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We see with the eyes,

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but we see with the brain as well.

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And seeing with the brain is often called imagination.

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And we are familiar with the landscapes of our own imagination,

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our inscapes. We've lived with them all our lives.

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But there are also hallucinations as well,

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and hallucinations are completely different.

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They don't seem to be of our creation.

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They don't seem to be under our control.

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They seem to come from the outside,

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and to mimic perception.

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So I am going to be talking about hallucinations,

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and a particular sort of visual hallucination

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which I see among my patients.

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A few months ago, I got a phone call

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from a nursing home where I work.

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They told me that one of their residents, an old lady in her 90s,

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was seeing things,

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and they wondered if she'd gone bonkers

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or, because she was an old lady,

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whether she'd had a stroke, or whether she had Alzheimer's.

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And so they asked me if I would come and see Rosalie,

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the old lady.

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I went in to see her.

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It was evident straight away

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that she was perfectly sane

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and lucid and of good intelligence,

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but she'd been very startled and very bewildered,

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because she'd been seeing things.

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And she told me --

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the nurses hadn't mentioned this --

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that she was blind,

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that she had been completely blind from macular degeneration for five years.

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But now, for the last few days, she'd been seeing things.

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So I said, "What sort of things?"

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And she said, "People in Eastern dress,

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in drapes, walking up and down stairs.

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A man who turns towards me and smiles.

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But he has huge teeth on one side of his mouth.

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Animals too.

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I see a white building. It's snowing, a soft snow.

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I see this horse with a harness, dragging the snow away.

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Then, one night, the scene changes.

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I see cats and dogs walking towards me.

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They come to a certain point and then stop.

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Then it changes again.

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I see a lot of children. They are walking up and down stairs.

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They wear bright colors, rose and blue,

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like Eastern dress."

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Sometimes, she said, before the people come on,

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she may hallucinate pink and blue squares on the floor,

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which seem to go up to the ceiling.

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I said, "Is this like a dream?"

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And she said, "No, it's not like a dream. It's like a movie."

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She said, "It's got color. It's got motion.

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But it's completely silent, like a silent movie."

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And she said that it's a rather boring movie.

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She said, "All these people with Eastern dress,

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walking up and down, very repetitive, very limited."

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(Laughter)

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And she has a sense of humor.

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She knew it was a hallucination.

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But she was frightened. She'd lived 95 years

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and she'd never had a hallucination before.

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She said that the hallucinations were unrelated

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to anything she was thinking or feeling or doing,

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that they seemed to come on by themselves, or disappear.

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She had no control over them.

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She said she didn't recognize

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any of the people or places

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in the hallucinations.

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And none of the people or the animals,

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well, they all seemed oblivious of her.

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And she didn't know what was going on.

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She wondered if she was going mad

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or losing her mind.

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Well, I examined her carefully.

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She was a bright old lady,

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perfectly sane. She had no medical problems.

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She wasn't on any medications which could produce hallucinations.

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But she was blind.

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And I then said to her,

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"I think I know what you have."

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I said, "There is a special form of visual hallucination

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which may go with deteriorating vision or blindness.

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This was originally described," I said,

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"right back in the 18th century,

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by a man called Charles Bonnet.

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And you have Charles Bonnet syndrome.

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There is nothing wrong with your brain. There is nothing wrong with your mind.

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You have Charles Bonnet syndrome."

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And she was very relieved at this,

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that there was nothing seriously the matter,

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and also rather curious.

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She said, "Who is this Charles Bonnet?"

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She said, "Did he have them himself?"

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And she said, "Tell all the nurses

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that I have Charles Bonnet syndrome."

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(Laughter)

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"I'm not crazy. I'm not demented. I have Charles Bonnet syndrome."

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Well, so I did tell the nurses.

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Now this, for me, is a common situation.

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I work in old-age homes, largely.

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I see a lot of elderly people

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who are hearing impaired or visually impaired.

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About 10 percent of the hearing impaired people

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get musical hallucinations.

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And about 10 percent of the visually impaired people

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get visual hallucinations.

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You don't have to be completely blind,

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only sufficiently impaired.

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Now with the original description in the 18th century,

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Charles Bonnet did not have them.

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His grandfather had these hallucinations.

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His grandfather was a magistrate, an elderly man.

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He'd had cataract surgery.

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His vision was pretty poor.

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And in 1759, he described to his grandson

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various things he was seeing.

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The first thing he said was he saw

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a handkerchief in midair.

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It was a large blue handkerchief

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with four orange circles.

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And he knew it was a hallucination.

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You don't have handkerchiefs in midair.

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And then he saw a big wheel in midair.

