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.

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