As imaging studies by the U.C.L.A. neuroscientist Naomi Eisenberger show, the same areas of the brain that register physical pain are active when someone feels socially rejected. That’s why being spurned by a lover hurts all over the body, but in no place you can point to.

http://opinionator.blogs.nytimes.com/2012/03/24/the-brain-on-love/?src=me&ref=general#