Neuroscientists in the US have shown for the first time that an electronic connection between brain and muscles can restore movement to paralysed limbs.

The experiment, carried out with macaque monkeys at the University of Washington in Seattle, could eventually increase the mobility of millions of people worldwide who are paralysed through spinal injury, stroke and brain disease. The findings were published on Wednesday in the online edition of Nature magazine.

The scientists used a "brain-computer interface", one of the hottest research topics in biology, which involved using electrodes implanted in the monkeys' motor cortex, the brain region which controls voluntary movements.

The electrodes were connected via external circuitry to a computer.

In return for food, the monkeys played a target practice game that required them to turn their wrists and to control movements of a cursor on the computer screen through neural activity. After they had mastered control of the cursor, the researchers temporarily paralysed the monkeys' wrist muscles with a local anaesthetic that blocked nerve conduction. Then the researchers converted the activity in the monkey's brain to electrical stimulation of the paralysed wrist muscles, via the external circuitry. The monkeys continued to play the target practice game - but now the cursor movements were driven by actual wrist movements, demonstrating that the monkey had regained control of the otherwise paralysed wrist, by the power of thought.

"This study demonstrates a novel approach to restoring movement through neuroprosthetic devices, one that would link a person's brain to the activation of individual muscles in a paralysed limb to produce natural control and movements," said Joseph Pancrazio of the National Institute of Neurological Disorders and Stroke, which funded the research.

The project is one of many investigating the potential for brain-computer interfaces to control paralysed limbs and prosthetic devices.

The University of Washington experiment is the first to combine a brain-computer interface with the technique, called functional electrical stimulation.

"If you have an arm whose muscles can be stimulated, a person can learn to reactivate them with this technology," said Eberhard Fetz, the study leader.