A fetus has millions of excess connections throughout its brain, but it's almost like the brain prunes itself as it develops. This keeps our senses separate. Mostly. But synesthetes have a gene or genes that allow some of these branches to grow wild. But why?
V.S. Ramachandran has a clue. Synesthesia is eight times more common in artists, writers, and musicians. And his theory is that those wild branches in synesthetes' brains help them create metaphors. "You've got excessive connections throughout the brain, that in turn provides a neural substrate [which] gives you the opportunity to link seemingly unrelated ideas and concepts, which is the basis of metaphor."
-- Michael May for Studio 360 (2/1/08)