Researchers at Emory University in Atlanta, Georgia, achieved the breakthrough by implanting hollow glass cone electrodes inside the brain's motor cortex - the part of the brain which controls movement - into which nerve cells grow and attach themselves.

Team leader Dr Philip Kennedy: "It is like training yourself to play tennis"

Two severely disabled volunteers who received the implants were able to control the cursor on a computer screen just by thinking about moving parts of their body.

Pointing the cursor at particular icons allowed them to communicate, making the computer voice phrases such as "I'm thirsty" or "please turn off the light".

The team hopes that as the technique is developed, the icons on the computer screen could perform more advanced functions, such as moving an artificial limb.

Simply by thinking of the movement, the computer could do what the body no longer can.

John Cavanagh, International Spinal Research Trust, interviewed on BBC One O'clock News

However, the leader of the team, Dr Philip Kennedy, said the system would not be widely available for some time.

"It is going to take many more patients ... I don't think people should get their hopes up too high yet. I think it's going to take several years," he said.

No wires

Each implant consists of a hollow glass cone about the size of a ball-point pen tip.

The BBC's Science Correspondent Pallab Ghosh explains how the implants work

The cones are laced with neurotrophic chemicals extracted from the patient's own knees which encourage nerve growth.

Over several months, the implant becomes naturally 'wired' into the patient's brain as neurones grow into the cones and attach themselves to the electrodes mounted inside.

When the person thinks of an action which would normally occur through the nervous system, it is transmitted from the electrode to the computer.

An FM transmitter under the scalp transmits the signal without wires, and power induction means no batteries are needed.

"We transmit that out, process the signals, feed it back to the patient, so he can hear the activity, and also see the cursor move. So he is learning to move the cursor from one icon to the other," Dr Kennedy explained.

More funding

The first volunteer was a woman with Lou Gehrig's disease, a neurodegenerative condition that gradually robs victims of their ability to move.

She received the implants 18 months ago and has since died of her disease.

A second volunteer, a 57-year-old man almost totally paralysed by a stroke, received the implants six months ago.