This TED performance by Derek Paravicini is truly amazing. Born more than 3 months early, Derek is blind and severely autistic, has perfect pitch and can play full melodies on the piano from memory. Adam Ockelford has been Derek's piano teacher from childhood, and explains that Derek understands music systematically: since he is unable to see the keys or read music, he memorizes how the melody should go, and then replays it.
The audience picked a song, and he played it from memory. He can also improvise songs for a completely different take on it.
It's so interesting how the brain works. It's like the brain is a constant improvisation shaped by DNA, circumstance, and our teachers and loved ones who encourage us to grown, learn, and inspire others down the road.