Hallucinations: Definition, Causes, And Symptoms

Why do people suffer from hallucinations? What happens in their brains?

The perception is the process by which living organisms capture information from the environment in order to process and acquire knowledge about this, being able to adapt to situations we live. 

However, in many cases, whether or not there is a  mental disorder, perceptions are produced that do not correspond to reality, and these perceptual alterations can be grouped mainly into distortions or deceptions.

Whereas in perceptual distortions a real stimulus is abnormally perceived, in perceptual delusions there is no stimulus that triggers the perceptual process. The clearest example of the latter type of perceptual disturbance is hallucinations.

Hallucinations: defining the concept

The concept that we have just mentioned, hallucination , has evolved throughout history and its description has been enriched over the years. Hallucination can be considered as  a perception that occurs in the absence of a stimulus that triggers it, with the sufferer having the feeling that it is real and that it occurs without the subject being able to control it (this characteristic being shared with obsessions, delusions and some delusions).

Although they are generally indicators of mental disorder (being a diagnostic criterion for  schizophrenia and may appear in other disorders, such as during manic episodes or during  depressions ), hallucinations can also appear in many other cases, such as neurological disorders, consumption of substances, epilepsy, tumors and even in non-pathological situations of high  anxiety or  stress (in the form of nervous paroxysm due to the object of our anxiety, for example).

An example of hallucination

Let’s see an example below to help us understand what a hallucination is

“A young man comes to see a psychologist. There, he tells his psychologist that he has come to him because he is very afraid. Initially, he is reluctant to speak with the professional, but throughout the interview he confesses that the reason for being in his office is that every time he looks in the mirror he hears a voice that speaks to him, insulting him, saying no will come to nothing in life and stating that it should disappear.

This example is a fictitious case in which the supposed patient has perceived a stimulus that does not really exist from a specific situation (looking in the mirror).  The young man has really had that perception, being for him a very real phenomenon that he cannot direct or control. In this way, we can consider that it has all the aforementioned characteristics.

However, not all hallucinations are always the same. There is a wide variety of typologies and classifications, among which the one that refers to the sensory modality in which they appear stands out. In addition, not all appear in the same conditions, and there are also multiple variants of the hallucinatory experience.

Types of hallucinations according to sensory modality

If we classify the hallucinatory experience according to the sensory modality in which they appear, we can find several categories.

1. Visual hallucinations

In the first place you can find visual hallucinations, perceived through the sense of sight. In this case the subject sees something that does not exist in reality. These stimuli can be very simple, such as flashes or lights. However, more complex elements such as characters, animated beings or vivid scenes can be seen.

It is possible that these elements are visualized with different measures than those that would be perceived if these stimuli were real, being called Lilliputian hallucinations in the case of smaller perceptions and Gulliverian in the case of seeing them enlarged. Within visual hallucinations there is also autoscopy, in which a subject sees herself from the outside of her body, in a way similar to that reported by patients with near-death experiences.

Visual hallucinations are especially common in organic conditions, trauma, and substance use, although they also appear in certain mental disorders.

2. Auditory hallucinations

Regarding auditory hallucinations, in which the perceiver hears something unreal, they can be simple noises or elements with complete meaning such as human speech. 

The clearest examples are second-person hallucinations, in which, as in the example described above, a voice speaks to the subject, third-person hallucinations in which voices that speak of the individual are heard among themselves, or imperative hallucinations, in the that the individual hears voices that order him to do or stop doing something. Hallucinations of this sensory modality are the most frequent in mental disorders, especially in paranoid schizophrenia.

3. Hallucinations of taste and smell

With regard to the senses of taste and smell, hallucinations in these senses are rare  and are usually related to the use of drugs or other substances, in addition to some neurological disorders such as temporal lobe epilepsy, or even tumors. They also appear in schizophrenia, usually related to delusions of poisoning or persecution.

4. Haptic hallucinations

The haptic hallucinations are those that refer to the sense of touch. This typology includes a large number of sensations, such as those of temperature, pain or tingling (the latter being called paresthesias, and highlighting among them a subtype called dermatozoal delirium in which there is the sensation of having small animals in the body, being typical consumption of substances such as cocaine).

Apart from these, related to the senses, two more subtypes can be identified.

In the first place, the kinesthetic or somatic hallucinations, which provoke sensations perceived regarding the organs themselves, normally associated with strange delusional processes.

Second and last, kinesthetic or kinesthetic hallucinations refer to sensations of movement of the body itself that are not produced in reality, being typical of Parkinson’s patients and substance use.