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But sometimes he wasn't sure whether he was hallucinating or not,

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because the hallucinations would fit

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in the context of the visions.

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So on one occasion, when his granddaughters were visiting them,

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he said, "And who are these handsome young men with you?"

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And they said, "Alas, Grandpapa, there are no handsome young men."

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And then the handsome young men disappeared.

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It's typical of these hallucinations

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that they may come in a flash and disappear in a flash.

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They don't usually fade in and out.

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They are rather sudden, and they change suddenly.

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Charles Lullin, the grandfather,

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saw hundreds of different figures,

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different landscapes of all sorts.

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On one occasion, he saw a man in a bathrobe smoking a pipe,

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and realized it was himself.

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That was the only figure he recognized.

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On one occasion when he was walking in the streets of Paris,

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he saw -- this was real -- a scaffolding.

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But when he got back home, he saw a miniature of the scaffolding

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six inches high, on his study table.

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This repetition of perception

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is sometimes called palinopsia.

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With him and with Rosalie,

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what seems to be going on --

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and Rosalie said, "What's going on?" --

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and I said that as you lose vision,

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as the visual parts of the brain are no longer getting any input,

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they become hyperactive and excitable,

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and they start to fire spontaneously.

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And you start to see things.

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The things you see can be very complicated indeed.

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With another patient of mine,

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who, also had some vision,

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the vision she had could be disturbing.

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On one occasion, she said she saw

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a man in a striped shirt in a restaurant.

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And he turned around. And then

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he divided into six figures in striped shirts,

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who started walking towards her.

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And then the six figures came together again, like a concertina.

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Once, when she was driving,

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or rather, her husband was driving,

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the road divided into four

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and she felt herself going simultaneously up four roads.

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She had very mobile hallucinations as well.

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A lot of them had to do with a car.

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Sometimes she would see a teenage boy

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sitting on the hood of the car.

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He was very tenacious and he moved rather gracefully

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when the car turned.

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And then when they came to a stop,

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the boy would do a sudden vertical takeoff, 100 foot in the air,

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and then disappear.

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Another patient of mine had a different sort of hallucination.

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This was a woman who didn't have trouble with her eyes,

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but the visual parts of her brain,

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a little tumor in the occipital cortex.

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And, above all, she would see cartoons.

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These cartoons would be transparent

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and would cover half the visual field, like a screen.

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And especially she saw cartoons of Kermit the Frog.

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(Laughter)

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Now, I don't watch Sesame Street,

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but she made a point of saying,

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"Why Kermit?" She said, "Kermit the Frog means nothing to me.

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You know, I was wondering about Freudian determinants.

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Why Kermit?

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Kermit the Frog means nothing to me."

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She didn't mind the cartoons too much.

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But what did disturb her was she got very persistent

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images or hallucinations of faces

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and as with Rosalie, the faces were often deformed,

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with very large teeth or very large eyes.

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And these frightened her.

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Well, what is going on with these people?

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As a physician, I have to try and define what's going on,

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and to reassure people,

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especially to reassure them that they're not going insane.

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Something like 10 percent, as I said,

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of visually impaired people get these.

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But no more than one percent of the people acknowledge them,

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because they are afraid they will be seen as insane or something.

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And if they do mention them to their own doctors

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they may be misdiagnosed.

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In particular, the notion is that if you see

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things or hear things, you're going mad,

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but the psychotic hallucinations are quite different.

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Psychotic hallucinations, whether they are visual or vocal,

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they address you. They accuse you.

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They seduce you. They humiliate you.

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They jeer at you.

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You interact with them.

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There is none of this quality of being addressed

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with these Charles Bonnet hallucinations.

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There is a film. You're seeing a film which has nothing to do with you,

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or that's how people think about it.

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There is also a rare thing called temporal lobe epilepsy,

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and sometimes, if one has this,

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one may feel oneself transported back

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to a time and place in the past.

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You're at a particular road junction.

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You smell chestnuts roasting.

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You hear the traffic. All the senses are involved.

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And you're waiting for your girl.

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And it's that Tuesday evening back in 1982.

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And the temporal lobe hallucinations

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are all-sense hallucinations,

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full of feeling, full of familiarity,

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located in space and time,

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coherent, dramatic.

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The Charles Bonnet ones are quite different.

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So in the Charles Bonnet hallucinations,

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you have all sorts of levels,

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from the geometrical hallucinations --

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the pink and blue squares the woman had --

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up to quite elaborate hallucinations

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with figures and especially faces.

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Faces, and sometimes deformed faces,

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are the single commonest thing

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in these hallucinations.

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And one of the second commonest is cartoons.

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So, what is going on?

