Oliver Sacks, Exploring How Hallucinations Happen

Nov 6, 2012
Originally published on November 8, 2012 10:58 am

In Oliver Sacks' book The Mind's Eye, the neurologist included an interesting footnote in a chapter about losing vision in one eye because of cancer that said: "In the '60s, during a period of experimenting with large doses of amphetamines, I experienced a different sort of vivid mental imagery."

He expands on this footnote in his new book, Hallucinations, where he writes about various types of hallucinations — visions triggered by grief, brain injury, migraines, medications and neurological disorders.

One chapter of the new book deals with altered states and Sacks' personal experimentation with hallucinogenic and mind-altering drugs in the '60s. He says the first time he tried marijuana, it induced fascinating perceptual distortion. He was looking at his hand, and it appeared to be retreating from him, yet getting larger and larger.

"I was fascinated that one could have such perceptual changes, and also that they went with a certain feeling of significance, an almost numinous feeling. I'm strongly atheist by disposition, but nonetheless when this happened, I couldn't help thinking, 'That must be what the hand of God is like.' "

Sacks tells Fresh Air's Terry Gross that he has always been fascinated with hallucinations — from reading about Pip's hallucination of Miss Havisham in Charles Dickens' Great Expectations to witnessing hallucinations of every sort as a medical student and doctor. He had a personal interest in the phenomenon, he explains, because his brother was a schizophrenic — and "would talk with his hallucinations."

Sacks has also had his share of non-induced hallucinations. One day while mountain climbing, he experienced an auditory hallucination after an injury that tore most of his thigh muscle and dislocated his knee. His first impulse was to go to sleep — but then he heard a voice that he didn't recognize yet trusted.

" 'No, that would be death,' " he recalls it saying. " 'Go on. You've got to keep going. Find a pace you can keep up and keep it up.' And this was a very clear, commanding voice. It was a life voice, and it was not to be disobeyed."

Neurologically, Sacks speculates that this type of auditory hallucination is something that announces itself in extremity, and is "the ultimate safeguard, some power or propensity which has been built into the structure of the mind, the emotions," and is not heard by most people in their lives.

Sacks notes that the medicalization of hallucinations really only occurred in the 19th century — and that subsequent to that, there was much more anxiety, secrecy and shame about hallucinations.

"I think hallucinations need to be discussed," he says. "There are all sorts of hallucinations, and then many sorts which are OK, like the ones I think which most of us have in bed at night before we fall asleep, when we can see all sorts of patterns or faces and scenes."

With the ability to visualize the brain through cutting-edge medical technologies, Sacks believes, the scientist's sense of the brain's complexity has been increased; it's now possible to see exactly what's going on in the brain while people are hallucinating.


Interview Highlights

On a memorable hallucination while taking LSD

"I had been reading about the color indigo, how it had been introduced into the spectrum by [Isaac] Newton rather late, and it seemed no two people quite agreed as to what indigo was, and I thought I would like to have an experience of indigo. And I built up a sort of pharmacological launchpad with amphetamines and LSD, and a little cannabis on top of that, and when I was really stoned I said, 'I want to see indigo now.' And as if thrown by a paintbrush, a huge pear-shaped blob of the purest indigo appeared on the wall.

"Again it had this luminous, numinous quality; I leaped toward it in a sort of ecstasy. I thought, 'This is the color of heaven.' ... I thought maybe this is not a color which actually exists on the Earth, or maybe it used to exist or no longer exists. All this went through my mind in 4 or 5 seconds, and then the blob disappeared, giving me a strong sense of loss and heartbrokenness, and I was haunted a little bit when I came down, wondering whether indigo did exist in the real world.

"I would turn over little stones. I once went to a museum to look at azurite, a copper mineral which is maybe the nearest [to] indigo, but that was disappointing. I did in fact have that experience again, but when I had it the second time, it was not with a drug, it was with music — and I think music can take one to the heights in a way comparable with drugs."

