Why Do We Hallucinate?

Have you ever done a double-take to try and make sense of something bizarre that you thought you saw? Or have you ever felt like there is someone in the room at night while you are falling asleep? Do you ever get chills down your spine because, just for a moment, you thought you saw something or felt something that wasn’t there at all? Those scary experiences may be the result of your brain playing a trick on you that is famously known as Hallucination!

source: disney.tumblr.com/giphy

source: disney.tumblr.com/giphy

What are Hallucinations?

The English word hallucination comes from the Latin verb ‘hallucinari’, which means ‘to wander in the mind’. Hallucinations are sensations that we experience even in the absence of sensory input from the environment. Hallucinations differ from illusions; illusions are misinterpretations of things that are actually present in the environment. Hallucinations are perceptions of things that are not actually present at all.

How can we sense something without it being present?

Our sensory systems are not foolproof, nor are they truthful records or carbon copies of things in the environment. A lot of what we see, hear, taste, smell and feel is also guided by our expectations and what we have experienced before. In other words, we mentally fill in the gaps with our expectations and experiences to form a complete picture of environmental input.

One explanation of hallucinations is that ‘at times, the brain, in order to fill in the gap between sensory input and expectation, goes into overdrive. The sensory neurons are still firing based on one’s expectations, even in the absence of input from the environment, which leads to a hallucination.

Do we only have hallucinations related to vision?

No! Seeing non-existent things is only one part of the whole gamut of hallucinations. We can have hallucinatory experiences related to any of our five senses: seeing, hearing, smelling, tasting and feeling. Most schizophrenics usually report auditory hallucinations, such as hearing voices telling them to do things, as well as other sounds. There are also other kinds of hallucinations, such as feeling one’s body float or feeling like you have an extra limb. Also, it’s not necessary that a hallucinatory episode be related to only one sense. It could be a combination of two or more senses as well. In other words, a non-existent person whom we can see and hear!.


The most common hallucination that we have probably all experienced at least once is the feeling of falling down or skipping a step and stumbling just as we are about to go to sleep. In clinical terms, these are called hypnogogic hallucinations, whereas those that are experienced just after waking up are called hypnopompic hallucinations. Hypnopompic hallucinations occur as a result of the brain not switching quick enough between the dream state and waking state.



When does the brain try to overcompensate, leading to hallucinations?

People who suffer from specific sorts of mental illnesses or physical ailments are the most likely to experience hallucinations. People with psychoses, mood and anxiety disorders, delirium, dementia and physical disturbances, such as tumors, or deficits of the visual system, such as scotomas or cataracts, are usually the victims of these hallucinations.

Use of certain synthetic or natural hallucinogens such as LSD, PCP etc. always induce hallucinations in the user while consumption of other substances such as alcohol, marijuana and heroin may at times but not always induce hallucinations. In fact, many people intentionally consume drugs to be able to enjoy the hallucinations. People who are in the habit of taking drugs and who suddenly stop using them generally experience hallucinations as a side effect.

souce: noisesoundsignal.tumblr.com/giphy

souce: noisesoundsignal.tumblr.com/giphy

Hallucinations are also brought on when you don’t get enough sleep at night or have not slept for many hours (commonly more than 24). Other reasons include going for extended periods without eating or drinking. Therefore, in the general population, the occurrence of hallucinations is a rare one-off incident, but is not completely unthinkable. It is the frequency of hallucinations that determine whether they hint at a deeper illness, are a side effect of it, or simply benign occurrences.


Why does a normal brain not hallucinate?

The question, therefore, is what is the difference between a normal and a diseased or drugged brain? Disease or injury damages the brain either structurally, which affects regions of the brain, or makes the chemical connections dysfunctional, whereas drugs only have the latter effect. Different disorders damage different areas, while different drugs act on different chemical substances (neurotransmitters) in the brain, but with the same side effect of inducing a hallucination. The type of hallucination that the person experiences will depend on the brain area being affected.



We can draw parallels between hallucinations and fevers as a major symptom. Just as a fever gives an indication that there is something wrong with the body, a hallucination is an indication that something in the brain is not right and needs further probing to identify the causative disorder.

In conclusion, it appears that hallucinations occur because the brain attempts to compensates for the compromised ability of our senses to function by being overly interpretative as a result of disease, disorder or dysfunction that directly affects the brain.


  1. Why Do Humans Hallucinate On Little Sleep? – Neurosciences Institute ( Stanford University )
  2. Nature.com
  3. WebMD.com
  4. Psychology Today
  5. Medical Daily
The short URL of the present article is: http://sciabc.us/i8Roc
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Rujuta has a MA in Counseling Psychology and MSc in Cognitive Science. She is currently pursuing a PhD in Cognitive Science from IIT Kanpur in India. Her primary area of interest being human memory and learning, she is also interested in the neuroscience of cognitive processes. She also identifies herself as a bibliophile and a harry potter fanatic.

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