LAST RESORTS Squeeze my hand, Stephen," the surgeon called. "Wiggle your feet." In an operating room at New York Weill Cornell Medical Center, doctors watched intently as Stephen R. Neiley III, roused from general anesthesia, gave a squeeze and a wiggle and went back to sleep. Reassured that the electrodes they had just implanted in his brain had done no harm, they went back to work. The next step was to tunnel wires from the electrodes through Mr. Neiley's scalp and neck to a pacemaker-like gadget that would be implanted in his chest. The operation was an experiment, with a...