In a lab at Harvard Medical School, a man is using his mind to wag a rat’s tail. To send his command, he merely glances at a strobe light flickering on a computer screen, and a set of electrodes stuck to his scalp detects the activity triggered in his brain. A computer processes and relays the electrodes’ signal to an ultrasound machine poised over the rat’s head. The machine delivers a train of low-energy ultrasound pulses into the rat’s brain,
