The U. of Pittsburgh arm relies on just two microelectrodes implanted in the patient's left motor cortex based on functional MRI scans that pinpointed the exact nerve clusters that lit up when they asked the patient to think about moving her arm and hand. A complex set of algorithms then turns the brain signals into their corresponding movements, allowing the patient to not only move the arm but to pick up and reorient objects--with a 91.6 percent rate of success (video here). She was even able to feed herself a chocolate bar. It took her just two weeks to gain full control of the hand (though she was able to move it after just two days), and her speed increased with practice, suggesting that both the algorithms and the human brain are capable of improving performance of these kinds of brain-machine interfaces over time.