Hallucinations

by Oliver Sacks

But generally, hallucinations are defined as percepts arising in the absence of any external reality—seeing things or hearing things that are not there.

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.

Thus Bonnet attributed his grandfather’s hallucinations to continuing activity in what he postulated were visual parts of the brain—an activity drawing on memory now that it could no longer draw on sensation.

There was, as ffytche et al. wrote in a 1998 paper, “a striking correspondence” between the particular hallucinatory experiences of each patient and the particular portions of the ventral visual pathway in the visual cortex which were activated. Hallucinations of faces, of color, of textures, and of objects, for example, each activated particular areas known to be involved in specific visual functions.

Ffytche et al. observed, moreover, a clear distinction between normal visual imagination and actual hallucination—thus, imagining a colored object, for example, did not activate the V4 area, while a colored hallucination did.

Writing of hallucinations in 1760, Bonnet said, “The mind would not be able to tell apart vision from reality.”

But while there are neurologically determined categories of visual hallucination, there may be personal and cultural determinants, too. No one can have hallucinations of musical notation or numbers or letters, for example, if they have not actually seen these at some point in real life.

One of the defining characteristics of Charles Bonnet hallucinations is the preservation of insight, the realization that a hallucination is not real.

The ability to evaluate one’s perceptions or hallucinations, however, may be compromised if there are other underlying problems in the brain, especially those which impair the frontal lobes, since the frontal lobes are the seat of judgment and self-evaluation. This may happen transiently, for example, with a stroke or head injury; fever or delirium; various medications, toxins, or metabolic imbalances; dehydration or lack of sleep.

Whether darkness and solitude is sought out by holy men in caves or forced upon prisoners in lightless dungeons, the deprivation of normal visual input can stimulate the inner eye instead, producing dreams, vivid imaginings, or hallucinations.

Unlike the top-down process of voluntary visual imagery, hallucination is the result of a direct, bottom-up activation of regions in the ventral visual pathway, regions rendered hyperexcitable by a lack of normal sensory input.

While humans can detect and identify perhaps ten thousand distinct smells, the number of possible smells is far greater, for there are more than five hundred different odorant receptor sites in the nasal mucosa, and stimulation of these (or their cerebral representations) may be combined in trillions of ways.

Bleuler wrote, “Almost every schizophrenic who is hospitalized hears ‘voices.’ ” But he emphasized that the reverse did not hold—that hearing voices did not necessarily denote schizophrenia.

More than 10 percent responded in the affirmative, and of those, more than a third heard voices. As John Watkins noted in his book Hearing Voices, hallucinated voices “having some kind of religious or supernatural content represented a small but significant minority of these reports.” Most of the hallucinations, however, were of a more quotidian character.

The voices that are sometimes heard by people with schizophrenia tend to be accusing, threatening, jeering, or persecuting. By contrast, the voices hallucinated by the “normal” are often quite unremarkable,

Until the eighteenth century, voices—like visions—were ascribed to supernatural agencies: gods or demons, angels or djinns.

Julian Jaynes, in his influential 1976 book, The Origin of Consciousness in the Breakdown of the Bicameral Mind, speculated that, not so long ago, all humans heard voices—generated internally, from the right hemisphere of the brain, but perceived (by the left hemisphere) as if external, and taken as direct communications from the gods. Sometime around 1000 B.C., Jaynes proposed, with the rise of modern consciousness, the voices became internalized and recognized as our own.

Musical hallucinations may arise from a stroke, a tumor, an aneurysm, an infectious disease, a neurodegenerative process, or toxic or metabolic disturbances.

Prolonged silence or auditory monotony may also cause auditory hallucinations;

(Music calls upon many more areas of the brain than any other activity—one reason why music therapy is useful for such a wide variety of conditions.)

The hallucinations of brain-stem origin seem to be associated with abnormalities in the acetylcholine transmitter system—abnormalities that may be aggravated by giving the patient L-dopa or similar drugs, which heighten the dopamine load on an already fragile and stressed cholinergic system.

Sometimes psychoses can be centered on delusions of persecution, and occasionally these lead to violent behavior: one such patient assaulted a harmless neighbor, whom she felt was “spying on her.

To live on a day-to-day basis is insufficient for human beings; we need to transcend, transport, escape; we need meaning, understanding, and explanation; we need to see overall patterns in our lives. We need hope, the sense of a future.

Many of us find the reconciliation that James speaks of and even Wordsworthian “intimations of immortality” in nature, art, creative thinking, or religion; some people can reach transcendent states through meditation or similar trance-inducing techniques or through prayer and spiritual exercises. But drugs offer a shortcut; they promise transcendence on demand.

I would take morning glory seeds instead (this was before morning glory seeds were treated with pesticides, as they are now, to prevent drug abuse).

She explained that auras like mine were due to a sort of electrical disturbance like a wave passing across the visual parts of the brain. A similar “wave” could pass over other parts of the brain, too, she said, so one might get a strange feeling on one side of the body or experience an odd smell or find oneself temporarily unable to speak.

Most migraine auras remain at the level of elementary hallucinations: phosphenes, fortifications, and geometrical figures of other sorts—but more complex hallucinations, though rare in migraine, do occur.

that the passage of fortifications in a migraine aura was indeed accompanied by just such a wave of electrical excitation.

