Hallucinations mimic real perceptions and sensations. They *appear real* but are unreal because they are not elicited or brought about by anything in our *external objective environment*. No external real stimulus is being received, yet we have a *perception of something* being really there.

<center><img src="https://gateway.ipfs.io/ipfs/QmQ114XLjrDdo6aj6E8invTk737QitLQejWcpbHxVySE9h" /><br/><em><a href="https://commons.wikimedia.org/wiki/File:August_Natterer_Meine_Augen_zur_Zeit_der_Erscheinungen.jpg">Credit: August Natterer/wikimedia, Public Domain</a></em></center>

Hallucination is not:

- **illusion** (a misrepresentation or distortion of something real)
- **delusion** (correct stimulus and perception but additional absurd significance or meaning attributed)
- **dreams** (unconscious image processing as an unreality)
- **imagery/imagination** (conscious image manipulation as an unreality)

<div class="pull-right"><center><img src="https://gateway.ipfs.io/ipfs/QmVfHnwSpvJfZr84Hrcg9khK31T94LJgsHCTjSwScsHWFy" /><br/><em><a href="https://en.wikipedia.org/wiki/File:Two_silhouette_profile_or_a_white_vase.jpg">Source</a>, <a href="https://creativecommons.org/licenses/by-sa/3.0/deed.en">CC BY-SA 3.0</a></em></center></div>

Hallucinatory experiences are authentically happening in the *brain*. There is *activity* taking place, but it generates false senses and produces an unreality we think is real. It's real in our minds, in the subjective reality we experience, but not a real objective reality. It's *self-generated* from within.

Distinguishing hallucinations from reality is difficult to do because the brain is generating these signals and we experience them nonetheless. But the signals aren't coming from things happening in the real world, these signals come from some substance (drugs, hallucinogens), illness (food poisoning), or other factor. 

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# Electro-Chemical Changes

<div class="pull-left"><center><img src="https://gateway.ipfs.io/ipfs/QmUDsN7Keuarb4Y4tJCeBzuawLXq9vtBUanGzY1U1Pnyzw" /><br/><em><a href="https://pixabay.com/en/brain-turn-on-education-read-book-3141247/">Pixabay, CC0 Creative Commons</a></em></center></div>

Visual hallucinations are the most obvious kind when we think of the topic of hallucinations. The same brain regions for imagery/images acre activated for both real view/perception and hallucinated imagery. Imagination works differently from hallucinations in the brain, more like regular perceptions. We can recall images in our mind's eye in *imagination*. Hallucinations are induced by *electro-chemical changes* and produce false perceptions. We are tricked into thinking the stimulus is external, but it's all a misperception from *imbalanced* electro-chemical physiology within.

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# In History

Human history has accounts of stories that sound like hallucinatory perceptions and senses about things that aren't there. Claims of *"holy"* or *"divine"* **voices, visions or revelations**, could possibly be true, but more likely true in the sense that they truly hallucinated visions or heard the voice of the "gods". A theory called the bicameral mind by Julian Jaynes suggests the evolutionary development of an **internal voice/monologue** was perceived to be from the *"gods"*.

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# Biological Factors

The likelihood of hallucinatory experiences increase from the age of 60 onwards. 5% of us will have one or more hallucinations in our life., regardless of age or health factors. When we are falling asleep, we can hallucinate sounds or shapes. Those who experience the loss of a loved one in extreme grief can also hallucinate their beloved.