On hallucinations that accompany bereavement

"With any hallucinations, if you can do functional brain imagery while they're going on, you will find that the parts of the brain usually involved in seeing or hearing — in perception — have become super active by themselves. And this is an autonomous activity; this does not happen with imagination. But hallucination, in a way, simulates perception, and the perceptual parts of the brain become active. ... There's obviously a very, very strong passionate feeling of love and loss with bereavement hallucinations, and I think intense emotion of any sort can produce a hallucination."

On the hallucinations accompanying his migraines

"I usually get the zigzag, but I may also see lattice patterns, like tessellations; sometimes these lattice patterns seem to cover people's faces or a piece of paper I'm writing on. I mostly get complex geometrical patterns; I've never actually seen ... images with a migraine, although on at least on two occasions, I've had a smell — in particular a smell of hot buttered toast — with a strong sense that I was about 3 years old, being put in a high chair, and about to be given hot buttered toast. A sort of olfactory hallucination often goes along with recollection in that sort of way.

"The first time I got that, I was in hospital and I went searching for the toast. The second time, I was driving on the Bronx River Parkway, where there was obviously no toast to be had."

How visual migraines may have inspired ancient patterned art

"There are all sorts of complex geometrical patterns, very symmetrical, some of them looking like the finest doily. ... Patterns like this tend to appear in migraine, but they may also appear with fever. They also appear with various drugs. They may also be seen as one is falling asleep, and one can't help comparing them with various forms of ornamental art and cave art, and wondering whether individuals or cultures have been inspired by some of these patterns which are built into the nervous system."

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross. My guest, neurologist Oliver Sacks, has explored perception, memory and consciousness through such bestselling books as "Awakenings," "The Man Who Mistook His Wife for a Hat" and "Musicophilia." His new book, "Hallucinations," draws on history, literature and the patients he's treated, patients who have experienced hallucinations brought on by neurological disorders, brain injuries, medications, fevers, blindness and more, hallucinations that range from the terrifying to the transcendent.

One chapter, called "Altered States," is about his own experiments with mind-altering drugs in the '60s, when he was a neurology resident. These drugs connected with the reason he wanted to be a neurologist, which was to study how the brain embodies consciousness and the self and to understand its amazing powers of perception and distortion.

Dr. Oliver Sacks, welcome back to FRESH AIR.

OLIVER SACKS: It's good to be with you again.

GROSS: In our previous interview two years ago, for your book "The Mind's Eye" about visual disturbances, you had a chapter about losing vision in one eye because of cancer, and you wrote in a footnote: In the '60s, during a period of experimenting with large doses of amphetamines, I experienced a different sort of vivid mental imagery.

And we talked about that a little bit because I was so surprised that such a big revelation that you'd taken large doses of amphetamines was confined to a little footnote. But now, your whole book is about hallucinations, and there's a whole chapter about the hallucinatory drugs you took when you were young.

Did you know that that footnote was going to become a book when you wrote it?

SACKS: No, by no means. I knew I would have a book on hallucinations, but the personal chapter was not in the manuscript until relatively late, and then it was evoked for me. I was actually in hospital with a broken hip and feeling rather bored and testy, and a friend said you sometimes talked about the '60s, can you tell me more?

So I told him stories, and he transcribed them and brought them back to me. And that's the way, the way they got into the book.

GROSS: And you're comfortable with that?

SACKS: Fairly comfortable, at least I'm talking about something which is long past. But I sort of regard myself as a subject for case history, as I regard anyone else. And fortunately, I survived it, and I'm here to tell the tale 45 years later.

GROSS: And an interesting tale it is, as we'll hear in a moment. But first, why did you want to write about hallucinations, hallucinations caused by medical problems, by drugs, by neurological disturbances, intentional hallucinations, unintentional hallucinations?

SACKS: Well, I think I've been interested in hallucinations almost all my life. And, you know, and I was fascinated by, say, "Great Expectations," reading about the hallucinations of Miss Havisham, which Pip has. A lot of Dickens books are about being haunted by hallucinations. But then as a medical student and a doctor, I saw hallucinations of every sort.

And with a brother who was schizophrenic, he would talk with his hallucinations, and that was a very different sort of experience. I've written bits about hallucinations, I think, in most of my earlier books, but I thought it was time to try and bring the whole lot together, the more so as we now have methods of looking at the brain and seeing exactly what goes on while people are hallucinating.

