Magic mushrooms work by shutting down parts of the brain, not expanding the mind, according to new research

Six thousand years ago palaeolithic hunters painted images on the walls of the Selva Pascuala caves in Spain that look remarkably similar to locally abundant Psilocybe hispanica, one of the many “magic mushrooms” that contains the hallucinogen psilocybin. The same or similar mushrooms have been used throughout the ages to induce states of religious ecstasy, spiritual enlightenment, mystical meanderings or simply to have a great time. But how do they work? Timothy Leary, who famously told a generation of Americans to “turn on, tune in, drop out”, claimed these “mind-expanding chemicals … acts as a chemical key – it opens the mind, frees the nervous system of its ordinary patterns and structures”.

But a few weeks ago an Imperial College-based research group headed by Professor David Nutt (who was sacked as the government’s chief drug adviser in 2009 after claiming that ecstasy and LSD were less dangerous than alcohol) reported a study that appears to show that, far from expanding the mind, psilocybin shuts it down. The researchers claim that by closing down certain regions of the brain that normally keep our minds on the reality rails, psilocybin may “enable a state of unconstrained cognition”. More “turn off, tune in, drop out”.

Professor Nutt suggests that psilocybin may be beneficial in the treatment of psychiatric diseases, such as depression, where the areas affected by the drug are often hyperactive. But perhaps one of the most intriguing aspects of the study is what it tells us about how our brains construct conscious experience.

The researchers used a technique known as functional magnetic resonance imaging (fMRI) to continuously scan the brains of 15 subjects who were given psilocybin (under medical supervision) and asked to perform a battery of tests and rate their experiences. The subjects reported profound changes in consciousness including dreamlike states, visual hallucinations, heightened imagination and a sense of joy; and even felt that their experiences possessed a supernatural quality – all feelings that I’m sure would have been familiar to our palaeolithic ancestors.

But what was novel about these studies was that the researchers were able to simultaneously monitor the flow of blood through the brain. They were surprised to discover that, far from switching on underused regions, the hallucinogen caused decreased blood flow through so-called “hub regions” of the brain that connect its many parts.

Making brains work better, or at least differently, by closing down bits is not new. Immersion in isolation tanks that minimise sensory experience have been a popular form of consciousness-raising alternative medicine and meditation since the 1970s. For more than a decade Allan Snyder of the University of Sydney has used transcranial magnetic stimulation (TMS) to inhibit the left anterior temporal lobe (LATL) of the brain. Under the influence of TMS, his otherwise normal subjects can perform tasks (naturalistic drawing, mental arithmetic, efficient proofreading) to a standard that is usually considered the reserve of autistic savants. Snyder believes that the LATL normally acts as a gatekeeper that keeps the nitty-gritty detail of the real world from gaining entry to our holistically focused conscious mind. People with a diagnosis of autism spectrum disorder, he claims, have direct access to the detail but at a price of losing the ability to handle the holistic stuff. The rest of us need our gatekeeper to be disabled before we can experience the world in all its detail.

Professor Nutt’s studies suggest that psilocybin undermines brain connectivity, targeting the informational hubs where parallel streams of information compete for attention. These hubs may act as mental bouncers, keeping unwanted guests from disturbing the sobriety of our conscious minds. Our palaeolithic hunter ancestors found that it is was sometimes fun to eat mushrooms that would give the bouncer a night off and thereby enjoy the company of more riotous mental guests.

But mushrooms were, and still are, a dangerous way of tinkering with brain chemistry. Thousands of people suffer from mushroom poisoning each year, mostly from eating supposedly edible mushrooms, but the occasional death has also been reported from ingestion of magic mushrooms. Professor Nutt’s study identifies those regions of the brain that are switched off by magic mushrooms. That knowledge, combined with the TMS-mediate manipulations provided by Allan Snyder’s work may eventually provide a safe means for us all to enjoy the kind of experience that is normally reserved for the less risk-averse.