**Losing our senses** can also induce hallucinatory experiences. Those who start to lose their sight often start to see things that aren't there, like in-color high detail people or figured that their vision no longer permits. Hearing loss can also create sounds that aren't there, where people hear notes or even full songs. A case of someone who experiences the loss of smell from Parkinson's disease suddenly began smelling burning leaves, burnt wood and bad onions to the point of making their eyes water. **These were physiological effects induced from psychological perception, a mind over body effect.**

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# Reverse Hallucination

<div class="pull-right"><center><img src="https://gateway.ipfs.io/ipfs/QmZuugY1cRQj8ujnicU4yaUDFugavufXiMGXR3m2PXG5SV" /><br/><em><a href="https://commons.wikimedia.org/wiki/File:Five_senses.jpg">Credit: Allan-Hermann Pool/wikimedia</a>, <a href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">CC BY-SA 4.0</a></em></center></div>

Even *partial* loss of senses can result in hallucinations. Being *exhausted* can reduce our sensory stimulus. Senses can be *reduced*, like can be done in *sensory deprivation*. When one sense dials down, others can be amplified. When vision or hearing is reduced the **brain fills in the gaps** to keep the world running according to our expectations. For touch however, it's always getting some form of input. You can't shut off sensing touch like you can close your eyes or clock your ears. The chair or the floor, there is always some sense pressure being applied to our bodies.

To cope with the frequent signals being input to the brain from our senses, the **brain filters signals for what to pay attention to**. Touches less than 250ms are dismissed. Constant touch eventually fades from attention. Most of us don't notice our socks, our pants, the food on our faces, or some pressure applied somewhere after some time. We feel nothing, even though there is something to sense there. This is a ***"reverse hallucination"***.

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# Hyperactivity

People with *schizophrenia* have issues with this "reverse hallucinations" to filter out what not to pay attention to, of not sensing things that are there to be sensed. After most people are inured to the vibrations of a bracelet, most schizophrenics will still notice. Schizophrenia seems to be more a sensory disorder than impaired cognition. This is why schizophrenia has been changed to *salience syndrome*, because the ability to weigh the salient importance of senses is diminished. Schizophrenics are known to sometimes see things as well.

Our brains **fill in the gaps with stories** we make up to try to explain what we feel, experience or think. Hyperawareness seems to be going on in people who hallucinate feeling insects on them. People who experience the insect feeling have often taken an over the counter stimulant which sends their brains into hyper-activity mode.

**The brain ultimately decides what we feel, see or hear around us, whether it's there or not. A properly regulated bio-electro-chemical system is important to stay in touch with reality.**

The brain doesn't seem to tolerate inactivity for long. A reduction in sensory input sometimes results in the brain creating some of its own. High-flying pilots and truck drivers on long trips have reported hallucinations.

We are normally **stimulated with thousands of sensations every second** to provide a **constant frame of reference** for consciousness. We don't notice many things that are applying pressure on our bodies unless we focus on it. There is noise all around us but we normalize it out. To **always pay attention** to everything would be an *inefficient* use of the brain.

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# Predicting the Future

<div class="pull-left"><center><img src="https://gateway.ipfs.io/ipfs/QmRdhtEujzwDGpkJosQWZ1pU2HFUk5KHziY3zGeBcnbG47" /><br/><em><a href="https://pixabay.com/p-1026092/?no_redirect">pixabay, CC0 Creative Commons</a></em></center></div>

The brain uses **patterns to predict** what will come. The way sound works, is for lower regions to process basics like pattern and pitch. This gets passed as s signal to higher brain processing regions for melody and key changes. Once we hear something, the brain has a pattern of it in memory stored. When we hear it again, the brain *recognizes the pattern*, and expects the rest of the sounds to come after the initially detected sound that matches a pattern.

**Heavy brain-power processing is reduced** with a quick verification made against reality to confirm the prediction which is then maintained. If the reality check fails, then we process the signal to higher areas instead of making the usual prediction. The recognized sounds and the patterns are correct for processing in the future. This is how we *recognize music* after only hearing a few notes, or a *movie* from only *seeing a few frames*.