GROSS: You're talking about functional MRIs.

SACKS: Yeah.

GROSS: So at the beginning of your chapter about your own experimentation with altered states, you write: Every culture has found chemical means of transcendence. At some point, the use of such intoxicants becomes institutionalized at a magical or sacramental level. What are you thinking of there?

SACKS: Well, I was thinking of peyote ceremonies with Native Americans, but similar ceremonies in Mexico with morning glory seeds - ololiuqui, similar ceremonies in Central America with magic mushrooms, similar ones in South American with both - I can't pronounce it, ayahuasca. And so there's - this seems to happen in every culture at some point.

GROSS: And you write that some drugs like hallucinogenic drugs promise transcendence on demand. Is that why you wanted to experiment with them?

SACKS: Well, I think it's one of the reasons. It's probably a little too high-sounding for all of my reasons. I mean, I think I sometimes just wanted pleasure. I wanted to see a visually and perhaps musically enhanced world. I wanted to know what it was like, and I think those are ways an observer part, as well as the participant. I would often keep notes when I got stoned.

GROSS: What - did it seem absurd to you to keep notes on the experience because the experience was so heightened and can be so absorbing to take notes on, it brings you outside of it while you're in it, which can seem absurd in that moment?

SACKS: Yes, well, I didn't always take notes on it. I especially tended to take notes, I think, if a trip turned frightening, and then the taking notes would help me stand outside this, in a way.

GROSS: What was the first time you tried a drug that induced perceptual distortions?

SACKS: I think it was in 1963, and I was in Los Angeles, at UCLA, doing a residency in neurology, but I was also much on the beach, on Venice Beach and Muscle Beach. And there, there was quite a drug culture, as there was also in Topanga Canyon, where I lived. And one day, someone offered me some pot.

And I took two puffs from it, and I'd been looking at my hand for some reason, and the hand seemed to retreat from me but at the same time getting larger and larger until it became a sort of cosmic hand across the universe. And I found that astounding.

GROSS: So what did you find most interesting, pleasing or disturbing about that first experience that made you want to seek more experiences like it?

SACKS: I was fascinated that one could have such perceptual changes and also that they went with a certain feeling of significance, an enormous numinous feeling. I'm strongly atheist by disposition, but nonetheless when this happened, I couldn't help thinking that must be what the hand of God is like, or how it is experienced.

GROSS: Were you already a neurology student?

SACKS: Yes, I was a neurology resident at that time, and the air was buzzing with discoveries and talk about neurotransmitters and drug actions and what one could do for people with psychosis or people with Parkinson's. And so the chemistry of the nervous system was a very hot topic and inviting one to try for oneself.

GROSS: So you started taking LSD in 1964, and you write that you took mind-altering drugs every weekend for a while. Give us a sense of one of the better experiences that you had that made you want to keep using it.

SACKS: Well, a particular experience was with a color. I had been reading about the color indigo, how it had been introduced into the spectrum by Newton rather late, and it seemed no two people quite agreed as to what indigo was, and I thought I would like to have an experience of indigo.

And I built up a sort of pharmacological launch pad with amphetamines and LSD and a little cannabis on top of that, and when I was really stoned I said: I want to see indigo now. And as if thrown by a paintbrush, a huge pear-shaped blob of the purest indigo appeared on the wall.

It again had this luminous, numinous quality. I leapt toward it in a sort of ecstasy. I thought: This is the color of heaven, or this is the color which Giotto tried to get all his life but never could. I thought maybe this is not a color which actually exists on the Earth, or maybe it used to exist or no longer exists.

And all this went through my mind in four or five seconds, and then the blob disappeared, giving me a strong sense of loss and heartbrokenness, and I was haunted a little bit when I came down, wondering whether indigo did exist in the real world.

And I would turn over little stones. I once went to a museum to look at azurite, a copper mineral which is maybe the nearest to indigo, but that was disappointing. I did in fact have that experience again, but when I had it the second time, it was not with a drug, it was with music, and I think music can take one to the heights in a way comparable with drugs.

But I think the indigo was my favorite hallucination.

