Performing even a simple movement is a rather complicated process. First, the brain has to signal its intent to perform an action, which then gets translated into the specific motions that are required to achieve that intention. Those motions require a series of muscle contractions; the signals for these need to be sent out of the brain, through the spinal cord, and to the appropriate destination.

For most people who suffer from paralysis, it's really these later steps that are affected—most of the setup can still go on in the brain, but damage keeps the signals from making their way to the muscles. If there were a way to eavesdrop on the brain, it might be possible to identify an individual's intent and translate that into some form of useful action.

This may sound like science fiction, but significant progress has been made in the area. As far back as 2006, researchers were already reporting that electrodes placed in a person's motor cortex would allow them to manipulate an on-screen object in a three-dimensional environment. More recently, monkeys with a similar implant were hooked up to a robotic arm, which they learned to use to perform some simple tasks.

Now, we've taken the next big step. Humans carrying similar implants were hooked up to a robotic arm, and they demonstrated that they could direct it to perform some simple tasks. Then one of them used it to take a sip of coffee.

The two individuals involved were implanted with the same device (termed "BrainGate") that had been used in the earlier experiments in which some individuals controlled a cursor. One of them, in fact, has been carrying the implanted electrodes for over five years now. That's quite significant, as scar tissue often forms at the site of the implants, and interferes with their ability to record brain activity. In this case, the activity readings had dropped somewhat over the years but were still able to generate sufficient signals for the system to work.

The hardware sits inside the primary motor cortex in the brain, where 96 electrodes listen in on the local activity of the neurons. By today's standards, that's not a lot of electrodes, but the BrainGate has the advantage of having been approved for use in test subjects by the FDA. The output gets fed into a computer system which can analyze the activity in real time.

Two different robotic arms were used during the experiments (The DLR Light-Weight Robot III from the German Aerospace Center and the DEKA Arm System). For both of these, the authors asked the subjects to watch as the arm went through a programmed series of movements. While watching, they were asked to imagine that they were controlling the arm. These imaginings set off activity in their motor cortex, which the computer dutifully tracked. Once the system was trained on this activity, the system was switched so that the participants were given control of the arm.

For the first task, they were asked to grasp a rubber ball attached to a stand that was easy to topple over. One subject, a 58-year-old woman, was able to reach the target successfully about half the time with the DLR arm; her rate went up to 70 percent with the DEKA system. The second participant, a 66-year-old male who has had the implant for five years, managed to hit the target over 95 percent of the time. The rate dropped for successfully grasping the ball but remained impressively high.

Pleased with this success, the researchers filled a plastic bottle with coffee, placed a straw in it, and asked the woman to have a drink. Out of six trials, they had to keep her from knocking it on the floor twice, but the other four times she successfully had a drink.

The success rates weren't enormous, but these experiments were really pretty limited. As noted above, it should be possible to get far more electrodes into the human motor cortex, providing a finer-grained view of the activity there. Plus, humans have the ability to learn how to control things better with practice, so more time with the existing systems may produce better results. Finally, in many systems, neurons rearrange their connections based on activity. If the participants used the arm as part of their daily routines, it's possible that the system would start seeing clearer signals that are easier to interpret.

Nature, 2012. DOI: 10.1038/nature11076 (About DOIs).