Oliver Sacks Explains the Biology of Hallucinations: “We See with the Eyes, But with the Brain as Well”

We all understand that hallucination involves seeing things that aren’t really there, but what are hallucinations themselves? “They don’t seem to be of our creation. They don’t seem to be under our control. They seem to come from the outside, and to mimic perception.” Those words come from Oliver Sacks, who would know. We featured a short clip of him discussing what he learned from his personal experience with LSD and amphetamines back in 2012, when his book Hallucinations had just come out. He died almost exactly three years later — and therefore just under a year ago — leaving behind a body of work from which we all stand to gain much understanding of the workings of the brain, as illuminated by both its normal and abnormal states.

In this 2009 TED Talk on what hallucinations reveal about our minds, Sacks tells of his experiences with one patient, elderly and blind, who kept “seeing” visions of “people in Eastern dress, in drapes, walking up and down stairs.” Another, with limited eyesight, “ said she saw a man in a striped shirt in a restaurant. And he turned around. And then he divided into six figures in striped shirts, who started walking towards her. And then the six figures came together again, like a concertina.” Another, with a small tumor on the occipital cortex, “would see cartoons. These cartoons would be transparent and would cover half the visual field, like a screen. And especially she saw cartoons of Kermit the Frog.”

Sacks connects all this to something called Charles Bonnet syndrome, first described by the naturalist of that name in 1760. Bonnet’s grandfather, who’d had cataract surgery (and 18th-century cataract surgery at that), said he saw things like handkerchiefs and wheels floating in midair. These hallucinations work differently than psychotic ones, which “address you. They accuse you. They seduce you. They humiliate you. They jeer at you.” But Charles Bonnet syndrome produces an experience more like watching a film — a term Sacks’ patients could use to describe it, though obviously nobody could have in Bonnet’s day.

Bonnet, Sacks concludes, “wondered how, thinking about these hallucinations, as he put it, the theater of the mind could be generated by the machinery of the brain. Now, 250 years later, I think we’re beginning to glimpse how this is done.” Thanks to Sacks’ inspiration of succeeding generations of neuroscientific researchers, that glimpse of how we “see with the eyes, but with the brain as well” will only widen.

Related Content:

Oliver Sacks’ Last Tweet Shows Beethoven’s “Ode to Joy” Movingly Flashmobbed in Spain

This is What Oliver Sacks Learned on LSD and Amphetamines

Oliver Sacks Contemplates Mortality (and His Terminal Cancer Diagnosis) in a Thoughtful, Poignant Letter

Based in Seoul, Colin Marshall writes and broadcasts on cities and culture. He’s at work on a book about Los Angeles, A Los Angeles Primer, the video series The City in Cinema, the crowdfunded journalism project Where Is the City of the Future?, and the Los Angeles Review of Books’ Korea Blog. Follow him on Twitter at @colinmarshall or on Facebook.

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