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# Silencing Hallucinations

<div class="pull-right"><center><img src="https://gateway.ipfs.io/ipfs/QmQDmPg6yMhmgV6Hyo3cbRhj1dHehiuRjLJNiAbHDk2E4f" /><br/><em><a href="https://commons.wikimedia.org/wiki/File:International_Symbol_for_Deafness.jpg">Credit: State of Rhode Island/wikimedia, Public Domain</a></em></center></div>

In someone going fully deaf, they can only hear a little. The higher regions of the brain aren't being reached to *fully process* the audio. One study by Newcastle University showed how a deaf woman had a quieting of her hallucinatory auditory experiences after listening to Bach at a high volume. The brain scans showed the area for melody and tones were being reached, and the brain no longer needed to **invent hallucinatory senses** to compensate.

In the most silent place on earth, a chamber at Orfield Laboratories in Minneapolis, Minnesota, you can hear your eyeballs move. Some people experience hallucinations, while others don't. The reason why this happens isn't clear yet, but the thinking is that electrical signals *excite or inhibit* areas that are affected or not affected. Neuronal activity is *promoted or impeded*. When something is going on in one place, it's not going on in another. Not all areas are active at once.

Charles Bonnet syndrome is underactivity that triggers the brain to hallucinate and fill in the gaps. But this time, there is no reality checking to course correct. A feedback loop is created where the brain self-references it's output as it's own input, and doesn't take input from the outside world.

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# Drugs

<div class="pull-left"><center><img src="https://gateway.ipfs.io/ipfs/QmeVmgFLMNQ66ns2SkRawreZVR71JFuYNKeheHQGUNAzps" /><br/><em><a href="https://www.flickr.com/photos/67194724@N03/8303093547">Credit: new 1lluminati/wikimedia</a>, <a href="https://creativecommons.org/licenses/by/2.0/">CC BY 2.0</a></em></center></div>

Drug use that produces hallucinations are the same *subjective induction* that isn't coming from reality. David Nutt did a small study with 20 people, giving them either LSD or a placebo along with a brain scan. Areas of the brain related to **vision, attention, movement and hearing** that don't normally communicate were *more connected*. Areas associated with a sense of **self and identity were less connected**.

People who take psychedelics, or those that meditate, are changing their electro-chemical functionality. Many experience a subjective inner-state induced by themselves or a substance, that has them feel their *self disintegrating* and feel as though they are *becoming one**with the universe. This is often called an alleged *"ego-death"*.

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# Reality Check Disrupted

Hallucinations have one thing in common, a **disruption of the normal reality checking mechanism** to make sure input is coming from the external reality, and not the **subjective internal processing in a feedback loop of fantasy**. In hallucinations, an *over-reliance* and *overemphasis* is placed on internally generated sensations, misinterpreting them as though they actually came from the external world.

A placebo "mind-over-body" *self-hypnosis* method can be used manage issues of hallucinating. By *monitoring thoughts* which affect how the brain will think about and expect/predict reality, people can avoid generating some hallucinations. Many can also learn to accept, rather than reject or be fearful of their hallucinations, and study or analyze them to try to understand more and gain more insight. Putting one's attention back onto something real, a real smell, real touch, can help to suppress the hallucination as well.

Hallucinations are a result of things not working properly internally. The way we normally construct reality is altered, producing an **altered state of consciousness**. Signals are not getting where they need to, or signals get mixed up in how they are normally processed, creating false sensory constructs that are taken to be real.

The brain does a lot of predictive processing and reality verification. When this goes *awry* and signals get *confused or lost*, the brain steps in to **fill some gaps** or do what the chemicals are making it do: create and process sensory *stimulus from itself* instead of taking it from objective reality as it 'is'. Our biology is fine tuned to work in reality in order to **properly perceive, conceive, understand and navigate it successfully**.

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References:
- [Hallucination](https://en.wikipedia.org/wiki/Hallucination)
- [Hallucinations and Perceptions](https://web.archive.org/web/20170112105146/http://www.drgriffith.net/hallucinations.htm)
- [Your Hallucinating Reality](https://www.newscientist.com/issue/3098/)
- ['Salience syndrome' replaces 'schizophrenia' in DSM-V and ICD-11: psychiatry's evidence-based entry into the 21st century?](https://www.ncbi.nlm.nih.gov/pubmed/19807717)

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