This technique takes a dead brain and permeates it with a transparent hydrogel matrix to keep proteins and nucleic acids in place. Then it removes the lipids. I guess the lipids are all that makes the brain opaque. At this point the brain is transparent but maintains its original structure so you can still label the proteins and nucleic acids.
President Obama: “Now, it’s time to get to work.”
NYT article: http://www.nytimes.com/2013/04/02/science/obama-to-unveil-initiative-to-map-the-human-brain.html