Mind Over Machine

With this discovery, the biggest supposed roadblock to making a brain-machine interface suddenly disappeared. Rather than needing to find the tiny handful of neurons responsible for a particular movement, scientists could, by listening to a small fraction of neurons in a brain, generate enough information to recognize many different commands. Think again of the brain as an orchestra: You don’t need to set up a microphone next to every instrument to tell whether the orchestra is playing Beethoven’s Fifth or Rhapsody in Blue. You could probably figure it out by listening to just a handful of musicians.


To test this supposition, Chapin and Nicolelis inserted electrodes into a rat’s brain and began monitoring 46 neurons. They then trained the rat to press a lever to get a drink of water, and used the electrodes to record the pattern of signals the animal produced to move its arm. Then Chapin and Nicolelis disconnected the lever from the water supply, so that pressing the lever did nothing. The rat went on pressing the lever, but now the scientists gave the rat a drink of water when it simply produced the "press lever" command in its brain. After a while, the rat stopped bothering to lift its arm, and just thought about lifting it.




Not long after the rat breakthrough, Nicolelis got a job at Duke and began setting up a new lab to take the research to a higher level. There he began to implant electrodes into monkeys instead of rats, hoping to get them to operate more complex equipment with their brains. Nicolelis teamed up with biomedical engineers at Duke to design new arrays of electrodes, along with high-capacity signal processors, that could handle the new challenge. "Miguel always wants more channels," says biomedical engineer Patrick Wolf with a grin. "It’s like, ’More power, Scotty.’"


By 2000, Nicolelis and his colleagues had invented a system that could recognize patterns in monkey brains well enough to let the animals swing a robot arm to the left or to the right with their thoughts. The success gave the researchers the confidence to set themselves a goal: to design a system that would allow paralyzed people to operate a prosthetic arm with a set of implanted electrodes. The arm
wouldn’t let people play a piano sonata, but it would let them do simpler things like drink a glass of water. "That’s a fairly complicated action," says Henriquez. "Going out, grabbing a glass, grabbing with enough pressure to not let it slip, raising it, drinking from it, and putting it back."


The next steps toward that goal would be to make the robot arm move in more intricate ways, and then to add a simple hand that could also follow a monkey’s commands. This is the system that’s online today: A monkey learns how to use it by sitting at a computer screen and using a joystick to move a cursor across the screen. When a dot appears on the screen, the monkey drags the cursor on top of it in order to get a squirt of juice through a tube rigged up next to its mouth. The electrodes in the monkey’s brain record the signals from its motor neurons as they form the commands that move its arm.


The signals are piped into a computer, which compares them to the joystick’s movements and figures out how to predict the latter from the former. Once the computer has grown familiar enough with the monkey’s brain patterns, it uses those signals rather than input from the joystick to move the cursor across the screen.


"After a while, like the rats before her, she realizes she
doesn’t have to move her hand," says Nicolelis. The monkey simply thinks the cursor across the screen.


Then the monkey learns to use its mind to control a robot. (The monkey, however, doesn’t realize the robot even exists; it is simply focused on moving the cursor to gain rewards.) The monkey operates the joystick again, but the signals from the joystick go to the robot arm. The cursor still moves across the screen; now, however, it’s responding to the robot’s movements rather than the joystick’s. The switch is awkward at first for the monkey—it’s a bit like learning to type with the tips of two pens instead of your fingers. But by watching the cursor move on the screen, the monkey manages to control the robot with its brain signals alone.