GROSS: My guest is neurologist Oliver Sacks. His new book is called "Hallucinations." We'll take more - talk more after a break. This is FRESH AIR.

(SOUNDBITE OF MUSIC)

GROSS: So if you're just joining us, my guest is Dr. Oliver Sacks, who's best known for his case studies in neurology. He's a neurologist, and he often writes about what people experience perceptually when they have neurological disorders. His books include "The Man Who Mistook His Wife For a Hat," "Musicophilia" and "Awakenings." His new book is called "Hallucinations."

So give us an example of a really bad time that you had on a hallucinogenic drug.

SACKS: Well, I think the worst time was also a rather puzzling time. It was in '65. I was new to New York. I was sleeping very badly. I was taking ever-increasing doses of a sleeping medication called chloral hydrate. And then one day I ran out of it. But I didn't think much of this, though when I went to work, I noticed I was rather tremulous, and at that time I was doing neuropathology, and it was my turn to slice a brain and describe all the structures, which I usually enjoyed doing and did easily.

But this time it was difficult, and I hesitate, and I felt my tremor was becoming more obvious. When the session was over, I went to have a coffee across the road, and suddenly my coffee turned green and then purple. And I looked up, there was a man paying at the register, and he seemed to have some huge proboscidean head like a sea elephant.

I was panicked. I didn't know what was happening. I ran across the street to a bus, got on it, but the people on the bus terrified me. They all seemed to have huge egg-shaped heads with eyes like the eyes of insects, compound eyes, which moved suddenly.

I wrote all this in my journal. I felt that I would get dangerously out of control one way or another, either with panic or catatonia or whatever, unless I made a note. And I somehow managed to get off the bus and onto a train and get off at the right stop that when I got off - I lived in the Village then, as I do again now - the houses, the buildings were flapping like flags in a high wind.

When I got back to my apartment, I phoned up a friend of mine, we'd interned together, her name was Carol Burnett, and I said: Carol, I want to say goodbye. I've gone mad. And she said: Oliver, what have you just taken? And I said: I haven't just taken anything. And she thought for a moment and said: What have you just stopped taking?

And I said: That's it, the chlor. And so this was the beginning of an attack of the DTs, the delirium tremens, not induced by alcohol withdrawal but by chloral withdrawal. It's a dangerous state. I should really have checked myself into hospital, but I didn't. I thought I wanted to go through it with some kindly medical supervision, and I did.

But there were many, many terrifying things there.

GROSS: Was it helpful while you were having these nightmarish hallucinations, because of withdrawal from the medicine that you were taking, was it helpful to know that they were medically induced hallucinations, that you weren't losing your mind and that this was going to end?

SACKS: Yeah, yeah, yeah, absolutely. When I realized it was medication and not madness, that was a relief so huge that I felt I could sit through the rest of it.

GROSS: As a neurologist, what did you learn from that experience?

SACKS: Well, I think I learned that one shouldn't be silly. But in particular, from that experience, there were all sorts of particular, odd visual perceptions. Sometimes I could not see continuous motion, I would only see a series of stills. And that fascinated me very much, and it made me in fact wonder whether the sense of visual motion is an illusion, whether in fact we see a series of stills.

I don't think I'd had that thought until I was seeing stills. I felt that almost every possible sensory combination was offered to me, every fantasy, every dreamlike distortion. And with hallucinations one remembers them, unlike dreams, and on the whole they're not like dreams because dreaming, you're asleep, you're only a dreaming consciousness, whereas here you're awake and observing yourself.

GROSS: So just another experience I want to ask you about here, you write about how your parents were both doctors, and once while they were out of town you raided their medicine cabinets and injected yourself with morphine to see what that would be like. And I was wondering if they ever found out.

SACKS: I don't think they found out, and if they did, they didn't say anything. That was a one and only time when I raided their medicine cabinet and also when I tried morphine, IV. The experience was both - was intriguing in a way, but it also lasted, to my shock, for 13 hours, when I thought it had only lasted for 20 minutes.

And it made me realize how dangerous the opiods were.

GROSS: Did it affect how you prescribe morphine as a doctor?

