The active ingredient in psychedelic mushrooms decreases brain activity, possibly explaining the vivid, mind-bending effects of the drug, a new study finds.

The decreases were focused in regions that serve as crossroads for information in the brain, meaning that information may flow more freely in a brain on mushrooms. The findings could be useful in developing hallucinogenic treatments for some mental disorders.

"There is increasing evidence that the regions affected are responsible for giving us our sense of self," study author Robin Carhart-Harris, a postdoctoral researcher at Imperial College London, wrote in an email to LiveScience.

"In other words, the regions affected make up what some people call our 'ego.' That activity decreases in the 'ego-network' supports what people often say about psychedelics, that they temporarily 'dissolve the ego.'" [10 Most Destructive Human Behaviors]

Quieting the brain

Psilocybin, the chemical that gives mushrooms their trippy properties, has long-lasting effects beyond the initial high. A recent Johns Hopkins University study found that a single experience with psilocybin in a controlled environment can alter personality long-term, making people more open to new experiences.

"Healthy people given psilocybin often describe their experiences as among the most meaningful of their whole lives, comparable to such things as the birth of their first child or getting married," Carhart-Harris said. "We wanted to know what is going on in people's brains to produce such profound effects."

The researchers asked 15 people who had used mushrooms in the past to lie in a functional magnetic resonance imaging (fRMI) scanner, which measures blood flow in the brain to determine brain activity in different regions.

After a few minutes, the researchers injected either psilocybin or a placebo into the participants' veins. (Each volunteer participated in two scans, so everyone had one experience with the hallucinogen and one with the placebo.) They then continued the scan to find out what changes occurred in brain activity.

A promising treatment?

The scans revealed a surprise: Psilocybin never increased activity in the brain, but only decreased activity in places, especially information transfer areas such as the thalamus, which sits smack in the middle of the brain.

"'Knocking out' these key hubs with psilocybin appears to allow information to travel more freely in the brain, probably explaining why people's imaginations become more vivid and animated and the world is experienced as unusual," Carhart-Harris said.

The researchers used multiple fMRI methods to validate their findings, and controlled for outside factors to be sure, for example, that psilocybin didn't cause breathing changes that, in turn, changed the brain. What actually seems to be happening, Carhart-Harris said, is that psilocybin mimics the effect of the brain chemical serotonin. In the brain, psilocybin sticks to serotonin receptors on brain cells, inhibiting the activity of those neurons. The effect lasts about a half-hour for a moderate dose given as an intravenous shot, Carhart-Harris said.

The researchers plan to further investigate these brain-bending effects as a treatment for depression. The regions quieted down by psilocybin are overactive in depression, Carhart-Harris said, so this mushroom ingredient could be an alternative treatment to lift mood.

But the findings aren't a license for anyone to start self-medicating with mushrooms, Carhart-Harris warned. The participants in this and other psilocybin studies have all been experienced and healthy psilocybin users in a controlled environment; some people can experience terrifying "bad trips" on psychedelics, he said. Without proper psychological care, the effects can be long-lasting and harmful.

"These are preliminary results, and a lot more research is required before claims can be made about the therapeutic value of psychedelics," Carhart-Harris said. "However, the initial signs are promising."

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