'Mind-expanding' mushrooms decrease brain activity
Instead of increasing brain activity, psilocybin – the active ingredient in magic mushrooms – suppresses brain activity while helping people to experience memories more vividly.
In the first of two studies, 30 volunteers had psilocybin infused into their blood while inside MRI scanners. The scans showed that brain activity decreased in hub regions of the brain – areas especially well-connected with other areas.
“Psychedelics are thought of as ‘mind-expanding’ drugs so it has commonly been assumed that they work by increasing brain activity, but surprisingly, we found that psilocybin actually caused activity to decrease in areas that have the densest connections with other areas,” said Professor David Nutt, senior author on both studies. “These hubs constrain our experience of the world and keep it orderly. We now know that deactivating these regions leads to a state in which the world is experienced as strange.”
Intensity of the effects reported by the participants – including visions of geometric patterns, odd bodily sensations and an altered sense of space and time – correlated with a decrease in oxygenation and blood flow in the medial prefrontal cortex (mPFC) and posterior cingulate cortex (PCC).
In the second study, ten volunteers viewed written cues that prompted them to think about memories associated with strong positive emotions while inside an MRI scanner. Recollections were more vivid after taking psilocybin compared with a placebo, and upon taking the substance, there was increased activity in the areas of the brain that process vision and other sensory information.
Participants were also asked to rate changes in the emotional wellbeing two weeks after taking psilocybin and the placebo. Their ratings of memory vividness under the drug showed a significant positive association with their wellbeing two weeks later.
“Psilocybin was used extensively in psychotherapy in the 1950s, but the biological rationale for its use has not been properly investigated until now,” said Dr Robin Carhart-Harris, first author. “Our finding support the idea that psilocybin facilitates access to personal memories and emotions.”
The studies are published in the Proceedings of the National Academy of Sciences (PNAS) and The British Journal of Psychiatry.