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Fascinatingly, in the last few years,

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it's been possible to do functional brain imagery,

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to do fMRI on people as they are hallucinating.

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And in fact, to find that different parts

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of the visual brain are activated

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as they are hallucinating.

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When people have these simple geometrical hallucinations,

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the primary visual cortex is activated.

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This is the part of the brain which perceives edges and patterns.

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You don't form images with your primary visual cortex.

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When images are formed,

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a higher part of the visual cortex

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is involved in the temporal lobe.

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And in particular, one area of the temporal lobe

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is called the fusiform gyrus.

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And it's known that if people have damage in the fusiform gyrus,

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they maybe lose the ability to recognize faces.

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But if there is an abnormal activity in the fusiform gyrus,

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they may hallucinate faces,

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and this is exactly what you find in some of these people.

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There is an area in the anterior part of this gyrus

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where teeth and eyes are represented,

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and that part of the gyrus is activated

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when people get the deformed hallucinations.

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There is another part of the brain

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which is especially activated

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when one sees cartoons.

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It's activated when one recognizes cartoons,

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when one draws cartoons, and when one hallucinates them.

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It's very interesting that that should be specific.

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There are other parts of the brain which are specifically involved

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with the recognition and hallucination

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of buildings and landscapes.

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Around 1970, it was found that there were not only parts of the brain,

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but particular cells.

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"Face cells" were discovered around 1970.

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And now we know that there are hundreds of other

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sorts of cells,

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which can be very, very specific.

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So you may not only have

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"car" cells,

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you may have "Aston Martin" cells.

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(Laughter)

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I saw an Aston Martin this morning.

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I had to bring it in.

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And now it's in there somewhere.

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(Laughter)

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Now, at this level, in what's called the inferotemporal cortex,

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there are only visual images,

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or figments or fragments.

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It's only at higher levels

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that the other senses join in

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and there are connections with memory and emotion.

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And in the Charles Bonnet syndrome,

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you don't go to those higher levels.

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You're in these levels of inferior visual cortex

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where you have thousands and tens of thousands

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and millions of images,

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or figments, or fragmentary figments,

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all neurally encoded

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in particular cells or small clusters of cells.

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Normally these are all part of

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the integrated stream of perception, or imagination,

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and one is not conscious of them.

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It is only if one is visually impaired or blind

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that the process is interrupted.

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And instead of getting normal perception,

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you're getting an anarchic,

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convulsive stimulation, or release,

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of all of these visual cells

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in the inferotemporal cortex.

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So, suddenly you see a face. Suddenly you see a car.

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Suddenly this, and suddenly that.

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The mind does its best to organize

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and to give some sort of coherence to this,

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but not terribly successfully.

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When these were first described,

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it was thought that they could be interpreted like dreams.

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But in fact people say,

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"I don't recognize the people. I can't form any associations."

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"Kermit means nothing to me."

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You don't get anywhere thinking of them as dreams.

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Well, I've more or less said what I wanted.

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I think I just want to recapitulate

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and say this is common.

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Think of the number of blind people.

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There must be hundreds of thousands of blind people

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who have these hallucinations,

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but are too scared to mention them.

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So this sort of thing needs to be brought into

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notice, for patients, for doctors, for the public.

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Finally, I think they are

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infinitely interesting and valuable,

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for giving one some insight as to how the brain works.

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Charles Bonnet said, 250 years ago --

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he wondered how, thinking these hallucinations,

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how, as he put it, the theater of the mind

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could be generated by the machinery of the brain.

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Now, 250 years later,

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I think we're beginning to glimpse how this is done.

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Thanks very much.

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(Applause)

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Chris Anderson: That was superb. Thank you so much.

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You speak about these things with so much insight

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and empathy for your patients.

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Have you yourself experienced any of the syndromes you write about?

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Oliver Sacks: I was afraid you'd ask that.

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(Laughter)

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Well, yeah, a lot of them.

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And actually I'm a little visually impaired myself.

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I'm blind in one eye, and not terribly good in the other.

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And I see the geometrical hallucinations.

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But they stop there.

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CA: And they don't disturb you?

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Because you understand what's doing it, it doesn't make you worried?

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OS: Well they don't disturb me any more than my tinnitus,

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which I ignore.

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They occasionally interest me,

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and I have many pictures of them in my notebooks.

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I've gone and had an fMRI myself,

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to see how my visual cortex is taking over.

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And when I see all these hexagons

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and complex things, which I also have,

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in visual migraine,

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I wonder whether everyone sees things like this,

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and whether things like cave art or ornamental art

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may have been derived from them a bit.

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CA: That was an utterly, utterly fascinating talk.

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Thank you so much for sharing.

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OS: Thank you. Thank you.

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(Applause)