they really ramp it up by prohibiting books or other media. that's basically the next level of solitary, because there has to be further layers of punishment built in. that and the fact you only get flavorless "nutriloaf" aka bread and water, modern form.
so just a featureless room with only your mind to occupy you for possibly a lifetime, or long stretches (weeks, months) if being used as a punishment. and if you lose it they just beat the shit out of you and possibly tie you down in a restraint chair.
i can see how people lose it just to create a sense of time by fighting with the guards