Fresh from the clogged tubes of teh intarwubs…
"Who we are, and how we function in the world around us, is very much nested in our relation to other people. Over a long period of time, solitary confinement undermines one’s sense of self. It undermines your ability to register and regulate emotion. The appropriateness of what you’re thinking and feeling is difficult to index, because we’re so dependent on contact with others for that feedback. And for some people, it becomes a struggle to maintain sanity.
That leads to the other reason why solitary is so often a part of torture protocols. When people’s sense of themselves is placed in jeopardy, they are more malleable and easily manipulated. In a certain sense, solitary confinement is thought to enhance the effectiveness of other torture techniques."