Turn off, tune in, drop out

Magic mushrooms reduce blood flow to parts of brain

When Timothy Leary advised his generation to “turn on” by taking psychedelic drugs, he got it all wrong. Turning off parts of the brain may be the real secret to expanding your mind, a new study of hallucinogenic mushrooms finds.

The study is the most detailed look yet at where and how psychedelics work in the human brain, says psychiatrist and neuropsychopharmacologist David Nutt of Imperial College London, whose team reports the findings online January 23 in the Proceedings of the National Academy of Sciences.

Nutt and colleagues recruited 15 people with previous experience taking hallucinogens. Each was injected with a small amount of psilocybin, the ingredient responsible for magic mushrooms’ mind-bending properties. The effect was immediate, peaking in just minutes and lasting for about an hour.

Before and after the volunteers tripped out — one described the experience as “dissolving,” another as “kneeling at the foot of God” — their brains were scanned. These measurements revealed decreases in the amount of blood flowing through parts of the volunteers’ brains. Surprised by the result, the researchers repeated the experiment with another group, using a different scanning technique. The same pattern of reduced activity emerged, most pronounced in the hubs that connect different parts of the brain — including the thalamus and parts of the cingulate cortex.

“The findings are astounding and are going to completely change how we understand the action of hallucinogens,” says psychiatrist and pharmacologist Bryan Roth of the University of North Carolina at Chapel Hill, who was not involved in the study. “They’re the complete opposite of what has been predicted.”

Previous studies suggested that hallucinogens stimulate certain kinds of neurons in mice. Nutt expected to see an uptick of activity in the visual regions of the brain, which would explain the kaleidoscopic hallucinations often experienced by magic mushroom users.

But suppressing core regions that help to coordinate and control the brain could have deeper, more philosophical consequences. It fits with how Aldous Huxley described the effects of mescaline — a hallucinogen that, in his words, flung wide the “doors of perception.”

“Decreasing the activity in certain hubs in the network may allow for a more unconstrained conscious experience,” says Matthew Johnson, an experimental psychologist at Johns Hopkins University School of Medicine in Baltimore who studies psilocybin and other hallucinogens. “These drugs may lift the filters that are at play in terms of limiting our perception of reality.”

Further work by Nutt’s team showed that the brain hubs responded together, linked by a neural circuit called the default mode network. Some scientists believe this highly interconnected brain superhighway is essential for maintaining a person’s sense of self.

Putting the brakes on this network could help to treat certain psychological conditions by opening the brain to new ways of thinking, researchers hope. Several studies have shown that psilocybin can change people’s attitudes for the better and may be useful for treating depression, a condition linked to too much activity in the default mode network.

“Chemically switching off might have very profound beneficial effects,” says Nutt, who suspects that psilocybin could also be useful for treating obsessive-compulsive disorder. “It may help people completely locked into a mindset that drives their lives.”

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