Why Do People Experience Hallucinations?
Definition of hallucination
Why does the mind produce such extraordinary - and at times frightening - experiences called hallucinations? Do we fully understand exactly what they are or why the brain creates them? Rita Carter author of 'Mapping the Mind' talks about hallucinations as:
"exceptionally intense self-generated sensory experiences."
A further explanation is offered by the Free Dictionary:
Hallucinations are false or distorted sensory experiences that appear to be real perceptions. These sensory impressions are generated by the mind rather than by any external stimuli, and may be seen, heard, felt, and even smelled or tasted.
Hallucinations occur therefore without any stimulus that is identifiable and suggests that there may be an abnormality in perception.
There is a mechanism in the brain that helps to distinguish between conscious perception and internal memory-based perceptions. When something alters this mechanism or damages it, then hallucinations can occur. However, this is quite a simplistic view as it doesn't cover why people experience hallucinations or why different forms occur. So let's have a closer look firstly at the various category of hallucination.
Definitions of similar words
Illusion - the condition of being deceived by a false perception or belief.
Delusion - a false belief held strongly by the person despite invalidating evidence to the contrary. Normal stimuli are seen but are given a bizarre interpretation.Frequently a symptom of mental illness
Psychosis - severe mental disorder that involves derangement of personality and loss of contact with reality
What kind of hallucinations do people experience?
Hallucinations can manifest in many forms and affect various senses - either one or more at the same time. When more than one sense is affected simultaneously people then experience multi-sensory hallucinations.
The form that hallucinations take are related to - vision, hearing, touch, taste and smell. So basically a person experiencing hallucinations will be seeing, hearing, feeling, tasting or smelling something that is not there in the physical sense.
The list below does not cover all the variations of hallucination that can occur as this subject is vast, but shows the most commons forms:
This is a false perception of sight and can involve various images such as shapes, figures, light flashes and colours. They can also be more complex in that people will see landscapes, animals or even bizarre situations. One of the most common forms, especially in mental health conditions, is a human like figure. In a number of cases these figures will take on religious or cultural form such as Jesus or the devil.
Auditory of course refers to hearing and are another common form of hallucination - also known as paracusia. The person experiencing auditory hallucinations often undergo a variety of manifestations:
- Hearing voices is the most common type of auditory hallucination and is usually associated with mental health conditions such as schizophrenia. The person often describes one or more voices either inside or outside their head. The voices usually make comments about the person that are often uncomplimentary, even at times threatening. However, the voices heard can also be complimentary.
- Exploding head syndrome - can also be associated with sleep disorders and some forms of epilepsy. People report very loud roaring, crashing, or various other noises within their heads. Although painless, the experience leaves people often distressed and frightened.
- Musical ear syndrome - (MES) a variety of sounds may be heard such as music, singing, orchestras or even what seems to be broadcasters describing a game.
Smell (olfactory) Hallucinations
This is also referred to as olfactory hallucinations in relation to the olfactory system that is responsible for enabling us to interpret smells. Phantosmia is the medical name for smelling something that isn't physically present. Frequently hallucinatory smells are not pleasant and have been described as rotting fish, urine, faeces, vomit, dead bodies and smoke among others. People can also experience parosmia where a person is able to smell actual items but they do not have the usual scent that everyone else would associate with those specific things. Frequently the person is convinced that unpleasant smells emanate from their own body. These forms of hallucination are usually associated with medical disorders rather than mental health conditions.
These are hallucinations that involve touch or different feelings of sensory pressure on the skin or even the internal organs. This form of hallucination is often associated with drug abuse where the person feels as if 'things' are moving under their skin and is known as 'formication'.
General Somatic Sensations
These can be particularly distressing hallucinations. They often take the form of the person perceiving that their body is misshapen or in some way grossly abnormal. Examples are:
- The person percieves their body being twisted or torn
- Flesh falling off
- Other kinds of mutilation.
- It is also common with this form of hallucination for the person to feel that their body has been invaded by animals such as snakes, lizards, insects etc.
This is a false perception of taste and they are not normally pleasant tastes either. For example, many people who suffer from epilepsy will say that they have a constant taste of metal in their mouth. With this type of hallucination the person usually suffers from a medical disorder rather than a mental health complaint.
What causes hallucinations?
