I don't remember the author off hand (maybe John Varley?) but there is a science fiction novel where people are kept as heads with all of their nerves hooked up

I don't remember the author off hand (maybe John Varley?) but there is a science fiction novel where people are kept as heads with all of their nerves hooked up in such a way that ANY sensation could be perfectly created. Needless to say, it was possible to go to some pretty dark places with this. Imagine, for example, feeling like you had to urinate but never being able to relieve yourself for all eternity. And that was one of the "lighter" abuses. shiver