But now scientists in the US have invented a device which retrains the undamaged side of the brain to take over the tasks of the damaged part.

"We have shown that a brain-computer interface using the uninjured hemisphere can achieve meaningful recovery in chronic stroke patients," said Prof Eric Leuthardt

In general, the left hemisphere controls the right side of the body and vice versa but about a decade ago, Prof Leuthardt and Dr David Bundy discovered that a small area of the brain on the same side of the limb sends the first ‘movement’ signal.

They theorised that if they could harness and amplify that initial signal, they could use it to control movement in a paralysed limb.

The new device comprises of a cap containing electrodes to pick up the brain signal and send it to a moveable brace on the arm. The device detects the wearer's intention to open or close the paralyzed hand, and moves it accordingly.