Psychedelic brew ayahuasca’s profound impact revealed in brain scans

The brew is so potent that practitioners report not only powerful hallucinations, but near-death experiences, contact with higher-dimensional beings, and life-transforming voyages through alternative realities. Often before throwing up, or having trouble at the other end.

Now, scientists have gleaned deep insights of their own by monitoring the brain on DMT, or dimethyltryptamine, the psychedelic compound found in Psychotria viridis, the flowering shrub that is mashed up and boiled in the Amazonian drink, ayahuasca.

The recordings reveal a profound impact across the brain, particularly in areas that are highly evolved in humans and instrumental in planning, language, memory, complex decision-making and imagination. The regions from which we conjure reality become hyperconnected, with communication more chaotic, fluid and flexible.

“At the dose we use, it is incredibly potent,” said Robin Carhart-Harris, a professor of neurology and psychiatry at the University of California, San Francisco. “People describe leaving this world and breaking through into another that is incredibly immersive and richly complex, sometimes being populated by other beings that they feel might hold special power over them, like gods.”

He added: “What we have seen is that DMT breaks down the basic networks of the brain, causing them to become less distinct from each other. We also see the major rhythms of the brain – that serve a largely inhibitory, constraining function – break down, and in concert, brain activity becomes more entropic or information-rich.”

Humans have sought the altered states brought on by ayahuasca for at least 1,000 years. In 2019, an archaeological dig at a Bolivian cave unearthed a leather pouch fashioned from three fox snouts. Analysis of the bag’s interior revealed traces of DMT, cocaine, probably from coca leaf, and other psychoactive substances. The bag, dating from AD900 to 1170, was wrapped in a bundle with little llama bone spatulas, wooden snuffing tablets and a brightly coloured headband.

The brew is typically made by boiling Banisteriopsis caapi, a giant vine, with leaves from the Psychotria viridis shrub. Its name comes from the Quechua language spoken by many Indigenous groups in the Andes, with aya meaning soul, ancestors or dead people, and wasca meaning vine or rope. Translations then vary from the spiritually enigmatic “vine of the soul” to the somewhat less inviting “rope of death”.

For the latest study, Chris Timmermann, head of the DMT research group at Imperial College London, recruited 20 healthy volunteers who received a 20mg injection of DMT and a placebo on separate visits to the lab. All were screened to ensure they were physically and mentally suitable for the study.

Using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), the scientists recorded the participants’ brain activity before, during and after the drug took hold. The volunteers gave updates throughout on how intense the experience felt. None vomited as the emetic is another ingredient in ayahuasca.

The results, published in the journal Proceedings of the National Academy of Sciences, provide the most advanced picture yet of the human brain on psychedelics. The recordings show how the brain’s normal hierarchical organisation breaks down, electrical activity becomes anarchic, and connectivity between regions soars, particularly those handling “higher level” functions such as imagination, which evolved most recently in humans. “The stronger the intensity of the experience, the more hyperconnected were those brain areas,” said Timmermann.

This ability to make brain activity more fluid and flexible is thought to underpin not only the profound psychedelic experience but the promising results from early clinical trial patients who were given DMT in combination with psychotherapy to treat depression. “DMT is short-acting, so it’s a very flexible tool compared with psilocybin [the active ingredient in magic mushrooms] and LSD which can last for six to 10 hours,” said Timmermann.

But while the scans and EEGs provide an unprecedented view of the brain on DMT, the researchers believe there is more to learn. “We suspect that while the newer, more evolved aspects of the brain dysregulate under DMT, older systems in the brain may be disinhibited,” said Carhart-Harris. “A similar kind of thing happens in dreaming. This is just the beginning in cracking the question of how DMT works to alter consciousness so dramatically.”