Mind Over Machine

The source of all those 1s and 0s is, of course, the brain’s billions of neurons. When a neuron gets an incoming stimulus at one end—for example, photons strike the retina, which sends that visual information to a nearby neuron—an electric pulse travels the neuron’s length. Depending on the
signals it receives, a neuron can crackle with hundreds of these impulses every second. When each impulse reaches the far end of the neuron, it triggers the cell to dump neurotransmitters that can spark a new impulse in a neighboring neuron. In this way, the signal gets passed around the brain like a baton in a footrace. Ultimately, this rapid-fire code gives rise to electrical impulses that travel along nerves that lead out of the brain and spread through the body, causing muscles to contract and relax in all sorts of different patterns, letting us blink, speak, walk, or play the sousaphone.


In the 1930s, neuroscientists began to record these impulses with implantable electrodes. Although each neuron is coated in an insulating sheath, an impulse still creates a weak electric field outside the cell. Researchers studying rat and monkey brains found that by placing the sensitive tip of an electrode near a neuron they could pick up the sudden changes in the electric field that occurred when signals coursed through the cell.


The more scientists studied this neural code, the more they realized that it wasn’t all that different from the on-off digital code of computers. If scientists could decipher the code—to translate one signal as "lift hand" and another as "look left," they could use the information to operate a machine. "This idea is not new," says John Chapin, a collaborator with the Duke researchers who works at the State University of New York Downstate Health Science Center in Brooklyn. "People have thought about it since the ’60s."


But most researchers assumed that each type of movement was governed by a specific handful of the brain’s billions of neurons—the need to monitor the whole brain in order to find those few would make the successful decoding a practical impossibility. "If you wanted to have a robot arm move left," Chapin explains, "you would have to find that small set of neurons that would carry the command to move to the left. But you don’t know where those cells are in advance."


Thus everything that was known at the time suggested that brain-machine interfaces were a fool’s errand. Everything, it turned out, was wrong.




In 1989, Miguel Nicolelis arrived from Brazil at Hahnemann University in Philadelphia, intent on cracking the neural code, regardless of how complex it might prove to be. At Hahnemann he found the perfect collaborator in John Chapin, who had spent the previous decade working on a device that could take 12 separate recordings from the brain at once; if the two of them could perfect it, they’d be the first to be able to listen to more than one neuron at a time.


Every aspect of the project posed new challenges. To work adequately, the electrodes needed to be tiny enough to be safely inserted into the brain, and precise enough to send a reliable stream of data to a computer. Conventional electrodes would get covered in scar tissue. The problem, Chapin and Nicolelis found, was that the electrodes, designed as rigid spikes, were damaging the surrounding brain tissue—so the scientists subbed in electrodes with flexible tips. "They have to float around," Nicolelis says. "But if they are rigid and move around, the brain can be dissected."


By the mid-’90s, Nicolelis and Chapin finally were inserting their arrays of electrodes into the brains of living rats—and what they discovered instantly challenged the conventional wisdom on the way neurons send their messages. What they found was that the commands for even the simplest of movements—twitching a whisker, for example—required far more than just a tiny cluster of neurons. In fact, a whole orchestra of neurons scattered across the brain played in synchrony. And the neurons behaved like an orchestra in another important way. Beethoven’s Fifth Symphony and Gershwin’s Rhapsody in Blue sound nothing alike, even if many of the same musicians are playing both pieces, on many of the same instruments, using many of the same notes. Likewise, many of the same neurons, it turned out, participated in generating many different kinds of body movement.