It may seem like science fiction, but scientists say they have developed a technology that enables a monkey to move a cursor on a computer screen simply by thinking about it.

The breakthrough could someday help totally paralyzed, "locked-in" patients operate external devices such as a robot arm, or a computer to surf the Internet.

The researchers's work focuses on a section of the primate brain known as the posterior parietal cortex. Using high-tech brain scans, the researchers determined that small clumps of cells in this region -- as few as 16 -- were active in the formation of the desire to carry out specific body movements.

Armed with this knowledge, the group implanted sensitive electrodes in the posterior parietal cortex of a rhesus monkey trained to play a simple video game. The monkey's brain was first analyzed on high-tech MRI as it used its hand to touch dots on a touch-sensitive computer screen.

After the monkey has done this task several times, they were able to determine, for the particular neuron, the different patterns of electrical activity when he is planning reaches in different directions.

Going one step further, the team then trained the monkey to simply think about a movement, without reaching out and touching the screen. A computer program, hooked up to the implanted electrodes, interpreted the monkey's thoughts by tracking flare-ups of brain cell activity.

The computer then moved a cursor on the computer screen in accordance with the monkey's desires -- left or right, up or down, wherever the electrical brain pattern tells us the monkey is planning to reach.

They found that the monkey became quite reluctant to move his arm to the reach command once the cursor was introduced into the game. Apparently it was easier just to think about reaching.

Giving completely paralyzed patients full mental control of robotic limbs or communication devices has long been a dream of those working to free such individuals from their locked-in state.

These patients are completely paralyzed and cannot speak, yet they are fully conscious and aware. Brainstem strokes, injury to the upper spinal cord or diseases such as ALS (Lou Gehrig's disease) condemn tens of thousands of patients to such an existence.

Restoring even the most rudimentary communication or motor function to such patients will drastically improve their quality of life.

Of course, roadblocks remain and the technology remains crude. Still, the researchers believe they can achieve over 90% accuracy in carrying out the simple commands the monkey has been trained to perform so far. A technology that could replicate more complex movements -- such as handwriting a letter or playing games with a robot arm -- could still be years or decades away.

Even more challenging are "Terminator"-type applications that would allow the minds of healthy individuals to meld with machines -- allowing drivers to "think" their way through traffic, for example, or granting pilots the ability to navigate the skies with their mind.

Annual Meeting of the Society for Neuroscience New York January 30, 2002