There was an interesting piece in last weekend’s Guardian (A Genius Explains) about a high-functioning autistic who is also a savant (i.e. he’s got amazingly intellectual abilities – he can recall pi to 22,514 decimal places for example). Autistic savants are more common than non-autistic savants, but usually they aren’t able to quite so lucidly explain how they manage to do the things they do.
The article left me curious, and a little jealous (“It’s mental imagery”, he said “It’s like maths without having to think.”) and makes me feel like we’re in for some interesting times ahead as research into savantism, synthesia, developmental cognitive neuroscience and mental imagery converges.
Mind Hacks 
I think synesthesia (=”abnormal wiring of the brains”) really is the key to undestanting what’s happening in the mind of an autistic savant. Read his last comment:
“I do love numbers,” he says. “It isn’t only an intellectual or aloof thing that I do. I really feel that there is an emotional attachment, a caring for numbers. I think this is a human thing – in the same way that a poet humanises a river or a tree through metaphor, my world gives me a sense of numbers as personal. It sounds silly, but numbers are my friends.”
Could it be, that brain areas which in most of us are associated to dealing with other people (like our ability to empathy, for example) are connected to numbers and other logical concepts in his brains? And if someone really is as intrested in numbers, as most of us are in other people, i don’t find it so suprising that he would also have some quite extraordinary abilities in that spesific area. Brains are fairly plastic, after all.
There is a very nice lecture about synesthesia in BBC, kept by Vilayanur Ramachandran: http://www.bbc.co.uk/radio4/reith2003/lecture4.shtml