"branes can be multiple dimensional"

So, is this a case of the branes floating in 11 dimensions at once, or that they can travel through different dimensions?

I've been reading (for about a year LOL!) a book called the "Holographic Universe". I usually have about 12 books going at once. The book takes QP and even expands the ideas into even more theoretical realms. I can wrap my brain around most of the ideas, but when they get to the mathematical part of any of the theories, my eyes start rolling back in my head. Mathematics is definitely not my forte. Have you read that book, and if so, what did you think about it?