The brains of people tripping on magic mushrooms have given the best picture yet of how psychedelic drugs work and British scientists say the findings suggest such drugs could be used to treat depression.
Two separate studies into the effects of psilocybin, the active ingredient in magic mushrooms, showed that contrary to scientists' expectations, it does not increase but rather suppresses activity in areas of the brain that are also dampened with other anti-depressant treatments.
"Psychedelics are thought of as 'mind-expanding' drugs so it has commonly been assumed that they work by increasing brain activity," said David Nutt of Imperial College London, who gave a briefing about the studies on Monday. "But, surprisingly, we found that psilocybin actually caused activity to decrease in areas that have the densest connections with other areas."
These so-called "hub" regions of the brain are known to play a role in constraining our experience of the world and keeping it orderly, he said.
"We now know that deactivating these regions leads to a state in which the world is experienced as strange."
In the first study, published in the Proceedings of the National Academy of Sciences (PNAS) journal, 30 volunteers had psilocybin infused into their blood while they were inside magnetic resonance imaging (MRI) scanners, which measure changes in brain activity.
It found activity decreased in "hub" regions and many volunteers described a feeling of the cogs being loosened and their sense of self being altered.
The second study, due to be published in the British Journal of Psychiatry on Thursday, involved 10 volunteers and found that psilocybin enhanced their recollections of personal memories.
Robin Carhart Harris from Imperial's department of medicine, who worked on both studies, said the results suggest psilocybin could be useful as an adjunct to psychotherapy.
Nutt cautioned that the new research was very preliminary and involved only small numbers of people.
"We're not saying go out there and eat magic mushrooms," he said. "But...this drug has such a fundamental impact on the brain that it's got to be meaningful -- it's got to be telling us something about how the brain works. So we should be studying it and optimizing it if there's a therapeutic benefit."
The key areas of the brain identified -- one called the medial prefrontal cortex (mPFC) and another called the posterior cingulate cortex (PCC) -- are the subject of debate among neuroscientists, but the PCC is thought by many to have a role in consciousness and self-identity.
The mPFC is known to be hyperactive in depression, and the researchers pointed out that other key treatments for depression including medicines like Prozac, as well as cognitive behavioral therapy (CBT) and deep brain stimulation, also appear to suppress mPFC activity.
Psilocybin's dampening action on this area may make it a useful and potentially long-acting antidepressant, Carhart-Harris said.
The studies also showed that psilocybin reduced blood flow in the hypothalamus - a part of the brain where people who suffer from a condition known as cluster headaches often have increased blood flow. This could explain why some cluster headache sufferers have said their symptoms improved after taking the psychedelic drug, the researcher said.
The studies, which are among only a handful conducted into psychedelic substances since the 1960s and 1970s, revive a promising field of study into mind-altering drugs which some experts say can offer powerful and sustained mood improvement and relief from anxiety.
Other experts echoed Nott's caution: "These findings are very interesting from the research viewpoint, but a great deal more work would be needed before most psychiatrists would think that psilocybin was a safe, effective and acceptable adjunct to psychotherapy," said Nick Craddock, a psychiatry professor from Cardiff University.
Kevin Healy, chair of the Royal College of Psychiatrists' faculty of medical psychotherapy said it was interesting research "but we are clearly nowhere near seeing psilocybin used regularly and widely in psychotherapy practice."