To derive a numerical measure of consciousness, Boly and her colleagues pulsed subjects’ heads with a brief electromagnetic wave, then measured neural responses using electrodes stuck to the scalp.
In 32 healthy, awake people, the electromagnetic impulse sent complex patterns of electrical activity reverberating throughout the brain. In healthy sleeping people, or people under general anaesthesia, the brain displayed shorter, simpler responses that stayed closer to the site of the initial stimulation. The researchers quantified these differences in a measure of response complexity.
