|Classification and external resources|
A delusion is a belief held with strong conviction despite superior evidence to the contrary. As a pathology, it is distinct from a belief based on false or incomplete information, confabulation, dogma, illusion, or other effects of perception.
Delusions typically occur in the context of neurological or mental illness, although they are not tied to any particular disease and have been found to occur in the context of many pathological states (both physical and mental). However, they are of particular diagnostic importance in psychotic disorders including schizophrenia, paraphrenia, manic episodes of bipolar disorder, and psychotic depression.
Although non-specific concepts of madness have been around for several thousand years, the psychiatrist and philosopher Karl Jaspers was the first to define the three main criteria for a belief to be considered delusional in his 1913 book General Psychopathology. These criteria are:
- certainty (held with absolute conviction)
- incorrigibility (not changeable by compelling counterargument or proof to the contrary)
- impossibility or falsity of content (implausible, bizarre or patently untrue)
Furthermore, when a false belief involves a value judgment, it is only considered as a delusion if it is so extreme that it cannot be or ever can be proven true (example: a man claims that he flew into the sun and flew back home. This would be considered a delusion).
Delusions are categorized into four different groups:
- Bizarre delusion: A delusion that is very strange and completely implausible; an example of a bizarre delusion would be that aliens have removed the reporting person's brain.
- Non-bizarre delusion: A delusion that, though false, is at least possible, e.g., the affected person mistakenly believes that he is under constant police surveillance.
- Mood-congruent delusion: Any delusion with content consistent with either a depressive or manic state, e.g., a depressed person believes that news anchors on television highly disapprove of him, or a person in a manic state might believe she is a powerful deity.
- Mood-neutral delusion: A delusion that does not relate to the sufferer's emotional state; for example, a belief that an extra limb is growing out of the back of one's head is neutral to either depression or mania.
In addition to these categories, delusions often manifest according to a consistent theme. Although delusions can have any theme, certain themes are more common. Some of the more common delusion themes are:
- Delusion of control: This is a false belief that another person, group of people, or external force controls one's general thoughts, feelings, impulses, or behavior.
- Cotard delusion: This is a false belief that one does not exist or has become deceased.
- Delusional jealousy: A person with this delusion falsely believes that a person is lying to them or that a spouse or lover is having an affair, with no proof to back up their claim.
- Delusion of guilt or sin (or delusion of self-accusation): This is a false feeling of remorse or guilt of delusional intensity.
- Delusion of mind being read: The false belief that other people can know one's thoughts.
- Delusion of thought insertion: the belief that another thinks through the mind of the person.
- Delusion of reference: The person falsely believes that insignificant remarks, events, or objects in one's environment have personal meaning or significance.
- Erotomania A delusion where someone believes another person is in love with them.
- Grandiose religious delusion: the belief that the affected person is a god, or chosen to act as a god.
- Somatic delusion: A delusion whose content pertains to bodily functioning, bodily sensations, or physical appearance. Usually the false belief is that the body is somehow diseased, abnormal, or changed. A specific example of this delusion is delusional parasitosis: a delusion in which one feels infested with an insect, bacteria, mite, spiders, lice, fleas, worms, or other organisms. Affected individuals may also report being repeatedly bitten. In some cases, entomologists are asked to investigate cases of mysterious bites. Sometimes physical manifestations may occur including skin lesions.
- Delusion of poverty: The person strongly believes that he is financially incapacitated. Although this type of delusion is less common now, it was particularly widespread in the days before state support.
Grandiose delusions 
Grandiose delusions are distinct from grandiosity, in that the sufferer does not have insight into his loss of touch with reality. An individual is convinced he has special powers, talents, or abilities. Sometimes, the individual may actually believe they are a famous person or character.
Grandiose delusions or delusions of grandeur are principally a subtype of delusional disorder but could possibly feature as a symptom of schizophrenia and manic episodes of bipolar disorder. Grandiose delusions are characterized by fantastical beliefs that one is famous, omnipotent, or otherwise very powerful. The delusions are generally fantastic, often with a supernatural, science-fictional, or religious bent. In colloquial usage, one who overestimates one's own abilities, talents, stature or situation is sometimes said to have 'delusions of grandeur'. This is generally due to excessive pride, rather than any actual delusions.
Persecutory delusions 
Persecutory delusions are the most common type of delusions and involve the theme of being followed, harassed, cheated, poisoned or drugged, conspired against, spied on, attacked, or otherwise obstructed in the pursuit of goals. Persecutory delusions are a condition in which the affected person wrongly believes that they are being persecuted. Specifically, they have been defined as containing two central elements:[page needed]
- The individual thinks that harm is occurring, or is going to occur.
