Hallucinations

In his psychology book Hallucinations (2012), Oliver Sacks explores the many reasons why humans experience hallucinations, from sensory deprivation to injury. He also considers the role that hallucinogenic and psychedelic drugs play in our modern society. Sacks’s own experiences with hallucinogenic drugs back in the 1960s fuelled his professional interest in the psychedelic experience and what it says about the human condition. Sacks was a prominent neurologist and chronic care practitioner who became a medical advisor at the Institute for Music and Neurologic Function (IMNF). He is best known for his book Awakenings, which has been adapted into a major motion picture.

Sacks wrote Hallucinations to achieve two goals: first, to remove the stigma around hallucinations. He notes that hallucinations are often linked solely to insanity or the consumption of illegal drugs when the reality is that anyone can experience hallucinatory events. Second, he wants to clarify what hallucinations are. Hallucinations are not simply visual events; they can affect any of the five human senses.

Sacks begins by defining what it means to experience a hallucinatory event. When someone smells, touches, tastes, hears, or feels something that isn’t there, they are hallucinating. In many instances, it is a frightening experience, particularly if the person sees something violent or hears menacing voices. After defining what he means by hallucinations, Sacks breaks down the different kinds of hallucinations that we know of and what causes them.



He begins with visual hallucinations experienced by blind or sensory-deprived people. When a blind person sees things that are not there, they are experiencing what is known as Charles Bonnet Syndrome (CBS). This happens because, although the person can’t see, the visual perception areas of their brain are still active. A similar phenomenon occurs when people are exposed to hours of complete darkness, otherwise known as the “prisoner’s cinema.”

Sensory deprivation doesn’t just affect the eyesight. It affects our sense of smell, too. When we lose our sense of smell for a while, we “imagine” smells that aren’t there. Brain scans show that, during a hallucination, the olfactory areas of the brain light up even when there is nothing to smell. That is why the experience feels so real to the person suffering from the hallucination—their brain thinks that it is real.

Auditory hallucinations, or hearing things that are not real, can happen to anyone. There is no need for sensory deprivation, illness, or drug use. We may hear someone talking or calling our name, but there is no one there. Such hallucinations are often linked to the supernatural or religious epiphanies, which Sacks dedicates an entire chapter to debunking.



There is no doubt, Sacks notes, that mind-altering drugs do cause hallucinations. He experienced these hallucinations himself when he experimented with psychedelics. The drugs alter brain chemistry, causing vivid hallucinatory episodes. Delirium, or fever, triggers a similar neurological response.

Although Sacks doesn’t consider dreams or nightmares and what they say about our psyche, he does look at sleep disorders and how they can cause hallucinations. Sleepwalking and sleep deprivation may cause sufferers to experience significant visual, physical, and olfactory hallucinations. Similarly, stress, anxiety, and grief may cause hallucinatory events. For example, those with PTSD often relive the traumatic event, and the experience feels real enough to traumatize them again.

Sacks also considers how migraines cause hallucinations. Very common, migraines are often accompanied by visual disturbances. For example, people see bright orbs, flashing lights, or small figures. Some people experience temporary blindness or blurred vision in one eye. Electronic or neurological disturbances cause these hallucinations, which is why epilepsy sufferers may also experience hallucinatory events. Treatment should always focus on restoring the brain’s altered chemistry to its healthy state.



There is also a chapter dedicated to phantom limb syndrome and bodily hallucinations. Patients experience phantom limb pain because the brain rewires itself following limb loss. Sometimes, these signals are mixed up and fire incorrectly; they may never go away completely. Phantom limb syndrome is understandably distressing for the patient and more must be done to understand the condition.

Connected to phantom limb syndrome is the idea of bodily hallucinations. People may feel that their organs are moving out of place, or that something is moving underneath their skin. They may even experience phantom touches and movement across the skin. These hallucinations are often linked to mental illness or disorders, such as dementia or schizophrenia, or consuming hallucinogenic drugs.

What Sacks makes clear in Hallucinations is that hallucinatory events can happen to anyone. They are not always a sign of drug abuse or mental illness. Similarly, religious or ecstatic hallucinations are not necessarily of divine origin. These hallucinations often stem from our deep, biological desire to belong to something greater than ourselves. Sacks refrains from religious commentary, but he does urge readers to take care when considering whether an allegedly divine hallucination is real.