In December of 2001, in a small, paper-crowded office on the third floor of the Beth Israel Deaconess Medical Center, in Boston, Alvaro Pascual-Leone, an associate professor of neurology at Harvard University, showed me a video in which a colleague used a small paddle made of coiled wires to stop a man from speaking. The man, who appeared to be in his mid-sixties, was seated in a chair in a hospital laboratory. Poised above the left side of his head, just above the temple, was a circular device that looked like a thin rubber donut attached to wires. A voice from offscreen instructed the man to read a series of words off of a piece of paper, and he began. For several seconds, the man spoke normally. Then, again offscreen, a technician pressed a button, and there was a sharp electric crack. Suddenly, the man went mute. His tongue protruded from his mouth, his face contorted, and he could be seen struggling to get words out. No matter how hard he tried, though, he was silent, save for a few dim grunting noises. When the device was finally shut off, after several seconds, the man looked up with a bemused expression on his face, as if to say, “Well, that was odd.”

The technology the researcher had used to perform this experiment, and in which Pascual-Leone is a leading expert, is called Transcranial Magnetic Stimulation. It is among the less well-known neurological tools to have emerged from the neuroscientific revolution, developed as it was on the periphery of that movement, in a physiology lab in Sheffield, England. TMS works according to the centuries-old principle of electromagnetic induction, in which an alternating magnetic field is used to produce an electrical current in a conductor—in this case, in the neurons of the human cortex. TMS was invented in 1985, but it is only recently, in the past five years or so, that its applications have advanced to the point that it has come to garner some real attention in both the scientific and the general press. It was that attention that had drawn me to Pascual-Leone. But, more important, it was that attention that had drawn him to me, for although Pascual-Leone is among the more prominent researchers of TMS, he is also concerned about it as a potential source or symbol of abuse.

“Let’s say you have these guys in these airplanes trying to detect enemy fighter pilots,” he said. He was referring to a study that showed that TMS, by directly interfering with an area in one hemisphere of the brain, could improve vision in the related eye, on the opposite side of the body. “So if you have one guy on the right side and one guy on the left side with a TMS machine on the parietal lobe improving attention to their side of space, that would be super! They’d kill much more. But is this an OK thing to test? Is it an OK thing to apply?”

He proposed another scenario: “You have all this work on false memories. You have all the work on making up stories. And so you can easily envision experiments aimed at trying to find out—it may not work, but still—trying to find out if you could block a certain area of a circuit and make people unable to lie. Is that the kind of experiment that would be appropriate?”