Helping yourself to a cup of coffee may seem like a small, everyday thing. But not if you are quadriplegic. Unlike paraplegics, for whom the robotic legs described in the previous article are being developed, quadriplegics have lost the use of all four limbs. Yet thanks to a project organised by John Donoghue of Brown University, in Rhode Island, and his colleagues, they too have hope. One of the participants in his experiments, a 58-year-old woman who is unable to use any of her limbs, can now pick up a bottle containing coffee and bring it close enough to her mouth to drink from it using a straw. She does so using a thought-controlled robotic arm fixed to a nearby stand. It is the first time she has managed something like that since she suffered a stroke, nearly 15 years ago.
    Arms are more complicated pieces of machinery than legs, so controlling them via electrodes attached to the skin of someone's scalp is not yet possible. Instead, brain activity has to be recorded directly. And that is what Dr. Donoghue is doing. Both his female participant and a second individual, a man of 66 also paralysed by a stroke, have worked with him before, as a result of which they have had small, multichannel electrodes implanted in the parts of the motor cortexes of their brains associated with hand movements. The woman's implant was put there in 2005; the man's five months before the latest trial, described in a paper just published in <em>Nature</em>.
    Dr. Donoghue and his team decoded signals from their participants' brains as they were asked to imagine controlling a robotic arm making preset movements. The volunteers were then encouraged to operate one of two robot arms by thinking about the movements they wanted to happen. When the software controlling the arms detected the relevant signals, the arms moved appropriately.
    Dr. Donoghue and his colleagues have thus shown that a mechanical arm can be controlled remotely by the brain of a person with paralysis. Controlling a true prosthetic-an arm that is attached to the individual's body-will be trickier, but in time even that may be possible. In the meantime, a robotic arm attached to (say) a wheelchair will be a real boon. For people who have little or no ability to move their arms Dr Donoghue's work promises liberation in the form of quotidian action that the able-bodied take for granted.  Dr. Donoghue's experiments include ______.