SACKS: Well, I don't prescribe morphine too often. In general I'm a - I act as a consultant, and I may suggest various medications without - you know, without myself prescribing them. But I think that morphine is indispensible for very severe pain. In England, for that matter, they use heroin, and I think that to deny morphine, say, to people with terminal pain on the ridiculous notion that they may become addicted to it is - is the height of cruelty.

I think there are times when morphine is needed.

GROSS: So I want to quote something you wrote about how you stopped doing amphetamines. You wrote: After taking amphetamines, I would feel I had made a crazy ascent into the stratosphere but had come back empty-handed and had nothing to show for it, that the experience had been as empty and vacuous as it was intense.

Then you write about how one time when you came down, you'd retained a sense of illumination and insight, and you had a revelation about migraine, and the next day you started writing about this, and you realized writing was where your real joy was, it was about writing for you, and you never took amphetamines again.

SACKS: Yeah. Well, I think one of the reasons I took drugs was somehow to regain the feeling of intellectual energy and enjoyment and maybe creativity, which I'd known years before as a boy in my days when I loved chemistry but which then seemed to have abandoned me.

And with that particular amphetamine trip, which went along with the fact that I was seeing patients with migraine, who I found fascinating and felt deeply for, and as well as a wonderful old book written in the 1860s on migraine, and the overwhelming feeling was that now it was the 1960s and we should have such a book again, and who would write it?

And a very loud inner voice said, you silly bugger, you're the man. And after that, something seemed to be switched on in my head, and basically I never took drugs again.

GROSS: Dr. Oliver Sacks will be back in the second half of the show. His new book is called "Hallucinations." I'm Terry Gross, and this is FRESH AIR.

(SOUNDBITE OF MUSIC)

GROSS: This is FRESH AIR. I'm Terry Gross, back with neurologist Oliver Sacks, author of the bestselling books "Awakenings," "The Man Who Mistook His Wife for a Hat" and "Musicophelia." His books are based on the patients he's treated, as well as medical history, literature and his own experiences. His new book, "Hallucinations" is about hallucinations brought on by neurological disorders, brain injuries, medications, fever, blindness, mind-altering drugs and more - hallucinations ranging from the terrifying to the transcendent.

So, you know how some people say the human brain is wired for God, you know, wired to...

SACKS: Uh-huh.

GROSS: ..to have religion. What's your take on that?

SACKS: I'm very intrigued by the relationship between drugs and religion and hallucination and religion. There's a long chapter on epilepsy, which at one time was called the sacred disease - although Hippocrates said there was nothing sacred about it. Although, he allowed sometimes the symptoms of epilepsy may be visionary and, in particular, there is a sort of seizure which some people get called an ecstatic seizure, when there will be a feeling of bliss or rapture, a feeling of being transported to heaven, sometimes of hearing angelic voices or seeing angels or communing with God.

Experiences like this can happen with seemingly quite irreligious people who have - who don't seem to have an iota of religious disposition, but the experience may be rather overwhelming and may lead to conversion.

GROSS: But it's interesting how often those visions - if we want to call it that - come from something that nowadays would be diagnosed as a disorder, and in fact are disorders like epilepsy or schizophrenia.

SACKS: Yes. Well, certainly. I think there's probably always been visions and voices, and these were variously ascribed to the divine or demonic or the muses. I think many poets still feel they depend on an inner voice, or a voice which tells them what to do.

The medicalization of hallucinations really only occurred in the 19th century, and following that, people became, I think, very much more anxious about hallucinations and secretive and ashamed, and the subject was much less discussed. I think hallucinations need to be discussed. There are all sorts of hallucinations, and there are many sorts which are OK, like the ones I think which most of us have when we're in bed at night before we fall asleep when we can see all sorts of patterns or faces or scenes.

GROSS: Now I want to ask you about visual migraines. And...

SACKS: Yes.

GROSS: I want you to describe the kind of visual distortions that people with migraines often get.

SACKS: Well, the most characteristic one starts as a brilliant, scintillating zigzag which expands over the course of a few minutes and becomes a huge crescent, which looks rather like a medieval fort. And this is sometimes called a fortification pattern. It is extremely bright, dazzlingly bright, and there may be an area of blindness around it. It takes something between 15 and 20 minutes to develop and disappear, and this is precisely coincident with a wave of electrical excitement crossing one's visual brain, one's occipital cortex.

