You have to be extremely concentrated for practicing, especially when it's a hard section. If your mind starts wandering around, you can forget it.Practice consciously. Don't do a mere and dumb repetition, letting your fingers take over. Your mind needs to be totally involved what you're doing, guiding your motions, improving your touch. Practicing is a rational act. It's not like going to the gym and walking on that machine while you read a book...
I will sit on the fence here, but let you know that in Charles Rosen's new book, Piano Notes, he contradicts this in it's entirety! He says: Think about other things while practising, since this will make the action of the fingers unconscious allowing the music to be made over the physical action. He even suggests reading a book while practising! But not one which is difficult to read, he recommends detective stories. He also mentioned that one of Liszt's biggest tips to his pupils was to read a book whilst practising, and did this himself! Ed