Lefties who write just like righties, holding the pen mirror-image, have two speech centers and are less likely to suffer aphasia after a stroke. That's all I can remember from the study I read, but I assume they have other important bits on both sides of the brain.

Us lefties who contort to write are indeed the exact opposite of righties, with the brain halves reversed. It sounds counterintuitive: you'd think the brains of mirror-image lefties would be the exact opposite of righties' brains, but.