Scientists in the US have enabled a paralysed woman to lift a drink to her lips with a thought-controlled robotic arm.
The development boosts hopes that tetraplegics may regain their independence.
Details of the ongoing clinical trial were published this week in the journal Nature.
On 12 April 2011, 58-year-old Cathy Hutchinson made history by using only her thoughts to get a robotic arm to grasp a flask of coffee on a table, lift it and hold it to her lips for a sip, researchers said.
14 years earlier, a stroke had left her paralysed and unable to speak, making her completely dependent on a caregiver.
In the first step six years ago, the same research group showed paralysed patients moving a cursor on a computer screen using only their thoughts.
The scientists then asked Ms Hutchinson and a 66-year-old man, identified only as Robert, to exert thought control over robotic arms "with enough precision to grab a foam target."
But Ms Hutchinson went further, succeeding in four out of six attempts to suck from the straw in the coffee flask.
The trials with what is described as the most advanced brain-machine interface, BrainGate, were conducted in the patients' homes.
Neuroscientist John Donoghue said the team had surgically implanted an electrode array the size of a baby aspirin onto the patients' motor cortex - the part of the brain that controls body movement.
The array's 96 hairpin electrodes pick up the electrical impulses of nearby neurons. The signals go to a computer where they are translated into commands that are sent to the robotic arm.
The scientists hope to improve the robotic arm so that it operates more smoothly and performs more complex tasks.
The study is a collaboration between the US Department of Veterans Affairs, Brown University, the Massachusetts General Hospital, Harvard Medical School and the German Aerospace Centre.
