The process is quite simple. This is a double cake, filled, and I´ve used foundant icing to create the shape of a real brain. Then, just colorized with food color spray.
1- Start by creating two cakes, with circular shape.
2- Fill the cakes what each flavor you want. This will make the cake more resistant to cuts that we gonna do, and make it more tasty of course.
3- Using a knife, make a longitudinal wedge on top and continue along front and back. 
4- I´ve used foundant icing. You can get the recipe on various websites or in Youtube, like this one: http://www.youtube.com/watch?v=ZU-PpjZQjLI
5- After place the foundant icing, use a scoop or a paletteknife to sculpt the brain nodules.
6- Finally, use the color food spray. First the red, spread it equally. Then you can use Blue or Purple to create a tumor impression, or the Red again on parts of the surface, to be more irregular colored. 
7- I didn´t took a photo, but the when you have done, sticky a knife on it.
cool and weird at the same time
tayn1 year ago
becouse the brain not red or pink!! You shuld know that.
waggy1011 year ago
Why does the brain have a brown/black spot???