For the study, the authors recruited 15 brave volunteers to receive injections of psilocybin or placebo, in alternate sessions, while being scanned in an fMRI machine. Taken intravenously, psilocybin alters consciousness in a mere 60 seconds, as opposed to the 40 minutes it normally takes when administered orally. And the high lasts a half an hour, not the five hours that typical users experience.
Provisions were made for the possibility that the participants might panic while high in the noisy, claustrophic setting of the scanner, but none of the volunteers did so. In fact, once they’d become accustomed to the noise and small space, “they quite liked being enclosed and felt secure,” Carhart-Harris says. All of the participants had previously been, as Jimi Hendrix put it, “experienced.”
Researchers had assumed that the hallucinations and bizarre sensations caused by psilocybin would have at least one part of the brain working overtime. But instead they found the opposite.
“The decline in activity was the most surprising finding,” says Carhart-Harris, “and anything that’s of surprise is usually important.”