The visions induced by an Amazonian brew used by shamans may be as real as anything the eyes actually see, according to brain scans of frequent users of the drug.
Draulio de Araujo of the Brain Institute at the Federal University of Rio Grande do Norte in Natal, Brazil, and colleagues recruited 10 frequent users of the brew – called ayahuasca. They asked the volunteers to look at images of people or animals while their brains were scanned using functional MRI, then asked the volunteers to close their eyes and imagine they were still viewing the image. Unsurprisingly, the researchers found that neural activity in the primary visual cortex dropped off when volunteers imagined seeing the image rather than actually viewing it.
But when the team then gave the volunteers a dose of ayahuasca and repeated the experiment, they found that the level of activity in the primary visual cortex was virtually indistinguishable when the volunteers were really viewing an image and when they were imagining it. This means visions seen have a real, neurological basis, says de Araujo – they are not made up or imagined.
Michael Brammer, head of the brain imaging unit at King's College London, says the study's statistics appear to indicate something relatively robust. However, he says it's difficult to pin down whether the eyes-closed responses on the drug are quantitatively the same as normal, eyes-open neural activity. "Functional MRI is not a one-to-one mapping of cerebral activity. If it were, things would be easier," he says.
Robin Carhart-Harris of Imperial College London has done similar fMRI work using the "magic mushroom" hallucinogen psilocybin. He says the results also have practical implications, such as for the application of psychedelics in psychotherapy.
Ayahuasca may also find its way into the psychiatrist's drug kit. The pharmacology of its ingredients tallies with the way some conventional drugs work; because of this, researchers are interested in ayahuasca's potential for treating addiction, depression or conditions such as post-traumatic stress disorder. One of the brew's two ingredients is the vine Banisteriopsis caapi, which contains chemicals that act as monoamine oxidase inhibitors – a major class of antidepressant drugs. The other ingredient is the shrub Psychotria viridis: it contains the powerful hallucinogen DMT (dimethyltryptamine), which acts on the mood-altering serotonergic system, the target of antidepressants such as Prozac.
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