Alien Hand Syndrome sees woman attacked by her own hand
In a nutshell, this woman suffered from epilepsy. Doctors remedied her ailment by "cutting out a small section of her brain." In her case, they did something a bit more drastic - they severed the corpus callosum - which is the link between the two halves of her brain. This effectively, it would seem, create two brains and thereby doubling the processing power - your very own dual-core processor!
Of course I would imagine there is a little bit of re-conditioning and training you would have to do to get both halves to not only work properly and independently, but also to work towards the same goal.
That BBC series, by the way, looks absolutely fascinating. I'll have to look it up and DVR it sometime.
via: Scott Adams blog