like this:
"He is a _________ , it is futile to torture him."