- The individual thinks that the persecutor has the intention to cause harm.
According to the DSM-IV-TR, persecutory delusions are the most common form of delusions in schizophrenia, where the person believes they are "being tormented, followed, tricked, spied on, or ridiculed." In the DSM-IV-TR, persecutory delusions are the main feature of the persecutory type of delusional disorder. When the focus is to remedy some injustice by legal action, they are sometimes called "querulous paranoia".
The modern definition and Jaspers' original criteria have been criticised, as counter-examples can be shown for every defining feature.
Studies on psychiatric patients show that delusions vary in intensity and conviction over time, which suggests that certainty and incorrigibility are not necessary components of a delusional belief.
Delusions do not necessarily have to be false or 'incorrect inferences about external reality'. Some religious or spiritual beliefs by their nature may not be falsifiable, and hence cannot be described as false or incorrect, no matter whether the person holding these beliefs was diagnosed as delusional or not.
In other situations the delusion may turn out to be true belief. For example, delusional jealousy, where a person believes that their partner is being unfaithful (and may even follow them into the bathroom believing them to be seeing their lover even during the briefest of partings) may result in the faithful partner being driven to infidelity by the constant and unreasonable strain put on them by their delusional spouse. In this case the delusion does not cease to be a delusion because the content later turns out to be true.
In other cases, the delusion may be assumed to be false by a doctor or psychiatrist assessing the belief, because it seems to be unlikely, bizarre or held with excessive conviction. Psychiatrists rarely have the time or resources to check the validity of a person’s claims leading to some true beliefs to be erroneously classified as delusional. This is known as the Martha Mitchell effect, after the wife of the attorney general who alleged that illegal activity was taking place in the White House. At the time her claims were thought to be signs of mental illness, and only after the Watergate scandal broke was she proved right (and hence sane).
Similar factors have led to criticisms of Jaspers' definition of true delusions as being ultimately 'un-understandable'. Critics (such as R. D. Laing) have argued that this leads to the diagnosis of delusions being based on the subjective understanding of a particular psychiatrist, who may not have access to all the information that might make a belief otherwise interpretable. R.D. Laing's hypothesis has been applied to some forms of projective therapy to "fix" a delusional system so that it cannot be altered by the patient. Psychiatric researchers at Yale University, Ohio State University and the Community Mental Health Center of Middle Georgia have used novels and motion picture films as the focus. Texts, plots and cinematography are discussed and the delusions approached tangentially. This use of fiction to decrease the malleability of a delusion was employed in a joint project by science-fiction author Philip Jose Farmer and Yale psychiatrist A. James Giannini. They wrote the novel Red Orc's Rage, which, recursively, deals with delusional adolescents who are treated with a form of projective therapy. In this novel's fictional setting other novels written by Farmer are discussed and the characters are symbolically integrated into the delusions of fictional patients.This particular novel was then applied to real-life clinical settings.
Another difficulty with the diagnosis of delusions is that almost all of these features can be found in "normal" beliefs. Many religious beliefs hold exactly the same features, yet are not universally considered delusional. These factors have led the psychiatrist Anthony David to note that "there is no acceptable (rather than accepted) definition of a delusion." In practice psychiatrists tend to diagnose a belief as delusional if it is either patently bizarre, causing significant distress, or excessively pre-occupies the patient, especially if the person is subsequently unswayed in belief by counter-evidence or reasonable arguments.
It is important to distinguish true delusions from other symptoms such as anxiety, fear, or paranoia. To diagnose delusions a mental state examination may be used. This test includes appearance, mood, affect, behavior, rate and continuity of speech,evidence of hallucinations or abnormal beliefs, thought content, orientation to time, place and person, attention and concentration, insight and judgment, as well as short-term memory.
Johnson-Laird suggests that delusions may be viewed as the natural consequence of failure to distinguish conceptual relevance. That is, the person takes irrelevant information and puts it in the form of disconnected experiences, then it is taken to be relevant in a manner that suggests false causal connections. Furthermore, the person takes the relevant information, in the form of counterexamples, and ignores it.
Development of specific delusions 
The top two factors mainly concerned in the germination of delusions are: 1. Disorder of brain functioning; and 2. background influences of temperament and personality.
Higher levels of dopamine qualify as a symptom of disorders of brain function. That they are needed to sustain certain delusions was examined by a preliminary study on delusional disorder (a psychotic syndrome) instigated to clarify if schizophrenia had a dopamine psychosis. There were positive results - delusions of jealousy and persecution had different levels of dopamine metabolite HVA and Homovanillyl alcohol (which may have been genetic). These can be only regarded as tentative results; the study called for future research with a larger population.
