In a small lab at Brown University in Providence, RI, a rhesus macaque sits in a chair facing a computer screen, gripping the handle of a device that looks a lot like a sailboat's tiller. For the moment, the monkey uses this device as if it were a computer joystick to control a simple video game: a colored dot appears on the screen, and the animal moves the cursor to meet it. Once the animal gets good at the task, though, the researchers in the adjoining room will flip a switch and it will be signals straight from the monkey's brain, not the joystick's movements, that drive the cursor.

This eerie feat is possible because the researchers, led by Brown neuroscientist John Donoghue, have implanted a tiny array of electrodes in the monkey's brain. The electrodes intercept signals from individual neurons in the brain, and a specially developed computer algorithm translates these signals into trajectories and velocities for the computer cursor. The researchers' ambitions, however, extend way beyond video-game-playing monkeys. Their hope is that their brain-machine interface system will give patients paralyzed by spinal-cord injuries or neurodegenerative diseases new abilities to interact with the world around them-using nothing more than the power of their thoughts.