Sometimes there are more complex things in a migraine. For example, Siri Hustvedt has described and written about how on one occasion, in a migraine aura, she saw a little man and his ox about six inches high on the ground. She had this Lilliputian hallucination which charmed her, and this again lasted a few minutes and then vanished.

One can, in fact, have almost any sort of hallucination with migraine, including hallucinations of smell or hearing or music, though the commonest ones are visual. And I would say there are a hundred visual migraines for anything involving another sense. If you're lucky, you don't go on from the visual migraine to the headache and nausea. I'm lucky that way. I don't. But my mother, who had this, would have the whole thing.

GROSS: Now, you speculate in the book that visual migraines, which can sometimes be patterns of color, might have inspired ancient art that's patterned art, or even, you know, patterned - ancient pattern rugs and things like that. Can you just describe some of your thoughts about that?

SACKS: Yeah. Well, besides the fortification, there are all sorts of complex, geometrical patterns, very symmetrical, some of them looking like the finest doily or something like this. And patterns like this tend to appear in migraine, but they may also appear with fever. They also appear with various drugs. They may also be seen as one is falling asleep.

And one can't help comparing them with various forms of ornamental art and cave art, and wondering whether individuals or cultures have been inspired by some of these patterns which are built into the nervous system. These patterns are generated when a - when millions of neurons are behaving in a particular sort of way. And I - at a higher level, I've, you know, one has wondered whether the sort of stories of imps and elves and sprites and fairies may have something to do with the sort of Lilliputian vision which Siri Hustvedt described, which is also not uncommon.

GROSS: Do you still get visual migraines?

SACKS: Yes. I got a particularly strong one after watching "The Book of Mormon."

GROSS: You're not blaming it on the show, are you?

(LAUGHTER)

SACKS: No. No. It was simply - for me, there was a - I think there was a huge - I think it's a brilliant, funny show, but for me, it was a huge sensory overload. It was much too bright and much too loud, and so I think this was my brain objecting to it.

GROSS: So what patterns do you see when you have a visual migraine?

SACKS: I usually get the zigzag, but I may also see lattice patterns, like tessellations. Sometimes these lattice patterns seem to cover people's faces or a piece of paper I'm writing on. I mostly get complex, geometrical patterns. I've never actually visually seen images with migraine, although on at least two occasions, I've had a smell, in particular a smell of hot, buttered toast with a strong sense that I was about of being three years old, being put in a high chair and about to be given some hot, buttered toast.

A sort of olfactory hallucination often goes with the recollection of that sort of way. The first time I got that, I was in the hospital and I went searching for the toast. The second time, I was driving along Bronx River Parkway where there's obviously no toast to be had.

GROSS: If you're just joining us, my guest is Dr. Oliver Sacks, and his new book is called "Hallucinations." He's also the author of "Musicophilia," "The Man Who Mistook His Wife for a Hat" and "Awakenings."

Let's take a short break here, and then we'll talk more about hallucinations. This is FRESH AIR.

(SOUNDBITE OF MUSIC)

GROSS: If you're just joining us, my guest is neurologist Dr. Oliver Sacks, best-known for such books as "The Man Who Mistook His Wife for a Hat," "Musicophilia," and "Awakenings." His new book is called "Hallucinations," and it's about medically induced hallucinations, naturally occurring hallucinations - like between waking and sleeping - and hallucinations that are side effects of drugs, hallucinations that are caused by various medical conditions. Yeah.

SACKS: Can I add to your list? Hallucinations which are caused by real-life experiences, such as bereavement.

GROSS: Yes. I'm glad you mentioned bereavement. And that is such a common form of hallucination, where, you know, you've lost somebody who you love and you think you've seen them or heard them say something. And when that happens, I think it's fair to say it feels like a visitation. How would you describe that?

SACKS: Yeah. Well, someone dies, there's a hole in your life and that hole can be briefly filled, I think, by a hallucination. Typically, the bereavement hallucinations - which are common; something like 40 or 50 percent of bereaved people get them occasionally - are often felt as very comfortable, comforting, and they may help them through the mourning process, and when one has mourned fully, they disappear.

