At 9:15 in the morning two or three times a week, Jan Scheuermann maneuvers her electric wheelchair into a research laboratory at the University of Pittsburgh, where she plugs her head into a highly sophisticated piece of equipment. Two ports in her scalp connect to a prosthetic limb, a sleek, black anthropomorphic arm that extends from a metal scaffold in the lab. She is one of a dozen or so volunteers worldwide who have received brain implants as part of multiyear experiments on how to manipulate objects with their thoughts alone. More than any other user of brain-controlled prostheses, Scheuermann has learned to wield the arm with exquisite dexterity, articulating individual fingers to shake hands and rearrange objects at a wide range of speeds. “Every day I go to work, I think, this is the coolest thing,” she says.