There seems to have been, throughout human history, a need to externalize and make art from these internal experiences, from the cross-hatchings of prehistoric cave paintings to the swirling psychedelic art of the 1960s. Do the arabesques and hexagons in our own minds, built into our brain organization, provide us with our first intimations of formal beauty?

And yet, some memories do, seemingly, remain vivid, minutely detailed, and relatively fixed throughout life. This is especially so with traumatic memories or memories carrying an intense emotional charge and significance.

He noted Dostoevsky’s increasingly obsessive preoccupation with morality and proper behavior, his growing tendency to “get embroiled in petty arguments,” his lack of humor, his relative indifference to sexuality, and, despite his high moral tone and seriousness, “a readiness to become angry on slight provocation.” Geschwind spoke of all this as an “interictal personality syndrome” (it is now called “Geschwind syndrome”). Patients with it often develop an intense preoccupation with religion (Geschwind referred to this as “hyper-religiosity”).

Devinsky and his colleague George Lai described how one of their patients had a seizure-related vision in which “he saw Christ and heard a voice that commanded him to kill his wife and then himself. He proceeded to act upon the hallucinations,” killing his wife and then stabbing himself.

Ecstatic or religious or mystical seizures occur in only a small number of those who have temporal lobe epilepsy.

One does not see with the eyes; one sees with the brain, which has dozens of different systems for analyzing the input from the eyes.

If, therefore, one occipital lobe is damaged (as by a stroke, for example), there will be blindness or impaired vision in the opposite half of the visual field—a hemianopia.

In contrast to the relatively brief and stereotyped hallucinations of migraine or epilepsy, the hallucinations of hemianopia may continue for days or weeks on end; and, far from being fixed or uniform in format, they tend to be ever changing.

Dominic ffytche and his colleagues have shown in fMRI studies that it is precisely this area in the right hemisphere which is activated when faces are hallucinated.

Activation of a homologous area in the left hemisphere may produce lexical hallucinations—of letters, numbers, musical notation, sometimes words or pseudowords, or even sentences.

Most hypnagogic images are not like true hallucinations: they are not felt as real, and they are not projected into external space. And yet they have many of the special features of hallucinations—they are involuntary, uncontrollable, autonomous; they may have preternatural colors and detail and undergo rapid and bizarre transformations unlike those of normal mental imagery.

Dreams call on one’s wishes and fears, and they often replay experiences from the previous day or two, assisting in the consolidation of memory. They sometimes seem to suggest the solution to a problem; they have a strongly personal quality and are determined mostly from above—they are largely “top-down” creations

Hypnopompic hallucinations are often seen with open eyes, in bright illumination; they are frequently projected into external space and seem to be totally solid and real. They sometimes give amusement or pleasure, but they often cause distress or even terror, for they may seem charged with intentionality and ready to attack the just-wakened hallucinator.

Hallucinations, in contrast, are startling and apt to be remembered in great detail—this is one of the central contrasts between sleep-related hallucinations and dreaming.

Indeed, one must wonder to what degree the very idea of monsters, ghostly spirits, or phantoms originated with such hallucinations. One can easily imagine that, coupled with a personal or cultural disposition to believe in a disembodied, spiritual realm, these hallucinations, though they have a real physiological basis, might reinforce a belief in the supernatural.

Yet reading Myers’s 1903 two-volume Human Personality and Its Survival After Bodily Death, as well as Phantasms of the Living, the compilation of case histories he and his colleagues (Gurney et al.) published in 1886, one feels that the majority of “psychical” or “paranormal” experiences described are, in fact, hallucinations—hallucinations arising in states of bereavement, social isolation, or sensory deprivation, and above all in drowsy or trancelike states.

It is now known that the hypothalamus secretes “wakefulness” hormones, orexins, and that these are deficient in people who have congenital narcolepsy. Damage to the hypothalamus, from a head injury or a tumor or disease, can also cause narcolepsy later in life.

Cataplexy—the sudden, complete loss of muscle tone with emotion or laughter—

people with narcolepsy can have dozens of “microsleeps” (some lasting for only a few seconds) and “in-between states” each day—and any or all of these may be charged with intensely vivid dreams, hallucinations, or some almost-indistinguishable fusion of the two.

They also found that if their subjects were woken during REM sleep, they would always report that they had been dreaming. It seemed, then, that dreaming was correlated with REM sleep.62 In REM sleep the body is paralyzed, except for shallow breathing and eye movements. Most people enter the REM stage ninety minutes or so after falling asleep, but people with narcolepsy (or those with sleep deprivation) may fall into REM at the very onset of sleep, plunging suddenly into dreaming and sleep paralysis;

But one does not have to have narcolepsy to experience sleep paralysis with hallucinations—indeed, J. A. Cheyne and his colleagues at the University of Waterloo have shown that somewhere between a third and half of the general population has had at least occasional episodes of this, and even a single episode may be unforgettable.

Hallucinatory experiences, whatever their cause, generate a world of imaginary beings and abodes—heaven, hell, fairyland. Such myths and beliefs are designed to clarify and reassure and, at the same time, to frighten and warn.