A man paralysed from the neck down has been able to open e-mails, control a television and move objects with a robotic arm, simply by thinking about it.

Matthew Nagle, 25, had a computer-linked implant placed in his brain that enabled him to operate devices by thought alone.

Brain-computer interfaces have been demonstrated before, in humans and animals, but this is the biggest step so far towards developing "bionic" systems that can restore motor function in people who have lost control of their limbs.

The results, described in the journal Nature, represent the culmination of decades of work, although scientists involved in the research said the technology was still in its infancy.

Mr Nagle, from Massachusetts in the United States, whose spinal cord was severed in a knife attack in 2001, received his implant in 2004.

Known as the BrainGate Neural Interface System, it consists of a sensor measuring just 4mm across containing 100 tiny electrodes, each thinner than a human hair. It is placed on the surface of the motor cortex, the area of the brain responsible for voluntary movement, and the implant’s signals are decoded and processed by a computer, allowing them to be translated into movement commands.

Mr Nagle first learned to move a computer cursor by focusing his thoughts on the task. Later, during 57 trial sessions at a rehabilitation centre in Massachusetts, he greatly expanded his repertoire of thought control.

He was able to open simulated e-mails, draw circular shapes on the computer screen, play a simple video game and change the channel and adjust the volume on a television.

Ultimately, he could open and close the fingers of an artificial hand and use a robotic arm to grasp and move objects.

Professor John Donoghue, who led the research and heads the brain-science programme at Brown University, Rhode Island, said: "The results hold promise to be able one day to activate limb muscles with these brain signals, effectively restoring brain-to-muscle control via a physical nervous system."

Previous attempts at linking brains to computers have had only limited success, such as getting patients to move a cursor to the left and right.

Experts had not been certain that the brain’s limb-control signals could still be found years after a paralysing spinal injury. But such doubts were put to rest by the success with Mr Nagle.

"We’re finding that, even years after spinal cord injury, the same signals that originally controlled a limb are available and can be utilised," Dr Leigh Hochberg, a neurologist and a member of the research team, said.