Hallucination: Definition, Types, and Examples

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Hallucination Definition

Perceiving something that appears to be real but is not is known as a hallucination. Some sources use it interchangeably with the term illusion. Delusions and hallucinations are both views or thoughts that something appears to be real.

However, when a person has a hallucination and perceives a picture, sound, or other sensation, he or she subsequently denies it is real based on facts or reasoning. Delusional people, on the other hand, think something is true despite evidence to the contrary.

Common Causes of Hallucination

Hallucination is a rare occurrence. However, it’s possible that it’s a regular occurrence among people with mental illnesses like schizophrenia. As a result, more than 70% of people with schizophrenia have visual hallucinations, while 60-90% feel they have heard voices.

Other diseases that cause hallucinations include Parkinson’s disease, Alzheimer’s disease, migraines, brain tumours, and epilepsy in some circumstances. In addition to these disorders, some medicines known as “hallucinogens” have been linked to hallucinations.

The chemical “Lysergic acid diethylamide,” for example, produces hallucination by binding to serotonin (5-hydroxytryptamine [5-HT]) receptors. Caffeine use was also linked to hallucinations. As a result, people who consume more than seven cups of instant coffee per day are three times more likely to “hear voices” than those who consume less.

In this example, experts explained that excessive coffee use raised cortisol (a stress hormone), which enhanced the likelihood of hallucination. People who are having hallucinations may be scared of what they are seeing.

It can be terrifying to see a vision such as an apparently floating light, hear footsteps, or feel a crawling sensation on the skin that is subsequently determined to be unreal.

Factors in Neurobiology

In essence, hallucinations are caused by problems in the structure and function of the brain’s primary and secondary sensory cortices. Visual hallucinations are linked to grey and white matter abnormalities in Alzheimer’s disease patients.

“Seeing,” “hearing,” or “feeling” things is a fleeting personal experience that occurs by chance. As a result, neurobiologists and scientists alike continue to struggle to comprehend the biological phenomena of hallucination.

Do Animals Hallucinate?

Scientists aren’t sure, but studies show that when lab mice are given a hallucinogen, they exhibit a head-twitch reaction (a hallucinatory activity). Some experts, however, contend that that was insufficient evidence that such animals were hallucinating.

However, a group of Stanford Medicine experts recently claimed that they were able to make lab mice hallucinate without any hallucinogen. Instead, they used the optogenetics method. They implanted light-sensitive genes into their brains in this example.

As a result, certain neurons are more likely to activate at specific light wavelengths. When neurons are stimulated by infrared laser light, the genes create two types of proteins: one that causes neurons to fire and another that causes neurons to glow green.

When the mice were exposed to a sequence of moving parallel lines, the scientists trained them to lick a water spout (i.e. perfectly vertical or horizontal lines). The scientists were able to determine which neurons were firing and so reacting based on the green glow response of the visual cortex.

These neurons were thought to be in charge of “seeing” the pattern of lines. The projections were gradually attenuated when the researchers used their customised laser to stimulate the specific neurons.

They eventually stopped exhibiting the line patterns, but the mice continued to lick the water spout when scientists used a laser to damage the same target neurons. As a result of the findings, the mice may have experienced “true hallucination,” perceiving “ghost” line patterns.

Hallucination Citations
  • Auditory verbal hallucination and the auditory network: From molecules to connectivity. Neuroscience . 2019 Jul 1;410:59-67.
  • Hallucination in Adolescence-Or, Nora in Nowhereland Between Neurosis and Psychosis. Psychoanal Rev . 2018 Oct;105(5):463-480.
  • Synesthesia, hallucination, and autism. Front Biosci (Landmark Ed) . 2021 Jan 1;26:797-809.
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