There are a number of reasons that can lead to a person experiencing hallucinations. These can range from sensory deprivation to drug abuse and the hallucinations can take a certain form depending on what the cause is.
Why hallucinations are formed by the brain under certain circumstances is not fully understood. One of the major difficulties trying to research this condition is that hallucinations occur spontaneously and can be fleeting, making in depth study difficult. However, there are two broad schools of thought. Topological theory suggests that hallucination happens due to abnormal activity in specific areas of the brain. Hodological theory suggests that it is the pathways connecting various areas of the brain that are responsible.
In more basic terms, chemicals in the brain - for example dopamine and serotonin - that transmit signals from one brain cell (neurone) to another are imbalanced or are in the wrong area of the brain, so causing dysfunction. In addition, other researchers also believe that the signals themselves are either faulty or wrong, so causing abnormal functioning.
Continuing research is on-going. For example Dr Dominic Ffytche, Institute of Psychiatry, London, has developed a new method of studying hallucinations after they have been artificially induced. This unique method may give greater insight into why the brain produces hallucinations under certain circumstances.
Other theories on how or why hallucinations occur are split into several categories:
- psychophysiologic- a disturbance in the structure of the brain
- psychobiochemical - this suggest that the chemicals and neurotransmitters, due to disturbance are creating hallucinations.
- psychodynamic - this theory suggests that hallucinations are due to the subconcious mind surfacing into consciousness.
- psychological - many researches believe that psychological factors also play a part in the hallucination experience.
There are a bewildering amount of theories about hallucinations - perhaps reflecting the complexity of the human mind. It is very likely that hallucinations don't occur due to one factor but probably a combination of many.
There are also numerous medical conditions where hallucinations have been experienced. Below are the most familiar complaints, but the list is not exhaustive:
1. Mental health conditions:
The psychotic disorders such as Schizophrenia, schizo affective disorder, delusional disorder, paraphrenia all have hallucinations as one of the main symptoms. In addition people with Bi-polar Affective Disorder and major depression that develop psychotic episodes are also known to produce hallucinations. It is also possible for people who are extremely stressed and anxious to have mild auditory hallucinations. In addition, those who have suffered a recent bereavement may also have these experiences.
2. Medical conditions:
Ailments that affect the central nervous system can cause hallucinations. Examples are:
- Brain Tumours, stroke, dementia.
- Delerium tremens (D.T's) - a severe manifestation of alcohol withdrawal that has, as one of the many medical symptoms, visual hallucinations.
- High fevers.
- Amputation of a limb - this can produce a very distressing condition called 'Phantom Limb Syndrome', where the person can still feel sensations and even pain in the limb that is no longer there.
- Hepatic encephalopathy - a condition of the liver where toxins build up affecting the brain.
- Encephalitis - infection of the brain by the Herpes virus where taste and smell hallucinations are the most common.
- Severe fatigue/sleep deprivation.
3. Sensory deprivation:
In an environment where the usual external stimuli such as - light, sight, sounds, smells are significantly reduced or absent, hallucinations can occur. In addition, people who have experienced extensive periods of time isolated from others can also experience sensory deprivation leading to hallucination. Various experiments carried out in sensory deprivation on healthy people found that in many cases, after only 15 minutes of secluding the participants from sights, sounds and smells, hallucinations were generated.
It's not just illegal substances that cause hallucinations. Many prescribed medications can also have this distressing affect. At times the hallucinations experienced may be just a one off, but it can also be a symptom of drug-induced psychosis. Many of the hallucinations that are drug induced are often visual. People have reported seeing lights, colours and shapes that resemble animal or human figures. Some of their hallucinations are misperceptions. For example a coat on a hanger is seen as a person.
5. Hypnagogic & hypnopompic hallucinations:
These are hallucinations that can be visual, auditory or any other type occurring between the transition periods of waking to sleeping (hypnagogic) or from sleeping to waking (hypnopompic). They are usually of very short duration but on occasion can last longer. In many cases these hallucinations occur with people who suffer from narcolepsy which is excessive day time sleepiness. However, people who are healthy can also experience them.
Hallucinations are only a small part of what can happen within the brain. The reasons for hallucinations and why the brain should produce them under so many different circumstances is still a mystery. What we can be sure of is that if the enigma of hallucinations is solved, it will give one of the greatest insights into the working of the human brain - but it will also no doubt stimulate further puzzles.