Snap, crackle, pop. I'm listening to a brain talking in a language that seems unintelligible, a chorus of millions of neurons firing, sounding to my ear like the electrical fuzz of a shortwave radio between stations. Then comes a distinctive "pop." I hear it again: "pop." I am watching a video. The brain in question belongs to a bearded man sitting in a chair. The victim of a stabbing three and a half years ago, he is paralyzed from the neck down. The ventilator that allows him to breathe is gurgling. Matthew Nagle, a 25-year-old former high-school football star from Weymouth, MA, has a round, titanium pedestal protruding half an inch from his head on the right side near the crown.

On July 4, 2001, Nagle became involved in a melee at Wessagussett Beach in Weymouth. He remembers only that fists began to fly and that a friend was under attack. Someone shouted something about a knife, and Nagle blacked out. Later that night, when his father, a police detective, got a call from the police, he was told that his son would probably die. The 20-centimeter blade had severed the spine in his neck, leaving him paralyzed and on a respirator. Nagle survived, but after years of immobility and tedium, he agreed to take part in a clinical trial to determine whether or not a human could safely manipulate a computer cursor using a brain-computer interface (BCI).