A monkey with a fingernail-size brain implant moved a cursor on a computer screen just by thinking -- the latest in a series of experiments that have raised hopes that paralyzed people might one day be able to control complex devices with their minds.

While humans have already been implanted with a similar device that allows control of a cursor, the set of thin wires used by the Brown University researchers is less bulky and worked by measuring fewer neurons.

Three rhesus monkeys were given the implants, which were first used to record signals from their motor cortex -- an area of the brain that controls movement -- as they manipulated a joystick with their hands. Then those signals were used to develop a program that enabled one of the monkeys to continue moving the cursor with its brain.

During dozens of trials over several months, the monkey moved the cursor just by thinking and used it to touch dots that appeared on the screen, earning orange juice as a reward, said John Donoghue, chairman of neuroscience at Brown.

The results are promising enough that the device could one day be used on humans, the researchers reported in the journal Nature. They would not speculate on how long that might take.

Anything that can be controlled with two- or three-dimensional coordinates can be controlled by similar implants, Donoghue said.

"Anything you can imagine can be engineered," he said.

Duke researcher Miguel Nicolelis said similar work has been done with rodents.

As for transferring the implant technology to humans, "I always estimate these transfers as somewhere between five and 10 years, but it's very encouraging," Nicolelis said.