Hallucinations.

by Oliver Sacks.

Contents

Cover

t.i.tle Page

Copyright

Dedication

Introduction

1. Silent Mult.i.tudes: Charles Bonnet Syndrome

2. The Prisoner's Cinema: Sensory Deprivation

3. A Few Nanograms of Wine: Hallucinatory Smells

4. Hearing Things

5. The Illusions of Parkinsonism

6. Altered States

7. Patterns: Visual Migraines

8. The "Sacred" Disease

9. Bisected: Hallucinations in the Half-Field

10. Delirious

11. On the Threshold of Sleep

12. Narcolepsy and Night Hags

13. The Haunted Mind

14. Doppelgangers: Hallucinating Oneself

15. Phantoms, Shadows, and Sensory Ghosts

Acknowledgments

Bibliography

Permissions Acknowledgments

A Note About the Author

Other Books by This Author

Introduction

When the word "hallucination" first came into use, in the early sixteenth century, it denoted only "a wandering mind." It was not until the 1830s that Jean-etienne Esquirol, a French psychiatrist, gave the term its present meaning-prior to that, what we now call hallucinations were referred to simply as "apparitions." Precise definitions of the word "hallucination" still vary considerably, chiefly because it is not always easy to discern where the boundary lies between hallucination, misperception, and illusion. But generally, hallucinations are defined as percepts arising in the absence of any external reality-seeing things or hearing things that are not there.1

Perceptions are, to some extent, shareable-you and I can agree that there is a tree; but if I say, "I see a tree there," and you see nothing of the sort, you will regard my "tree" as a hallucination, something concocted by my brain or mind, and imperceptible to you or anyone else. To the hallucinator, though, hallucinations seem very real; they can mimic perception in every respect, starting with the way they are projected into the external world.

Hallucinations tend to be startling. This is sometimes because of their content-a gigantic spider in the middle of the room or tiny people six inches tall-but, more fundamentally, it is because there is no "consensual validation"; no one else sees what you see, and you realize with a shock that the giant spider or the tiny people must be "in your head."

When you conjure up ordinary images-of a rectangle, or a friend's face, or the Eiffel Tower-the images stay in your head. They are not projected into external s.p.a.ce like a hallucination, and they lack the detailed quality of a percept or a hallucination. You actively create such voluntary images and can revise them as you please. In contrast, you are pa.s.sive and helpless in the face of hallucinations: they happen to you, autonomously-they appear and disappear when they please, not when you please.

There is another mode of hallucination, sometimes called pseudo-hallucination, in which hallucinations are not projected into external s.p.a.ce but are seen, so to speak, on the inside of one's eyelids-such hallucinations typically occur in near-sleep states, with closed eyes. But these inner hallucinations have all the other hallmarks of hallucinations: they are involuntary, uncontrollable, and may have preternatural color and detail or bizarre forms and transformations, quite unlike normal visual imagery.

Hallucinations may overlap with misperceptions or illusions. If, looking at someone's face, I see only half a face, this is a misperception. The distinction becomes less clear with more complex situations. If I look at someone standing in front of me and see not a single figure but five identical figures in a row, is this "polyopia" a misperception or a hallucination? If I see someone cross the room from left to right, then see them crossing the room in precisely the same way again and again, is this sort of repet.i.tion (a "palinopsia") a perceptual aberration, a hallucination, or both? We tend to speak of such things as misperceptions or illusions if there is something there to begin with-a human figure, for example-whereas hallucinations are conjured out of thin air. But many of my patients experience outright hallucinations, illusions, and complex misperceptions, and sometimes the line between these is difficult to draw.

Though the phenomena of hallucination are probably as old as the human brain, our understanding of them has greatly increased over the last few decades.2 This new knowledge comes especially from our ability to image the brain and to monitor its electrical and metabolic activities while people are hallucinating. Such techniques, coupled with implanted-electrode studies (in patients with intractable epilepsy who need surgery), have allowed us to define which parts of the brain are responsible for different sorts of hallucinations. For instance, an area in the right inferotemporal cortex normally involved in the perception of faces, if abnormally activated, may cause people to hallucinate faces. There is a corresponding area on the other side of the brain normally employed in reading-the visual word form area in the fusiform gyrus; if this is abnormally stimulated, it may give rise to hallucinations of letters or pseudowords.

Hallucinations are "positive" phenomena, as opposed to the negative symptoms, the deficits or losses caused by accident or disease, which neurology is cla.s.sically based on. The phenomenology of hallucinations often points to the brain structures and mechanisms involved and can therefore, potentially, provide more direct insight into the workings of the brain.

Hallucinations have always had an important place in our mental lives and in our culture. Indeed, one must wonder to what extent hallucinatory experiences have given rise to our art, folklore, and even religion. Do the geometric patterns seen in migraine and other conditions prefigure the motifs of Aboriginal art? Did Lilliputian hallucinations (which are not uncommon) give rise to the elves, imps, leprechauns, and fairies in our folklore? Do the terrifying hallucinations of the night-mare, being ridden and suffocated by a malign presence, play a part in generating our concepts of demons and witches or malignant aliens? Do "ecstatic" seizures, such as Dostoevsky had, play a part in generating our sense of the divine? Do out-of-body experiences allow the feeling that one can be disembodied? Does the substancelessness of hallucinations encourage a belief in ghosts and spirits? Why has every culture known to us sought and found hallucinogenic drugs and used them, first and foremost, for sacramental purposes?

This is not a new thought-in 1845, Alexandre Brierre de Boismont, in the first systematic medical book on the subject, explored such ideas in a chapter t.i.tled "Hallucinations in Relation to Psychology, History, Morality, and Religion." Anthropologists including Weston La Barre and Richard Evans Schultes, among others, have doc.u.mented the role of hallucinations in societies around the globe.3 Time has only broadened and deepened our appreciation of the great cultural importance of what might at first seem to be little more than a neurological quirk.

I will say very little in this book about the vast and fascinating realm of dreams (which, one can argue, are hallucinations of a sort), other than to touch on the dreamlike quality of some hallucinations and on the "dreamy states" which occur in some seizures. Some have proposed a continuum of dream states and hallucinations (and this may be especially so with hypnagogic and hypnopompic hallucinations), but, in general, hallucinations are quite unlike dreams.

Hallucinations often seem to have the creativity of imagination, dreams, or fantasy-or the vivid detail and externality of perception. But hallucination is none of these, though it may share some neurophysiological mechanisms with each. Hallucination is a unique and special category of consciousness and mental life.

The hallucinations often experienced by people with schizophrenia also demand a separate consideration, a book of their own, for they cannot be divorced from the often profoundly altered inner life and life circ.u.mstances of those with schizophrenia. So I will refer relatively little to schizophrenic hallucinations here, focusing instead on the hallucinations that can occur in "organic" psychoses-the transient psychoses sometimes a.s.sociated with delirium, epilepsy, drug use, and certain medical conditions.

Many cultures regard hallucination, like dreams, as a special, privileged state of consciousness-one that is actively sought through spiritual practices, meditation, drugs, or solitude. But in modern Western culture, hallucinations are more often considered to portend madness or something dire happening to the brain-even though the vast majority of hallucinations have no such dark implications. There is great stigma here, and patients are often reluctant to admit to hallucinating, afraid that their friends and even their doctors will think they are losing their minds. I have been very fortunate that, in my own practice and in correspondence with readers (which I think of, in some ways, as an extension of my practice), I have encountered so many people willing to share their experiences. Many of them have expressed the hope that telling their stories will help defuse the often cruel misunderstandings which surround the whole subject.