 Researchers at Washington University in St. Louis scanned the brains of seven people who took either a stimulant or psilocybin, the active substance in magic mushrooms. Dr. Joshua Siegel says the drug caused dramatic changes in networks of brain cells that usually fire at the same time. What's going on during psilocybin is that populations of neurons that are normally in synchrony are out of synchrony. The change was greatest in a brain network that creates a person's sense of space, time, and self.