We often hear that imagining something will not make it so. But scientists have now overturned that adage, making a science-fiction dream come true.  U.S. researchers have shown that a paralyzed patient can use thoughts to control some aspects of his or her environment.

Matthew Nagle, 26, of Weymouth, Massachusetts, is paralyzed below the shoulders because he was stabbed in the neck during a fight. But his inability to move his limbs does not mean that he and others like him will forever be unable to perform some of the daily activities the rest of us do.

Brown University nerve scientist John Donoghue and colleagues give new hope to such patients in a paper in the journal Nature.

"The paper is about the technology that we've developed to help a paralyzed person communicate with the outside world again, to be able to use their thoughts to control devices," said Mr. Donoghue.

Such patients might never be able to levitate a fork to feed themselves, but under Donoghue's supervision, Nagle was able to do things just as exciting. With a tiny electronic sensor implanted in his brain, he was able to use a television, a robot arm, and even a computer.

"We have the patient imagine that he's tracking a cursor on a screen," he explained.  "The patient is able to just think about moving and the cursor will move pretty much in the motion that the hand would take, if you were to imagine, say, moving left or right."

Nagle opened e-mail, changed the volume on a television, opened and closed a prosthetic hand and performed basic actions with a multi-jointed robotic arm.

The implanted brain sensor making this possible had an array of electrodes that recorded nerve activity in an area typically involved in arm movement. This is the first demonstration that such brain activity persists in paralyzed people. The information recorded by the electrodes was decoded and processed by a computer, allowing nerve firing patterns to be translated into movement commands that drove the devices.

But John Donoghue told Nature magazine, the movements are not yet smooth.

"The motion of the cursor by thought is wobbly and unstable," he noted.  "What that means is that, at least, we haven't found out how to exploit the brain's plasticity. So, we need to change the computer to make the control signal better. We're doing that, and actually having some good success."

A way to improve performance is described in a second Nature paper by Stanford University researchers. Nerve scientist Krishna Shenoy and colleagues implanted sensors in monkey brains that recorded nerve activity further ahead in the circuit involved in arm movement, not near the nerve cells controlling the movement itself, but those involved with the intention to move.

"These cells relate to how you wish to move your arm and through mathematical algorithms we're able to interpret those neurosignals to predict, which way one would wish to move their arm," he said.

This is how it sounds.

The scientists were able to predict the intended location of movements before the monkeys made them.

Both sets of researchers say the implants are better than previous experiments with electrodes attached outside the scalp. The internal electrodes record nerve signals for specific movements, whereas the scalp electrodes sense activity throughout the brain.

Krishna Shenoy's Stanford University colleague, spine specialist Stephen Ryu, says the research could help improve the quality of life for paralyzed people.

"But, in order to actually translate this to something, which will be helpful to people, we're going to have to take it to another level, where we can show that they're both safe, and that they're effective, and can replace function that's already been previously lost," said Mr. Ryu.

A major issue is that the brain implants still require a lot of equipment. Ryu says that, to become practical, the devices will need to be much smaller and automated.

"I think it is only a matter of time before we really start to see some true promise from these things."