I think that you are talking about what happens to Winston Smith's mind as he is being tortured. I think that you are talking, specifically, about something that is said in Chapter 19, or Part 3, Chapter 2.
In that chapter, we are told that Winston sole concern is to figure out what it is that they want him to confess to. He no longer cares about anything else, so he confesses to all sorts of things that he has never done, including ones that they surely know he hadn't done. All he wants is for the torture to stop.
His sole concern was to find out what they wanted him to confess, and then confess it quickly, before the bullying started anew.