You've probably seen sensory maps (homunculus) that show how much of the brain is devoted to the senses from different parts of the body. This picture shows a sort of sensory map for a mouse in that the body parts are resized to show how much of the brain is devoted to each. The face spots represent the whiskers. It looks like a children's cartoon version of a mouse, doesn't it? An article at The Loom shows the same mouse drawn in normal proportions, and also a sensory map in which scientists manipulated the genes of baby mice to see how the map would be affected. They already knew that experience shapes the sensory map as an animals grows, but genetics and therefore chemistry also play a part. Read more about this research in the article by Carl Zimmer. Link
(Image credit: Andreas Zembrzycki and Jamie Simon, Salk Institute for Biological Studies)