Mark Jackson is playing a computer game with his mind. As he reclines in bed, three blue circles appear on a laptop screen a few feet away. One turns red: the target. Jackson is in control of a white circle, which he needs to steer into the target without running into the blue obstacles. The game is a bit like Pac-Man. Except instead of a joystick, Jackson uses his thoughts to control his little white circle. To move left, he thinks about clenching his right fist once. To move right, he thinks about doing it twice in a row, like a double click.
Jackson, who is 65 and paralyzed, is