Dr Miguel Nicolelis knew he was on to something special when he implanted a device that allowed a monkey to control the game using only her thoughts.

Nicolelis and colleagues revealed their invention to the world in a report published at the Public Library of Science Biology journal on Monday.
   
Changes in the way the monkey's brain cells worked suggested the brain was physically adjusting to the device, they reported in the new online science journal.
   
What’s the point?

Nicolelis hopes the device will eventually allow paralysed patients to use their upper bodies - virtually, if not physically.
   
"The monkey suddenly realised that she didn't need to move her arm at all," Nicolelis said in a statement.
   
"Her arm muscles went completely quiet, she kept the arm at her side and she controlled the robot arm using only her brain and visual feedback."
   
Three years ago, Nicolelis and colleagues at Duke University in North Carolina reported that they had allowed a monkey to move a robotic arm using only her thoughts and implanted electrodes.

But the monkey continued to move her arm.
   
In the latest experiment, they said two monkeys figured out what was happening and played a computer game using thoughts alone.
   
Aurora and Ivy
   
"It's very different because these animals now receive feedback information," Nicolelis added in a telephone interview. 

It seems monkeys could learn to correct their errors and achieve a very high level of proficiency, using brain activity alone to reproduce reaching and grabbing hand movements.
   

"Her arm muscles went completely quiet, she kept the arm at her side and she controlled the robot arm using only her brain and visual feedback"

Dr Miguel Nicolelis,
Duke University in North Carolina

Nicolelis and colleagues first implanted microelectrodes - each smaller than the diameter of a human hair - into the brains of two female rhesus macaque monkeys, named Aurora and Ivy.
   
One got 96 electrodes in her frontal and parietal lobes - known to be the source of commands for muscular movement. The second monkey got 320 implants.
  
The electrodes transmit faint signals to a computer system the researchers have developed to recognise patterns of signals that represent particular movements by an animal's arm. These signals are translated and in turn control a robotic arm.
   
Playing level 2

At first, the animals were taught to use a joystick to control the cursor of a video game - which Nicolelis said they enjoyed playing.

The researchers recorded and analysed the electrical activity of the neurons near the implanted electrodes.
   
As the game became more complex, the monkeys learned how to control the cursor.
   
The group has started working with a small group of human patients, but Nicolelis said he could not give any details yet.
   
Benefits

Potential users include 200,000 people in the United States alone who have partial or nearly total permanent paralysis.

An estimated 11,000 people a year suffer severe spinal cord injuries, for instance, and sufferers of Parkinson's disease and amyotrophic lateral sclerosis, also called ALS or Lou Gehrig's disease, may also become paralysed.
   
"We hope the brain will learn to adapt to the devices and incorporate them as if they were the patient's own limbs," Nicolelis said.