GROSS: How, as a neurologist, would you interpret those hallucinations?

SACKS: Well, with any hallucinations, if you can say do functional brain imagery while they're going on, you will find that the parts of the brain usually involved in seeing or hearing - in perception - are, in fact, being active, have become super-active by themselves. And this is an autonomous activity. This does not happen with imagination. But hallucination, in a way, simulates perception, and the perceptual parts of the brain become active. And - but, you know, what else is going on, there's obviously a very, very strong, passionate feeling of love and loss with bereavement hallucinations, and I think intense emotion of any sort can produce a hallucination.

GROSS: Say you had actually seen - say it really was like a visitation from the person who you're mourning, what would be happening in your brain, compared to the activation that you're describing in a hallucination? In other words, like, does the FMRI, the functional brain imagery prove that it really wasn't a visitation, that it was just something induced by your brain?

SACKS: Well, you would see a precise coincidence between the visitation and quite major changes in the brain, and you cannot reduce the visitation to those changes, but you also cannot just discuss those changes without saying it was experienced as a visitation. I mean, the whole hard question of neurology or of science or philosophy is how to connect brain activity with experience and mind. And all we could say, on the whole, is that things go parallel.

GROSS: I'm just curious. Like how - how do you do functional brain imagery of somebody who has had a hallucination? I mean, they're probably not hooked up to the FMRI...

SACKS: Yeah.

GROSS: ...when they're feeling like they had this visitation from a lost loved one.

SACKS: Well, there, it will be difficult, because hallucinations like this are rare and sporadic and unpredictable. But there are other people - and I am especially interested in this, because I've worked in old age homes for the last 40 years or so, and I've seen many, many elderly people who are intellectually intact, but have impaired vision or hearing, have visual or auditory hallucinations on this basis.

The visual one they call Charles Bonnet Syndrome, and people may see faces. They may see landscapes, patterns, musical notation, for hours a day. And in this situation, you can have someone inside a functional MRI, and they can, say, raise a finger when they are hallucinating. You may then say to them: You are hallucinating faces. They may say, how the hell do you know? And you will say, because the face recognizing part of your brain suddenly became very active.

GROSS: Wow. Uh-huh...

SACKS: And it is this sort of thing, especially with patients with Charles Bonnet Syndrome, that you can plot, you can map the brain by the sort of hallucinations people get.

GROSS: You write in your book "Hallucinations" about an auditory hallucination you had that really might've saved your life. You were mountain climbing and you'd injured your foot or your leg and part of you just wanted to just, like, slow down, sleep. But then you heard a voice which said what?

SACKS: Yeah. Well, the impulse to sleep - I'd torn off most of the thigh muscles and the knee was dislocating backwards. And at one point I got quite shocked and must have a little sleep. And the voice said, no, that would be death. Go on. You've got to keep going. Find a pace you can keep up and keep it up. And this was a very clear commanding voice. It was a sort of life voice and it was not to be disobeyed.

GROSS: And so you kept going in spite of the horrible shape that your leg and knee was in.

SACKS: Yeah. I was sort of lowering myself down with my arms. I had splinted the leg as best I could with an umbrella stick and my anorak, which I tore in two. Incidentally, I thought that was going to be the last day of my life and it had every prospect of being, but I was found at twilight by two hunters. This was in north Norway.

But that voice was crucial for me and I've heard many other stories like this. One of them was from a young woman who was brokenhearted after a love affair and determined to commit suicide. And she had a bottle of sleeping tablets and a tumbler of whisky to wash them down and she had raised the tablets to her mouth when she heard a voice saying: Don't do that, I wouldn't do that if I were you, you won't always be feeling the way you're feeling now.

And she - it was a man's voice. She didn't recognize it. She was fairly startled. She said, who was that? Who was that? And she said a figure materialized in a chair opposite her for a few seconds, a figure in 18th century dress that vanished. But she feels that hallucination saved her life. And I think her story is not that uncommon. Nor mine, for that matter.

