While this paper is cool, I'm not sure it reflects a real scientific advance. O'Craven and Kanwisher showed in 2000 that brain regions that when subjects imagine faces or scenes, face- or scene-selective brain areas are selectively activated (
http://www.pet.au.dk/~andreas/seminars/cog-exp/files/OCraven...). This paper builds on that previous result by showing that this result also holds for hypnagogic imagery. It's interesting but not really unexpected.