It is too simplistic to say that a certain measure of dopamine will bring about a specific delusion. Studies show age and gender to be influential and it is most likely that HVA levels change during the life course of some syndromes.
On the influence personality, it has been said: "Jaspers considered there is a subtle change in personality due to the illness itself; and this creates the condition for the development of the delusional atmosphere in which the delusional intuition arises."
Cultural factors have "a decisive influence in shaping delusions". For example, delusions of guilt and punishment are frequent in a Western, Christian country like Austria, but not in Pakistan - where it is more likely persecution. Similarly, in a series of case studies, delusions of guilt and punishment were found in Austrian patients with Parkinson's being treated with l-dopa - a dopamine agonist.
To define delusional thinking in a specific patient, it is important to consult a local psychiatrist who can make a thorough examination before diagnosing the problem. Explaining the causes of delusions continues to be challenging and several theories have been developed. One is the genetic or biological theory, which states that close relatives of people with delusional disorder are at increased risk of delusional traits. Another theory is the dysfunctional cognitive processing, which states that delusions may arise from distorted ways people have of explaining life to themselves. A third theory is called motivated or defensive delusions. This one states that some of those persons who are predisposed might suffer the onset of delusional disorder in those moments when coping with life and maintaining high self-esteem becomes a significant challenge. In this case, the person views others as the cause of their personal difficulties in order to preserve a positive self-view.
This condition is more common among people who have poor hearing or sight. Also, ongoing stressors have been associated with a higher possibility of developing delusions. Examples of such stressors are immigration or low socio-economic status.
Researcher, Orrin Devinsky, MD, from the NYU Langone Medical Center, performed a study that revealed a consistent pattern of injury to the frontal lobe and right hemisphere of the human brain in patients with certain delusions and brain disorders. Devinsky explains that the cognitive deficits caused by those injuries to the right hemisphere, results in the over compensation by the left hemisphere of the brain for the injury, which causes delusions.
A study carried out by a team from The Warwick Medical School at the University of Warwick, Coventry, England, led by Andrea Schreier, Ph. D., indicated that children who suffered bullying are more likely to develop psychotic symptoms in early adolescence. The background facts demonstrated that hallucinations and delusions are common in childhood as well as in adulthood and that children who experience such symptoms are more prone to develop psychosis later in life. Furthermore, the study demonstrated that the risk of psychotic symptoms, including delusions, was multiplied by two for children who suffered bullying at age eight or ten. The authors remark that bullying can cause chronic stress that may have an effect on a genetic predisposition to schizophrenia and result in setting off the symptoms.
See also 
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- Jaspers, Karl (1913). Allgemeine Psychopathologie. Ein Leitfaden für Studierende, Ärzte und Psychologen. Berlin: J. Springer.
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- Diagnostic and Statistical Manual of Mental Disorders Fourth edition Text Revision (DSM-IV-TR) American Psychiatric Association (2000)
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- Maher B.A. (1988). "Anomalous experience and delusional thinking: The logic of explanations". In Oltmanns T., Maher B. Delusional Beliefs. New York: Wiley Interscience. ISBN 0-471-83635-4.
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- AJ Giannini. Afterword. (in) PJ Farmer. Red Orc's Rage.NY, Tor Books, 1991, pp.279-282.
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- "A New Definition of Delusional Ideation in Terms of Model Restriction". Retrieved 2010-08-06.
- Sims, Andrew (2002). Symptoms in the mind: an introduction to descriptive psychopathology. Philadelphia: W. B. Saunders. p. 127. ISBN 0-7020-2627-1.
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- Cited text
- Jaspers, Karl (1997). General Psychopathology 1. Baltimore: Johns Hopkins University Press. ISBN 0-8018-5775-9.
Further reading 
- Bell V, Halligan PW, Ellis H (2003). "Beliefs about delusions" (PDF). The Psychologist 16 (8): 418–423.
- Blackwood, Nigel J.; Howard, Robert J.; Bentall, Richard P.; Murray, Robin M. (April 2001). "Cognitive Neuropsychiatric Models of Persecutory Delusions". American Journal of Psychiatry 158 (4): 527–539. doi:10.1176/appi.ajp.158.4.527. PMID 11282685.
- Coltheart M., Davies M., ed. (2000). Pathologies of belief. Oxford: Blackwell. ISBN 0-631-22136-0.
- Persaud, R. (2003). From the Edge of the Couch: Bizarre Psychiatric Cases and What They Teach Us About Ourselves. Bantam. ISBN 0-553-81346-3.