Senior author David Nutt of Imperial College London said psychedelics are thought of as "mind-expanding" drugs so it is commonly assumed they work by increasing brain activity. Nutt said he and his colleagues were surprised to learn, however, that psilocybin -- a naturally occurring psychedelic compound produced by psilocybin mushrooms -- caused activity to decrease in brain areas that have the densest connections with other areas.
"These hubs constrain our experience of the world and keep it orderly," Nutt said in a statement.
In one study, published in Proceedings of the National Academy of Sciences, 30 healthy volunteers had psilocybin infused into their blood while inside magnetic resonance imaging scanners, which measure changes in brain activity. The scans showed that activity decreased in "hub" regions of the brain as many effective depression treatments do.
In a second study, scheduled to be published online by the British Journal of Psychiatry Thursday, psilocybin was found to enhance volunteers' recollections of personal memories, suggesting it could be useful as an adjunct to psychotherapy.
Ten volunteers viewed written cues that prompted them to think about memories associated with strong positive emotions. The participants rated their recollections as being more vivid after taking psilocybin compared with a placebo. Their ratings of memory vividness under the drug showed a significant positive correlation with their well being two weeks afterward.
In a previous study of 12 people last year, researchers found people with anxiety who were given a single psilocybin treatment had decreased depression scores six months later, Nutt said.