GROSS: Whose voice did you hear? Was it your voice, a stranger's voice?

SACKS: Not my voice. I often hear my voice. I am always sort of cursing or muttering to myself. But this was a very clear, assured voice. Not a voice I recognized but a voice I trusted. Which I suppose I realized came from some part of me, because there's no other place it could've come from.

GROSS: What do you speculate goes on neurologically when, in a state of extreme danger like you were in, a voice tells you to do the thing that you need to do to save your life?

SACKS: It seems to me almost like an ultimate safeguard. Some power, propensity, which is sort of built into the structure of the mind and the emotions. Probably I would think most people would go through a life and never hear it. It only announces itself in extremity.

GROSS: If you're just joining us, my guest is neurologist Oliver Sacks, who's best known for his books "The Man Who Mistook His Wife for a Hat," "Musicophilia" and "Awakenings." His new book is called "Hallucinations" and it's about the various things that can cause hallucinations and what's happening in the brain when you're hallucinating.

Let's take a short break here, then we'll talk more about hallucinations. This is FRESH AIR.

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GROSS: If you're just joining us, my guest is neurologist Oliver Sacks, who's well known for his bestsellers "The Man Who Mistook His Wife for a Hat," "Musicophilia" and "Awakenings." His new book is called "Hallucinations" and it's about disorders, drugs, and other things that can cause hallucinations and what's happening in the brain when we have hallucinations.

It seems to me you've had a neurologically eventful life.

(LAUGHTER)

GROSS: Honestly, like you've had migraines from like the age of four and, you know, you heard the voice when you were mountain climbing and would have died had you not kept walking in spite of a severe leg injury. You've had spinal pain and, you know, wanted to understand the, you know, nerve causes of that. You've had visual disorders.

And it just seems like you have experienced so much, which I know has been useful to you as a doctor, but it seems like a lot for one person to go through.

SACKS: Yeah. I...

GROSS: You've lost your sight in one eye because of cancer, and that started out with all kinds of distortions.

SACKS: Yes. Well, I expect it has been a lot in a way, but I feel I'm lucky. I'm close to 80 and I'm still in fairly good shape. Especially if I can go swimming. I limp a bit on land but I'm powerful in the water. And it's true I've only got one eye now and the other one needs some surgery. But I manage.

I suspect that most people may have quite a lot of neurological things to which they don't pay much attention. I think I probably differ from others only in having paid attention to things.

GROSS: How much are you practicing now? You said you're about 80.

SACKS: Yeah. I usually have a couple of half days a week in which I go to a place and I see occasional patients in my own office.

GROSS: What has been the most dramatic change you've seen in your field since you started as a neurology resident in the '60s?

SACKS: I think probably the ability to visualize the brain in life with functional imaging or PET scanning, and if the brain is exposed to record from individual cells. But there's been a whole change of orientation. We now, for example, think of vision - what one sees - as being constructed. We know that the image on the back of the retina then has to be analyzed by 40 or 50 different systems in the brain.

And then all of these work together to produce the final image. The sense of the brain's complexity and wonder, I think, has been increased. We are now very much looking at consciousness as a central problem, whereas that was regarded as either not a problem or an insoluble problem or a mystery 30 years ago. We have found forms of treatment which could not have been imagined a few years ago.

In particular I think of the use of stem cells and other things for neurodegenerative disease. I think neurology has both expanded and become much more hopeful than it was when I entered it. So neurology is fun now.

GROSS: Well, Dr. Sacks, it's just such a pleasure to talk with you. You're always so interesting. I thank you so much for coming back to our show.

SACKS: Well, thank you so much. And I always love talking with you and I love the way you keep me focused, or you try to keep me focused.

(LAUGHTER)

SACKS: Although I'm incorrigible.

GROSS: You're great. I really appreciate you talking with us. Be well and thank you again so much.

SACKS: Thank you.

GROSS: Dr. Oliver Sacks is the author of the new book "Hallucinations." You can read an excerpt on our website, freshair.npr.org, where you can also download podcasts of our show. And you can follow us on Twitter at nprfreshair and on Tumblr on nprfreshair.tumblr.com. Transcript provided by NPR, Copyright NPR.