On seeing the word hallucinations, most people — including many physicians — are likely to react by imagining a person suffering from serious mental illness who needs psychiatric care. The experience of perceiving things that are not there is deeply entrenched in our everyday world as an abnormal event, usually an ominous indicator of severe emotional disturbance. Yet hallucinations are common phenomena in many people without any form of mental illness. In Hallucinations, Oliver Sacks, MD, offers a wide-ranging and detailed survey of hallucinatory phenomena based on his extensive neurological background, the insights offered by many of his patients and correspondents, and his personal knowledge of these perceptual states.
With the erudition, meticulousness, and compassion that have come to characterize its author, the book explores a common and increasingly better understood manifestation of brain activity, admirably attempting to debunk the many unfortunate misunderstandings about the subject.
Dr. Sacks begins with an account of Charles Bonnet syndrome, a condition in which visual hallucinations develop in people with encroaching visual loss. Typically formed hallucinations of a non-threatening nature, the visions of the Charles Bonnet syndrome are distinguished by preserved insight — the understanding that they are not real — a feature that clearly differentiates them from the hallucinations of psychosis. Release of the central visual system confronted with visual impairment is implicated as a plausible explanation. The lucid discussion of this syndrome points out how little appreciated it remains, even by doctors, and that many cases are overlooked or misdiagnosed. In this wise book, no better example of clarifying a misunderstood situation exists; the experienced neurologist will recognize the frequency of benign visual hallucinations in older people with all manner of visual impairment — some of whom are erroneously diagnosed with mental illness and, sadly, treated with medications they most assuredly do not need.
Later on, a remarkable chapter on altered states appears. Here, Dr. Sacks discusses the topic of drug-induced hallucinations based on his own experience with various recreational drugs. “I started with cannabis,” he writes, launching into a vivid description of his use of this drug and many others, including amphetamine, LSD, various prescription medicines, and even intravenous morphine. As a neurology resident in California in the early 1960s, Dr. Sacks had not only the motivation to explore psychoactive drugs for which this era is well known, but also ready access to a variety of such substances. His recounting of these adventures is penetrating and unabashedly honest. A few years later, for example, after moving to New York to take a fellowship in neuropathology and neurochemistry, a series of particularly frightening visual hallucinations leads him to call a physician friend urgently for advice; immensely relieved after being told he is likely in a state of delirium tremens from stopping large doses of chloral hydrate a few days before, he realizes how much better this condition is than schizophrenic psychosis.
While not the first physician, or surely the last, to experiment with hallucinogenic and other centrally-active drugs, Dr. Sacks brings the unique perspective of a keenly observant neurologist with his own drug history to the discussion of perceptual phenomena elicited by these chemicals.
As for psychosis associated with mental illness, Dr. Sacks devotes relatively little attention to schizophrenic hallucinations, embedded as they are within the profoundly disordered inner life of people with this disease. Rather, he writes at length about auditory hallucinations in other settings.
Once again, eager to dispel the stigma associated with hallucinations generally, he points out that most people who hear voices are not schizophrenic, a fact well known to the Swiss psychiatrist Eugen Bleuler; Dr. Sacks cites startling data that as many as a third of normal people admit to having heard voices at some point in their lives. While such a statistic may seem exaggerated, it is surely true that many people have auditory hallucinations they recognize as unreal, and never develop psychotic illness.
Many neurologists, for example, doubtless are familiar with the condition musical hallucinosis in those with advancing deafness. Similar to Charles Bonnet syndrome and its putative release of the visual system, musical hallucinations in hearing-impaired people likely represent physiologic activation of deafferented auditory cortices.
Not to be neglected in a book like this is migraine. Continuing in his confessional manner, Dr. Sacks considers his own migraines, which began when he was a small child with an episode featuring a dazzling fortification pattern followed by a scotoma that evolved almost to hemianopia. He did not have a headache, but naturally, as a three-year old, he was terrified. Fortunately, his mother, also a migraineur, promptly taught him about the visual aura of migraine, and he now believes this disorder is one reason he chose to be a neurologist.
Dr. Sacks emphasizes that migrainous hallucinations in no way suggest psychosis, and recounts helping many patients by assuring them that they can report these visions to their physicians without the risk of being considered psychotic. Instead, the disorder may in fact contribute to creativity, as the bizarre alterations of size and shape in Lewis Carroll's Alice in Wonderland may have been inspired by its author's classic migraines.
Another hallucination covered in this account is the curious syndrome of the phantom limb. First understood by the neurologist Silas Weir Mitchell in Civil War soldiers with amputations, the sensation of a limb being present when it is no longer there is akin to the visual and auditory hallucinations in people with visual or hearing loss. The author takes on this topic with characteristic erudition. In a fascinating footnote, the reader learns that Herman Melville, several years before Mitchell's work, depicted the phantom limb syndrome in Moby Dick: Captain Ahab, who has lost a leg to his nemesis the whale, receives a new leg from the ship's carpenter and perceives “ . . . only one distinct leg to the eye, yet two to the soul.”
Perhaps most provocative of all the ideas Sacks explores is the relationship between hallucinations and religion. This highly charged theme is taken up at several points. A central neurologic concern is the often-discussed religiosity of people with temporal lobe epilepsy. The diverse psychic phenomenology of these seizures is reviewed, along with interesting suggestions that ecstatic seizures have a distinctly religious flavor (“theophanies”) and are often associated with right temporal foci. Indeed, Joan of Arc may have had such seizures, with the result of inspiring thousands to action centuries ago. In this and other passages, the neurobiological correlates of religious passion and conviction are thoughtfully considered.
Many more intriguing examples of hallucinations are covered in this most readable book, all reflecting the author's abiding interest in how the brain underlies the vast panoply of human experience.
Hallucinations will be a rewarding read for anyone interested in brain-behavior relationships. Delving deeply into clinical phenomena often called “positive” — as opposed to the “negative” features, or deficits, that typically attract the neurologist's interest — the book engagingly helps fill a gap in our understanding. Dr. Sacks is undoubtedly the best known ambassador of neurology to the general public, bringing to light extraordinary phenomena, known to many people but often concealed, that can be understood as based in brain structure and function. But all of us, whatever our background, are better off for his consistently graceful and scholarly edification.
Dr. Filley is professor of neurology and psychiatry and director of the Behavioral Neurology Section at the University of Colorado-Denver School of Medicine.
WATCH IT: Oliver Sacks, MD, neurologist and author of Hallucinations, presented a special TED lecture in 2009 on the underlying neurological substrates of Charles Bonnet syndrome, in which visually impaired people experience lucid hallucinations. http://bit.ly/aNQ4KB.
©2012 American Academy of Neurology
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