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.
See more: https://www.newscientist.com/article/dn20978-drug-hallucinations-look-real-in-the-brain/