The idea came from hearing about people who were kidnapped by Colombia's guerrilla and criminal groups. The biggest problem these people faced was being bored. They sat out in the jungle for long spans of time, and weren't allowed to do much of anything.
I've heard stories from people in solitary confinement, that it's similar. That keeping yourself sane and occupied is one of the hardest things to do.
I'm strongly motivated by boredom, so these stories resonate with me, as a personal dystopic myth.
My reaction to this is to use tattoos as a possible way to alleviate the hypothesized problem. When incarcerated, you would be removed of all posessions, but wouldn't be stripped of tattoos.
So, you would tattoo some sort of puzzle. Something whose description is short, but whose completion would take a large amount of time.
Ciphers are one example, if only because they're intrinsicly designed to be easy to create and hard to solve.