The team subjected a group of volunteers to a brief electromagnetic pulse via cranial electrodes, and watched the ripple of brain activity it produced. The pulse produced patterns of activity through the brains of 32 alert, healthy people. In asleep, healthy people, the pulse produced a shorter response, which stayed physically closer to the location of the pulse, Nature says. The varying brain activity was quantified according to its complexity, and Boly and her colleagues used this to up with a "response complexity" metric. Then they tried the same technique on a group of people who had been diagnosed as vegetative, minimally conscious or "locked-in." In the vegetative people, the pulses looked a lot like the sleeping-subject brain patterns. As the patients' levels of consciousness increased, so did the complexity of their brain responses.