As already mentioned, regardless of where they are perceived, it is also useful to know how they are perceived. In this sense we find different options.

Different modes of false perception

The so-called functional hallucinations are unleashed in the presence of a stimulus that triggers another, this time hallucinatory, in the same sensory modality. This hallucination occurs, begins and ends at the same time as the stimulus that originates it. An example would be the perception of someone who perceives the tune of the news every time he hears traffic noise.

The same phenomenon occurs in reflex hallucination, only this time the unreal perception occurs in a different sensory modality. This is the case in the above example.

The extracampina hallucination occurs in cases where the false perception occurs outside the perceptual field of the individual. That is to say, something is perceived beyond what could be perceived. An example is seeing someone behind a wall, with no other information that could suggest their existence.

Another form of hallucination is the absence of perception of something that exists, called negative hallucination. However, in this case the behavior of the patients is not influenced as if they perceive that there is nothing, so that in many cases it has been doubted that there is a true lack of perception. An example is negative autoscopy, in which the person does not perceive himself when looking in a mirror.

Finally, it is worth noting the existence of pseudohallucinations. These are perceptions with the same characteristics as hallucinations with the exception that the subject is aware that they are unreal elements.

Why does a hallucination occur?

We have been able to see some of the main modalities and types of hallucinations, but why do they occur? 

Although there is no single explanation in this regard, various authors have tried to shed light on this type of phenomenon, some of the most accepted being those that consider that the hallucinating subject erroneously attributes his internal experiences to external factors.

An example of this is the theory of metacognitive discrimination of Slade and Bentall, according to which the hallucinatory phenomenon is based on the inability to distinguish real from imaginary perception. These authors consider that this ability to distinguish, which is created and can be modified through learning, may be due to an excess of activation due to stress, lack or excess of environmental stimulation, high suggestibility, the presence of expectations regarding what is going to be perceived, among other options.

Another example, focused on auditory hallucinations, is  Hoffman’s theory of subvocalization, which indicates that these hallucinations are the subject’s perception of their own subvocal speech (that is, our internal voice) as something alien to themselves. (theory that has generated therapies to treat auditory hallucinations with some effectiveness). However, Hoffman considered that this fact was not due to a lack of discrimination, but to the generation of involuntary internal discursive acts.

Thus, hallucinations are ways of “reading” reality in the wrong way, as if there were elements that are really there even though our senses seem to indicate otherwise. However, in the case of hallucinations our sensory organs work perfectly, what changes is the way in which our brain processes the information that arrives. Normally this means that our memories are mixed with sensory data in an abnormal way, linking previously experienced visual stimuli to what is happening around us.

For example, this is what happens when we spend a lot of time in the dark or blindfolded so that our eyes do not register anything; the brain begins to invent things because of the anomaly that supposes not to receive data through this sensory pathway while awake.

The brain that creates an imaginary environment

The existence of hallucinations reminds us that we do not just record data about what is happening around us, but that our nervous system has the mechanisms to “build” scenes that tell us what is happening around us. Some diseases can trigger hallucinations in an uncontrolled way, but these are part of our daily lives, even if we do not realize it.

Bibliographic references:

  • American Psychiatric Association (2002). DSM-IV-TR. Diagnostic and Statistical Manual of Mental Disorders. Spanish edition. Barcelona: Masson. (Original in English from 2000).
  • Baños, R. and Perpiña, C. (2002). Psychopathological exploration. Madrid: Synthesis.
  • Belloch, A., Baños, R. and Perpiñá, C. (2008) Psychopathology of perception and imagination. In A. Belloch, B. Sandín and F. Ramos (Eds.) Manual of Psychopathology (2nd edition). Vol I. Madrid: McGraw Hill Interamericana.
  • Hoffman, RE (1986). Verbal hallucinations and language production processes in schizophrenia. Behavioral and Brain Science, 9, 503-548.
  • Ochoa E. & De la Fuente ML (1990). “Psychopathology of Attention, Perception and Consciousness”. In Medical Psychology, Psychopathology and Psychiatry, Vol. II. Ed. Interamericana. McGraw-Hill. Fuentenebro. Madrid, pp. 489-506.
  • Seva, A. (1979). “Psychopathology of Perception”. In: Clinical Psychiatry. Ed. Spaxs. Barcelona, ​​pp 173-180.
  • Santos, JL (2012). Psychopathology. CEDE Preparation Manual PIR, 01. CEDE. Madrid.
  • Slade, PD. & Bentall, RP (1988). Sensory deception: A scientific analysis of hallucination. Baltimore: The Johns Hopkins University. 

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