In the first installment of the World Science Festival’s new series, Science & Story, famed neurologist Oliver Sacks joined award-winning journalist John Hockenberry to discuss Sacks’ latest book, which explores the surreal world of hallucinations.

Oliver Sacks

Ask Oliver Sacks

Renowned neurologist Oliver Sacks answers your questions about the secret world of hallucinations.  These queries came to us via Twitter, Facebook and e-mail.

Q. Are the visual or auditory hallucinations in blind or deaf people analogous to sensations in a phantom limb?

A. Not really. Phantom limbs occur because there is a stable, lifelong image of the limbs in the brain—the body-image. If a limb is amputated, part of this body-image is now exposed, so to speak (normally, it is seamlessly incorporated), and intrudes into consciousness as a phantom. There is no such schema underlying visual or auditory perceptions, and if visual or auditory hallucinations occur, they will be concocted from fragments (often disassembled and reassembled) of memory images.

Q. What is the relationship between Lewy Body Dementia and hallucinations?

A. Lewy bodies are abnormal aggregates of protein inside nerve cells, and Lewy Body disease is a malignant form of Parkinson’s disease involving progressive dementia, as well. Visual misperceptions and hallucinations are much commoner in Lewy Body dementia than in Alzheimer’s disease; this is because Lewy bodies are especially common in the visual association cortex, as well as in the brainstem.

Q. Why do hallucinations such as auras and phosphenes take on geometric patterns?

A. The simpler, stabler geometric patterns mirror the functional architecture of the primary visual cortex (V1), especially its columns of neurons with their specific orientation sensitivities. The more complex geometric patterns, which form and reform and transform, probably reflect the ever-changing, often chaotic, self-organizing patterns of activity in a large pool of visual neurons. In either case, one is, so to speak, seeing the basic organizational features of one’s own visual cortex, visible as hallucinations because of their abnormally excited states.

Q. Is déjà vu a type of hallucination?

A. One can regard déjà vu as a hallucination, but it is more properly regarded as an illusion—an illusion of familiarity. Déjà vu does not invent anything, like a hallucination—it transforms what is actually present and perceived.


  • Removing the Stigma from Hallucination

    For centuries, hallucinations have been associated with mental illness. In his latest book, neurologist Oliver Sacks sheds light on this previously taboo and misrepresented subject.

  • Finding Indigo: An Adventure in Pharmocology

    Since the mid-1660s when a young Isaac Newton first separated the colors of the visible spectrum, modern scientists have stopped recognizing indigo as a color. But that didn’t stop a young Oliver Sacks from searching for it.

  • If We Could Cure Hallucinations, Should We?

    During the live question and answer session, Oliver Sacks was asked, “What if we could stop all hallucinations?”

  • The Smell of Green Thunder: How Does Synesthesia Differ from Hallucination?

    In a condition called synesthesia, the signals between the senses are often crossed. Are these experiences hallucinations? Or are they just as real as the rest of the world around them?


Oliver Sacks—The Justin Bieber of Neurologists

“The Justin Bieber of Neurologists”—that’s how NPR’s John Hockenberry, noting that the World Science Festival program, “Hallucinations with Oliver Sacks,” had sold out in a matter of hours, described the celebrated doctor and best-selling author.

Hallucinations and the Cheating Brain

There is disappointment in the air. I am asked “what goes on in the brain when you hallucinate?” And my reply, however enthusiastically delivered, invariably falls short of expectations.

Purple Octopuses on Parade

In my experience, Oliver Sacks always brings a story, and this time it was early in our conversation for the World Science Festival that he showed once again he has so many stories to tell.

A Flash of Hallucination

As a medical student 30 years ago, I met a physician with a tumor deep in his right frontal lobe that caused seizures. During his seizures, his left arm became stiff, but this was preceded by "the feeling of extreme embarrassment, as though I had made a very foolish remark."

What Is Migraine Aura?

Migraine aura is the collective name given to the many types of neurological symptoms that may occur just before or during a migraine headache. Said to be experienced by 1 in 5 migraineurs—20 to 30% of people—aura is a fully reversible neurological syndrome, which can develop over five minutes and last for up to two hours.

Uncharted Territory

Just around the corner from the head shops that line St. Marks Place, the Cooper Union still houses the very stage where the likes of Lincoln, Mark Twain, the leader of the Lakota Sioux, and Susan B. Anthony spoke to presumably packed houses about the most vital issues of their day.

Photo Gallery

“The Poet Laureate of Medicine”Oliver Sacks speaks about his latest book, which explores the bewitching and surreal world of hallucinations.

World Science Festival Co-Founder Tracy Day introduces the event.

Hallucinations by Oliver SacksThe famed neurologist's newest book was released on November 6, 2012

Program moderator John Hockenberry.

Backstage at Hallucinations with Oliver Sacks.

“I want to open the subject up.”–Oliver Sacks speaks on the stigma surrounding hallucinations

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